Therapeutic Potential of Marine Probiotics: A Survey on the Anticancer and Antibacterial Effects of Pseudoalteromonas spp.

Due to the increasing limitations and negative impacts of the current options for preventing and managing diseases, including chemotherapeutic drugs and radiation, alternative therapies are needed, especially ones utilizing and maximizing natural products (NPs). NPs abound with diverse bioactive primary and secondary metabolites and compounds with therapeutic properties. Marine probiotics are beneficial microorganisms that inhabit marine environments and can benefit their hosts by improving health, growth, and disease resistance. Several studies have shown they possess potential bioactive and therapeutic actions against diverse disease conditions, thus opening the way for possible exploitation of their benefits through their application. Pseudoalteromonas spp. are a widely distributed heterotrophic, flagellated, non-spore-forming, rod-shaped, and gram-negative marine probiotic bacteria species with reported therapeutic capabilities, including anti-cancer and -bacterial effects. This review discusses the basic concepts of marine probiotics and their therapeutic effects. Additionally, a survey of the anticancer and antibacterial effects of Pseudoalteromonas spp. is presented. Finally, marine probiotic production, advances, prospects, and future perspectives is presented.


Introduction
Natural products (NPs) are highly structurally diversified, ubiquitous life forms and derivatives of living organisms and minerals. They have been used extensively, especially in traditional medicine, to manage diverse diseases [1]. They have also contributed immensely to drug discovery in making current conventional drugs, serving as a direct source of medicinal substances, raw materials in drug production, lead compound design prototypes, and taxonomic biomarkers for new drug search and discovery [2]. NPs are associated with prominent, apparent beneficial properties [3] (as shown in Table 1) against conventional drugs or radiotherapy (as implicated in cancer management), including minimal side effects, toxicity, allergenicity, and low-cost isolation, identification, characterization, and production.
Synthetic drugs, including antibiotics used in aquaculture, primarily aim to prevent infection, leading to fatalities of "aquatic products" with correspondingly low productivity. However, their irrational use undermines the purpose. Although used optimally, it does not guarantee a clean bill of zero health risks to humans [4]. These drugs, including chloramphenicol, sulfamethazine, oxytetracycline, and furazolidone, remain residues 1 Chemotherapeutic drugs

Methodology
This paper is organized into three parts. The first part is a general review of the background of marine probiotics, sources, and some therapeutic effects. The second part is an extensive survey presenting relevant literature on the involvement of Pseudoalteromonas spp. in the prevention and management of cancer and bacterial diseases. The third section reviews marine probiotic production, prospects, advances, and future perspectives.
For the second part, the classical literature search of titles, abstracts, and keywords across four databases, including PubMed, ScienceDirect, Scopus, and google scholar (as a secondary database), was done using the 'Pseudoalteromonas spp.', 'cancer', 'anticancer', and antibacterial', as keywords. The study used most original articles published in the last ten (10) years (2013)(2014)(2015)(2016)(2017)(2018)(2019)(2020)(2021)(2022)(2023). The literature search was performed using the Boolean connectors: "And" or "Or" where necessary. Original articles reporting the anticancer and antibacterial effects of Pseudoalteromonas spp. in the stated years were included. All articles outside the study year range, not written in English, not reporting on Pseudoalteromonas spp., review articles, and not reporting anticancer and antibacterial effects were excluded. Some of the limitations of the review include the exclusion of subscription-based articles requiring payment for access. Also, most articles obtained using the keywords were review articles.

Probiotics, Sources, and Classifications
Probiotics resulting from the Greek words "Pro bios," which translates to "for life" [21], are a class of microorganisms, including bacteria, viruses (such as bacteriophages), and fungi (yeast and mold) that can be ingested or topically applied for dietary and numerous medicinal (physiological and immunological) purposes [8,22,23]. Examples include Bifidobacterium, Streptococcus, Bacillus, Escherichia coli, Lactobacillus, Saccharomyces, Coccobacilli, and Propionibacterium and are in varying classifications, mechanisms of action, and corresponding functions. They preserve specific qualities, including, but not limited to, the ability to inhibit pathogens in the gut, navigate and survive via intestinal transit and gastric/bile secretions, adhere to the mucosa of the intestine, have immunomodulating and other biological effects [10,24]. Probiotic strains should be thoroughly characterized, safe for the intended application, backed by at least one successful human clinical trial per generally accepted scientific criteria, and alive in adequate numbers in the product at the time of usage [25]. Other considerations in choosing for medicinal purposes include non-toxicity, non-pathogenicity, beneficial effects, and appreciable shelf life. Probiotics have been applied in managing diverse medical conditions [10]. Also, several preclinical and clinical trials have suggested potent therapeutic applications.
such as Lactobacilli and Bifidobacteria, modify the mucosa by increasing the production of chemokines and host defense peptides, inducing dendritic cell maturation, and increasing cell proliferation and apoptosis [51]. Marine probiotics can modulate cancer by inducing apoptosis, inhibiting mutagenic activity, downregulating oncogene expression, inducing autophagy, inhibiting kinases, reactivating tumor suppressors, preventing metastasis, and producing meta-biotics, as already shown in B. animalis, B. infantis, B. bifidum, L. paracasei, L. acidophilus, and L. plantarum I-UL4 against MFC7 cancer cells [53,54]. Although probiotics alone may not suffice in treating cancer, they can mitigate colorectal cancer (CRC) by enhancing the efficacy of treatments and acting on the immune system [56]. Studies have shown that probiotic strains, specifically lactic acid bacteria mixtures, can differentially induce and modulate macrophage pro-and anti-inflammatory cytokines and phagocytosis [53]. It also can mitigate the effects of DMH-induced colon shortening and positively affect leukocyte count and colon tumor growth [56]. The combinations also induce the excretion of proinflammatory IL-18 by tumor cells and are crucial in mitigating CRC [56]. Probiotics generally exhibit antitumor activities by enhancing the intestinal microbiota, degrading possible carcinogens, and modulating gut-associated and systemic immune responses [57]. Worthy of mention is that several anticancer drugs of marine origin are in clinical use with sufficient approvals, including cytarabine, vidarabine, nelarabine, fludarabine phosphate, trabectedin, eribulin mesylate, brentuximab vedotin, polatuzumabvedotin, enfortumabvedotin, belantamabmafodotin, plitidepsin, lurbinectedin, bryostatins, discodermolide, eleutherobin, and sarcodictyin [41,58]. With the increasing popularity of antibiotic stewardship, the misuse and abuse of antimicrobials in developed and developing countries have remained high, with an attendant increase in the development of bacterial resistance. Especially with its forecasted implications [59], possible avenues for developing newer antimicrobials must be exploited. Marine probiotics are a potential source of antimicrobial substances. Pereira et al. [59] showed that marine-isolated L. lactis and E. faecium produce effective bacteriocin antibiotics [59]. The bacteriocin-producing potential of Lactococcus spp. also agrees with Sarika et al. s study [60]. Other marine probiotics that can produce antibacterial substances have continued to emerge. Pseudoalteromonas spp. and Vibrio spp. produced antibacterial substances with activity comparable to established antibiotics [61]. Marine lactic acid bacteria of the genera Lactococcus spp., Enterococcus spp., Lactobacillus spp., and Leuconostoc spp. have been reported to produce antimicrobial substances against Vibrio spp. With the increasing popularity of antibiotic stewardship, the misuse and abuse of antimicrobials in developed and developing countries have remained high, with an attendant increase in the development of bacterial resistance. Especially with its forecasted implications [59], possible avenues for developing newer antimicrobials must be exploited. Marine probiotics are a potential source of antimicrobial substances. Pereira et al. [59] showed that marine-isolated L. lactis and E. faecium produce effective bacteriocin antibiotics [59]. The bacteriocin-producing potential of Lactococcus spp. also agrees with Sarika et al.'s study [60]. Other marine probiotics that can produce antibacterial substances have continued to emerge. Pseudoalteromonas spp. and Vibrio spp. produced antibacterial substances with activity comparable to established antibiotics [61]. Marine lactic acid bacteria of the genera Lactococcus spp., Enterococcus spp., Lactobacillus spp., and Leuconostoc spp. have been reported to produce antimicrobial substances against Vibrio spp. and Photobacterium spp. [62]. Kaktchan et al. [63] revealed that Lactococcus spp., cultured in an earthen pond, could produce a bacteriocin-like substance that inhibits the growth of Vibrio spp. and Pseudomonas aeruginosa.
Immune system arsenals generally recognize viral antigens, preventing their multiplication within the host [64]. However, research should remain proactive, as infective agents constantly change and could sprout newer pathogenic strains. Although the exact mechanisms of action are still unclear, some probiotics have shown a solid ability to prevent viral multiplication in fish and can be used as antiviral agents. Lactobacillus spp. and B. subtilis boosted viral resistance by preventing viral infections in Paralychthus olivaceus and grouper fish, respectively [65,66]. The production of antiviral compounds by Pseudoalteromonas spp. has protected Prawns and Sea breams against viral pathogens [67]. Other studies have also shown the possibility and potential of deploying probiotics in the marine environment as agents to prevent viral infections [68,69]. A robust immune system correlates well with defense against infections and diseases. Studies on the immune-enhancing potential of marine probiotics have shown promising results [33,37]. Wasana et al. [47] reported the expression of the immunomodulatory genes in zebrafish larvae exposed to a novel Pseudoalteromonas xiamenensis, a marine probiotic that induced the down-regulation of proinflammatory cytokine genes. In another study, a significant reduction in the levels of proinflammatory cytokines was observed in CRC patients who received six viable probiotics of Lactobacillus and Bifidobacterium strains [70].
The propensity of reactive oxygen and reactive nitrogen species as free radicals to alter the body's proteins, lipids, and DNA is a significant cause of some human diseases [71]. Due to synthetic antioxidants' toxic effects [72], marine probiotics have been studied as a natural source of antioxidants. In a study, Alsharmmari et al. [73] espoused the novel marine probiotic, Enterococcus durans, which possesses an efficient antioxidant potential. Other studies that corroborated and supported the possible use of marine probiotics as potential sources of antioxidants are those by Husain et al. [73] and Angulo et al. [74].
Representative marine probiotic-derived drugs and their microbial sources are presented in Table 2. Therapeutic potentials of marine probiotics are illustrated in Figure 2.

Pseudoalteromonas spp.; Therapeutic Potentials and Systematic Survey
Of the class Gammaproteobacteria; the cold-adapted Pseudoalteromonas spp. are widely distributed heterotrophic, flagellated, non-spore-forming, rod-shaped gram-negative marine probiotic bacteria with up to 37 to 48 specified species [70][71][72] proposed and separated from Alteromonas as a genus in the last 28 years [81]. The relatively low number of studies on the genus could be attributed to the recency of the genus proposal. In addition, it is difficult to reach and manage these isolates [82]. They are abundant, comprise 20 to 60% of the marine microbial community, and are often associated with particles [83]. They are well known for possessing and releasing a broad range of extracellular bioactive sub-

Pseudoalteromonas spp.; Therapeutic Potentials and Systematic Survey
Of the class Gammaproteobacteria; the cold-adapted Pseudoalteromonas spp. are widely distributed heterotrophic, flagellated, non-spore-forming, rod-shaped gram-negative marine probiotic bacteria with up to 37 to 48 specified species [70][71][72] proposed and separated from Alteromonas as a genus in the last 28 years [81]. The relatively low number of studies on the genus could be attributed to the recency of the genus proposal. In addition, it is difficult to reach and manage these isolates [82]. They are abundant, comprise 20 to 60% of the marine microbial community, and are often associated with particles [83]. They are well known for possessing and releasing a broad range of extracellular bioactive substances, including enzymes, pigments, protease, and polysaccharides, with many biotechnological and pharmaceutical applications [84][85][86]. They are implicated in the cycling of nutrients, including carbon and nitrogen, and in the intestinal microbiota of marine life forms, assisting in maintaining physiological functions [87]. Recent studies have shown the Pseudoalteromonas spp. to possess diverse bioactive/therapeutic potentials involving their metabolites, including having anticancer (Table 3) and antibacterial effects (Table 4) via different mechanisms. They are presented here in four categories, including (1) genes and proteins/enzymes, (2) polymers, polysaccharides, and peptides, (3) extracts and organic compounds, and (4) nanoparticles, as studies have been reported in these lines.    Activates specific well-regulated molecular pathways, Pyroptotic cell death signaling, which triggers the transcription of Caspase -1 and subsequent proinflammatory cytokines [97] Nanoparticles

P. shioyasakiensis
Reduction and cytotoxicity effects of P. shioyasakiensis-based nanoparticles.
Estimation of cell viabilities.
Selenium and tellurium nanoparticles of P. shioyasakiensis -Different pathways and enzymes, including reductases, siderophores, glutaredoxin, and glutathione, in converting selenium and tellurium to their nanoparticles; however, the specific mechanisms used by the isolates were not covered. [83]

Anticancer Pseudoalteromonas spp. Proteins/Enzymes
Denge et al. [88] compared immobilized and lyophilized k-selenocarrageenase, a potential adjuvant for cancer drugs obtained from Pseudoalteromonas sp. Xi13. Although the lyophilized enzyme had a better recovery rate (70%), the immobilized enzyme exhibited better stability after several uses. Mechanistically, k-selenocarrageenase acts by degrading k-selenocarrageenan to selenium oligosaccharides, addressing the issues of water solubility and the high molecular weight of the former [88]. In a study involving the complete genome sequencing of the same isolate, Wang et al. [89] suggested the mechanism of the k-Selenocarrageenase action to involve complex glycoside hydrolase. They also confirmed the anticancer effects of selenium oligosaccharides (specifically, disaccharides and tetrasaccharides) in a concentration-dependent manner in HeLa cervical cancer cells. Hong et al. [90] reported the catalytic activity and thermostability enhancement of two mutant kcarrageenases produced from P. tetradonis, which produces even numbered k-carrageenan oligosaccharides by catalyzing k-carrageenans via the PoPMuSiC algorithm. Compared to wild-type k-carrageenase, the enzyme mutants displayed better enzyme activity, attributed to better enzyme flexibility and fewer structural deviations. Zhao et al. [91] demonstrated the expression of the same enzyme from P. porphyrae LL1 in Brevibacillus choshinensis, which also presented considerable stability across a broad pH range. They showed that Mg 2+ drastically enhanced the enzyme's activity and that the enzymatic hydrolysates were made of An-G4S-type neocarrabiose units, the end products of which were neo-carratetraose. Also, Zhao et al. [92] isolated stable, high hydrolyzing k-carrageenase from Pseudoalteromonas sp. ZDY3 with Km and K cal /K m of 3.67 mg/mL and 53 mL/mg/s, respectively. The enzyme end-products were k-neocarratetraose and k-neocarrabiose. Arylsulfatase, which plays a potential role in cancer cell detection, was isolated by Zhu et al. [93] from a library of P. carrageenovora arylsulfatase mutants, which showed improved thermal and pH stability compared with the wild-type enzyme. Soliev et al. [94] determined the effects of prodigiosin (2-methyl-3-pentylprodiginine, 2-methyl-3-heptylprodiginine, 2-methyl-3butylprodiginine, and 2-methyl-3-hexylprodiginine) produced by Pseudoalteromonas sp. strain 1020R on protein kinases and phosphate as targets of cancer cell death through apoptosis in leukemia cell lines (HL60, K562, and U937). They reported the dose-dependent inhibition of two phosphates, including protein phosphatase 2A and tyrosine phosphatase 1B. However, the prodigiosins were largely inactive against the protein kinases. Thus, they suggested protein-phosphatase inhibition-based cytotoxicity in leukemia cancer cells. Also, the mechanism activation is independent of the p53 protein owing to the low concentration of the prodigiosin in the leukemia cell amidst the apoptosis.

Anticancer Pseudoalteromonas spp. Polymer, Polysaccharides, and Peptides
Di Guida et al. [95] reported antitumor effects against colon cancer cells (compared to the untreated cell, reducing 60% of colon cancer cell viabilities at 600 µg/mL after 72 h and with a nontoxic lower cell viability reduction (20%), when compared to the untreated control cells, at 200 µg/mL, after 72 h) by a capsular polysaccharide made up of N-acetylated aminosugars, isolated from P. nigrifaciens Sq02-Rif T and obtained within a fish gut, which activates Caspases-3 and -9 on the CaCo-2 and HCT-116 of the cancer cells and induces apoptosis. Ueoka et al. [96] showed the iron chelating activity and cytotoxic effects (against human T lymphocyte cells) of a novel Pseudoalteropeptide A (lipopeptide) isolated from P. piscicida SWA4_PA4.

Anticancer Pseudoalteromonas spp. Extracts and Organic Compounds
The antiproliferative activity of ethyl acetate extract and the bioactive compounds of P. haloplanktis TAC125 against A549 lung epithelial cancer cells were investigated by Sannino et al. [97]. 4-hydroxybenzoic acid from the extract was identified as an anticancer cell proliferation (with IC 50 value ≤ 1 µg/mL) compound in the bacterial extract; it exhibited a specific gene and protein level well-regulated pathway termed pyroptotic cell death signaling, which triggers the transcription of Caspase-1 (an inflammasome) and subsequently the release of IL18β and IL18 encoding genes (proinflammatory cytokines).

Anticancer Pseudoalteromonas Nanoparticles
Beleneva et al. [83] used a green technology to synthesize the nanoparticles of selenium and tellurium using three different isolates of P. shioyasakiensis from a marine test facility in Vietnam, which presented high reduction process effects and human breast cancer and dermal fibroblasts cytotoxicity effects, with the selenium-based nanoparticles of the isolates outperforming the tellurium-based nanoparticles.  [98] demonstrated the P. aeruginosa-implicated biofilm inhibition by alginolytic enzymes produced by thirty-six bacterial isolates, including Pseudoalteromonas sp. 1400, which yielded alginate lyase and had the highest alginolytic activity. The purified enzyme had dual lyase activity of degrading poly-glucuronic and -mannuronic acids and had significant combined antibiofilm activities with carbenicillin and ciprofloxacin, reducing the P. aeruginosa biofilms' surface area, biovolume, and thickness. In a follow-up investigation, using immunofluorescent staining and chromatography, Daboor et al. [99] confirmed the antibiofilm-enhancing effects of the alginate lyase enzyme, AlyP1400, against P. aeruginosa CF2F-implicated biofilm. Also, the hydrolytic and disruptive impact of the enzyme against the extracellular alginate produced by P. aeruginosa CF27 is reported to be instrumental to the anti-biofilm's activities. Thogersen et al. [100] assayed the bioactive violacein and indolmycin produced by a mutant P. luteoviolacea S4054, which had inhibition activities against Staphylococcus aureus and Vibrio anguillarum. The UHPLC-UV/Vis studies utilized in comparing the expression of the bioactive compounds with those produced by a wild strain revealed a lower and higher production of violacein and indolmycin, respectively, compared to the wild strain. The study concluded that although the significant antibacterial compounds of Pseudoalteromonas sp. are yet to be identified, the two bioactive compounds also contribute to the observed antibacterial properties.

Antibacterial
The complete genome elucidation of P. phenolica KCTC 12086 T , which could produce antibiotic compounds including polybrominated-diphenyl ethers, -bipyrroles, and -biphenyls, with proven antibacterial effects against certain bacteria, including methicillinresistant S. aureus, E. faecium, Enterococcus seriolicida, and Enterococcus faecalis has been reported by Choe et al. [101]. The result showed the presence of two 4,868,993 bp chromosomes with 4,264,659 bp coding regions, which encode a total of 4168 proteins. Also, 28 rRNA (9 operons), six ncRNAs, 113 tRNAs, eight pseudo-genes, and one tmRNA were detected. Furthermore, the bmp cluster (1-10), responsible for producing polybrominated compounds, was observed at different nucleotide positions on the chromosome. Other hydrolysis enzyme coding regions reported, including collagenases, phytase, chitinases, and proteases detected, further support the potential applicability of the isolate. Similarly, the genome of P. xiamenensis STKMTI.2 isolated from a mangrove soil sediment in Indonesia was elucidated by Handayani et al. [102], which consisted of 4,563,326 bp with a GC content of 43.2%, two circular and linear plasmids, one chromosome, 25 rRNAs, four ncRNAs, 4824 coding sequences, and a CRISPR. The CRISPR gene detected was attributed to the production of brominated marine phenols/pyrroles and secondary metabolites, including bmp 8 and 9 and peptides, butyrolactone, prodigiosin, RiPP-like, and Lant I, and justified the suspicion of P. xiamenensis STKMTI.2 for generating broad-spectrum antimicrobial compounds. The genome of Pseudoalteromonas sp. NC201 (from the coastal area of New Caledonia) with antibacterial potentials and has already been assessed for its probiotic effects through enhancement of survival rates in Litopenaeus stylirostris infected with Vibrio nigripulchritudo [103] was also sequenced by Sorieul et al. [104]. The analysis revealed 115 contigs (>100 bp). Of the contigs, 65 presented six scaffolds with an approximate GC content of 43.25%; two were the largest and represented 4.13 Mbp chromosome and 1.24 Mbp chromid, respectively. The remaining sequences comprised insertion sequences and ribosomal RNA operons in repetitive regions and clusters. These results indicated the ability of the isolate to synthesize antibacterial peptides, including bacteriocins and gramicidin/tyrocidine. In addition, the lodA and lodB genes, which are related to amino acid oxidases, suggested the production of oxygen peroxide, which can have bacterial inhibitory effects. Marchetti et al. [105] studied and sequenced the tam operon, which initiates the synthesis of P. tunicate-produced tambjamine YP1, a natural bipyrrole antibiotic, and reported to possess other bioactive potentials. They described the tam operon as possessing 19 genes, comprising a fused C-terminal acyl carrier protein and N-terminal adenylation domain, bound C 11 and 12 acyl-adenylate intermediates, transfers chain length of fatty acids from C6-C13 to an isolated acyl carrier protein domain, and thus shows the initiations of the production of tambjamine YP1 via the linkage of the pyrrole and fatty acid pathways. Maansson et al. [106] analyzed different geographic sort isolates of P. luteoviolacea for biosynthetic richness and diversity using metabolomic and sequencing techniques. The study reported enormous diversity in the 13 analyzed isolates, with only 2 and 7% of the chemical features and biosynthetic genes, respectively, common in the isolates. Genome sequencing of the isolates revealed the presence of biosynthetic clusters that were attributed to the generation of indolmycin, an antibacterial compound. Rond et al. [107] studied P. rubra, a cyclized prodiginine-producing bacterium. The genome sequence revealed an unclustered gene responsible for the enzyme that catalyzes regiospecific C-H and prodigiosin cyclization to cyclo-prodigiosin. Prodiginines are natural products with potent bioactive properties, including antibacterial and anticancer effects. Yu et al. [108] sequenced P. flavipulchra JG1, responsible for producing Pseudoalteromonas flavipulchra antibacterial protein (PfaP) for specific genes or clusters responsible for the expression of the antibacterial protein, which has been proven to have inhibitory effects against certain bacteria, including Bacillus spp., Aeromonas spp., and Vibrio spp. The isolate also produced p-hydroxybenzoic acid, trans-cinnamic acid, N-hydroxybenzoisoxazolone, 6-bromoindolyl-3-acetic acid, and 2 -deoxyadenosine, with inhibitory effects against some microorganisms, including the previously mentioned bacterial species. The results showed that P. flavipulchra JG1 had a total of 5,565,361 bp with a GC content and open reading frames of 43.23% and 4913. The tandem repeats, transposons, and insert sequences were 180, 143, and 5, respectively. It possesses a complex system of genes belonging to ABC-type antimicrobial peptide transport and siderophore export systems, penicillin-binding and beta-lactamase class C proteins, and efflux pumps, all contributing to the generation of bioactive metabolites. Specifically, PfaP, the reported most potent bioactive metabolite of the isolate, oxidizes certain amino acids to α-keto acids, hydrogen peroxide, and ammonium. Hydrogen peroxide decomposes into other metabolites, which exhibit antimicrobial effects. Diaz et al. [109] also sequenced P. piscicida 36Y_RITHPW, which produces bioactive compounds with inhibition effects against multi-resistant Vibrio parahaemolyticus implicated in shrimp hepatopancreatic necrosis disease. Summarily, 4548, 4217, and 71 genes, protein-coding sequences, and RNA sequences were reported. In addition to other findings, the authors elucidated the expression of bacteriocins and peptides (ribosomally produced and responsible for antibacterial properties) by 12 genes in a cluster, including polyketide synthase/non-ribosomal peptide synthase (PKS/NRPS), lantipeptide gene, type 1 PKS, 7 NRPS, and aryl-polyene/NRPS hybrid clusters. In agreement, the genome sequence of P. piscicida strain DE2-B by Richard et al. [110] revealed relatively the same genes responsible for the production of antimicrobial proteolytic enzymes and compounding, including peptides, polyketides, and alkaloids; thus, the P. piscicida strain DE2-B's ability to inhibit some bacteria, including, V. parahaemolyticus. Jouault et al. [111] sequenced Pseudalteromonas sp. 3J6 and identified gene sequences, including the alt gene, which encodes 139 residue proteins and is responsible for the expression of alterocin, a protein implicated in inhibiting P. aeruginosa biofilms. Generally, the genome, GC content, and coding region of the Pseudalteromonas sp. 3J6 were approximately 4.6 Mb, 39.93%, and 3789, respectively.      [115] Provide the depolarization of the bacterial membrane and the subsequent cell permeabilization and lysis. [113,114] P. shioyasakiensis and P. mariniglutinosa.
Bacterial isolation, degradation, and isolation of monomers, antibacterial assay LPS inhibition by CD14 binding and cytokine secretion blockage from LPSstimulated cells. [116] Degradation of Poly-hydroxybutyrate-co hydroxy-hexanoate (PHBH) to antibacterial monomers [115]   The transferable outer surface positioned vesicle/pilus-like structure likely contributes to the inhibition activities observed and is described as a novel mechanism of antibacterial activity by the isolate. [120] The transferable outer surface positioned vesicle/pilus-like structure likely contributes to the inhibition activities observed and is described as a novel mechanism of antibacterial activity by the isolate. [120] Pseudoalteromonas sp. type strain S4498  The interference of the quorum sensing system of the S. epidermis by the AI-2 signaling process. [128] Not available [127]  The interference of the quorum sensing system of the S. epidermis by the AI-2 signaling process. [128] P. rubra TKJD 22 Isolation of organic compounds from Tunicate-associated bacteria and antibacterial activities of compounds.

Isatin
Not available [129] The interference of the quorum sensing system of the S. epidermis by the AI-2 signaling process. [128] P. rubra TKJD 22 Isolation of organic compounds from Tunicate-associated bacteria and antibacterial activities of compounds. The interference of the quorum sensing system of the S. epidermis by the AI-2 signaling process. [128] P. rubra TKJD 22 Isolation of organic compounds from Tunicate-associated bacteria and antibacterial activities of compounds.

Isatin
Not available [129] Not available [129]    NB: '*' in the Alterocin/Alterin structure is hydroxylation at C 3 position. On the isolation, identification, and bacterial origin suspicion of low molecular weight antimicrobial peptides of oyster hemolymph, Defer et al. [112] assayed the culture supernatant of different bacteria resident in the hemolymph for their antibacterial effects. Three strains of Pseudoalteromonas spp., designated hCg-6, hCg-10, and hCg-42, with sequence results suspecting the first two to be P. prydzensis/mariniglutinosa and the last to be P. paragorgicola/elyakovii, displayed ranging antibacterial activities against Aeromonas hydrophila CIP 7614, Listonella anguillarum NCBIM 829, Yersinia ruckeri ATCC 29473, Bacillus megaterium ATCC 10778, Lactococcus garviae ATCC 43921, and Salmonella enterica CIP 829. Two of the strains (hCg-6 and hCg-42) also showed BLIS-production abilities. Desriac et al. [113] showed the antibacterial activity of seven alterins with ranging molecular masses (924-982 Da) extracted from two Pseudoalteromonas spp. (hCg-6 and hCg-42) of healthy hemolymph microbiota of Crassostrea gigas (oyster) against several gram-negative bacteria, including Vibrio harveyi ORM4 and V. parahaemolyticus 13-028A/3. The produced alterins belong to the family of cationic cyclo-lipopeptides, which bind to bacterial lipopolysaccharides, provoking membrane depolarization and subsequent cell permeability and lysis [113]. Similarly, Offret et al. [114] obtained alterins from a group of 5 Pseudoalteromonas spp. isolated from the oyster hemolymph and also demonstrated ranging antibacterial activities against E. coli ATCC 25922, V. harveyi OMM4, V. pectenicida CIP 105190, V. tasmaniensis LGP32, and V. tapetis CECT 4600. These studies suggest that alterins can be potent lipopolysaccharide-neutralizing and synergistic antibiotic peptides. The polymer poly-hydroxybutyrate-co-hydroxy-hexanoate (PHBH), through its degradation products, including 3-hydroxy-butyrate and -hexanoate and hydroxy-alkanoic acids, is reported to have antibacterial activities. A review of a specific study found that it inhibits Vibrio penaeicida and increases the survival rate of shrimp exposed to V. penaeicida following consumption of PHBH-supplemented feed [115]. However, the study [108] reported the high PHBH degrading abilities of certain gram-negative bacteria, including P. shioyasakiensis and P. mariniglutinosa. This degradation action showed inhibitory/suppression effects against V. penaeicida through the generation of antibacterial monomer products, thus suggesting the potential application in aquaculture for the protection of shrimps against infection by V. penaeicida through diet supplementation with PHBH and the corresponding implicated PHBH-degrading P. shioyasakiensis and P. mariniglutinosa. No inhibitory effects were observed when V. penaeicida was challenged with Pseudoalteromonas spp., without PHBH. Kozuma et al. [116] tested an array of secondary metabolites of Pseudoalteromonas sp. SANK 71903 has potential inhibitory effects against lipopolysaccharides (LPS) and typical LPSbearing bacteria. Cyclic Peptides, Ogipeptins (A-D), closely related to Polymyxin B, were identified and showed the ability to inhibit LPS through CD14 binding with 1C 50 values of Ogipeptin-A = 4.8 nm, -B = 6.0 nm, -C = 4.1 nm, and -D = 5.6 nm and blockage of cytokine secretion from LPS-stimulated cells. They showed antibacterial effects against E. coli, with minimum inhibitory concentrations ranging from 0.25-1.0 µg/mL.

Antibacterial Pseudoalteromonas spp. Extracts and Organic Compounds
In vitro and in vivo studies by Wasana et al. [117] demonstrated the probiotic potential of P. ruthenica S6031. Broth culture spots of the isolate on microbial lawns of P. aeruginosa, Edwardsiella piscicida, A. hydrophila, and Candida albicans revealed significant positive inhibition against E. piscicida and A. hydrophila. In E. piscicida-challenged Zebra fish, there was higher cumulative per cent survival of the animals exposed to P. ruthenica-supplemented feed, outperforming the control group without supplements. It also revealed the induction of several immune-stress response gene transcripts and the downregulation of the proinflammatory genes. Thus, the study showed that the treatment group animals had better disease tolerance than the control group, making P. ruthenica S6031 a good potential probiotic isolate. The organic compound, korormicin, produced by many Pseudoalteromonas spp., including Pseudoalteromonas strain J010, is acknowledged by Maynard et al. [118] to have antibacterial activities, including against Vibrio spp., Aliivibrio sp, and Pseudomonas sp.
They, however, through MICs and DNA sequence data, disclosed that, though korormicin is a potent inhibitor of NA + -pumping NADH (quinone oxidoreductase), the antibacterial effects are not due to the inhibition of the stated enzyme, but to the release of reactive O 2 species via the electron transfer initiation in the enzyme, which promotes O 2 and some redox cofactor's reaction. In vitro, in vivo, and PCR evaluations by Wang et al. [119] showed antibacterial activities against V. parahaemolyticus, respective enhancement and decrease of the survival rates of V. parahaemolyticus-infected shrimps following exposure to Pseudoaltermonas spp-supplemented feed and shrimp hindgut presumptive Vibrio sp. counts, and reduced the copy number of V. parahaemolyticus toxin production gene, PirA vp , respectively, by two Pseudoalteromonas spp. coded CDM8 and CDA22. Following proper identification, Wang et al. [120] described the antibacterial mechanisms of one of the isolates, P. flavipulchra CDM8, which also showed potent inhibition activities against Bacillus spp. and Vibrio spp. Using antimicrobial biofilm assays and microscopy, they showed its broad-spectrum antimicrobial activity against both gram-positive and -negative bacteria using filter-impregnated culture from the isolate. They described the mechanism to involve P. flavipulchra CDM8 metabolites, including hydrogen peroxide, PfaP-like antibacterial proteins, and other molecules. They also identified a transferable outer surface-positioned vesicle/pilus-like structure, which likely contributes to the observed inhibition activities and is described as a novel mechanism of antibacterial activity by the isolate. Using several genome analysis tools, including the antiSMASH (a secondary metabolite prediction tool) and bioassays, Paulsen et al. [121] identified, among others, a highly halogenated tetrabromopyrrole as the main antibacterial metabolite of Pseudoalteromonas sp. type strain S4498. Genome studies revealed that the strain had a genome size of 5.4 Mb and a GC content of 43%. However, they suggested that tetrabromopyrrole induced its antimicrobial effects through its signaling properties, cellular stress induction, and dibromo maleimide activity, the oxidized by-product. Desriac et al. [122], in an assay of the different cell-free cultures of 843 species/strains obtained within the haemolymphs microbiota of bivalve species from the sea, showed the Pseudoalteromonas strains to possess the most potent antimicrobial abilities (against 12 marine gram-positive and -negative pathogens), with one Pseudoalteromonas sp. (designated as hCg-51) beating the other isolates with inhibition at an extreme dilution of 1:1024. They also presented a dose-dependent beneficial effect of the strain on the hemocyte survival rates. Thus, suggesting their strong probiotic potential. Similarly, Offret et al. [123] assayed a collection of 11 Pseudolateromonas spp. obtained from the hemolymph of mussels and oysters for their antibacterial activities against V. harveyi. The results showed that more than half of the isolates (54%) had varying inhibition activities, with one coded hCg-6 outperforming the others in the collection, with an impressive inhibition zone of 19 mm. The Pseudoalteromons sp. (hCg-6) also revealed significant probiotic activities following the increment in the survival rate of Abalone exposed to hCg-6 and subsequently infected with V. harveyi. Also, Tangestani et al. [124] reported antibacterial activities against E. coli, Staphylococcus epidermis, and Kocuria rhizophila by solvent extracts of two Pseudoalteromonas spp., among other marine bacteria isolated from the surface of various marine macroalgae. The two relevant isolates were phylogenetically confirmed to be P. issachenkonii and P. haloplanktis TAC125, associated with the seaweeds Splachnidium rugosum, and Carpophyllum maschalocarpum, respectively. Papa et al. [125] reported the antibiofilm activity of the culture supernatant of P. haloplanktis TAC125 against S. epidermidis by disrupting the S. epidermidis biofilm multicellular structure. Sannino et al. [126], via a defined culture and fermentation system, produced and accumulated methylamine, a volatile organic compound (VOC), from P. haloplanktis TAC125, which by the minimum volatile inhibitory concentrations, presented a dose-dependent inhibition of different strains of Burkholderia spp. and E. coli. Venuti et al. [127] assayed the antibacterial properties of pentadecanol, a metabolite of P. haloplanktis, and the derivatives against Listeria monocytogenes, using the minimum inhibitory concentrations. The results showed that the derivatives, including the ester, acetal, and carboxylic acid, had no inhibitory effects against the test isolates; however, pentadecanol showed potent antibacterial properties and exhibited a MIC of 0.6 mg/mL. Similarly, Casillo et al. [128] isolated pentadacanol from the same P. haloplanktis, and they demonstrated its antibiofilm activity against S. epidermis. They suggested the mechanism of action of inhibiting the biofilm from involving the interference of the quorum sensing system of the S. epidermis through the AI-2 signaling process. Using 16S RNA sequencing and NMR elucidation, an organic compound was obtained and determined to be isatin, respectively, from P. rubra TKJD 22 associated with marine tunicates by Ayuningrum et al. [129]. The isatin demonstrated inhibition effects against both the laboratory-isolated and MDR-ESBL E. coli. Tebben et al. [130] isolated bioactive compounds from the ethanol extract of Pseudoalteromonas strain J010, which were elucidated using MS and NMR techniques. Among others, novel 4 -(3,4,5-tribromo-1H-pyrrol-2-yl) methyl)phenol (a bromopyrrole), 5 koromicins, and tetrabromopyrrole were identified and presented ranging antibacterial activities against S. aureus and other gram-negative bacteria, including Vibrio spp., P. aeruginosa, Pseudoalteromonas spp., and Shewanella aquimarina. In another study, following the inhibition activities of the crude extract fractions of Pseudoalteromonas piscicida S2040 against P. aeruginosa, Sonnenschein et al. [131] isolated bromoand dibromoalterochromides, myxochelins A and B, and alteramide A, chosen for their antibacterial effects. Eliseikina et al. [132] isolated Pseudoalteromonas piscicida 2202, a natural flora of Modiolus kurillenis, which had selective antimicrobial activity against S. aureus, C. albicans, and B. subtilis and no significant activity against E. coli and P. aeruginosa. They, however, suggested caution in the application as potent probiotic agent. Among other heterotrophic bacteria, Setiaji et al. [133] employed Pseudoalteromonas sp. JS19 MT102924.1 in an ethyl acetate extraction system to yield secondary metabolites, through which the phytochemical analysis showed the presence of alkanes, carbonyls, alcohols, and alkenes. The extract had antibacterial activities with inhibition zones of 9.8, 10.8, and 9.8 mm against A. hydrophilia, Vibrio alginolyticus, and P. aeruginosa, respectively.

Antibacterial Pseudoalteromonas spp. Nanoparticles
Beleneva et al. [83] reported high concentration (500 and 1000 µg/mL) antimicrobial effects of the selenium and tellurium-based nanoparticles of the isolates of P. shioyasakiensis against typed cultures of E. coli, P. aeruginosa, S. aureus, B. subtilis, and additionally a fungus (C. albicans), with the tellurium-based nanoparticles having overall more significant effects.

Discussion
The review revealed that none of the literature evaluated the genetic basis for the anticancer properties of Pseudoalteromonas spp. However, involved k-selenocarrageenases/kcarrageenans, arylsulfatase, and prodigiosin as the pigments and enzymes, capsular polysaccharides, and polysaccharides and Pseudoalteropeptide A in the polymer, polysaccharide, and peptide category, a crude extract of P. haloplanktis, selenium, and tellurium nanoparticles in the reported anticancer activities. The reported antibacterial properties involved the production of bioactive pigments and enzymes, including alginate lyase (AlyP1400), violacein, and indolmycin, specific gene sequences and clusters responsible for the expression and production of polybrominated compounds, peptides, polyketides, alkaloids, tambjamine YP1, cylco-prodigine, PFaP, alterocins/alterins, and other compounds including 3-hydroxy-butyrate, 3-hydroxy-hexanoate, hydroxy-alkanoic acids, korormicin, hydrogen peroxide, tetrabromopyrrole, methylamine, isatin, brominated compounds, and nanoparticles by representative tests Psesudoaltromonas spp. Much of the literature summarized in Figure 3, however, is currently in the preliminary stages; without an in-depth analysis of the mechanistic and physiological basis of the observed bioactive properties as such, the current review provided the basis and a standpoint for the advancement of the studies including the isolation and extensive characterization of the bioactive compounds with a view to possible clinical application and commercialization.

Production and Development of Marine Probiotics
Marine probiotics have proven therapeutic applications; however, adequate exploitation and utilization of these properties hinge on optimal industrial-scale production and development. These involve several steps, including isolation, identification, and characterization of potential probiotic strains and testing their efficacy and safety in various applications [134,135]. The first step in marine probiotics production is isolating and identifying likely probiotic strains from marine environments and involves collecting samples from marine ecosystems, such as seawater, sediments, and aquatic organisms and isolating potential probiotic strains using standard microbiological and molecular techniques. The identified strains are then characterized for their morphology, physiology, and biochemistry to profile their potential as probiotics [135]. They are screened and selected for their probiotic properties, including their ability to survive in the host gut system, produce anticancer and antimicrobial compounds, or stimulate the host s immune system [136]. The selected strains are tested for their safety and efficacy in various applications [137], after which they are mass-produced. Marine probiotics can be produced using different techniques such as batch, fed-batch, and continuous cultures [138,139]. The production process involves growing the selected strains in a suitable growth medium and harvesting and processing the cells to obtain the final product [137,140]. The produced marine probiotics are formulated into an appropriate delivery system, such as capsules, powders, or liquid formulations, to maintain viability, stability, and efficacy during storage and transportation [141,142], and the final application of the produced probiotics in the intended fields, such as aquaculture, animal feed, and human health.
However, the current industrial production of marine probiotics is hindered by several factors, most importantly, the high cost of culture media required for optimal growth [28]. Optimal media for propagating marine probiotics should contain sufficient organic nitrogen, peptones, and protein hydrolysates from various sources. These media constituents are, however, expensive [28]. However, alternative sources of these essential elements/compounds from nature, such as organic marine wastes from fish and other life

Production and Development of Marine Probiotics
Marine probiotics have proven therapeutic applications; however, adequate exploitation and utilization of these properties hinge on optimal industrial-scale production and development. These involve several steps, including isolation, identification, and characterization of potential probiotic strains and testing their efficacy and safety in various applications [134,135]. The first step in marine probiotics production is isolating and identifying likely probiotic strains from marine environments and involves collecting samples from marine ecosystems, such as seawater, sediments, and aquatic organisms and isolating potential probiotic strains using standard microbiological and molecular techniques. The identified strains are then characterized for their morphology, physiology, and biochemistry to profile their potential as probiotics [135]. They are screened and selected for their probiotic properties, including their ability to survive in the host gut system, produce anticancer and antimicrobial compounds, or stimulate the host's immune system [136]. The selected strains are tested for their safety and efficacy in various applications [137], after which they are mass-produced. Marine probiotics can be produced using different techniques such as batch, fed-batch, and continuous cultures [138,139]. The production process involves growing the selected strains in a suitable growth medium and harvesting and processing the cells to obtain the final product [137,140]. The produced marine probiotics are formulated into an appropriate delivery system, such as capsules, powders, or liquid formulations, to maintain viability, stability, and efficacy during storage and transportation [141,142], and the final application of the produced probiotics in the intended fields, such as aquaculture, animal feed, and human health.
However, the current industrial production of marine probiotics is hindered by several factors, most importantly, the high cost of culture media required for optimal growth [28]. Optimal media for propagating marine probiotics should contain sufficient organic nitrogen, peptones, and protein hydrolysates from various sources. These media constituents are, however, expensive [28]. However, alternative sources of these essential elements/compounds from nature, such as organic marine wastes from fish and other life forms, are imperative. An example is the sourcing of fish peptones from different fish waste materials and by-products by Vázquez et al. [28] which resulted in 120 times better growth of the test probiotics Pseudomonas fluorescens and Phaeobacter sp. The development of these media nutrient requirements is ongoing through various studies and, with time, will ensure the scale-up of the production of proven probiotics for commercial use in the treatment of different medical conditions, including cancer and bacterial infections [143].

Limitations, Prospects, Future Perspectives
Studies in aquaculture have identified diverse marine bacterial species as potent probiotics [111][112][113]. Some identified bacteria can be considered safe (GRAS) for humans, while others are pathogenic. Since these marine probiotics have shown the potential to produce substances that could be of health benefit to humans, there is a need for innovative research to harness these benefits. In the development of marine probiotics, one major challenge is to isolate and identify potential strains [32,144]. In addressing low specificity and side effects associated with chemotherapeutic drugs and radiotherapy, there is a need to search for novel and non-toxic compounds from natural sources [79]. While the potential of terrestrial probiotics in cancer management has been explored, the function of marine probiotics is not yet fully understood. Several studies, including animal models and cell lines, have shown the promising therapeutic effects of marine probiotics. However, clinical trials are necessary to understand the therapeutic mechanisms [51] fully. Randomized, double-anonymized, placebo-controlled clinical trials are crucial to gaining broader acceptance in the medical community [49,57]. Although drug discovery and development from marine sources have inherent limitations, advances in analytical instrumentation, screening platforms, scalable synthetic approaches, and antibody-drug conjugates (ADCs) have expanded the clinical arsenal for therapeutic application [145]. In addition, omics approaches, including probiotic genome, metagenome, transcriptome, and metatranscriptome sequencing, are yet to be fully explored in cancer studies. These methods can enhance the detection and understanding of several bioactive mechanisms.
Biotechnological concepts and approaches are still evolving. In this review, we strongly recommend two possible biotechnological approaches that could yield beneficial products from these organisms; first, the selective identification and deletion of the virulence-causing gene(s) in the pathogenic marine probiotics while optimizing the expression of the genes responsible for producing the beneficial substances. The process affords the removal of the virulence factor and ensures the safety of use. This approach has yielded substances of pharmaceutical importance [146] and hindered the expression of patulin, a mycotoxin by P. expansum [147]. Second, the elucidation, manipulation, and optimization of the genes responsible for producing the bioactive agents using recombinant DNA (rDNA) technologies [148].

Conclusions
The need for alternative medicinal agents to synthetic/chemotherapeutic drugs and radiation (as it applies to cancer) in managing prevalent diseases is evident. Marine probiotics are, however, proven to be viable bioactive synthetic microorganisms. Specifically, Pseudoalteromonas spp., a group of marine probiotics, has shown potential therapeutic application against diseases, including cancer and bacterial-implicated diseases, through their activities and byproducts or metabolites. The production of therapeutic/bioactive agents from marine probiotics looks promising; however, the need for intensified research cannot be over-emphasized to enable optimal utilization of the potential therein.