Antifungal Compounds from Microbial Symbionts Associated with Aquatic Animals and Cellular Targets: A Review

Fungal infections continue to be a serious public health problem, leading to an estimated 1.6 million deaths annually. It remains a major cause of mortality for people with a weak or affected immune system, such as those suffering from cancer under aggressive chemotherapies. On the other hand, pathogenic fungi are counted among the most destructive factors affecting crops, causing a third of all food crop losses annually and critically affecting the worldwide economy and food security. However, the limited number currently available and the cytotoxicity of the conventional antifungal drugs, which are not yet properly diversified in terms of mode of action, in addition to resistance phenomena, make the search for new antifungals imperative to improve both human health and food protection. Symbiosis has been a crucial alternative for drug discovery, through which many antimicrobials have been discovered. This review highlights some antifungal models of a defensive symbiosis of microbial symbiont natural products derived from interacting with aquatic animals as one of the best opportunities. Some recorded compounds with supposed novel cell targets such as apoptosis could lead to the development of a multitherapy involving the mutual treatment of fungal infections and other metabolic diseases involving apoptosis in their pathogenesis pathways.


Introduction
Fungal infections are caused by pathogenic fungi that can be superficial at the level of the skin or biological mucosa, or they can be systemic, disseminated inside the whole body or on a particular inner organ, such as the lung, brain, heart, liver, and blood. These infections continue to be a serious public health problem, leading to an estimated 1.6 million deaths annually [1]. Fungal infections are dangerous and remain a major cause of mortality for people with a weak or affected immune system, such as those suffering from cancer under aggressive chemotherapies. Besides, the number of immunocompromised is growing due to an increase in the availability of hospital care, the introduction of suppressive immunotherapy, and the emerging immune diseases such as immunodeficiency viral infections, cancers, and organ transplantation that make these vulnerable populations exposed to such opportunistic fungal infections. On the other hand, pathogenic fungi are counted among the most destructive factors affecting crops, causing a third of all food crop losses annually, which critically affects the worldwide economy and food security. Aquaculture is also impaired by pathogenic fungi, which reduce fish production yield. According to the FAO's report from 2009 to 2010 (https://www.fao.org accessed on 2 February 2023), fungal infections affect the most important crops in the world in order of occurrence: maize, potatoes, soybean, rice, and wheat. Because of these crop losses, 61% of the worldwide population will lack food [2,3]. However, the limited number currently available and the cytotoxicity of the conventional antifungal drugs, which are not yet properly diversified in terms of mode of action, in addition to resistance phenomena, make the research for new antifungals imperative to improve both human health and crop protection [4][5][6]. For many years, research carried out for drug discovery has involved a lot of natural and artificial sources. Among them, natural sources seemed to represent the most abundant and diverse place to find new bioactive molecules. In that way, symbiosis has been a crucial alternative for drug discovery, through which many antimicrobials have been discovered. Symbiosis can be mutualistic, commensal, or parasitic. Further, it can be optional when both organisms live independently or obligatory when these organisms need each other to survive. During that biological collaboration, a set of secondary metabolites is produced, playing an important role in the management of the interactions between the concerned organisms [7]. These metabolites could serve as a starting point for drug discovery and production.
The discovery of antimicrobials derived from microorganisms involved in symbiosis constitutes a field of research that is not widely explored. However, some bioactive molecules against pathogenic fungi have been isolated from bacteria on Acromyrmex octospinosus ants. Nystatin P1 is an antifungal compound produced by Pseudonocardia sp. through a nystatin-like biosynthetic gene cluster identified in the bacteria as symbionts on A. octospinosus [8]. Moreover, it was recently shown that candicidin and antimycins are also produced by Streptomyces sp. symbionts and exhibit antifungal activity against Candida albicans (C. albicans) and Escovopsis sp. [9,10]. Griseofulvin too (7-chloro-4,6,2 -trimethoxy-6methylgris-2 -en-3,4 -dione) is an antifungal mycotoxin isolated from Penicillium species. It has been widely used for the treatment of superficial dermatomycoses [11]. The mycotoxin was first isolated from a terrestrial fungus, the mold Penicillium griseofulvum [12]. The bioactive compound was also detected in the aquatic animal sponge Axinella verrucosa (A. verrucosa) through its fungal symbiont from the Penicillium genus. The ethyl acetate extract of the Penicillium yielded the production of griseofulvin [13].
This review highlights the involvement of microbial symbiont interactions with aquatic animals and the possibility of biomimicry of these interactions for the discovery of new bio antifungals with new cellular targets to better fight antimicrobial resistance and provides recommendations for future research concerning antifungal discovery. The next sections of this work will be focused on the explanations of why attention is being turned to microbial symbiosis with aquatic animals, in particular, some antifungal compounds isolated from such symbiosis together with their cellular targets and recommendations concerning future research studies.

A Microbial Symbiosis Approach Associated with Aquatic Animals for Antimicrobial Discovery
The current available antifungal drugs exhibit toxicity and resistance phenomena. Pathogenic fungi are eukaryotic cells, just as are human cells. So, they share the same targets, which do not ease the development of new drugs and lead to cytotoxicity. On the other hand, the limited available classes or cell targets of these antifungals promote the development of antibiotic resistance. Regarding the current and persistent problem in that research field, new antifungal molecules are now in the development process. However, a lot of these new molecules still target the same fungal cell sites [6], which predicts future resistance. So, to contribute to expanding the research on new compounds with new cell targets, aquatic environments with an emphasis on microbial symbiosis in aquatic animals are proposed here as potent bioresources.
Water as oceans is the most abundant molecule on the earth's surface, occupying more than 70% of the surface of the planet with the highest worldwide biodiversity [14]. About 1.5 million species have already been discovered worldwide. Of those, 1.5 million, or 80%, are of terrestrial origin, whereas aquatic environments only account for 20% [15]. However, some scientists affirmed that the more complex or larger an ecosystem is, the greater its biodiversity. According to this approach, aquatic ecosystems, which are more abundant on the planet, may contain more new species than terrestrial surfaces. But the lowest percentage of the identified species in water environments could be justified by   [32,33] [49] Candida sp.

Iturin
A. aerophoba is a sponge that contains a large number of bacteria. Antimicrobial activities of bacterial isolates from A. aerophoba were tested against many microbial pathogens. The results showed that B. subtilis strains A184, A190, and A202 exhibited strong activity against the fungus C. albicans [13,90]. According to some research results, the fungicidal activity in Bacillus is an indicator of the presence of lipopeptide from the iturin (compound 9) class [90]. Compound 9 is included in the lipopeptide group, which acts as an immune stimulator in plants. Its main structure is heptapeptides linked to a β-amino fatty acid chain with a length of 14 to 17 carbons and a molecular mass of~1.1 kDa [91]. The differences in heptapeptides show derivative compounds of iturin (e.g., bacillomycin, mycosubtilin) [44]. Their action mechanism involves the disturbance of the plasma membrane of the fungal target. The compound affects the morphology and membrane structure of yeast cells by increasing the electrical conductance of bimolecular lipid membranes and acting as a nontoxic and nonpyrogenic immunological adjuvant [43,46].

3,5-Dibromo-2-(3,5-dibromo-2-methoxyphenoxy)phenol
It has been proven that Vibrio sp. bacteria isolated from the sponge Dysidea sp. were able to biosynthesize 3,5-dibromo-2-(3 ,5 -dibromo-2 -methoxyphenoxy) phenol (compound 10). The compound was isolated from ethanol extracts of the sponge Dysidea sp. It belongs to the group of brominated diphenyl ethers, with a molecular mass of 531.82 g/mol [47]. Inhibitory parameters of compound 10 were determined against pathogenic fungi. A. fumigatus, A. fumigatus, C. albicans, and C. tropicalis were inhibited at 7.8 mg/mL. A. flavus and C. glabrata have shown susceptibility concentrations of 1.95 mg/mL and 15.2 mg/mL, respectively. Moreover, the compound exhibited fungicidal activity against A. fumigatus at 15.62 mg/mL and against C. albicans at 7.81 mg/mL. The investigation of a possible target revealed the disruption of the fungal cell membrane, expressed primarily in the leakage of potassium ions [48].

YM-202204
YM-202204 (compound 11) is an antifungal that also exhibits antibacterial properties. It was discovered in the culture broth of the marine fungus Phoma sp. Q60596. The structure is a pyrone determined by several spectroscopic experiments as a lactone compound appearing as a yellow syrup with a molecular mass of 646 g/mol [49]. Some researchers have shown that pyrenes could also be isolated from other fungi, such as Fusarium species [49,92]. C. albicans, C. neoformans, and A. fumigatus were highly susceptible to compound 11. The latter inhibited glycosyl-phosphatidyl-inositol (GPI)-anchoring in yeast cell membranes [49].

Theopalauamide
T. swinhoei is a Palauan sponge that contains bacterial symbionts that produce theopala uamide (compound 13). These bacterial symbionts are composed of C. Entotheonella palauensis from the d-subdivision of proteobacteria. Compound 13 is an antifungal, bicyclic glycopeptide presented in the form of a white powder with a molecular mass of 1746.9 g/mol [57]. Concerning its biological activity, yeast chemical-genomic approaches were used to determine the mode of action. The results of several research approaches have shown that theopalauamide represents a new class of sterol-binding compound. Biochemical experiments have specifically identified ergosterol as the primary target of theopalauamide [55,56].

Immunomodulation and Apoptosis
Mammals share with some pathogenic fungi two orthologous apoptosis genes: apoptosisinducing factor (Aif) and endonuclease G (NuGl) that are responsible for programmed cell death (PCD), which represent challenging antifungal targets [94,95]. Two compounds (indole-3-carboxaldehyde and isatin) can modulate the immune system in order to stop the fungal infection and activate a cell-programmed death in the pathogen.

Indole 3-carboxaldehyde
Microbial symbiosis relationships with animals are not strange. Surface bacteria from amphibians' skin are beneficial to the host amphibian [96]. The fungus J. lividum, living at the skin surface of the red-backed salamander P. cinereus (characterized by its ability to exploit both aquatic and terrestrial habitats), synthesizes secondary metabolites that inhibit the pathogenic fungus B. dendrobatidis, which is a chytrid causing Chytridiomycosis. Indole-3-carboxaldehyde (compound 14) is the heteroarenecarbaldehyde produced. The indole is a heteroarenecarbaldehyde, an indole alkaloid with 145.16 g/mol of molecular mass. The latter inhibits the pathogen's growth at 68.9 µM. These results suggest that cutaneous symbiosis bacteria lead to amphibian resistance to fungal diseases. In addition, compound 14 also interferes with the growth of C. albicans by reducing vulvovagival candidiasis, as shown in an in vivo model study. The presence of compound 14 in the animal organism acts as immunomodulatory by stimulating the production of IL-22 via the aryl hydrocarbon receptor (AhR), promoting IL-18 expression, and providing protection against Candida infection [59].

Isatin
P. macrodactylus is a shrimp that is highly resistant to a fungal infection at its embryonic stage. The pathogenic fungus that causes the infection is L. callinectes, which also affects many other crustaceans. A particular bacterium, Alteromonas sp., spreads at the external envelope of the crustacean embryos and produces 2,3-indolinedione, commonly called isatin (compound 15). The compound inhibits the pathogenic fungus. Compound 15, which is also found in plants and other animals, possesses an indole ring structure, which is common to many pharmaceuticals and heterocyclic natural products of biological interest [97]. If exposed to the fungus, bacteria-free embryos quickly die, whereas similar embryos reinoculated with the bacteria or treated only with compound 15 survive. So, the symbiotic Alteromonas sp. bacteria protect P. macrodactylus embryos against L. callinectes infection by releasing the antifungal compound 15 [62]. In addition, other scientists have revealed the susceptibility of C. albicans, C. monosa, C. glabrata, T. longifusus, M. canis, and A. flavus to indole (0.25-1 mg/mL) [60,61]. While studying the mechanism of action of compound 15, closely related compounds have shown apoptotic effects on C. albicans at sub-inhibitory concentrations, suggesting targeting apoptosis could be considered as an alternative to be explored for antifungal drug discovery [63].

Cell Differentiation and Multiplication
Griseofulvine, majusculamide C, and surfactin are the three organic compounds that act as chemical interference in the multiplication and differentiation of pathogenic fungi by blocking mitosis and the genetic material of the pathogens.

Griseofulvin
The Penicillium fungus was isolated from the sponge A. verrucosa in the Mediterranean Sea. The microorganism Penicillium sp. has been submitted to an ethyl acetate maceration to obtain solvent extracts containing griseofulvin (compound 6) [13]. Compound 6 or 7-chloro-4,6,2 -trimethoxy-6 -methylgris-2 -en-3,4 -dione (352.8 g/mol) is a mycotoxin produced by various species of Penicillium [98]. Compound 6 disrupts the mitotic spindle by interacting with the polymerized microtubules, leading to the production of multinucleate fungal cells and stopping cell division at metaphase. The inhibition of nucleic acid synthesis and the formation of hyphal cell wall material also may be involved. The result is distortion, irregular swelling, and spiral curling of the hyphae. The bioactive molecule is fungistatic in mature dermatophytic cells and fungicidal in immature ones [99]. The isolated compound is a widely used antifungal drug for the treatment of superficial dermatomycoses. However, because it is carcinogenic and teratogenic in animal models, there is considerable concern regarding its clinical application. Further, it produces numerical chromosome aberrations in human lymphocytes and cell lines. There are conflicting reports on the ability of compound 6 to induce structural chromosomal aberrations. However, compound 6 induces micronucleus formation both in isolated peripheral lymphocytes and lymphocytes from whole blood cultures [11].

Majusculamide C
A cyclic depsipeptide, majusculamide C (compound 7), was isolated from the sponge P. trachys collected at the Enewetak Atoll (Marshall Island, Pacific Ocean). It was originally isolated from the toxic blue-green alga Lyngbya majuscula obtained from the same site. Compound 7 exhibited antifungal activity against pathogens of commercially important plants [13,38]. The compound is active against several plant pathogenic fungi such as R. solani, P. aphanidermatum, A. euteiches, and P. infestans at concentrations of, respectively, 4 µM, <1 µM, 2 µM, and 1 µM [40]. The cyclic depsipeptide acts as a microfilamentdepolymerizing agent that shows potent fungicidal activity and may have been used in the treatment of resistant fungi-inducing diseases of domestic plants and crops [41].

Surfactin
The microflora of A. aerophoba constituted by bacteria B. subtilis A190 B. subtilis A184 was responsible for surfactin class secondary metabolites production [13]. Surfactin (compound 8), with a molecular weight of 1036.3 g/mol, was thus characterized as a lipopeptide composed of a heptapeptide with the following sequence: L-Glu1-L-Leu2-D-Leu3-L-Val4-L-Asp5-D-Leu6-L-Leu7, forming a lactone ring structure with a β-hydroxy fatty acid chain. Bearing both a hydrophilic peptide portion and a lipophilic fatty acid chain, compound 8 is amphiphilic, leading to exceptional biosurfactant activities and diverse biological activities [100]. The surfactin group has two polar amino acid residues, such as Glu and Asp, and it has been concluded that they bind with DNA via hydrogen bonds. The compound affected F. moniliforme growth by causing morphological changes in hyphae, suggesting that it markedly contributed to inhibiting fungal growth. DNA binding results indicated that the lipopeptide negatively influenced the maintenance of DNA integrity by binding to F. moniliforme DNA, which might in turn genetically affect DNA function for F. moniliforme growth [42].

Cellular Enzymes
Brefeldin A and roridin A were found to be cellular enzyme inhibitors. They inhibit acid phosphatase and dehydrogenase activity, applying their functions to the secretory pathways and the respiratory chain, respectively.

Brefeldin A
Penicillium species isolated from Annella sea fan yielded Brefeldin A (compound 1).
The compound (C 16 H 24 O 4 ) is a macrolide with a molecular mass of 280.36 g/mol and possesses antibiotic properties [26,27]. The pathogenic fungus M. gypseum SH-MU-4 has shown a high susceptibility to compound 1, exhibiting a minimum inhibitory concentration value of 228.57 mM [101]. The study of the mode of action has revealed a dose-dependent inhibition of the cell-surface enzyme acid phosphatase (APase) in the periplasm of C. albicans, leading to intracellular accumulations of enzyme protein. Cells grown in the presence of compound 1 became denser than those grown in the absence of the active compound. It has been concluded that fungal cell-surface growth was also blocked by treatments containing compound 18. The APase that was accumulated intracellularly migrated faster on SDS-PAGE, suggesting less N-linked glycosylation compared with the mature periplasmic APase produced in the absence of BFA. Pulse-chase experiments and gel-filtration of oligosaccharides released by Endo H treatment suggested that the core-glycosylated precursor form of APase accumulated in the presence of BFA [27].

Roridin A
Roridin A (compound 2) from Myrotheeium roridum and Fusarium sp. is a sesquiterpene mycotoxin (12, 13-epoxy-trichothec-9-ene moiety) developed by these microorganisms with a molecular mass of 532.6 g/mol [102,103]. To obtain the compound, organic solvent extraction is used by macerating Myrothecium sp. inside ethyl acetate-ethanol (EtOAc). The producing symbiont is isolated from the marine sponge Axinella sp. The EtOAc symbiont extract has inhibited the growth of S. sclerotiorum, S. cerevisiae, and M. grisea. After separation by silica gel column fractionation and high-performance liquid chromatography (HLPC), roridin A and trichothecenes have been purified. The inhibitory concentrations of the compounds revealed MIC values close to those of fluconazole [29]. The bioactive agent showed antifungal activity against S. cerevisiae, M. grisea, and S. sclerotiorum with minimum inhibitory concentrations (MIC) of 31.25, 125, and 31.25 µg/mL, respectively. In vitro antifungal tests showed that the purified fractions were active against A. niger, T. rubrum, and C. albicans with MICs of 31.25, 62.5, and 125 µg/mL, respectively [30]. Compound 2 was able to inhibit the dehydrogenase activity of S. cerevisiae by up to 1 µg/mL. Furthermore, preliminary attention to the structure-fungitoxicity relationship of roridin A, whose MICs are comparable to ketoconazole, allowed a temporary observation that the presence of a hydroxyl group at C-13, as well as the ether bondage between C-5 and C-13, could increase almost equally the fungicidal action against A. niger and T. rubrum [30].

Resistance Factors
Multidrug resistance factors evolve from drug efficacy failure, which is characterized by the development of tolerance to a range of drugs. There are also natural resistance factors, such as the development of spores when the fungus enters the nutritive restriction stage of its life. Modiolide A from Paraphaeosphaeria sp. and Fumiquinazoline A (compound 4) from A. fumigatus were able to thwart fungal resistance.

Modiolide A
Modiolide A (compound 3) is produced by a fungus, Paraphaeosphaeria sp. (N-119), isolated from a marine horse mussel. The organic natural product appears as a colorless oil with a molecular mass of 198.22 g/mol and a chemical structure determined using spectroscopy. Compound 3 exhibited a wide antimicrobial potential against N. crassa, a pathogenic fungus, with a MIC value of 3 µg/mL, and against the bacteria Micrococcus luteus with an inhibition concentration of up to 16.7 µg/mL as MIC [32]. Moreover, it impairs P. capsici by destroying 100% of its zoospore motility within 30 min at a concentration of 0.5 µg/mL. Its zoosporicidal potency is probably due to the presence of epoxidecontaining cyclic lactones, which may be responsible for the inhibitory and zoosporicidal activities [104]. These spores, which can locate the host using their infectious propagules and accumulate at the sites of the infection through particular chemical signals, highly contribute to the pathogenic success of the Phytophthora genus. Moreover, any impairment of the spore motility greatly reduces its pathogenesis [105,106].

Fumiquinazoline
Fumiquinazoline A (compound 21; 445.5 g/mol) originated from the pathogenic fungus A. fumigatus, located at the gastrointestinal tract as endosymbionts of the fish Pseudolabrus japonicas. The mycelia of the fungus were cultured, and the compound was extracted. It was shown that compound 21 possesses cytotoxic activity against P388 lymphocytic leukemia cells [35]. The natural product was also capable of expressing antifungal activities against phytopathogenic fungi such as B. cinerea, A. solani, A. alternata (Fries) Keissler, C. gloeosporioides, F. solani, F. oxysporum f. sp. Niveum, F. oxysporum f. sp. Vasinfectum, and Gibberella saubinettii with MIC values ranging from 12.5-50 µg/mL. It is worth pointing out that the activity was more pronounced toward B. cinerea, A. solani, A. alternata, and G. saubinettii than toward Fusarium species. In addition, compound 21 highlighted an antifeedant activity with a moderate antifeedant index (AFI) of 45%. Moreover, fumiquinazoline A showed moderate activity with an AFI of 45.0%. However, when structural modifications occur on the active compound by inserting one hydroxyl group into C-3 to produce 3-hydroxyfumiquinazoline A, the antifeedant activity has considerably decreased, up to an AFI of 7.5 [34]. The structures of fumiquinazolines are quinazolinones fused with a simple piperazine ring system or more complex spiro moieties. The fused rings, the basic amine, and the rich stereochemistry are structural features useful for structure-activity relationship studies [36].

Cell Wall
The fungal cell wall is the first point of contact that initiates infection. The synthesis of cellular fungal components and the surface proteins represent capital targets to develop more efficient therapeutics or vaccines [107].

Chitinase 34 kDa
Chitinase 34 kDa (compound 5) is an enzyme extracted from the bacterial strain DA11 identified as Streptomyces sp. by 16S rDNA sequencing (GenBank accession no. DQ180128). The bacterial strain grows as a symbiont on the sponge C. austrialiensis [37]. A volume of 20 µL of the compound has been tested for its eventual antifungal activity against A. niger and C. albicans. After 120 h of incubation, an inhibition zone as a circle around compound 5 containing discs was identified, characterizing the inhibition surface of the fungus growth. The antifungal inhibition diameters were 10.98 ± 0.49 mm for A. niger and 10.48 ± 0.45 mm for C. albicans. The obtained results demonstrate the antifungal activity of the purified chitinase, which acts by degrading chitin from the cell wall. Potential uses of chitinases as biocontrol agents have been reported [108]. Chitinases from S. griseus have also shown antifungal activity against Aspergillus sp., Phycomyces blakesleeanus, Trichoderma reesei, A. nidulans, B. cinerea, Fusarium culmorum, Gulgnardia bidwellii, and Sclerotia sclerotiorum. The enzyme remains active at 85% within temperatures ranging from 30 • C to 45 • C. These results were comparable to those obtained from a chitinase isolated from a novel marine sediment Streptomyces strain, which exhibited activity at an interval temperature of 20 • C to 65 • C. For this last example, the best activity was noticed between 45 • C and 50 • C [109]. Moreover, it is also known that pH influences ionizations at the catalytic site. In that way, for some other Streptomyces species, the optimum chitinase activity was found to be included within a pH interval of 3.3 to 7.5 [110]. So, enzymatic functional features show that the extracted marine chitinase can be active under basic conditions because of its high pH tolerance and a maximum salinity tolerance of 45 g‰ psu. The latter justifies one of the characteristics of marine microorganisms, which is to tolerate salt in their living environment [111].

Relevant Information for Future Research
Six main classes of antifungal drugs are currently available for the treatment of fungal infections. They include polyenes that act on membranes by binding ergosterol and azoles that lead to the accumulation of 14-methyl-sterol. Echinochandines target β-1,3-glucane on the cell wall, allylamines inhibit epoxydase, and griseofulvine acts on microtubule polymerization [114]. Some of the following identified compounds in the study highlighted novel insights into antifungal activity targets. In the study, three new targets were suggested. Fungal cellular enzymes such as acid phosphatase, GTPase, and dehydrogenase are targeted by Brefeldin A and Roridin A (compounds 1 and 2). Moreover, modiolide A (compound 3) acting on resistance factors, such as the fungal spore motility of P. capsici zoospores [32], constitutes a leading opportunity for developing therapeutics to specifically inhibit resistance factors. Finally, immunomodulation and apoptosis pathways were impaired by indole-3-carboxaldehyde and isatin (compounds 14 and 15), which targeted immune cells as an immunomodulator in the vulvocandidiasis model and as an apoptosis enhancer on Candida and Aspergillus microorganisms. To the best of our knowledge, there are not yet conventional antifungal drugs targeting these three targets: cellular enzymes, resistance factors, and the immune/apoptotic pathway. However, the challenge behind this resides in the fact that these fungal eukaryotic cells sometimes share the same cellular features as human eukaryotic cells, such as cellular enzymes, the immune system, and apoptosis. For example, apoptosis biochemical mechanisms are also integrated into human cells' metabolic pathways [95,96,115]. Unless a specific antifungal therapy is only for cancer, people acting on apoptosis should be considered. So, deep investigations through preclinical and clinical trials involving toxicity studies may produce effective results in the development of new antifungal drugs with novel cell targets from aquatic sources. Actually, from these reports, spore motility seems to represent the best suggested novel antifungal target to investigate. Even the combination of these compounds with different and new cell targets may lead to promising effects.
The multiple advantages of the combination approach have already been shown [116][117][118]. This approach exploits various beneficial characteristics associated with each combination product for the improvement of the effectiveness, the reduction of toxicity, the reduction of the doses to be administered, and the reduction of the features associated with the development of drug resistance [119]. In addition, this approach would involve a greater diversity of secondary metabolites in antimicrobial action. Combinations could therefore possibly target several metabolic pathways at once, thereby enhancing the desired therapeutic effect, most likely through synergistic interactions [120]. That is also the case with diacetylphloroglucinol (compound 16), which acts at the same time on the mitochondrial membrane and causes hyphal disorganization. In addition, tyrosol (compound 17) affects cell membrane permeability and inhibits the biofilm on Candida at the same time to produce the inhibition activity.

Conclusions
The present study gives insights into how to learn from the microbial symbiosis associated with aquatic animals and develop mimicry strategies for the development of infectious disease treatments, particularly in the field of antifungals. Natural products derived from such symbiotic interactions may be mimicked, or the physical behavior of some fungi to protect the host could also be integrated into the antimicrobial development strategies. One example of chemically mediated defense from a microbial symbiont to protect its host is the case of P. macrodactylus embryos (crustacean), which defend themselves through the action of a symbiont bacteria, Alteromonas sp., to fight the fungal infection caused by L. callinectes on its embryos [62] by producing isatin, an antimicrobial agent to impair the progression of the infection, where close derivative isatin compounds act by activating the pathogen apoptosis pathway. Thus, three main targets to investigate in preclinical and clinical trials have been identified as potent antifungal cell targets as well as antifungal agents in cancer therapies. Besides, it is worth noting the presence of the identified antifungal targets here in this study as acid phosphatases, GTPases, and apoptosis, which are also involved in some cancer pathologies. Some of the mentioned compounds with apoptotic effects could also be involved in the drug discovery process of metabolic diseases because the same pathogenesis pathway as apoptosis activation is highlighted in cancer (compounds 1, 2, 7, 15, 21, 26, and 27).