Search Results (11)

The blue crab (Callinectes sapidus) is an invasive alien species in the Mediterranean Sea, posing threats to biodiversity, fisheries, and aquaculture. Climate change has worsened these challenges, influencing the distribution of bacterial species, including Shewanella species, which are sensitive to changes in temperature and salinity. In this study, 300 blue crabs were sampled between June and October 2024 from the Sacca di Goro (Northern Adriatic Sea, Italy) to investigate the prevalence of Shewanella species in their haemolymph. The prevalence was found to be 7% (21/300), with species such as S. mesophila, S. algae, S. cowelliana, and S. baltica identified, particularly in the months of September and October. Molecular techniques, including MALDI-TOF MS and rpoB gene amplification, were used to identify isolates. Antibiotic susceptibility testing (AST) revealed a trend of resistance to beta-lactam antibiotics. A network analysis was also conducted to examine the global trends of Shewanella research in relation to humans, animals, and the marine environment. While proper cooking eliminates the risk to consumers, handling without personal protective equipment can increase exposure, particularly for vulnerable individuals such as those who are elderly or immunocompromised. Mild symptoms are observed in children. Further studies, particularly with a One Health approach, are crucial to better understand the transmission dynamics and evolving antibiotic resistance of Shewanella species. Full article

Two typical fish products—fermented mandarin fish and semi-dried yellow croaker—are associated with biogenic amines (BAs), which are harmful to human health. The objective of this study was to investigate the bacterial ecology of the two fish products and to determine their capacity for producing BAs. Putrescine and cadaverine were major BAs detected in the fish products. Concentrations of BAs were significantly corrected with microbial count (p < 0.05). BA-producing isolates (33) in the two fish products were all multiple BA producers. Several of them, including Lactobacillus sakei, Bacillus cereus and Hafnia alvei isolated from fermented mandarin fish, as well as Shewanella baltica, Aeromonas veronii, and Photobacterium phosphoreum isolated from semi-dried yellow croaker, showed remarkable BA-producing capacity. Hafnia alvei produced the greatest abundance of putrescine, cadaverine, tyramine and 2-phenylethylamine. Lactobacillus sakei mainly produced tryptamine and putrescine. Photobacterium phosphoreum showed the strongest histamine-producing capacity. Full article

Although antibiotics are the main therapy for bacterial infections, the reports showed that the overuse (or misuse) of antibiotics will results in several problems such as the development of antibiotic-resistant strains, persistence of drug residues, and numerous environmental concerns. Therefore, finding antibiotic alternatives is considered of vital importance. Investigation of the antimicrobial properties of several plant substances and extracts is of great value to replace antibiotics. With this objective, this study aimed to evaluate the antimicrobial activities of an ethanolic extract prepared from olive mill wastewater (OMWW), which is a by-product of olive oil production with considerable environmental burden, against 38 bacterial strains, including fish-associated pathogens, non-pathogenic isolates, collection strains, and one yeast strain, Candida albicans. Disk diffusion, minimum inhibitory concentration (MIC), and minimum bactericidal/fungicidal concentration (MBC/MFC) tests were used to determine the antimicrobial activity of the OMWWE. According to the results, OMWWE provoked strong inhibitory effects against Shewanella baltica strain SY-S145. It also showed a moderate inhibitory effect on Plesiomonas shigelloides strain SY-PS16 and Vibrio anguillarum strain SY-L24. The MIC and MBC of OMWWE on Shewanella baltica SY-S145, Vibrio gigantis strain C24, and V. anguillarum strain SY-L24 were 500 µg/mL. The MIC and MBC on V. parahaemolyticus ATCC 17802 were 1000 µg/mL, whereas the values for Aeromonas salmonicida ATCC 33658 were 500 µg/mL and 1000 µg/mL, respectively. To put it briefly, the OMWW extract showed high antimicrobial activity and can act as an environmentally friendly additive for the control and prevention of diseases caused by A. veronii, A. hydrophila, P. shigelloides, S. baltica, V. anguillarum, and V. parahaemolyticus. Its active agents also prevented infections of both fish-associated pathogens and food spoiling bacteria, which means it can not only help in the disease control mechanism but also in improving the safety of food by reduction of the microbial contamination. Full article

Microbial fuel cells (MFC) are emerging technologies that can produce electricity while treating wastewater. A series of tests were carried out to evaluate the efficiency of this technology for treating dairy wastewater (DWW). The experiments used Shewanella baltica as an exoelectrogen in a small single MFC to treat simulated DWW. The impacts of various operational factors, specifically pH, hydraulic retention time (HRT), and chemical oxygen demand (COD) in the influent to the anode chamber, were investigated, and the effect of these variables on the output performance of the cell was evaluated. The best performance of the MFC was found when the pH, HRT, and COD were 8, 6.66 h, and 20,632 mg/L, respectively, in the scaled experimental setup. Under these conditions, the maximum power density and percentage removal of COD in terms of wastewater treatment ability were found to be 138 mW/m² and 71%, respectively. It may be concluded that MFCs are suitable treatment technologies for treating dairy wastewater while potentially simultaneously generating power. Full article

Myrosinase can hydrolyze glucosinolates to generate isothiocyanates, which have cancer prevention and anti-cancer properties. The main sources of myrosinase are cruciferous plants. To further improve the efficiency of isothiocyanates preparation, it is necessary to explore novel sources of myrosinases. In this study, we described a bacterium, Shewanella baltica Myr-37, isolated from marine mud, capable of producing a novel myrosinase (Smyr37) with a molecular weight of 100 kDa. The crude enzyme of Smyr37 showed the highest activity at 50 °C and pH 8.0. The sinigrin- and glucoraphanin-hydrolyzing activities of Smyr37 were 6.95 and 5.87 U/mg, respectively. Moreover, when the reaction temperature was 40 °C and pH was 7.0, the crude enzyme of Smyr37 could efficiently degrade glucoraphanin into sulforaphane within 25 min with a yield of 0.57 mg/mL. The corresponding conversion efficiency of sulforaphane from glucoraphanin was 89%. In summary, S. baltica Myr-37 myrosinase Smyr37, a novel myrosinase, can be used in the preparation of isothiocyanates. Full article

Microbial fuel cells (MFCs) are a kind of bioreactor for generating electricity, facilitated by exoelectrogens while treating wastewater. The present article focuses on the performance of an air cathode plexiglass MFC in terms of chemical oxygen demand (COD) removal efficiency and power output by performing two sets of experiments. The proton exchange membrane and electrode materials were Nafion 117 and carbon felts, whereas, for stable biofilm formation on the anode surface, a pure culture of Shewanella baltica 20 was used. Firstly, sterile Luria-Bertani (LB) media containing lactate, ranging from 20 to 100 mM, was continuously fed to an MFC, and a maximum power density of 55 mW/m² was observed. Similarly, artificial wastewater with COD ranging from 3250 mg/L to 10,272 mg/L was supplied to the MFC in the second set of experiments. In this case, the maximum power density and COD removal efficiency were 12 mW/m² and 57%, respectively. In both cases, the hydraulic retention time (HRT) was 1.5 h. It was found that electricity generation depends on the characteristics of the wastewater. These initial findings confirm that the design aspects of an MFC, i.e., surface area to volume ratio, and external resistance with respect to the quality of influent need to be optimised to improve the MFC’s performance. Full article

The genus Shewanella is widely distributed in niches ranging from an aquatic environment to spoiled fish and is loaded with various ecologically and commercially important metabolites. Bacterial species under this genus find application in bioelectricity generation and bioremediation due to their capability to use pollutants as the terminal electron acceptor and could produce health-beneficial omega-3 fatty acids, particularly eicosapentaenoic acid (EPA). Here, the genome sequence of an EPA-producing bacterium, Shewanella sp. N2AIL, isolated from the gastrointestinal tract of Tilapia fish, is reported. The genome size of the strain was 4.8 Mb with a GC content of 46.3% containing 4385 protein-coding genes. Taxonogenomic analysis assigned this strain to the genus Shewanella on the basis of average nucleotide identity (ANI) and in silico DNA-DNA hybridization (DDH), phylogenetically most closely related with S. baltica NCTC 10735^T. The comparative genome analysis with the type strain of S. baltica revealed 693 unique genes in the strain N2AIL, highlighting the variation at the strain level. The genes associated with stress adaptation, secondary metabolite production, antibiotic resistance, and metal reduction were identified in the genome suggesting the potential of the bacterium to be explored as an industrially important strain. PUFA synthase gene cluster of size ~20.5 kb comprising all the essential domains for EPA biosynthesis arranged in five ORFs was also identified in the strain N2AIL. The study provides genomic insights into the diverse genes of Shewanella sp. N2AIL, which is particularly involved in adaptation strategies and prospecting secondary metabolite potential, specifically the biosynthesis of omega-3 polyunsaturated fatty acids. Full article

The effects of modified atmosphere packaging (MAP) with various CO₂ concentrations on the bacterial community and shelf-life of smoked chicken legs during 25 d of storage at 4 °C were evaluated herein. Four treatments were stored in pallets (PAL) and MAP under 20% (M20), 60% (M60), and 100% (M100) CO₂, respectively. The results indicated that the MAP treatments provided the legs with higher redness and hardness and lower yellowness, luminance, and lipid oxidation, compared with the PAL treatment. In addition, the MAP treatments effectively inhibited the growth of viable bacteria, delayed bacterial spoilage, and extended the shelf-life of the samples. The M60 and M100 treatments had a better inhibition effect on bacteria. In terms of bacterial community, Carnobacterium, Pseudomonas, Brochothrix, and Lactococcus were the most predominant genera in the 25 d-stored MAP samples, with Carnobacterium maltaromaticum, Pseudomonas fragi, Shewanella baltica, and Lactococcus piscium being the dominant species. However, while the inhibition effects of the M60 and M100 treatments on the bacterial community at Day 25 were similar, the outer package of the M100 treatment collapsed. Overall, the M60 treatment may be a promising approach to improving the quality and extending the shelf-life of smoked chicken legs. Full article

Osmotic changes are common challenges for marine microorganisms. Bacteria have developed numerous ways of dealing with this stress, including reprogramming of global cellular processes. However, specific molecular adaptation mechanisms to osmotic stress have mainly been investigated in terrestrial model bacteria. In this work, we aimed to elucidate the basis of adjustment to prolonged salinity challenges at the proteome level in marine bacteria. The objects of our studies were three representatives of bacteria inhabiting various marine environments, Shewanella baltica, Vibrio harveyi and Aliivibrio fischeri. The proteomic studies were performed with bacteria cultivated in increased and decreased salinity, followed by proteolytic digestion of samples which were then subjected to liquid chromatography with tandem mass spectrometry analysis. We show that bacteria adjust at all levels of their biological processes, from DNA topology through gene expression regulation and proteasome assembly, to transport and cellular metabolism. The finding that many similar adaptation strategies were observed for both low- and high-salinity conditions is particularly striking. The results show that adaptation to salinity challenge involves the accumulation of DNA-binding proteins and increased polyamine uptake. We hypothesize that their function is to coat and protect the nucleoid to counteract adverse changes in DNA topology due to ionic shifts. Full article

The cultivable microbiota isolated from three sea bass products (whole, gutted, and filleted fish from the same batch) during chilled storage and the effect of primary processing on microbial communities in gutted and filleted fish were studied. Microbiological and sensory changes were also monitored. A total of 200 colonies were collected from TSA plates at the beginning and the end of fish shelf-life, differentiated by High Resolution Sequencing (HRM) and identified by sequencing analysis of the V3–V4 region of the 16S rRNA gene. Pseudomonas spp. followed by potential pathogenic bacteria were initially found, while Pseudomonasgessardii followed by other Pseudomonas or Shewanella species dominated at the end of fish shelf-life. P. gessardii was the most dominant phylotype in the whole sea bass, P. gessardii and S. baltica in gutted fish, while P. gessardii and P. fluorescens were the most dominant bacteria in sea bass fillets. To conclude, primary processing and storage affect microbial communities of gutted and filleted fish compared to the whole fish. HRM analysis can easily differentiate bacteria isolated from fish products and reveal the contamination due to handling and/or processing, and so help stakeholders to immediately tackle problems related with microbial quality or safety of fish. Full article

Marine bacteria display significant versatility in adaptation to variations in the environment and stress conditions, including temperature shifts. Shewanella baltica plays a major role in denitrification and bioremediation in the marine environment, but is also identified to be responsible for spoilage of ice-stored seafood. We aimed to characterize transcriptional response of S. baltica to cold stress in order to achieve a better insight into mechanisms governing its adaptation. We exposed bacterial cells to 8 °C for 90 and 180 min, and assessed changes in the bacterial transcriptome with RNA sequencing validated with the RT-qPCR method. We found that S. baltica general response to cold stress is associated with massive downregulation of gene expression, which covered about 70% of differentially expressed genes. Enrichment analysis revealed upregulation of only few pathways, including aminoacyl-tRNA biosynthesis, sulfur metabolism and the flagellar assembly process. Downregulation was observed for fatty acid degradation, amino acid metabolism and a bacterial secretion system. We found that the entire type II secretion system was transcriptionally shut down at low temperatures. We also observed transcriptional reprogramming through the induction of RpoE and repression of RpoD sigma factors to mediate the cold stress response. Our study revealed how diverse and complex the cold stress response in S. baltica is. Full article