Shewanella Species Research Articles

Activity of Bambara Groundnut Seed Coat Extract Against Shewanella Species: Efficacy and Mechanisms of Action.

The Bambara groundnut is the indigenous legume in the southern part of Thailand. It contains a seed coat rich in polyphenols, which can serve as natural antimicrobial agents. The extracts from red and white seed coats of Bambara groundnuts, namely RSC and WSC, respectively, were prepared using an ultrasound-assisted extraction process. The extraction yield, total phenolic content (TPC), and antimicrobial activity of both extracts were examined. The RSC extract demonstrated a significantly higher extraction yield (8.35%) than WSC extract (2.34%) (p < 0.05). Furthermore, the TPC of RSC extract (420.98 ± 0.27 mg of gallic acid/g dry extract) was higher than that of WSC extract (28.29 ± 0.91 mg of gallic acid/g dry extract). The RSC extract exhibited stronger inhibition against Shewanella putrefaciens and S. algae than its WSC counterpart. Liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF/MS) analysis indicated that the RSC extract was rich in flavonoids and polyphenols, while the WSC extract contained more triterpenoid saponins. Time-kill kinetics showed that the RSC extract reduced bacterial loads in a dose-dependent manner. Scanning electron microscopic images revealed that drastic bacterial cell membrane damage with a rough surface and the deformation of cells was caused by the extract. Furthermore, confocal laser scanning microscopic (CLSM) images confirmed the inhibition of S. algae biofilm formation by RSC extract. RSC extract also suppressed bacterial motility, induced protein leakage, and reduced extracellular protease activity, thus highlighting its potent bactericidal effects. These findings suggested that the RSC extract rich in phenolic compounds could serve as an antimicrobial agent and hold promise as a natural preservative for perishable foods, especially seafoods.

A hotspot of diversity: novel Shewanella species isolated from Baltic Sea sediments delineate a sympatric species complex.

Two bacterial strains, SP1S1-4T and SP2S1-2T, were isolated from sediment samples collected in the Stockholm archipelago in November 2021. Following whole-genome sequencing, these strains were identified as tentatively belonging to two novel Shewanella genospecies, based on digital DNA-DNA hybridization, as implemented in the Type Strain Genome Server. Shewanella septentrionalis, Shewanella baltica and Shewanella hafniensis were, in this order and within a narrow genomic relatedness range, their closest genotypic relatives. Additional sampling and sequencing efforts led to the retrieval of distinct isolates that were monophyletic with SP1S1-4T and SP2S1-2T, respectively, based on phylogenomic analysis of whole-genome sequences. Comparative analyses of genome sequence data, which included blast-based average nucleotide identity, core genome-based and core proteome-based phylogenomics, in addition to MALDI-TOF MS-based protein profiling, confirmed the distinctness of the putative novel genospecies with respect to their closest genotypic relatives. A comprehensive phenotypic characterisation of SP1S1-4T and SP2S1-2T revealed only minor differences with respect to the type strains of S. septentrionalis, S. baltica and S. hafniensis. Based on the collective phylogenomic, proteomic, and phenotypic evidence presented here, we describe two novel genospecies within the genus Shewanella, for which the names Shewanella scandinavica sp. nov. and Shewanella vaxholmensis sp. nov. are proposed. The type strains are, respectively, SP2S1-2T (=CCUG 76457T=CECT 30688T), with a draft genome sequence of 5 041 805 bp and a G+C content of 46.3 mol%, and SP1S1-4T (=CCUG 76453T=CECT 30684T), with a draft genome sequence of 4 920147 bp and a G+C content of 46.0 mol%. Our findings suggest the existence of a species complex formed by the species S. baltica, S. septentrionalis, S. scandinavica sp. nov., and S. vaxholmensis sp. nov., with S. hafniensis falling in the periphery, where distinct genomic species clusters could be identified. However, this does not exclude the possibility of a continuum of genomic diversity within this sedimental ecosystem, as discussed herein with additional sequenced isolates.

Shewanella phaeophyticola sp. nov. and Vibrio algarum sp. nov., isolated from marine brown algae.

Two Gram-stain-negative, rod-shaped bacteria, designated as strains KJ10-1T and KJ40-1T, were isolated from marine brown algae. Both strains were catalase-positive, oxidase-positive, and facultative aerobic. Strain KJ10-1T exhibited optimal growth at 25 °C, pH 7.0, and 3 % NaCl, whereas strain KJ40-1T showed optimal growth at 25 °C, pH 7.0, and 2 % NaCl. The respiratory quinones of strain KJ10-1T were ubiquinone-8, ubiquinone-7, menaquinone-7, and methylated menaquinone-7, while the respiratory quinone of strain KJ40-1T was only ubiquinone-8. As major fatty acids, strain KJ10-1T contained C16 : 0, C17 : 1 ω8c, iso-C15 : 0, and summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c) and strain KJ40-1T contained C16 : 0 and summed features 3 and 8 (C18 : 1 ω7c and/or C18 : 1 ω6c). The major polar lipids in strain KJ10-1T were phosphatidylethanolamine, phosphatidylglycerol, and an unidentified aminolipid, whereas those in strain KJ40-1T were phosphatidylethanolamine, phosphatidylglycerol, and diphosphatidylglycerol. The DNA G+C contents of strains KJ10-1T and KJ40-1T were 42.1 and 40.8 mol%, respectively. Based on 16S rRNA gene sequences, strains KJ10-1T and KJ40-1T exhibited the closest relatedness to Shewanella saliphila MMS16-UL250T (98.6 %) and Vibrio rumoiensis S-1T (95.4 %), respectively. Phylogenetic analyses, based on both 16S rRNA and 92 housekeeping genes, showed that the strains formed distinct phylogenic lineages within the genera Shewanella and Vibrio. Digital DNA-DNA hybridization and orthologous average nucleotide identity values between strain KJ10-1T and other Shewanella species, as well as between strain KJ40-1T and other Vibrio species, were below the thresholds commonly accepted for prokaryotic species delineation. Based on the phenotypic, chemotaxonomic, and phylogenetic data, strains KJ10-1T and KJ40-1T represent novel species of the genera Shewanella and Vibrio, respectively, for which the names Shewanella phaeophyticola sp. nov. and Vibrio algarum sp. nov. are proposed, respectively. The type strains of S. phaeophyticola and V. algarum are KJ10-1T (=KACC 22589T=JCM 35409T) and KJ40-1T (=KACC 22588T=JCM 35410T), respectively.

Analysis of clinical characteristics of infections caused by Shewanella species

PurposeThe Shewanella genus is a rare pathogen of marine origin. In recent years, there has been a continuous increase in infection cases caused by this bacterium, and we have observed the uniqueness of infections caused by this microorganism. Materials and methodsThis study conducted a retrospective analysis of the medical history and laboratory examination data of patients infected with the Shewanella genus over the past decade. Additionally, it employed bioinformatics methods to analyze the relevant virulence factors and antibiotic resistance genes associated with the Shewanella genus. ResultsOver the past 10 years, we have isolated 51 cases of Shewanella, with 68.82% being Shewanella putrefaciens (35/51 cases) and 31.37% being Shewanella algae (16/51 cases). Infected individuals often had underlying diseases, with 39.22% (20/51) having malignant tumors and 25.49% (13/51) having liver and biliary system diseases primarily characterized by stones. The majority of patients, 62.74% (32/51), exhibited mixed infections, including one case with a combination of infections from three other types of bacteria and five cases with a combination of infections from two other types of bacteria. The identified microorganisms were commonly resistant to ticarcillin-clavulanic acid (23.5%), followed by cefoperazone-sulbactam (19.6%), ciprofloxacin (17.6%), and cefotaxime (17.6%). Bioinformatics analysis indicates that Shewanella can express bile hydrolysis regulators and fatty acid metabolism regulators that aid in adapting to the unique environment of the biliary tract. Additionally, it expresses abundant catalase, superoxide dismutase, and two-component signal transduction system proteins, which may be related to environmental adaptation. Shewanella also expresses various antibiotic resistance genes, including beta-lactamases and aminoglycoside modification enzymes. Iron carriers may be one of its important virulence factors. ConclusionsWe speculate that the Shewanella genus may exist as a specific colonizer in the human body, and under certain conditions, it may act as a pathogen, leading to biliary infections in the host.

Shewanella goraebulensis sp. nov., isolated from sea water.

A novel Gram-stain-negative, facultatively anaerobic and rod-shaped bacterial strain, designated as DAU312T, was isolated from the sea water of the eastern coast of the Republic of Korea. Optimal growth was observed at 25 °C, pH 7.0-8.0 and with NaCl concentrations of 2.0 % (w/v). Catalase and oxidase activities were detected. On the basis of 16S rRNA gene sequences, strain DAU312T showed the highest similarity (99.2 %) to the type strain Shewanella electrodiphila MAR441T. The complete genome sequence of strain DAU312T contains 4 893 483 bp and 40.5 mol% G+C. Phylogenetic analyses based on 16S rRNA gene sequences and the up-to-date bacterial core genes showed that strain DAU312T, S. electrodiphila MAR441T and S. olleyana were all part of the same monophyletic clade. Their average nucleotide identity, digital DNA-DNA hybridization and two-way average amino acid identity values with each other and type strains of close Shewanella species were 83.4-77.5 %, 27.3-22.0 % and 89.8-81.2 %, respectively. The major cellular fatty acids (>10 %) were iso-C15 : 0, summed feature 3 (C16 : 1 ω7с and/or C16 : 1 ω6с) and C16 : 0. Phosphatidylethanolamine and phosphatidylglycerol were the main polar lipids. The respiratory quinones were Q-7, Q-8, MK-7 and MMK-7. Based on these polyphasic taxonomic findings, the name Shewanella goraebulensis sp. nov. is suggested for strain DAU312T, which is considered to represent a novel species of the genus Shewanella. The type strain is DAU312T (=KCTC 72427 T=JCM 35744T=KCCM 43478T).

Polyphasic Characterization and Genomic Insights into an Aerobic Denitrifying Bacterium, Shewanella zhuhaiensis sp. nov., Isolated from a Tidal Flat Sediment.

A new, facultatively anaerobic, light-yellow, and rod-shaped bacterium designated as 3B26T isolated from Qi'ao Island's tidal flat sediment was identified. Strain 3B26T can hydrolyze gelatin, aesculin, and skim milk. The major cellular fatty acids were identified as iso-C15:0, referred to as summed feature 3, and C16:0; the polar lipids consisted of phosphatidylethanolamine, phosphatidylglycerol, and phospholipid; and the quinones contained Q-7, Q-8, MK-7, and MMK7. The genomic size of strain 3B26T was 4,682,650 bp, and its genomic DNA G + C content was 54.8%. While a 16S rRNA gene-based phylogenetic analysis confirmed that strain 3B26T belongs to the genus Shewanella, both phylogenomic inference and genomic comparison revealed that strain 3B26T is distinguishable from its relatives, and digital DNA-DNA hybridization (dDDH) values of 24.4-62.6% and average nucleotide identities (ANIs) of 83.5-95.6% between them were below the 70% dDDH and 96% ANI thresholds for bacterial species delineation. Genomic functional analysis demonstrated that strain 3B26T possesses complete gene clusters of eicosapentaenoic acid biosynthesis and denitrification. Based on the evidence above, strain 3B26T is considered to represent a novel species of the genus Shewanella, and the name Shewanella zhuhaiensis sp. nov. (type strain 3B26T = GDMCC 1.2057T = KCTC 82339T) is proposed.

Liquid-chromatography mass spectrometry describes post-translational modification of Shewanella outer membrane proteins

Electrogenic bacteria deliver excess respiratory electrons to externally located metal oxide particles and electrodes. The biochemical basis for this process is arguably best understood for species of Shewanella where the integral membrane complex termed MtrCAB is key to electron transfer across the bacterial outer membranes. A crystal structure was recently resolved for MtrCAB from S. baltica OS185. However, X-ray diffraction did not resolve the N-terminal residues so that the lipidation status of proteins in the mature complex was poorly described. Here we report liquid chromatography mass spectrometry revealing the intact mass values for all three proteins in the MtrCAB complexes purified from Shewanella oneidensis MR-1 and S. baltica OS185. The masses of MtrA and MtrB are consistent with both proteins being processed by Signal Peptidase I and covalent attachment of ten c-type hemes to MtrA. The mass of MtrC is most reasonably interpreted as arising from protein processed by Signal Peptidase II to produce a diacylated lipoprotein containing ten c-type hemes. Our two-step protocol for liquid-chromatography mass spectrometry used a reverse phase column to achieve on-column detergent removal prior to gradient protein resolution and elution. We envisage the method will be capable of simultaneously resolving the intact mass values for multiple proteins in other membrane protein complexes.

Shewanella algae, an Emerging Pathogen, Causing Skin and Soft Tissue Infections

Abstract Shewanella species, gram-negative saprophytic bacteria, are frequently found in warmer marine environments and soil. Among the Shewanella genus, Shewanella algae and Shewanella putrefaciens cause human infections, with S. algae being more common. Shewanella species are opportunistic bacteria and are being identified as potential pathogens causing wide range of illnesses in both immunocompromised and immunocompetent patients. Diagnosis can be difficult because of limited awareness and microbiologic data. However, high index of clinical suspicion and history of recent exposure to marine environments can help in facilitating early diagnosis. Delay may lead to sepsis and multiorgan failure. Infections can be identified in cases without exposure to aquatic environments, as seen in our case. A 39-year-old man with no marine exposure presented with progressively worsening lower extremity cellulitis with positive wound cultures for S. algae. We aim to increase awareness of this rare emerging pathogen so that treatment can be tailored rapidly and appropriately.

Oxidation of Sb(III) by Shewanella species with the assistance of extracellular organic matter

Antimony (Sb) is a toxic substance that poses a serious ecological threat when released into the environment. The species and redox state of Sb determine its environmental toxicity and fate. Understanding the redox transformations and biogeochemical cycling of Sb is crucial for analyzing and predicting its environmental behavior. Dissolved organic matter (DOM) in the environment greatly affects the fate of Sb. Microbially produced DOM is a vital component of environmental DOM; however, its specific role in Sb(III) oxidation has not been experimentally confirmed. In this work, the oxidation capacity of several Shewanella strains and their derived DOM to Sb(III) was confirmed. The oxidation rate of Sb(III) shows a positive correlation with DOM concentration, with higher rates observed under neutral and weak alkaline conditions, regardless of the presence of light. Incubation experiments indicated that extracellular enzymes and common reactive oxygen species were not involved in the oxidation of Sb(III). Characteristics of DOM suggests that microbial humic acid-like and fulvic acid-like substances are the potential contributors to Sb(III) oxidation. These findings not only experimentally validate the role of bacterial-derived DOM in Sb(III) oxidation but also reveal the significance of Shewanella and biogenic DOM in the biogeochemical cycling of Sb.

Phylogenetic analysis of Shewanella spp. isolated from fish.

Different species of Shewanella spp. widely inhabit freshwater and marine environments. Some of them are opportunistic fish pathogens. The application of high-throughput sequencing enabled the characterization and taxonomic reclassification of many Shewanella spp. species. Still, some strains collected from fish need to be better recognized. The aim of the present study was to classify and determine the phylogenetic relationships of Shewanella spp. collected from fish. The complete genomes of 94 strains of Shewanella spp. from different fish species were sequenced using Illumina platform (MiSeq). The 16S rRNA gene, genomic features and whole-genome relationships of those bacteria were comprehensively analysed in comparison to reference strains. Whole-genome analysis showed that the tested Shewanella spp. strains were clustered into six groups similar to reference strains of S. xiamenensis, S. oneidensis, S. glacialipiscicola, S. hafniensis, S. baltica and S. oncorhynchi. Our study indicates that the whole-genome sequence analysis enabled taxonomic classification and assessment of the diversity of the Shewanella spp. strains, as opposed to recently the gold standard method of 16S rRNA amplicon sequencing. The high genetic diversity and low similarity to the reference genome of S. oneidensis indicate that the group of strains may be a subspecies or even new species. Furthermore, we showed that the most frequent Shewanella spp. species occurring in freshwater fish in our study is the recently described species S. oncorhynchi.

Isolation and genomics of ten novel Shewanella species from mangrove wetland.

Mangrove bacteria largely compose the microbial community of the coastal ecosystem and are directly associated with nutrient cycling. In the present study, 12 Gram-negative and motile strains were isolated from a mangrove wetland in Zhangzhou, China. Pairwise comparisons (based on 16S rRNA gene sequences) and phylogenetic analysis indicated that these 12 strains belong to the genus Shewanella. The 16S rRNA gene sequence similarities among the 12 Shewanella strains and their related type strains ranged from 98.8 to 99.8 %, but they still could not be considered as known species. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between the 12 strains and their related type strains were below the cut-off values (ANI 95-96% and dDDH 70 %) for prokaryotic species delineation. The DNA G+C contents of the present study strains ranged from 44.4 to 53.8 %. The predominant menaquinone present in all strains was MK-7. The present study strains (except FJAT-53532T) also contained ubiquinones (Q-8 and Q-7). The polar lipid phosphatidylglycerol and fatty acid iso-C15 : 0 was noticed in all strains. Based on phenotypic, chemotaxonomic, phylogenetic and genomic comparisons, we propose that these 12 strains represent 10 novel species within the genus Shewanella, with the names Shewanella psychrotolerans sp. nov. (FJAT-53749T=GDMCC 1.2398T=KCTC 82649T), Shewanella zhangzhouensis sp. nov. (FJAT-52072T=MCCC 1K05363T=KCTC 82447T), Shewanella rhizosphaerae sp. nov. (FJAT-53764T=GDMCC 1.2349T=KCTC 82648T), Shewanella mesophila sp. nov. (FJAT-53870T=GDMCC 1.2346T= KCTC 82640T), Shewanella halotolerans sp. nov. (FJAT-53555T=GDMCC 1.2344T=KCTC 82645T), Shewanella aegiceratis sp. nov. (FJAT-53532T=GDMCC 1.2343T=KCTC 82644T), Shewanella alkalitolerans sp. nov. (FJAT-54031T=GDMCC 1.2347T=KCTC 82642T), Shewanella spartinae sp. nov. (FJAT-53681T=GDMCC 1.2345T=KCTC 82641T), Shewanella acanthi sp. nov. (FJAT-51860T=GDMCC 1.2342T=KCTC 82650T) and Shewanella mangrovisoli sp. nov. (FJAT-51754T=GDMCC 1.2341T= KCTC 82647T).

High-throughput sequencing reveals the dominance of Shewanella species in the intestinal microbiota of barbour’s seahorses (Hippocampus barbouri)

In this study, taxonomic classification of intestinal microbiota from healthy Barbour’s seahorses (Hippocampus barbouri) was determined as it plays an important role in host nutrition and immunity. Genomic DNA was extracted from the intestinal mucus samples of eleven Barbour’s seahorses, which were subjected to high-throughput sequencing of bacterial 16 S rRNA genes targeting V3-V4 regions. The results showed that there were 302,891 amplicon sequence reads representing all samples, with 46 total operational taxonomic units (OTU). Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria were the most predominant phyla observed, with 13 classes, 22 orders, 28 families, and 35 genera, respectively. The results also revealed that the most abundant OTUs were affiliated with the genus Shewanella. Findings in this study may shed light on further studies in exploring the potential implications of intestinal microbiota to seahorses in terms of health status, development, growth, and survival. This could also be used as baseline data for preliminary screening of bacterial species as potential probiotics.

Shewanella subflava sp. nov., a novel multi-resistant bacterium, isolated from the estuary of the Fenhe River into the Yellow River.

A aerobic, gram-negative, rod-shaped and polar-flagellum bacterial strain, designated as FYR11-62T, was isolated from the estuary of the Fenhe River into the Yellow River in Shanxi Province, China. The isolate was able to grow at 4-37°C (optimum, 25°C), pH 5.5-9.5 (optimum, pH 7.5) and in the presence of 0-7.0% (w/v) NaCl (optimum, 1.0% NaCl). Phylogenetic analyses based on 16S rRNA genes and 1597 single-copy orthologous clusters indicated that strain FYR11-62T affiliated with the genus Shewanella and shared the highest 16S rRNA gene sequence similarity to Shewanella aestuarii SC18T (98.3%) and Shewanella gaetbuli TF-27T (97.3%), respectively. The major fatty acids were summed feature 3 (C16:1 ω7c and/or C16:1 ω6c), C16:0 and iso-C15:0. The major polar lipids were phosphatidylethanolamine and phosphatidylglycerol. The main quinones were Q-7 and Q-8. The genomic DNA G + C content was 41.6%. Gene annotation showed that strain FYR11-62T possessed 30 antibiotic resistance genes, implying its multiple antidrug resistance. The average nucleotide identity and digital DNA-DNA hybridization values between strain FYR11-62T and its closely related species were all below the thresholds for species delineation. The phylogenetic position together with the results of the analysis of morphological, physiological and genomic features support the classification of strain FYR11-62T (= MCCC 1K07242T = KCTC 92244T) as a novel species of the genus Shewanella, for which the name Shewanella subflava sp. nov. is proposed.

Genomic Analysis of the Deep-Sea Bacterium Shewanella sp. MTB7 Reveals Backgrounds Related to Its Deep-Sea Environment Adaptation

Shewanella species are widely distributed in various environments, especially deep-sea sediments, due to their remarkable ability to utilize multiple electron receptors and versatile metabolic capabilities. In this study, a novel facultatively anaerobic, psychrophilic, and piezotolerant bacterium, Shewanella sp. MTB7, was isolated from the Mariana Trench at a depth of 5900 m. Here, we report its complete genome sequence and adaptation strategies for survival in deep-sea environments. MTB7 contains what is currently the third-largest genome among all isolated Shewanella strains and shows higher coding density than neighboring strains. Metabolically, MTB7 is predicted to utilize various carbon and nitrogen sources. D-amino acid utilization and HGT-derived purine-degrading genes could contribute to its oligotrophic adaptation. For respiration, the cytochrome o ubiquinol oxidase genes cyoABCDE, typically expressed at high oxygen concentrations, are missing. Conversely, a series of anaerobic respiratory genes are employed, including fumarate reductase, polysulfide reductase, trimethylamine-N-oxide reductase, crotonobetaine reductase, and Mtr subunits. The glycine reductase genes and the triplication of dimethyl sulfoxide reductase genes absent in neighboring strains could also help MTB7 survive in low-oxygen environments. Many genes encoding cold-shock proteins, glycine betaine transporters and biosynthetic enzymes, and reactive oxygen species-scavenging proteins could contribute to its low-temperature adaptation. The genomic analysis of MTB7 will deepen our understanding of microbial adaptation strategies in deep-sea environments.

Unraveling Biohydrogen Production and Sugar Utilization Systems in the Electricigen Shewanella marisflavi BBL25.

Identification of novel, electricity-producing bacteria has garnered remarkable interest because of the various applications of electricigens in microbial fuel cell and bioelectrochemical systems. Shewanella marisflavi BBL25, an electricity-generating microorganism, uses various carbon sources and shows broader sugar utilization than the better-known S. oneidensis MR-1. To determine the sugar-utilizing genes and electricity production and transfer system in S. marisflavi BBL25, we performed an in-depth analysis using whole-genome sequencing. We identified various genes associated with carbon source utilization and the electron transfer system, similar to those of S. oneidensis MR-1. In addition, we identified genes related to hydrogen production systems in S. marisflavi BBL25, which were different from those in S. oneidensis MR-1. When we cultured S. marisflavi BBL25 under anaerobic conditions, the strain produced 427.58 ± 5.85 μl of biohydrogen from pyruvate and 877.43 ± 28.53 μl from xylose. As S. oneidensis MR-1 could not utilize glucose well, we introduced the glk gene from S. marisflavi BBL25 into S. oneidensis MR-1, resulting in a 117.35% increase in growth and a 17.64% increase in glucose consumption. The results of S. marisflavi BBL25 genome sequencing aided in the understanding of sugar utilization, electron transfer systems, and hydrogen production systems in other Shewanella species.

Ecological drivers and potential functions of viral communities in flooded arsenic-contaminated paddy soils

This work revealed the profile of viral communities in paddy soils with different levels of arsenic (As) contamination during the flooded period. The structure of viral communities differed significantly in highly and moderately As-contaminated soils. The diversity of soil viral communities under high As contamination decreased. Siphoviridae, Podoviridae, Myoviridae, and Microviridae were the dominant viral families in all samples, and the relative abundances of five of the top 20 viral genera were significantly different between highly and moderately As-contaminated groups. Seventeen dissimilatory As(V)-reducing bacteria were predicted to host 161 viral operational taxonomic units (vOTUs), mainly affiliated with the genera of Sulfurospirillum, Deferribacter, Bacillus and Fusibacter. Among them, 28 vOTUs were also associated with Fe(III)-reducing bacteria, which belonged to different species of the genus Shewanella. Procrustes analysis showed that the community structure of soil viruses was strongly correlated with both prokaryotic community structure and geochemical properties. Random forest analyses revealed that the Total-Fe, DCB-Fe and oxalate-Fe were the most significant variables on viral community richness, while the total-As concentration was an important factor on the Shannon index. Furthermore, As resistance genes (ArsC, ArsR and ArsD), As methylation genes (arsM) and As transporter genes (Pst and Pit) were identified among the auxiliary metabolic genes (AMGs) of the virome. This work revealed that the viruses might influence microbial adaptation in response to As-induced stress, and provided a perspective on the potential virus-mediated biogeochemical cycling of As.

A Review on Spoilage Microorganisms in Fresh and Processed Aquatic Food Products

Aquatic food products are greatly perishable owing to their biological compositions. Spoilage is defined as any alteration in food products that lead to unacceptable attributes to the consumers, mainly through sensory perception. Microbial spoilage is a common type of spoilage among seafood products. In this paper, we reviewed and discussed the various spoilage microorganisms (molds, yeasts, and bacteria) in fresh and processed fish and fishery products. Many studies reported that processed fishery products, such as salted, dried, and hot-smoked fish, are commonly spoiled by molds, mainly under the genus of Aspergillus and Penicillium. Yeasts as spoilage agents have been associated with fish and fishery products stored at low temperatures, notably dominated by two genera, Candida and Rhodotorula, while other yeast species have also been linked to heavily-salted fish and fermented aquatic foods. The important genera of spoilage bacteria that have been documented in fresh and processed fish and fishery products were Pseudomonas, Alcaligenes, Aeromonas, Enterobacter, Bacillus, Enterococcus, Psychrobacter, Escherichia coli, Listeria, Brochothrix, and Shewanella species. Microorganisms play an important role in the spoilage of processed and fresh fish/fishery products. Further research should be undertaken to fully understand the microbial world, particularly associated with aquatic food products.

Antibacterial mechanism of lactobionic acid against Shewanella baltica and Shewanella putrefaciens and its application on refrigerated shrimp

Lactobionic acid (LBA) is a novel antibacterial agent that has attracted much interest in recent years. However, the study on the antibacterial effect of LBA on spoilage bacteria is rare. This study aims to investigate the antibacterial activity and mechanism of LBA on Shewanella baltica and Shewanella putrefaciens, which are the common spoilage microorganisms in chilled seafood. The results demonstrated that LBA was an effective bacteriostat against S. baltica and S. putrefaciens, with the minimum inhibitor concentration (MIC) of 8 mg/mL. Both the two Shewanella species could be completely killed by LBA at 2 MIC. LBA damaged the cell membrane integrity and increased outer membrane permeability, causing the increase in protein leakage and conductivity, which was supported by the bacterial morphology observed with scanning electron microscopy. Besides, LBA could interact with the bacterial genome DNA, resulting in the dysfunction of cell function. Moreover, LBA exhibited an effectively inhibitory effect on slowing down microbial growth, melanosis and lipid oxidation rate in refrigerated shrimp. These results suggest that LBA would be a promising antibacterial compound used in seafood.

Recombineering in Non-Model Bacteria.

The technology of recombineering, in vivo genetic engineering, was initially developed in Escherichia coli and uses bacteriophage-encoded homologous recombination proteins to efficiently recombine DNA at short homologies (35 to 50 nt). Because the technology is homology driven, genomic DNA can be modified precisely and independently of restriction site location. Recombineering uses linear DNA substrates that are introduced into the cell by electroporation; these can be PCR products, synthetic double-strand DNA (dsDNA), or single-strand DNA (ssDNA). Here we describe the applications, challenges, and factors affecting ssDNA and dsDNA recombineering in a variety of non-model bacteria, both Gram-negative and -positive, and recent breakthroughs in the field. We list different microbes in which the widely used phage λ Red and Rac RecET recombination systems have been used for in vivo genetic engineering. New homologous ssDNA and dsDNA recombineering systems isolated from non-model bacteria are also described. The Basic Protocol outlines a method for ssDNA recombineering in the non-model species of Shewanella. The Alternate Protocol describes the use of CRISPR/Cas as a counter-selection system in conjunction with recombineering to enhance recovery of recombinants. We provide additional background information, pertinent considerations for experimental design, and parameters critical for success. The design of ssDNA oligonucleotides (oligos) and various internet-based tools for oligo selection from genome sequences are also described, as is the use of oligo-mediated recombination. This simple form of genome editing uses only ssDNA oligo(s) and does not require an exogenous recombination system. The information presented here should help researchers identify a recombineering system suitable for their microbe(s) of interest. If no system has been characterized for a specific microbe, researchers can find guidance in developing a recombineering system from scratch. We provide a flowchart of decision-making paths for strategically applying annealase-dependent or oligo-mediated recombination in non-model and undomesticated bacteria. © 2022 Wiley Periodicals LLC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA. Basic Protocol: ssDNA recombineering in Shewanella species Alternate Protocol: ssDNA recombineering coupled to CRISPR/Cas9 in Shewanella species.

Global occurrence of the bacteria with capability for extracellular reduction of iodate.

The γ-proteobacterium Shewanella oneidensis MR-1 reduces iodate to iodide extracellularly. Both dmsEFAB and mtrCAB gene clusters are involved in extracellular reduction of iodate by S. oneidensis MR-1. DmsEFAB reduces iodate to hypoiodous acid and hydrogen peroxide (H2O2). Subsequently, H2O2 is reduced by MtrCAB to facilitate DmsEFAB-mediated extracellular reduction of iodate. To investigate the distribution of bacteria with the capability for extracellular reduction of iodate, bacterial genomes were systematically searched for both dmsEFAB and mtrCAB gene clusters. The dmsEFAB and mtrCAB gene clusters were found in three Ferrimonas and 26 Shewanella species. Coexistence of both dmsEFAB and mtrCAB gene clusters in these bacteria suggests their potentials for extracellular reduction of iodate. Further analyses demonstrated that these bacteria were isolated from a variety of ecosystems, including the lakes, rivers, and subsurface rocks in East and Southeast Asia, North Africa, and North America. Importantly, most of the bacteria with both dmsEFAB and mtrCAB gene clusters were found in different marine environments, which ranged from the Arctic Ocean to Antarctic coastal marine environments as well as from the Atlantic Ocean to the Indian and Pacific Oceans. Widespread distribution of the bacteria with capability for extracellular reduction of iodate around the world suggests their significant importance in global biogeochemical cycling of iodine. The genetic organization of dmsEFAB and mtrCAB gene clusters also varied substantially. The identified mtrCAB gene clusters often contained additional genes for multiheme c-type cytochromes. The numbers of dmsEFAB gene cluster detected in a given bacterial genome ranged from one to six. In latter, duplications of dmsEFAB gene clusters occurred. These results suggest different paths for these bacteria to acquire their capability for extracellular reduction of iodate.