The viable but non-culturable (VBNC) status of Shewanella putrefaciens (S. putrefaciens) with thermosonication (TS) treatment.

Although thermosonication (TS) treatment has been widely used in food sterilization, the viable but non-culturable (VBNC) of bacteria with TS treatment has still concerned potential food safety and public health. The molecular mechanism of VBNC status of bacteria with TS treatment is not clearly known. Therefore, in this study, we used Shewanella putrefaciens, which was a common putrefactive bacteria in aquatic products, to study the VBNC state of bacteria with TS treatment. Firstly, our results revealed that S. putrefaciens still could enter the VBNC state after TS treatments: 50 kHz, 300 W, 30 min ultrasonic treatment and 70 °C heating; Subsequently, we found the VBNC state of S. putrefaciens can resist the damage of TS treatment, such as cell wall break, DNA degradation, etc; Finally, four-dimensional data-independent acquisition-based proteomics showed that under VBNC state, S. putrefaciens upregulated functional proteins to resist TS treatment, such as: ribosomal proteins to accelerate the synthesis of stress proteins to counteract TS treatments, ornithine decarboxylase SpeF and MraY to repair TS treatment-induced damage, etc. Meanwhile, S. putrefaciens downregulates metabolic and transport functional proteins such as dehydrogenase to reduce the metabolism. Importantly, among those proteins, the ribosomal transcriptional regulatory protein family, such as rpsB, etc, may be the key proteins for S. putrefaciens entering VBNC state. This finding can provide some new strategies for preventing VBNC status of bacteria with TS treatment, such as: inhibition of key proteins, etc.

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.

Engineering Shewanella oneidensis-Carbon Felt Biohybrid Electrode Decorated with Bacterial Cellulose Aerogel-Electropolymerized Anthraquinone to Boost Energy and Chemicals Production.

Interfacial electron transfer between electroactive microorganisms (EAMs) and electrodes underlies a wide range of bio-electrochemical systems with diverse applications. However, the electron transfer rate at the biotic-electrode interface remains low due to high transmembrane and cell-electrode interfacial electron transfer resistance. Herein, a modular engineering strategy is adopted to construct a Shewanella oneidensis-carbon felt biohybrid electrode decorated with bacterial cellulose aerogel-electropolymerized anthraquinone to boost cell-electrode interfacial electron transfer. First, a heterologous riboflavin synthesis and secretion pathway is constructed to increase flavin-mediated transmembrane electron transfer. Second, outer membrane c-Cyts OmcF is screened and optimized via protein engineering strategy to accelerate contacted-based transmembrane electron transfer. Third, a S. oneidensis-carbon felt biohybrid electrode decorated with bacterial cellulose aerogel and electropolymerized anthraquinone is constructed to boost the interfacial electron transfer. As a result, the internal resistance decreased to 42 Ω, 480.8-fold lower than that of the wild-type (WT) S. oneidensis MR-1. The maximum power density reached 4286.6 ± 202.1 mW m-2, 72.8-fold higher than that of WT. Lastly, the engineered biohybrid electrode exhibited superior abilities for bioelectricity harvest, Cr6+ reduction, and CO2 reduction. This study showed that enhancing transmembrane and cell-electrode interfacial electron transfer is a promising way to increase the extracellular electron transfer of EAMs.

Genetic Code Expansion in Shewanella oneidensis MR-1 Allows Site-Specific Incorporation of Bioorthogonal Functional Groups into a c-Type Cytochrome.

Genetic code expansion has enabled cellular synthesis of proteins containing unique chemical functional groups to allow the understanding and modulation of biological systems and engineer new biotechnology. Here, we report the development of efficient methods for site-specific incorporation of structurally diverse noncanonical amino acids (ncAAs) into proteins expressed in the electroactive bacterium Shewanella oneidensis MR-1. We demonstrate that the biosynthetic machinery for ncAA incorporation is compatible and orthogonal to the endogenous pathways of S. oneidensis MR-1 for protein synthesis, maturation of c-type cytochromes, and protein secretion. This allowed the efficient synthesis of a c-type cytochrome, MtrC, containing site-specifically incorporated ncAA in S. oneidensis MR-1 cells. We demonstrate that site-specific replacement of surface residues in MtrC with ncAAs does not influence its three-dimensional structure and redox properties. We also demonstrate that site-specifically incorporated bioorthogonal functional groups could be used for efficient site-selective labeling of MtrC with fluorophores. These synthetic biology developments pave the way to expand the chemical repertoire of designer proteins expressed in S. oneidensis MR-1.

Impact of chitin-derived ß-N-acetyl-D-glucosaminyl-(1,4)-D-glucosamine on chitinase up-regulation in Shewanella baltica.

The first steps in chitin degradation in marine bacteria involve chitinase, which produces N,N'-diacetylchitobiose (GlcNAc)2 from chitin. Moreover, in Vibrio bacteria, chitinase activity is enhanced by heterodisaccharide ß-N-acetyl-D-glucosaminyl-(1,4)-D-glucosamine (GlcNAc-GlcN) produced from (GlcNAc)2 by chitin oligosaccharide deacetylase (COD). However, the role of COD in other marine bacteria, such as Shewanella, remains unexplored. This study investigates GlcNAc-GlcN's impact on chitinase gene expression and enzyme production in S. baltica ATCC BAA-1091, drawing parallels with Vibrio parahaemolyticus RIMD2210633. Using real-time quantitative PCR, the study assesses the up-regulation of chitinase gene expression in S. baltica in response to GlcNAc-GlcN, informed by COD's known ability to produce GlcNAc-GlcN from (GlcNAc)2. In Vibrio, GlcNAc-GlcN considerably up-regulates chitinase gene expression. This study posits a similar regulatory mechanism in S. baltica, with preliminary investigations indicating COD's capacity to produce GlcNAc-GlcN. This study highlights the importance of exploring GlcNAc-GlcN's regulatory role in chitin metabolism across diverse marine bacteria. The potential induction of chitinase production in S. baltica suggests broader ecological implications. Further research is crucial for a comprehensive understanding of chitin utilization and regulatory pathways in marine bacterial genera.

Clinical Presentation and Outcomes Following Infection With Vibrio spp, Aeromonas spp, Chromobacterium violaceum, and Shewanella spp Water-Associated Organisms in Tropical Australia, 2015-2022.

Background: Water-associated bacterial infections cause a wide spectrum of disease. Although many of these infections are typically due to human host commensal Staphylococcal or Streptococcal spp, water exposure can result in infections with environmental gram negatives such as Vibrio spp, Aeromonas spp, Chromobacterium violaceum, and Shewanella spp (collectively VACS). Methods: We performed a retrospective analysis of the epidemiology, clinical presentation, and outcomes of deep and superficial infections associated with VACS organisms in our health service between 1 January 2015 and 31 December 2023. Results: We identified 317 patient episodes of infection with VACS organisms over this period. Of these, Aeromonas spp (63%) was the most common, followed by Vibrio spp (19%), Shewanella spp (13%), and C violaceum (5%). The majority were isolated from males (74.4%) and involved the lower limb (67.5%). Mild infections were more common than severe presentations, with only 15 (4.7%) admissions to the intensive care unit and 8 (2.5%) deaths. Colonization occurred in 6.9% of patients, in contrast to the perceived severity of some of these bacteria. Copathogens were common and included Staphylococcus aureus (48%) and enteric bacteria (57%). The majority of patients (60%) had no documented water exposure. Initial empiric antimicrobial therapy presumptively covered the susceptibilities of the isolated organisms in 47.3% of patients; however, a lack of VACS-covering empirical therapy was not associated with readmission. Conclusions: The isolation of a VACS organism in our setting was often not associated with documented water exposure, which has implications for empiric antimicrobial therapy. Severe disease and death were uncommon.

Engineering bionanoreactor in bacteria for efficient hydrogen production.

Hydrogen production through water splitting is a vital strategy for renewable and sustainable clean energy. In this study, we developed an approach integrating nanomaterial engineering and synthetic biology to establish a bionanoreactor system for efficient hydrogen production. The periplasmic space (20 to 30 nm) of an electroactive bacterium, Shewanella oneidensis MR-1, was engineered to serve as a bionanoreactor to enhance the interaction between electrons and protons, catalyzed by hydrogenases for hydrogen generation. To optimize electron transfer, we used the microbially reduced graphene oxide (rGO) to coat the electrode, which improved the electron transfer from the electrode to the cells. Native MtrCAB protein complex on S. oneidensis and self-assembled iron sulfide (FeS) nanoparticles acted in tandem to facilitate electron transfer from an electrode to the periplasm. To enhance proton transport, S. oneidensis MR-1 was engineered to express Gloeobacter rhodopsin (GR) and the light-harvesting antenna canthaxanthin. This led to efficient proton pumping when exposed to light, resulting in a 35.6% increase in the rate of hydrogen production. The overexpression of native [FeFe]-hydrogenase further improved the hydrogen production rate by 56.8%. The bionanoreactor engineered in S. oneidensis MR-1 achieved a hydrogen yield of 80.4 µmol/mg protein/day with a Faraday efficiency of 80% at a potential of -0.75 V. This periplasmic bionanoreactor combines the strengths of both nanomaterial and biological components, providing an efficient approach for microbial electrosynthesis.

Antibacterial mechanism of CO2 combined with low temperature against Shewanella putrefaciens by biochemical and metabolomics analysis.

To further reveal the inhibition mechanism of carbon dioxide (CO2) on Shewanella putrefaciens (S. putrefaciens), influence on metabolic function was studied by biochemical and metabolomics analysis. Accordingly, reduction of intracellular pH (pHi), depolarization of cell membrane and accumulation of reactive oxygen species (ROS) indicated that CO2 changed the membrane permeability of S. putrefaciens. Besides, adenosine triphosphate (ATP), ATPase, nicotinamide adenine dinucleotide (NAD+/NADH) and ratios of NADH/NAD+ were detected, indicating a role of CO2 in repressing respiratory pathway and electron transport. According to metabolomics results, CO2 induced differential expressions of metabolites, disordered respiratory chain and weakened energy metabolism of S. putrefaciens. Inhibition of respiratory rate-limiting enzymes also revealed that electron transfer of respiratory chain was blocked, cell respiration was weakened, and thus energy supply was insufficient under CO2 stress. These results revealed that CO2 caused disruption of metabolic function, which might be the main cause of growth inhibition for S. putrefaciens.

Quahogging in a Marine Habitat: An Extremely Rare Source of an Organism to Cause Endocarditis.

A 66-year-old man with a history of apical variant hypertrophic cardiomyopathy, heart failure with preserved ejection fraction (HFpEF), severe pulmonary hypertension, and prior Group B streptococcal mitral valve endocarditis four months before, presented with generalized body shakes and urinary incontinence. Computed tomography angiography revealed an acute left M1 occlusion. The patient underwent mechanical thrombectomy. Within 24 hours of presentation, he developed hypotension, tachycardia, and fever. Infectious workup revealed a leukocytosis. One out of two sets of blood cultures revealed bacteremia with Shewanella algae. A transthoracic echocardiogram revealed a large mitral valve vegetation with multiple mobile components portending a high thromboembolic risk, as evidenced by his acute presentation with multiple embolic infarcts. He was diagnosed with infectious endocarditis caused by Shewanella algae, a rare marine environment pathogen. He was treated with ciprofloxacin 750 mg twice daily orally and meropenem 2 g every eight hours intravenously with an initial decrease in the mitral valve vegetation size. He was discharged on ceftriaxone 2g and ciprofloxacin 750mg every 12 hours for a total of six weeks from his first negative blood cultures. He was monitored through transthoracic echocardiography as he continued medical management with levofloxacin 750 mg daily. Six months after his discharge from the hospital he developed worsening heart failure and elected to pursue comfort measures only.

INTRAVENOUS CENTRAL CATHETER COLONIZATION BY SHEWANELLA PUTREFACIENS IN A BURNED PATIENT.

Shewanella putrefaciens is an opportunistic pathogen rarely responsible for human infection. However, it has been reported that it causes skin and soft tissue infections and bacteremia in immune-compromised patients, such as cellulitis, abscesses, bacteremia, and wound infection. It is an oxidase and catalase-positive non-fermenter gram-negative rod that produces hydrogen sulfide. We report the case of a 90-year-old woman, who presented an invasive infectious burn wound associated with Shewanella putrefaciens bacteremia. She was admitted into the burn center of the military hospital M.S Nekkache of Algiers, suffering from 40% TBSA with a history of diabetes. After one week of admission, the patient complained of a high fever. Microbiological culture of the catheter tip was positive and showed pale colonies on the MacConkey agar, non-lactose fermenting plate. Nutritive agar medium culture showed red pale tan colonies with a concentration >103 CFU. Identification and antibiotic susceptibility were obtained by the Phoenix system (Becton-Dickinson, USA) as Shewanella putrefaciens. This was confirmed by standards and semi-automated microbiological techniques. Gram stain showed Gram-negative bacilli with positive oxidase and catalase reactions. Production of hydrogen sulfide was confirmed by the semi-automated API 20NE method (biomerieux, France). The isolate was resistant to gentamicin, amikacin, ceftazidime, aztreonam, amoxicillin- clavulanic acid, cefepime, trimethoprim/sulfamethoxazole, and nitrofurantoin. In our case, S. putrefaciens was found in a mixed culture with Klebsiella pneumoniae. No earlier exposure of the patient to marine water had been noticed. Blood culture indicated colonies growth of Acinetobacter baumannii. No further isolation of this bacteria was noticed after treatment. The patient was given imipenem, vancomycin and colistin. Despite our best efforts, the patient could not be saved because of sepsis and renal function failure.

Shewanella putrefaciens est une bactérie opportuniste, rarement responsable d'infections humaines. Elle a toutefois été rapportée comme cause d'infections de la peau et des tissus mous (cellulites, abcès, surinfections de plaies) et de bactériémies chez des patients immunodéprimés. C'est un bacille à Gram négatif non fermentant, oxydase et catalase +, producteur de sulfure d'hydrogène. Nous présentons le cas d'une patiente diabétique de 90 ans ayant subi une bactériémie issue d'une surinfection de brûlure à Shewanella putrefaciens. Elle était hospitalisée dans l'hôpital militaire MS. Nekkache d'Alger à la suite d'une brûlure touchant 40% SCT. Une fièvre élevée a été constatée à J7. La culture de l'extrémité distale du cathéter montrait, sur gélose de McConkey, des colonies pâles non fermentantes. Sur milieu enrichi, on observait >103 CFU rouge pâle, identifiées à Shewanella putrefaciens par le système Phoenix (Beckton-Dickinson), identification confirmée par les techniques microbiologiques standard et semi- automatiques. La coloration de Gram était négative, les réactions catalasique et oxydasique étaient positives. La production de sulfure d'hydrogène était par API 20NE semi- automatique (BioMérieux). La bactérie résistait à gentamicine, amikacine, ceftazidime, aztréonam, amoxicilline- acide clavulanique, céfépime, triméthoprime- sulfaméthoxazole et nitrofurantoïne. Shewanella putrefaciens était associée à Klebsiella pneumoniæ et les hémocultures poussaient à Acinetobacter baumannii. Il n'y avait pas de notion d'exposition antérieure à l'eau de mer. La bactérie n'a pas été retrouvée après traitement par imipénème, vancomycine et colimycine. La patiente est toutefois décédée de sepsis et insuffisance rénale aiguë.

Emergence of mcr-4.3 genes in a novel Shewanella specie isolated from the Arctic environment.

Mobile colistin resistance (mcr) genes are pivotal contributors to last-line of antimicrobial resistance in human infections. Shewanella, historically recognized as a natural environmental bacterium with metal reduction capabilities, recently has been observed in clinical settings. However, limited knowledge has been explored on genetic differences between strains from non-clinical and clinical strains. In this study, we conducted the whole genome sequencing on six Arctic strains, illustrated the phylogenetic relationships on published 393 Shewanella strains that categorized the genus into four lineages (L1 to L4). Over 86.4% of clinical strain group (CG) strains belonged to L1 and L4, carrying mcr-4 genes and a complete metal-reduction pathways gene cluster. Remarkably, a novel Arctic Shewanella strain in L3, exhibits similar genetic characteristics with CG strains that carried both mcr-4 genes and a complete metal reduction pathway gene cluster. It raised concerns about the transmission ability from environment to clinic setting causing in the potential infections, and emphasized the need for monitoring the emerging strains with human infections.

Heme d formation in a Shewanella benthica hemoglobin.

In our continued investigations of microbial globins, we solved the structure of a truncated hemoglobin from Shewanella benthica, an obligate psychropiezophilic bacterium. The distal side of the heme active site is lined mostly with hydrophobic residues, with the exception of a tyrosine, Tyr34 (CD1) and a histidine, His24 (B13). We found that purified SbHbN, when crystallized in the ferric form with polyethylene glycol as precipitant, turned into a green color over weeks. The electron density obtained from the green crystals accommodated a trans heme d, a chlorin-type derivative featuring a γ-spirolactone and a vicinal hydroxyl group on a pyrroline ring. In solution, exposure of the protein to one equivalent of hydrogen peroxide resulted in a similar green color change, but caused by the formation of multiple products. These were oxidation species released on protein denaturation, likely including heme d, and a species with heme covalently attached to the polypeptide. The Tyr34Phe replacement prevented the formation of both heme d and the covalent linkage. The ready modification of heme b by SbHbN expands the range of chemistries supported by the globin fold and offers a route to a novel heme cofactor.

Single-walled Carbon Nanotubes Wrapped with Charged Polysaccharides Enhance Extracellular Electron Transfer.

Microbial electrochemical systems (MESs) rely on the microbes' ability to transfer charges from their anaerobic respiratory processes to electrodes through extracellular electron transfer (EET). To increase the generally low output signal in devices, advanced bioelectrical interfaces tend to augment this problem by attaching conducting nanoparticles, such as positively charged multiwalled carbon nanotubes (CNTs), to the base carbon electrode to electrostatically attract the negatively charged bacterial cell membrane. On the other hand, some reports point to the importance of the magnitude of the surface charge of functionalized single-walled CNTs (SWCNTs) as well as the size of functional groups for interaction with the cell membrane, rather than their polarity. To shed light on these phenomena, in this study, we prepared and characterized well-solubilized aqueous dispersions of SWCNTs functionalized by either positively or negatively charged cellulose-derivative polymers, as well as with positively charged or neutral small molecular surfactants, and tested the electrochemical performance of Shewanella oneidensis MR-1 in MESs in the presence of these functionalized SWCNTs. By simple injection into the MESs, the positively charged polymeric SWCNTs attached to the base carbon felt (CF) electrode, and as fluorescence microscopy revealed, allowed bacteria to attach to these structures. As a result, EET currents continuously increased over several days of monitoring, without bacterial growth in the electrolyte. Negatively charged polymeric SWCNTs also resulted in continuously increasing EET currents and a large number of bacteria on CF, although SWCNTs did not attach to CF. In contrast, SWCNTs functionalized by small-sized surfactants led to a decrease in both currents and the amount of bacteria in the solution, presumably due to the detachment of surfactants from SWCNTs and their detrimental interaction with cells. We expect our results will help researchers in designing materials for smart bioelectrical interfaces for low-scale microbial energy harvesting, sensing, and energy conversion applications.

Implications of ammonia stress for the pathogenicity of Shewanella spp. in Oreochromis niloticus: effects on hematological, biochemical, immunological, and histopathological parameters.

Environmental stressors (such as ammonia) in aquaculture could increase the risk of pathogenicity, posing a more severe threat to farmed fish. The aim of this study was to investigate the effects of ammonia stress on the pathogenicity of Shewanella spp. in Oreochromis niloticus. First, a 96-hour static test was used to determine the median lethal concentration (LC50) of unionized ammonia to Nile tilapia. After 96 h of exposure, the Un-ionized ammonia (UIA) LC50 was estimated to be 4.26 mg/L. Second, an experiment was conducted to test the effect of unionized ammonia stress on the pathogenicity of Shewanella spp. in O. niloticus for 30 days. A study involved 180 fish divided into six groups, with the first group serving as a control. The second group (AMN1/10) and the third group (AMN1/20) were not challenged and were exposed to 1/10 (0.42 mg/L) and 1/20 (0.21 mg/L) of the 96-hour LC50 of UIA, respectively. Then 0.2 mL (0.14 × 105) of Shewanella spp. was intraperitoneally injected into the fourth (SH), fifth (SH + AMN1/10), and sixth (SH + AMN1/20) groups, which were subjected to 0, 1/10 (0.42 mg/L), and 1/20 (0.21 mg/L) of the 96-hour LC50 of UIA, respectively. The survival rate, hematological indices, immunological parameters, and antioxidant activity of the fish significantly decreased when they were exposed to ammonia and Shewanella infection separately or together. Histopathological changes were also observed in the kidney and liver. Furthermore, both individual and combined exposures significantly altered renal and hepatic function, with notable increases in glucose and cortisol levels, as well as in the expression of proinflammatory cytokine genes (TNF-α and IL-1ß). However, the detrimental effects of co-exposure to ammonia stress and Shewanella infection were greater than those of separate exposures. As a result, we may say that increased ammonia concentrations enhance the infection of Shewanella spp. These findings could contribute to a better understanding of Shewanella infection in Nile tilapia.

Excitation of Reactive Oxygen Species and Damage to the Cell Membrane, Protein, and DNA are Important Inhibition Mechanisms of CO2 on Shewanella putrefaciens at 4 °C.

To explore whether oxidative stress caused by 100% CO2 is an inhibitory mechanism against Shewanella putrefaciens, the oxidative stress reaction, antioxidant activity, and damage to the cell membrane, protein, and DNA of CO2-incubated S. putrefaciens at 4 °C were evaluated. Research demonstrated that CO2 caused more severe reactive oxygen species (ROS) accumulation. Simultaneously, weaker •OH/H2O2/O2•--scavenging activity and decreased T-VOC and GSH content were also observed. The activities of antioxidant enzymes (SOD, POD, CAT, and GPX) continuously declined, which might be attributed to the CO2-mediated decrease in the pH value. Correspondingly, the cell membrane was damaged with hyperpolarization, increased permeability, and more severe lipid peroxidation. The expression of total and membrane protein decreased, and the synthesis and activity of extracellular protease were inhibited. DNA was also subjected to oxidative damage and expressed at a lower level. All results collaboratively confirmed that ROS excitation and inhibition of antioxidant activity were important inhibition mechanisms of CO2 on S. putrefaciens.

Distinct influence of model electron shuttles on anaerobic mononitrophenols reduction in aquatic environments by Shewanella oneidensis MR-1.

The environmental fate and risks of mononitrophenols (mono-NPs), the simplest nitrophenols (NPs) often found in aquatic environments, are profoundly influenced by anaerobic bioreduction and co-existing electron shuttles (ESs), but little is known about the underlying mechanisms. Here, we elucidate the pathways of anaerobic mono-NPs bioreduction by Shewanella oneidensis MR-1 and assess the effect of model ESs on these processes. We found that all three mono-NPs isomers could be readily reduced to their corresponding aminophenols by S. oneidensis MR-1 under anaerobic conditions. CymA, a core component of the Mtr respiratory pathway, performs a dynamic role in these bioreduction, which is highly dependent on the bioreduction kinetics. The exogenous addition of quinones was found to accelerate the mono-NPs bioreduction through interactions with key outer-membrane proteins (e.g., OmcA and MtrC), and all these processes matched well to linear free energy relationships (LFERs). Surprisingly, adding riboflavin did not influence the bioreduction of all three mono-NPs isomers, which may be due to the contribution of OmcA and MtrC to these bioreduction processes and their downregulated expression. This study enhances our understanding of the environmental fate of mono-NPs and their bioconversion processes, providing valuable insights for the bioremediation of nitrophenol-contaminated sites.

Antibiofilm and antivirulence activity of selenium nanoparticles synthesized from cell-free extract of moderately halophilic bacteria.

Biofilm-forming microbes can pose a major health risk that is difficult to combat. Nanotechnology, on the other hand, represents a novel technique for combating and eliminating biofilm-forming microbes. In this study, the selenium nanoparticles (SeNPs) were biosynthesized from moderate halophilic bacteria isolated from Pichavaram mangrove sediments. The bacterial strain S8 was found to be efficient for SeNPs synthesis and hence identified by 16s r RNA sequencing as Shewanella sp. In UV- spectral analysis the SeNPs displayed a peak at 320 nm due to surface plasmon resonance (SPR). The cell-free extract of Shewanella sp. and SeNPs indicates that the various functional groups in the cell-free extract were mainly involved in the synthesis and stabilization of SeNPs. The SeNPs had a spherical form with average diameter of 49 ± 0.01 nm, according to the FESEM analysis. The EDX shows the distinctive peaks of selenium at 1.37, 11.22.12.49 Kev. In the agar well diffusion method, the SeNPs show inhibitory activity against all the test pathogens with the highest activity noted against P.aeruginosa with a zone of inhibition of 22.7 ± 0.3 mm. The minimal inhibitory concentration (MIC) value of 80 µg/ml, minimal bactericidal concentration (MBC) of 160 µg/ml, and susceptibility constant of 0.043 µg/ml show that SeNPs highly effective against P.aeruginosa. The Sub-MIC value of SeNPs of 20 µg/ml was found to inhibit P.aeruginosa biofilm by 85% as compared to the control. Further, the anti-virulence properties viz., pyocyanin, pyoverdine, hemolytic, and protease inhibition revealed the synthesized SeNPs from halophilic bacteria control the pathogenicity of P.aeruginosa.

Acrylate Reductase of an Anaerobic Electron Transport Chain of the Marine Bacterium Shewanella woodyi.

Many microorganisms are capable of anaerobic respiration in the absence of oxygen, by using different organic compounds as terminal acceptors in electron transport chain. We identify here an anaerobic respiratory chain protein responsible for acrylate reduction in the marine bacterium Shewanella woodyi. When the periplasmic proteins of S. woodyi were separated by ion exchange chromatography, acrylate reductase activity copurified with an ArdA protein (Swoo_0275). Heterologous expression of S. woodyi ardA gene (swoo_0275) in Shewanella oneidensis MR-1 cells did not result in the appearance in them of periplasmic acrylate reductase activity, but such activity was detected when the ardA gene was co-expressed with an ardB gene (swoo_0276). Together, these genes encode flavocytochrome c ArdAB, which is thus responsible for acrylate reduction in S. woodyi cells. ArdAB was highly specific for acrylate as substrate and reduced only methacrylate (at a 22-fold lower rate) among a series of other tested 2-enoates. In line with these findings, acrylate and methacrylate induced ardA gene expression in S. woodyi under anaerobic conditions, which was accompanied by the appearance of periplasmic acrylate reductase activity. ArdAB-linked acrylate reduction supports dimethylsulfoniopropionate-dependent anaerobic respiration in S. woodyi and, possibly, other marine bacteria.

Enhanced antibacterial and corrosion resistance of copper-containing 2205 duplex stainless steel against the corrosive bacterium Shewanella algae.

2205 DSS is an excellent corrosion-resistant engineering metal material, but it is still threatened by microbiological corrosion. The addition of copper elements is a new approach to improving the resistance of 2205 DSS to microbiological corrosion. In this study, 2205-Cu DSS was compared with 2205 DSS to study its antimicrobial properties and resistance to microbiological corrosion in the presence of the electroactive bacterium Shewanella algae. The results showed that compared to 2205 DSS, the biofilm thickness and the number of live bacteria on the surface of 2205-Cu DSS were significantly reduced, demonstrating excellent antimicrobial properties against S. algae. Electrochemical tests and surface morphology characterization results showed that the corrosion rate and pitting of 2205-Cu DSS by S. algae were lower than that of 2205 DSS, indicating better resistance to microbiological corrosion. The good antimicrobial properties and resistance to microbiological corrosion exhibited by 2205-Cu DSS are attributed to the contact antimicrobial properties of copper elements in the 2205-Cu DSS matrix and the release of copper ions for antimicrobial effects. This study provides a new strategy for combating microbiological corrosion.

Characterization of CRISPR-Cas Systems in Shewanella algae and Shewanella haliotis: Insights into the Adaptation and Survival of Marine Pathogens.

CRISPR-Cas systems are adaptive immune mechanisms present in most prokaryotes that play an important role in the adaptation of bacteria and archaea to new environments. Shewanella algae is a marine zoonotic pathogen with worldwide distribution, which accounts for the majority of clinical cases of Shewanella infections. However, the characterization of Shewanella algae CRISPR-Cas systems has not been well investigated yet. Through whole genome sequence analysis, we characterized the CRISPR-Cas systems in S. algae. Our results indicate that CRISPR-Cas systems are prevalent in S. algae, with the majority of strains containing the Type I-F system. This study provides new insights into the diversity and function of CRISPR-Cas systems in S. algae and highlights their potential role in the adaptation and survival of these marine pathogens.