Shewanella Species Research Articles

Pressure-Regulated Gene Expression and Enzymatic Activity of the Two Periplasmic Nitrate Reductases in the Deep-Sea Bacterium Shewanella piezotolerans WP3.

Shewanella species are widely distributed in marine environments, from the shallow coasts to the deepest sea bottom. Most Shewanella species possess two isoforms of periplasmic nitrate reductases (NAP-α and NAP-β) and are able to generate energy through nitrate reduction. However, the contributions of the two NAP systems to bacterial deep-sea adaptation remain unclear. In this study, we found that the deep-sea denitrifier Shewanella piezotolerans WP3 was capable of performing nitrate respiration under high hydrostatic pressure (HHP) conditions. In the wild-type strain, NAP-β played a dominant role and was induced by both the substrate and an elevated pressure, whereas NAP-α was constitutively expressed at a relatively lower level. Genetic studies showed that each NAP system alone was sufficient to fully sustain nitrate-dependent growth and that both NAP systems exhibited substrate and pressure inducible expression patterns when the other set was absent. Biochemical assays further demonstrated that NAP-α had a higher tolerance to elevated pressure. Collectively, we report for the first time the distinct properties and contributions of the two NAP systems to nitrate reduction under different pressure conditions. The results will shed light on the mechanisms of bacterial HHP adaptation and nitrogen cycling in the deep-sea environment.

On-going applications of Shewanella species in microbial electrochemical system for bioenergy, bioremediation and biosensing.

Microbial electrochemical system (MES) has attracted ever-growing interest as a promising platform for renewable energy conversion and bioelectrochemical remediation. Shewanella species, the dissimilatory metal reduction model bacteria with versatile extracellular electron transfer (EET) strategies, are the well-received microorganisms in diverse MES devices for various practical applications as well as microbial EET mechanism investigation. Meanwhile, the available genomic information and the unceasing established gene-editing toolbox offer an unprecedented opportunity to boost the applications of Shewanella species in MES. This review thoroughly summarizes the status quo of the applications of Shewanella species in microbial fuel cells for bioelectricity generation, microbial electrosynthesis for biotransformation of valuable chemicals and bioremediation of environment-hazardous pollutants with synoptical discussion on their EET mechanism. Recent advances in rational design and genetic engineering of Shewanella strains for either promoting the MES performance or broadening their applications are surveyed. Moreover, some emerging applications beyond electricity generation, such as biosensing and biocomputing, are also documented. The challenges and perspectives for Shewanella-based MES are also discussed elaborately for the sake of not only discovering new scientific lights on microbial extracellular respiratory but also propelling practical applications.

Shewanella submarina sp. nov., a gammaproteobacterium isolated from marine water.

A curved-rod-shaped bacterium was isolated from a marine (100 m depth) water sample collected from Bay of Bengal, Visakhapatnam, India. Strain NIO-S14T, was Gram-stain-negative, motile and pale-yellow. NIO-S14T was able to grow aerobically and anaerobically and could utilize a number of organic substrates. Major fatty acids were C12 : 0, iso-C13 : 0, C14 : 0, iso-C15 : 0, C16 : 0 and C16 : 1ω7c and/or C16 : 1ω6c (summed feature 3). NIO-S14T contained diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, two unidentified aminophospholipids and six unidentified lipids as polar lipids. The DNA G+C content of NIO-S14T was 47.9 mol%. The 16S rRNA gene sequence comparisons indicated that the isolate represented a member of the family Shewanellaceae within the class Gammaproteobacteria. According to the results of 16S rRNA gene sequence analysis, NIO-S14T was closely related to Shewanella coralliiwith a pair-wise sequence similarity of 99.26 %. On the basis of the sequence comparison, NIO-S14T clustered with Shewanella coralliiand together they clustered with Shewanella mangroviand seven other species of the genus Shewanella but were distantly related. DNA-DNA hybridization between NIO-S14T and Shewanella corallii DSM 21332Trevealed a relatedness of 35 %. Distinct morphological, physiological and genotypic differences from these previously described taxa supported the classification of NIO-S14T as a representative of a novel species of the genus Shewanella, for which the name Shewanellasubmarina sp. nov. is proposed. The type strain of Shewanellasubmarina is NIO-S14T (=MTCC 12524T=KCTC 52277T=LMG 30752T).

Biosynthesis of Nanomaterials by Shewanella Species for Application in Lithium Ion Batteries.

Nanomaterials exhibit extraordinary properties based on their size, shape, chemical composition, and crystal structure. Owing to their unique properties nanomaterials are preferred over their bulk counterparts for a number of applications. Although conventional physical and chemical routes were established for the massive production of nanomaterials, there are some drawbacks such as environmental burden and high cost that cannot be disregarded. Recently, there has been great interest toward the green synthesis of inorganic nanomaterials. It has been reported that dissimilatory metal reduction by microorganisms is a cost-effective process to remediate toxic organic and inorganic compounds under anaerobic conditions. Particularly, members of the Shewanella genus have been utilized to produce various biogenic nanomaterials with unique micro/nanostructured morphologies through redox transformations as well as to remove harmful metals and metalloids in eco-efficient and environment-friendly methods under ambient conditions. In the present mini-review, we specifically address the active utilization of microbial respiration processes for the synthesis of novel functional biogenic nanomaterials by the members of the Shewanella genus. This biosynthetic method may provide alternative approaches to produce electrode materials for sustainable energy storage applications.

Rare Shewanella spp. associated with pulmonary and bloodstream infections of cancer patients, China: a case report

BackgroundMembers of Shewanella species are opportunistic pathogens that are found in marine environments. Currently more than sixty species have been identified, whereas the most commonly clinical cases associated with Shewanella species have involved only two species, i.e., S. algae and S. putrefaciens. We present two cases of pulmonary and bloodstream infections caused by two rare Shewanella spp. strains from patients of gastrointestinal cancer.Case presentationTwo male patients with a history of gastrointestinal cancer presented to hospital with pulmonary and bloodstream infections, respectively. The infective pathogens of both cases were primarily isolated and identified as Shewanella algae (case I) and Shewanella putrefaciens (case II) by phenotypic features and VITEK 2 system, but they were further confirmed as Shewanella haliotis and Shewanella upenei by 16S rRNA gene sequence analysis. The major bacterial composition of the bronchoalveolar lavage in case I was also identified as Shewanella by 16S rRNA amplicon sequencing analysis. Antimicrobial susceptibility testing showed that the two strains had broad susceptibility, but S. haliotis in the case I was resistant to ciprofloxacin and levofloxacin and S. upenei in the case II was intermediate to imipenem, piperacillin/tazobactam and ciprofloxacin.ConclusionsTo the best of our knowledge, this is the first cases of the pulmonary and bloodstream infections caused by Shewanella spp. from clinical patients in mainland China. Shewanella as a potential pathogen in China should not be ignored.

Characterization of ExeM, an Extracellular Nuclease of Shewanella oneidensis MR-1.

Bacterial extracellular nucleases have multiple functions in processes as diverse as nutrient acquisition, natural transformation, biofilm formation, or defense against neutrophil extracellular traps (NETs). Here we explored the properties of ExeM in Shewanella oneidensis MR-1, an extracellular nuclease, which is widely conserved among species of Shewanella, Vibrio, Aeromonas, and others. In S. oneidensis, ExeM is crucial for normal biofilm formation. In vitro activity measurements on heterologously produced ExeM revealed that this enzyme is a sugar-unspecific endonuclease, which requires Ca2+ and Mg2+/Mn2+ as co-factors for full activity. ExeM was almost exclusively localized to the cytoplasmic membrane fraction, even when a putative C-terminal membrane anchor was deleted. In contrast, ExeM was not detected in medium supernatants. Based on the results we hypothesize that ExeM predominantly interacts with DNA in close proximity to the cell, e.g., to promote biofilm formation and defense against NETs, or to control uptake of DNA.

ZomB is essential for flagellar motor reversals in Shewanella putrefaciens and Vibrio parahaemolyticus.

The ability of most bacterial flagellar motors to reverse the direction of rotation is crucial for efficient chemotaxis. In Escherichia coli, motor reversals are mediated by binding of phosphorylated chemotaxis protein CheY to components of the flagellar rotor, FliM and FliN, which induces a conformational switch of the flagellar C-ring. Here, we show that for Shewanella putrefaciens, Vibrio parahaemolyticus and likely a number of other species an additional transmembrane protein, ZomB, is critically required for motor reversals as mutants lacking ZomB exclusively exhibit straightforward swimming also upon full phosphorylation or overproduction of CheY. ZomB is recruited to the cell poles by and is destabilized in the absence of the polar landmark protein HubP. ZomB also co-localizes to and may thus interact with the flagellar motor. The ΔzomB phenotype was suppressed by mutations in the very C-terminal region of FliM. We propose that the flagellar motors of Shewanella, Vibrio and numerous other species harboring orthologs to ZomB are locked in counterclockwise rotation and may require interaction with ZomB to enable the conformational switch required for motor reversals. Regulation of ZomB activity or abundance may provide these species with an additional means to modulate chemotaxis efficiency.

Shewanella saliphila sp. nov., Shewanella ulleungensis sp. nov. and Shewanella litoralis sp. nov., isolated from coastal seawater

Three Gram-negative, non-spore-forming, rod-shaped and motile bacterial strains, designated MMS16-UL250T, MMS16-UL253T and MMS16-UL482T, were isolated from coastal seawater and subjected to taxonomic characterization. All isolates grew at 4-30 °C (optimum, 25 °C), at pH 6-10 (pH 7) and in the presence of up to 8 % NaCl (2.5-4.5 %). The 16S rRNA gene sequence similarities between the three isolates and Shewanella algicola St-6T, the closest species, were 98.1-99.2 %, and those among the isolates were 98.5-99.0 %. In the phylogenetic tree, MMS16-UL250T formed a cluster with S. algicola St-6T, but the DNA-DNA relatedness between the two strains was 28.8±1.5 %, thus confirming their separation at species level. The other two strains formed separate phylogenetic lines respectively. The main quinones for all strains were Q-7, Q-8, MK-7 and MMK-7, which is typical for Shewanella. The major polar lipids of all strains were phosphatidylglycerol and phosphatidylethanolamine, and the common major fatty acid was a summed feature consisting of C16 : 1ω7c and/or C16 : 1ω6c while the proportions varied among the three strains. The DNA G+C contents of the strains also varied between 42.1 and 43.7 mol%. Phenotypic properties distinguished each strain from S. algicola as well as from one another. Based on the polyphasic analysis, each strain is considered to represent a novel species of Shewanella, for which the names Shewanellasaliphila sp. nov. (type strain, MMS16-UL250T=KCTC 62131T=JCM 32304T), Shewanella ulleungensis sp. nov. (type strain, MMS16-UL253T=KCTC 62130T=JCM 32305T) and Shewanella litoralis sp. nov. (type strain, MMS16-UL482T=KCTC 62129T=JCM 32306T) are proposed.

NanoSIMS imaging of extracellular electron transport processes during microbial iron(III) reduction.

ABSTRACTMicrobial iron(III) reduction can have a profound effect on the fate of contaminants in natural and engineered environments. Different mechanisms of extracellular electron transport are used by Geobacter and Shewanella spp. to reduce insoluble Fe(III) minerals. Here we prepared a thin film of iron(III)-(oxyhydr)oxide doped with arsenic, and allowed the mineral coating to be colonised by Geobacter sulfurreducens or Shewanella ANA3 labelled with 13C from organic electron donors. This preserved the spatial relationship between metabolically active Fe(III)-reducing bacteria and the iron(III)-(oxyhydr)oxide that they were respiring. NanoSIMS imaging showed cells of G. sulfurreducens were co-located with the iron(III)-(oxyhydr)oxide surface and were significantly more 13C-enriched compared to cells located away from the mineral, consistent with Geobacter species requiring direct contact with an extracellular electron acceptor to support growth. There was no such intimate relationship between 13C-enriched S. ANA3 and the iron(III)-(oxyhydr)oxide surface, consistent with Shewanella species being able to reduce Fe(III) indirectly using a secreted endogenous mediator. Some differences were observed in the amount of As relative to Fe in the local environment of G. sulfurreducens compared to the bulk mineral, highlighting the usefulness of this type of analysis for probing interactions between microbial cells and Fe-trace metal distributions in biogeochemical experiments.

Estimates of abundance and diversity of Shewanella genus in natural and engineered aqueous environments with newly designed primers

Shewanella species have a diverse respiratory ability and wide distribution in environments and play an important role in bioremediation and the biogeochemical cycles of elements. Primers with more accuracy and broader coverage are required with consideration of the increasing number of Shewanella species and evaluation of their roles in various environments. In this work, a new primer set of 640F/815R was developed to quantify the abundance of Shewanella species in natural and engineered environments. In silico tools for primer evaluation, quantitative polymerase chain reaction (qPCR) and clone library results showed that 640F/815R had a higher specificity and coverage than the previous primers in quantitative analysis of Shewanella. Another newly developed primer pair of 211F/815cR was also adopted to analyze the Shewanella diversity and demonstrated to be the best candidate in terms of specificity and coverage. We detected more Shewanella-related species in freshwater environments and found them to be substantially different from those in marine environments. Abundance and diversity of Shewanella species in wastewater treatment plants were largely affected by the process and operating conditions. Overall, this study suggests that investigations of abundance and diversity of Shewanella in various environments are of great importance to evaluate their ecophysiology and potential ecological roles.

Distribution and Genetic Characteristics of SXT/R391 Integrative Conjugative Elements in Shewanella spp. From China.

The genus Shewanella consists of facultatively anaerobic Gram-negative bacteria, which are regarded as potential agents of food contamination and opportunistic human pathogens. Information about the distribution and genetic characteristics of SXT/R391 integrative conjugative elements (ICEs) in Shewanella species is limited. Here, 91 Shewanella strains collected from diverse samples in China were studied for the presence of SXT/R391 ICEs. Three positive strains, classified as Shewanella upenei, were obtained from patients and water from a local mill. In light of their close clonal relationships and high sequence similarity, a representative ICE was selected and designated ICESupCHN110003. The BLASTn searches against GenBank showed that ICEVchBan5 was most closely related to ICESupCHN110003, with the coverage of 76% and identity of 99%. The phylogenetic tree of concatenated core genes demonstrated that ICESupCHN110003 formed a distinct branch outside the cluster comprising ICEValA056-1, ICEPmiCHN2410, and ICEPmiChn1. Comparison of the genetic structures revealed that ICESupCHN110003 encoded uncommon genes in hotspots, such as specific type III restriction-modification system, conferring adaptive functions to the host. Based on the low coverage in the sequence analysis, independent clade in the phylogenetic tree, and unique inserted fragments in hotspots, ICESupCHN110003 represented a novel SXT/R391 element, which widened the list of ICEs. Furthermore, the antibiotic resistance genes floR, strA, strB, and sul2 in ICESupCHN110003 and resistance to multiple drugs of the positive isolates were detected. A cross-species transfer capability of the SXT/R391 ICEs was also discovered. In summary, it is necessary to reinforce continuous surveillance of SXT/R391 ICEs in the genus Shewanella.

Modeling of Continuous Microbial Fuel Cell (CMFC) for Control Applications

Sustainability and resource management is one of the major concerns for scientific community now days. In this context, in many fields of research, the focus is centred on the re-utilization of used resources with no further damage to the environment. Microbial fuel cell (MFC) is one of the technologies, where electricity is generated from waste-water. MFC is an electrochemical device that converts organic matter directly into the electricity with high efficiency. MFCs offer certain advantages such as minimum sludge production, cost effective and operation at normal condition. Despite its wide range of potential applications and ease of feed stocks, commercialisation of this technology did not realized till now1. The major limitations for the commercialization are the scale up of the process2 and continuous operations. To perform continuous operation for longer time, it is extremely important to understand the dynamics of the system. Dynamics of the system can be understood by performing exhaustive experiments and analysing the data thus obtained. But performing exhaustive experiments is a time consuming as well expensive task. The other approach is to model the system to understand the dynamics. In literature very few researcher worked on the modeling of continuous microbial fuel cell (CMFC). Although batch modeling of MFC have been reported earlier, a very few studies had focused on understanding the dynamics of the system. First dynamic study was carried out by Zhang et al3, and there model is based on electron transfer using mediator. Later, Picioreanu et al4 modeled the bio-film development on the anode electrode in MFC. Marcus et al5 and Pinto et al6 developed 1-D model for multispecies electron donor and acceptor for bio-film anode based on the material balance, Ohm’s law and Nernst-Monod kinetics to describe the rate of electron donor oxidation. In 2017, Esfandyari et al7, developed batch process model considering direct electron transfer through bio-film to the electron acceptor. In this talk, we will present a continuous model developed for MFC and dynamic analysis of potential controlled variables. Dynamic analysis will provide deeper insights of the various physical phenomena of the microbial fuel cell. In present work, model presented by Esfandyari et al7 which is a batch model is taken as the basis. Batch model developed in this work is validated with the work of Esfandyari7 and Picioreanu et al4 for typical dynamic responses. The batch model is then converted into the dual chamber continuous model. In continuous model, substrate (Lactate) and oxygen is continuously fed to the anode and cathode chamber respectively as shown in Figure 1. Coolant is supplied through the jacket to maintain the required operating temperature of the cell. Bacteria species Shewanella is used as the catalyst to oxidise electron donor. The electrons produced are then reaching the cathode electrode via external circuit producing the power. Protons migrate to the cathode through the proton exchange membrane. In the cathode chamber, transferred electrons and migrated protons are reacted with dissolved oxygen to produce water. To understand the dynamic of the MFC, the step change study of the important parameters i.e. substrate concentration, current produced and coolant flow have been simulated. The simulation result of this model is shown in Figure 2, where time variations of the current shows first order dynamic. The settling time observed to be approximately 20 days. It is also noted that the current obtained from the same size of fuel cell in continuous system is higher than the batch. Once the impact of pH is accounted into the model, the dynamic analysis with respective various potential manipulated variables i.e. pH of the solution, flow rate of the substrate and coolant flow rate will be studied to get further insight of the microbial fuel cell. The model, thus developed will be used as a system for devising an effective control and optimization strategies for the microbial fuel cell.

Shewanella putrefaciens CN32 outer membrane cytochromes MtrC and UndA reduce electron shuttles to produce electricity in microbial fuel cells

The extracellular electron transfer (EET) process of Shewanella species is believed to be indispensable for their anaerobic respiration with an electrode. However, the function of outer membrane c-type cytochromes (OM c-Cyts, the primary components of the EET pathway) is still controversial. In this study, we investigated the effect of two OM c-Cyts (MtrC and UndA) of Shewanella putrefaciens CN32 with respect to electricity production and anodic EET efficiency. Deletion of the mtrC gene severely prolonged the microbial fuel cell (MFC) start-up time and decreased electricity production due to depressed flavin-mediated electron transfer, whereas deletion of the undA gene did not have a significant impact. Strikingly, the depression of EET by the deletion of mtrC could be partially relieved by acclimation, which might be due to an increase in the transmembrane transport of electron shuttles and/or the activation of other redox proteins. These results suggested that MtrC may be the primary reductase of flavins to ensure fast indirect EET, which plays a crucial role in MFC electricity generation.

Characterization of moderately halotolerant selenate- and tellurite-reducing bacteria isolated from brackish areas in Osaka.

Moderately halotolerant selenate- and tellurite-reducing bacteria were characterized for wastewater treatment applications. A selenate-reducing strain 9a was isolated from the biofilm of a leachate treatment plant at a sea-based waste disposal site. A tellurite-reducing strain Taa was isolated from an enrichment culture derived from brackish sediment. Both bacterial strains were Shewanella species. Strain 9a could anaerobically remove 45-70% of 1.0mM selenate and selenite from water containing up to 3% NaCl within 4days, while strain Taa could anaerobically and aerobically remove 70-90% of 0.4mM tellurite from water containing up to 6% NaCl within 3days. Globular particles of insoluble selenium were observed both outside and inside the cells of strain 9a. The insoluble tellurium formed by strain Taa was globular under microaerobic conditions but nanorod under aerobic conditions. These bacteria will yield a range of useful selenium and tellurium nanomaterials as well as wastewater treatment applications.

Characterization of a Long-Lived Alginate Lyase Derived from Shewanella Species YH1.

Polysaccharides from seaweeds are widely used in various fields, including the food, biomedical material, cosmetic, and biofuel industries. Alginate, which is a major polysaccharide in brown algae, and the products of its degradation (oligosaccharides) have been used in stabilizers, thickeners, and gelling agents, especially in the food industry. Discovering novel alginate lyases with unique characteristics for the efficient production of oligosaccharides may be relevant for the food and pharmaceutical fields. In this study, we identified a unique alginate lyase derived from an alginate-utilizing bacterium, Shewanella species YH1. The recombinant enzyme (rAlgSV1-PL7) was produced in an Escherichia coli system and it was classified in the Polysaccharide Lyase family 7. The optimal temperature and pH for rAlgSV1-PL7 activity were around 45 °C and 8, respectively. Interestingly, we observed that rAlgSV1-PL7 retained over 80% of its enzyme activity after incubation at 30 °C for at least 20 days, indicating that rAlgSV1-PL7 is a long-lived enzyme. Moreover, the degradation of alginate by rAlgSV1-PL7 produced one to four sugars because of the broad substrate specificity of this enzyme. Our findings suggest that rAlgSV1-PL7 may represent a new commercially useful enzyme.

Shewanella carassii sp. nov., isolated from surface swabs of crucian carp and faeces of a diarrhoea patient.

Two strains, 08MAS2251T and LZ2016-166, were isolated from diverse samples in China collected from the surface of crucian carp and the faeces of a diarrhoea patient, respectively. Both strains were pink-orange coloured, Gram-negative, oxidase- and catalase-positive, facultative anaerobic and motile bacteria, produced H2S and reduced nitrates to nitrites. Growth occurred in the presence of 0-9 % (w/v) NaCl and at 10-42 °C. The optimum conditions were with 1 % (w/v) NaCl and at 35 °C. The phylogenetic tree of 16S rRNA gene demonstrated that strains 08MAS2251T and LZ2016-166 clustered in a distinctive clade next to the species Shewanella chilikensis JC5T within the genus Shewanella. Meanwhile, gyrB gene sequence analysis indicated that the two strains formed an independent branch that was clearly separate from all the other Shewanella species with sequence similarities from 68.49 to 95.74 %. The DNA G+C content of strain 08MAS2251T was 52.68 mol%. Genomic relatedness of in silico DNA-DNA hybridization between strain 08MAS2251T and phylogenetic neighbours ranged from 50.5-51.8 %, below the cutoff of 70 %. In addition, corresponding average nucleotide identity values were between 93.01 to 93.49%, which were lower than 95 % threshold. The major fatty acids of strain 08MAS2251T were C17 : 1ω8c (27.2 %), iso-C15 : 0 (22.5 %), summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c; 8.7 %), C16 : 0 (6.2 %), iso-C13 : 0 (5.6 %) and C17 : 0 (4.5 %). Based on phenotypic and genetic analysis, strains 08MAS2251T and LZ2016-166 are identified as a novel species of the genus Shewanella, for which the name Shewanellacarassii sp. nov. is proposed. The type strain is 08MAS2251T (=DSM 104682T=CGMCC 1.16033T).

Biofabrication of gold nanoparticles by Shewanella species

BackgroundShewanella oneidensis MR-1 (MR-1) and Shewanella xiamenensis BC01 (SXM) are facultative anaerobic bacteria that exhibit outstanding performance in the dissimilatory reduction of metal ions. Shewanella species have been reported to produce metal nanoparticles, but the mechanism and optimization are still not extensively studied and clearly understood. Herein, the effects of pH, biomass, gold ion concentration, and photoinduction are evaluated to optimize gold nanoparticle (Au@NP) production by Shewanella.ResultsThe highest amount of Au@NPs produced by SXM and MR-1 were 108 and 62 ppm, respectively, at pH 5 when 2.4 g/L biomass was immersed in 300 ppm gold ions and 50 mM lactate under a light intensity of 100 µmol/m2/s. By scanning election microscopy and zeta potential analysis, the proposed mechanism of Au@NP formation was that Shewanella used lactate as electron donors for the Mtr pathway, stimulated by photosensitive proteins resulting in the nucleation of NPs on the cell membrane. Besides, the resting cells retained the ability for biofabrication of nanoparticles for nearly 25 days.ConclusionsThe optimal conditions evaluated for Au@NPs production by Shewanella were biomass, pH, ions concentration, and photoinduction. To the best of our knowledge, this is the first attempt to explore a two-step mechanism for Au@NPs formation in Shewanella. First, the HAuCl4 solution reacted with sodium lactate to form metallic gold ions. Second, the metallic gold ions were adsorbed onto the outer membrane of cell, and the formation of Au@NPs at the surface was triggered. Shewanella-based Au@NPs production could be a potential ecofriendly solution for the recovery of Au ions from secondary resources like industrial waste.

A comparative analysis of tellurite detoxification by members of the genus Shewanella.

The increasing industrial utilization of tellurium has resulted in an important environmental pollution with the soluble, extremely toxic oxyanion tellurite. In this context, the use of microorganisms for detoxifying tellurite or tellurium biorecovery has gained great interest. The ability of different Shewanella strains to reduce tellurite to elemental tellurium was assessed; the results showed that the reduction process is dependent on electron transport and the ∆pH gradient. While S. baltica OS155 showed the highest tellurite resistance, S. putrefaciens was the most efficient in reducing tellurite. Moreover, pH-dependent tellurite transformation was associated with tellurium precipitation as tellurium dioxide. In summary, this work highlights the high tellurite reduction/detoxification ability exhibited by a number of Shewanella species, which could represent the starting point to develop friendly methods for the recovery of elemental tellurium (or tellurium dioxide).

Effect of the anode potential on the physiology and proteome of Shewanella oneidensis MR-1

Shewanella species respire using iron and manganese oxides as well as electrodes as solid terminal electron acceptors. Shewanella oneidenis MR-1 exploits mediated as well as direct extracellular electron transfer (EET) modes to transfer electrons at different formal potentials. These different EET modes at different potentials may utilise alternate electron transfer pathways. Therefore, we investigated how different anode potentials, providing different maximum microbial energy gains impacted S. oneidensis microbial physiology. Using quantitative proteomics, comparative analysis of the cellular variations to different anode potentials was performed. A label-free proteomic mass spectrometric analysis method, SWATH-MS, was used to gather quantitative information to determine physiological changes of Shewanella oneidensis MR-1 grown at different anodic potentials. S. oneidensis was cultured and grown in electrochemical cells at the set anode potentials of +0.71V, +0.21V & −0.19V versus SHE reference electrode, while the current production was monitored. At maximum current, electrodes were removed and whole-cell proteins extracted. Subsequent SWATH-MS analysis revealed information on 740 identified proteins across the three electrode potentials. For the first time, we show the abundance of S. oneidensis electron transfer proteins differs with electrode potential.

Shewanella species as the origin of blaOXA-48 genes: insights into gene diversity, associated phenotypes and possible transfer mechanisms

Chromosome-encoded beta-lactamases of Shewanella spp. have been indicated as probable progenitors of blaOXA-48-like genes. However, these have been detected in few Shewanella spp. and dissemination mechanisms are unclear. Thus, our main objective was to confirm the role of Shewanella species as progenitors of blaOXA-48-like genes.In silico analysis of Shewanella genomes was performed to detect blaOXA-48-like genes and context, and 43 environmental Shewanella spp. were characterised. Clonal relatedness was determined by BOX-PCR. Phylogenetic affiliation was assessed by 16S rDNA and gyrB sequencing. Antibiotic susceptibility phenotypes were determined. The blaOXA-48-like genes and genetic context were inspected by PCR, hybridisation and sequence analysis. Gene variants were cloned in Escherichia coli and MICs were determined. Shewanella isolates were screened for integrons, plasmids and insertion sequences.Analysis of Shewanella spp. genomes showed that putative blaOXA-48-like is present in the majority and in an identical context. Isolates presenting unique BOX profiles affiliated with 11 Shewanella spp. blaOXA-48-like genes were detected in 22 isolates from 6 species. Genes encoded enzymes identical to OXA-48, OXA-204, OXA-181, and 7 new variants differing from OXA-48 from 2 to 82 amino acids. IS1999 was detected in 24 isolates, although not in the vicinity of blaOXA-48 genes. Recombinant E. coli strains presented altered MICs.The presence/absence of blaOXA-48-like genes was species-related. Gene variants encoded enzymes with hydrolytic spectra similar to OXA-48-like from non–shewanellae. From the mobile elements previously described in association with blaOXA-48-like genes, only the IS1999 was found in Shewanella, which indicates its relevance in blaOXA-48-like genes transfer to other hosts.