Humic acids facilitated microbial reduction of polymeric Pu(IV) under anaerobic conditions

Flavins and humic substances have been extensively studied with emphasis on their ability to transfer extracellular electrons to insoluble metal oxides. Nevertheless, whether the low-solubility Pu(IV) polymers are microbially reduced to aqueous Pu(III) remains uncertain. Experiments were conducted under anaerobic and slightly alkaline conditions to study the difference between humic acids and flavins to transport extracellular electrons to Pu(IV) polymers. Our study demonstrates that Shewanella putrefaciens was unable to directly reduce polymeric Pu(IV) with a notably low reduction rate (3.4×10^-12mol/L Pu(III)_aq within 144h). The relatively high redox potential of flavins reveals the thermodynamically unfavorable reduction: E_h(PuO₂(am)/Pu³⁺)<E_h^o'(FMN/FMNH₂)≈E_h^o'(RBF/RBFH₂)≈-220mV at pH7.2. The microbially reduced humic acids facilitated the extracellular electron transfer to the polymers and reduced polymeric Pu(IV) (2.1×10^-10mol/L Pu(III)_aq) 62 times more rapidly than the flavins. The driving force for electron transfer explains the observed reduction: E_h(HA_ox/HA_red)<E_h(PuO₂(am)/Pu³⁺) when S. putrefaciens oxidized lactate and respired on the humic acids. In contrast, flavins were able to substantially reduce aqueous Pu(IV)-EDTA (1.9×10^-9mol/L Pu(III)_aq) because of the available driving force for electron transfer: Δ_rG_m=-F[E_h(PuL₂^4-/PuL₂^5-)-E_h^o'(FMN/FMNH₂)]=-33.5kJ/mol is a result of E_h(PuL₂^4-/PuL₂^5-)≫E_h(PuO₂(am)/Pu³⁺), where L is the EDTA ligand. In the presence of humic acids, the reduction of Pu(IV)-EDTA exhibited the most rapid rate (2.2×10^-9mol/L Pu(III)_aq). This result further demonstrates that humic acids facilitated the extracellular electron transfer to polymeric and aqueous Pu(IV). Reductive solubilization of the polymers may enhance Pu mobility in the geosphere and hence increases risks to human health.

Effects of humic acid concentration on the microbially-mediated reductive solubilization of Pu(IV) polymers

The role of humic acid concentration in the microbially-mediated reductive solubilization of Pu(IV) polymers remains unclear until now. The effects of humic concentration (0-150.5mg/L) on the rate and extent of reduction of polymeric Pu(IV) were studied under anaerobic and pH 7.2 conditions. The results show that Shewanella putrefaciens, secreting flavins as endogenous electron shuttles, cannot notably stimulate the reduction of polymeric Pu(IV). In the presence of humic acids, the reduction rate of polymeric Pu(IV) increased with increasing humic concentrations (0-15.0mg/L): e.g., a 102-fold increase from 4.1×10^-15 (HA=0) to 4.2×10^-13mol Pu(III)_aq/h (HA=15.0mg/L). The bioreduced humic acids by S. putrefaciens facilitated the extracellular electron transfer to Pu(IV) polymers and thus the reduction of polymeric Pu(IV) to Pu(III)_aq became thermodynamically favorable. However, the reduction rate did not increase but decrease with increasing humic concentrations from 15.0 to 150.5mg/L. Humic coatings formed on the polymer surfaces at relatively high humic concentrations limited the electron transfer to the polymers and thus decreased the reduction rate. The finding of the dynamic role of humic acids in the bioreductive solubilization may be helpful in evaluating Pu mobility in the geosphere.

Antimicrobial peptide AMPNT-6 from Bacillus subtilis inhibits biofilm formation by Shewanella putrefaciens and disrupts its preformed biofilms on both abiotic and shrimp shell surfaces

Shewanella putrefaciens biofilm formation is of great concern for the shrimp industry because it adheres easily to food and food-contact surfaces and is a source of persistent and unseen contamination that causes shrimp spoilage and economic losses to the shrimp industry. Different concentrations of an antimicrobial lipopeptide, the fermentation product of Bacillus subtilis, AMPNT-6, were tested for the ability to reduce adhesion and disrupt S. putrefaciens preformed biofilms on two different contact surfaces (shrimp shell, stainless steel sheet). AMPNT-6 displayed a marked dose- and time-dependent anti-adhesive effect>biofilm removal. 3MIC AMPNT-6 was able both to remove biofilm and prevent bacteria from forming biofilm in a 96-well polystyrene microplate used as the model surface. 2MIC AMPNT-6 prevented bacteria from adhering to the microplate surface to form biofilm for 3h and removed already existing biofilm within 24h. Secretion of extracellular polymeric substances incubated in LB broth for 24h by S. putrefaciens was minimal at 3× MIC AMPNT-6. Scanning electron microscopy showed that damage to S. putrefaciens bacteria by AMPNT-6 possibly contributed to the non-adherence to the surfaces. Disruption of the mature biofilm structure by AMPNT-6 contributed to biofilm removal. It is concluded that AMPNT-6 can be used effectively to prevent attachment and also detach S. putrefaciens biofilms from shrimp shells, stainless steel sheets and polystyrene surfaces.

favoured by hypoxic aquatic environments

Microbiological analyses were conducted on wild eels from the L'Albufera Lake (Spain). A total of 174 individuals were collected in two surveys (i.e. year 2008 and autumn-winter 2014) among those caught by local fishermen into the lagoon. The prevalence of Shewanella putrefaciens group was 1.7% in 2008 and rose above 32% in 2014. It was due to an outbreak of shewanellosis that presented a morbidity rate of 64%. S. putrefaciens group strains were isolated as pure cultures from the sick eels that showed white ulcers surrounded by a reddish inflammation, damage of the mouth, extensive skin discoloration, exophthalmia, ascites and bad odour. The S. putrefaciens group was recovered from freshwater samples taken at the L'Albufera system, along autumn-winter 2015. Its counts significantly increased in freshwater parallel to hypoxia and temperature rising. Shewanellae strains were identified as S. putrefaciens and S. xiamenensis by 16S rRNA gene sequencing. These isolates recovered from sick eels or freshwater were virulent for European eel by IP challenge (LD₅₀ 10⁶  CFU g^-1 body weight). They also caused 30-38% cumulative mortality, in European eels challenged by a 2-h bath (10⁷  CFU mL^-1 ). These results suggest that shewanellosis could be transmitted through water highlighting the fact that hypoxic conditions increase this bacterium levels in water.

Changes of membrane fatty acids and proteins of Shewanella putrefaciens treated with cinnamon oil and gamma irradiation

BACKGROUND

In order to detect the antimicrobial mechanism of combined treatment of cinnamon oil and gamma irradiation (GI), the membrane fatty acids and proteins characteristics of Shewanella putrefaciens (S. putrefaciens) treated with cinnamon oil and GI, and the distribution of cinnamon oil in S. putrefaciens were observed in this study.

RESULTS

The membrane lipid profile of S. putrefaciens was notably damaged by treatments of cinnamon oil and the combination of cinnamon oil and GI, with significantly fatty acids decrease in C14:0, C16:0, C16:1, C17:1, C18:1 (p < 0.05). The SDS-PAGE result showed that GI did not have obvious effect on membrane proteins (MP), but GI combined with cinnamon oil changed the MP subunits. Cinnamaldehyde, the main component of cinnamon oil, can not transport into S. putrefaciens obviously. It was transformed into cinnamyl alcohol in the nutrient broth with the action of S. putrefaciens. This indicated that the antimicrobial action of cinnamon oil mainly happened on the membrane of S. putrefaciens.

CONCLUSION

Cinnamon oil could act on the membrane of S. putrefaciens with the damage of fatty acids and proteins, and GI would increase the destructive capability of cinnamon oil on the membrane fatty acids and proteins of S. putrefaciens.

[Osteomyelitis due to Shewanella putrefaciens: case report and literature review]

Shewanella putrefaciens is a Gram-negative bacillus and marine pathogen that rarely causes disease in humans. We report a case of osteomyelitis by this organism in a 48-year-old male patient, who presented with pain and erythema of the right foot that was initially diagnosed as cellulitis and did not revert despite treatment. He was transferred to Lima where osteomyelitis was diagnosed and started on empirical treatment with partial regression. A biopsy and culture of the compromised area found S. putrefaciens. The infection was treated according to the antibiotic sensitivity profile of the pathogen. S. putrefaciens infection represents a rare opportunistic infection of devitalized or exposed areas of the body. It is associated with residence in coastal areas and commonly affects the skin and soft tissues. Exceptional cases of osteomyelitis have been reported, but this is the first that involves the metatarsal bones.

A Comparison of Molecular Biology Mechanism of Shewanella putrefaciens between Fresh and Terrestrial Sewage Wastewater

Municipal and industrial wastewater is often discharged into the environment without appropriate treatment, especially in developing countries. As a result, many rivers and oceans are contaminated. It is urgent to control and administer treatments to these contaminated rivers and oceans. However, most mechanisms of bacterial colonization in contaminated rivers and oceans were unknown, especially in sewage outlets. We found Shewanella putrefaciens to be the primary bacteria in the terrestrial sewage wastewater outlets around Ningbo City, China. Therefore, in this study, we applied a combination of differential proteomics, metabolomics, and real-time fluorescent quantitative PCR techniques to identify bacteria intracellular metabolites. We found S. putrefaciens had 12 different proteins differentially expressed in freshwater culture than when grown in wastewater, referring to the formation of biological membranes (Omp35, OmpW), energy metabolism (SOD, deoxyribose-phosphate pyrophosphokinase), fatty acid metabolism (beta-ketoacyl synthase), secondary metabolism, TCA cycle, lysine degradation (2-oxoglutarate reductase), and propionic acid metabolism (succinyl coenzyme A synthetase). The sequences of these 12 differentially expressed proteins were aligned with sequences downloaded from NCBI. There are also 27 differentially concentrated metabolites detected by NMR, including alcohols (ethanol, isopropanol), amines (dimethylamine, ethanolamine), amino acids (alanine, leucine), amine compounds (bilinerurine), nucleic acid compounds (nucleosides, inosines), and organic acids (formate, acetate). Formate and ethanolamine show significant difference between the two environments and are possibly involved in energy metabolism, glycerophospholipid and ether lipids metabolism to provide energy supply, and material basis for engraftment in sewage. Because understanding S. putrefaciens's biological mechanism of colonization (protein, gene express, and metabolites) in terrestrial sewage outlets is so important to administering and improving contaminated river and to predicting and steering performance, we delved into the biological mechanism that sheds light on the effect of environmental conditions on metabolic pathways.

Antibiotic and heavy metal resistance in Shewanella putrefaciens strains isolated from shellfishes collected from West Sea, Korea

The aim of the present study was to determine the antibiotic resistance patterns and distribution of heavy-metal resistance in Shewanella putrefaciens strains isolated from shellfishes collected from West Sea; and to determine the relationship, if any, between antibiotic and heavy-metal resistance in these strains. Among the 15 strains isolated, two strains, SY1 and SY2, showed heavy-metal resistance in addition to high resistance to seven antibiotics: cephalothin, gentamicin, erythromycin, vancomycin, ampicillin, rifampicin, and streptomycin. We conclude that heavy-metal contamination imposes long-term, widespread, and recalcitrant selection pressure, which potentially contributes to the maintenance and spread of antibiotic resistance factors in bacteria. Moreover, this fact holds both environmental and clinical importance.

Influence of clay minerals on sorption and bioreduction of arsenic under anoxic conditions

Adsorption of As(V) on various clay minerals including kaolinite (KGa-1), montmorillonite (SWy-1) and nontronites (NAU-1 and NAU-2), and subsequent bioreduction of sorbed As(V) to As(III) by bacterium Shewanella putrefaciens strain CN-32 were investigated. Nontronites showed relatively higher sorption capacity for As(V) primarily due to higher iron oxide content. Freundlich equation well described the sorption of As(V) on NAU-1, NAU-2 and SWy-1, while As(V) sorption isotherm with KGa-1 fitted well in the Langmuir model. The bacterium rapidly reduced 50% of dissolved As(V) to As(III) in 2 h, followed by its complete reduction (>ca. 98%) within 12 h. In contrast, sorption of As(V) to the mineral surfaces interferes with the activity of bacterium, resulting in low bioreduction of As(V) by 27% for 5 days of incubation. S. putrefaciens also promoted the reduction of Fe(III) present in the clay mineral to Fe(II). This study indicates that the sorption and subsequent bioreduction of As(V) on clay minerals can significantly influence the mobility of As(V) in subsurface environment.

Phenotypical and genotypical characterization of Shewanella putrefaciens strains isolated from diseased freshwater fish

Between 2007 and 2012, a variety of disease outbreaks most often characterized by skin disorders were observed among different species of freshwater fish in Poland. In most cases, the clinical signs included focally necrotized gills, necrotic skin lesions or ulcers. Internally, haemorrhages, oedematous kidney and abnormal spleen enlargement were generally noted. The disorders were accompanied by increased mortality. Most of the problems concerned cultured common carp Cyprinus carpio L. and rainbow trout Oncorhynchus mykiss (Walbaum). Fish have been examined from a number of these farms, and additionally, the wild and ornamental fish with similar clinical signs of diseases were also tested. Bacteria were isolated consistently from lesions and internal organs. They had characteristic orange-pigmented colonies which grew in pure culture or constituted 55-95% of total bacterial flora. One hundred and eighteen isolates were collected and biochemically identified as Shewanella putrefaciens group, and this was confirmed by sequencing. Challenge tests confirmed the pathogenicity of these bacteria. This is the first report characterizing and describing S. putrefaciens as a pathogen of different species of freshwater fish in Europe.

Case report and literature review of carbapenem resistant shewanella putrefaciens isolated from ascitic fluid

Shewanella species are Gram-negative, non-fermentative, oxidase positive, motile bacilli with the major phenotypic characteristic of production of large amounts of hydrogen sulfide. Shewanella putrefaciens, primarily considered to be an environmental bacterium, is infrequently recovered from clinical specimens. Herein, we report a case of ascitic fluid infection with carbapenem resistant Shewanella putrefaciens in a patient with underlying liver disorder requiring repeated ascitic fluid tapping. Proper antibiotic therapy helped in complete recovery of the patient.

Improvement of power generation using Shewanella putrefaciens mediated bioanode in a single chambered microbial fuel cell: effect of different anodic operating conditions

Three different approaches were employed to improve single chambered microbial fuel cell (sMFC) performance using Shewanella putrefaciens as biocatalyst. Taguchi design was used to identify the key process parameter (anolyte concentration, CaCl₂ and initial anolyte pH) for maximization of volumetric power. Supplementation of CaCl₂ was found most significant and maximum power density of 4.92 W/m(3) was achieved. In subsequent approaches, effect on power output by riboflavin supplementation to anolyte and anode surface modification using nano-hematite (Fe₂O₃) was observed. Volumetric power density was increased by 44% with addition of 100 nM riboflavin to anolyte while with 0.8 mg/cm(2) nano-Fe₂O₃ impregnated anode power density and columbic efficiency increased by 40% and 33% respectively. Cyclic voltammetry revealed improvement in electrochemical activity of Shewanella with nano-Fe₂O₃ loading and electrochemical impedance depicted inverse relationship between charge transfer resistance and nano-Fe₂O₃ loading. This study suggests anodic improvement strategies for maximization of power output.

Effects of bacteriophage on the quality and shelf life of Paralichthys olivaceus during chilled storage

BACKGROUND

The microbiological spoilage of fishery foods is mainly due to specific spoilage organisms (SSOs), with Shewanella putrefaciens being the SSO of most chilled marine fish. Bacteriophages have shown excellent capability to control micro-organisms. The aim of this study was to determine a specific bacteriophage to prevent spoilage by reducing SSO (S. putrefaciens) levels in the marine fish Paralichthys olivaceus (olive flounder) under chilled storage.

RESULTS

Chilled flounder fillets were inoculated with S. putrefaciens and treated with different concentrations of bacteriophage Spp001 ranging from 10(4) to 10(8) plaque-forming units (pfu) mL(-1) . Bacterial growth (including total viable count and SSO) of the bacteriophage-treated groups was significantly inhibited compared with that of the negative control group (P < 0.05). Sensory evaluation and biochemical parameters revealed that the bacteriophage could extend the shelf life of chilled flounder fillets (from <4 to 14 days) with good esthetic quality, even at low temperature (4 °C). Furthermore, bacteriophage concentrations of 10(6) and 10(8) pfu mL(-1) were more effective than the chemical preservative potassium sorbate (5 g L(-1) ).

CONCLUSION

The bacteriophage Spp001 offered effective biocontrol of S. putrefaciens under chilled conditions, retaining the quality characteristics of spiked fish fillets, and thus could be a potential candidate for use in chilled fish fillet biopreservation.

Bacteremia and empyema caused by Shewanella algae in a trauma patient

OBJECTIVE

To describe the first reported case of bacteremia and empyema caused by Shewanella algae and summarize the existing literature on Shewanella human infection.

CASE SUMMARY

A 25-year-old healthy male was shot through the chest into the abdomen and fled into an adjacent body of seawater. He underwent surgical repair of his injuries, including pleural decortication. Leukocytosis, bandemia, and copious yellow bronchorrhea led to cultures; piperacillin/tazobactam and vancomycin were started for broad-spectrum empiric management based on the local intensive care unit antibiogram. Blood and pleural fluid cultures revealed S algae. Sputum cultures grew methicillin-sensitive Staphylococcus aureus and Haemophilus influenzae. He was successfully managed with an empiric and then tailored antibiotic regimen.

DISCUSSION

Shewanella algae is a rare Gram-negative bacillus that has infrequently been reported to cause infection. It is found predominantly in men. Shewanella algae infections span bacteremia to necrotizing soft tissue infection and are associated with injury and seawater exposure. Shewanella is susceptible to the majority of third- and fourth-generation cephalosporins, aminoglycosides, chloramphenicol, erythromycin, aztreonam, and fluoroquinolones, but are less predictably susceptible to tetracycline and trimethoprim/sulfamethoxazole and carbapenem agents. Shewanella infection is associated with medical comorbidities, in particular, renal failure and cardiovascular disease.

CONCLUSIONS

To our knowledge, this is the first case report of bacteremia and empyema caused by S algae. Such a case involving a young healthy individual should encourage health care providers to be aware of the potential infections caused by unusual pathogens, and to employ appropriate empiric antibiotic therapy based on reported sensitivity profiles. Based on available susceptibilities, we recommend using a third or fourth-generation cephalosporin as first-line pharmacologic management with regimen de-escalation based on culture-derived data.

Preparation and characterization of stable cross-linked enzyme aggregates of novel laccase enzyme from Shewanella putrefaciens and using malachite green decolorization

A novel type laccase from Shewanella putrefaciens was identified, expressed in Escherichia coli, characterized, prepared in cross-linked enzyme aggregates (CLEA) for industrial applications and investigated of decolorization activity on malchite green dye. Enzyme characterization was investigated by enzyme assay, SDS-PAGE and other biochemical reactions. Moreover, cross-linked enzyme aggregates were prepared and characterized. Saturated ammonium sulphate solution was used as the precipitating agent and cross linked with glutaraldehyde. These CLEA-laccase aggregates showed more catalytic efficiency and more stabilities compared to free laccase against harsh conditions of thermal and chemical agents as well as high reusability. Also it showed more decolorization ability. These results suggest that this CLEA is potentially usable in industrial applications.

Shewanella putrefaciens, a rare cause of osteomyelitis

Shewanella putrefaciens is a Gram-negative bacillus with a distinguishable characteristic of hydrogen sulfide production and routinely found in a marine environment. This organism has been cultured as a pathogen in a small number of soft tissue infections, but has rarely been the causative agent in osteomyelitis. This case report details calcaneal osteomyelitis due to S putrefaciens in a 77-year-old male with bilateral heel ulcerations and peripheral vascular disease.

Emerging infections: shewanella - a series of five cases

Background:

Shewanella spp. are unusual cause of disease in humans; however, reports of Shewanella infections have been increasing. Shewanella is a ubiquitous organism that has been isolated from many foods, sewage, and both from fresh and salt water. Earlier it was named as Pseudomonas putrefaciens or Shewanella putrefaciens. There are several reports describing this organism causing human infections such as cellulitis, abscesses, bacteremia, wound infection, etc. It is oxidase and catalase-positive non-fermenter gram-negative rod that produces hydrogen sulfide.

Aims:

The study was conducted to identify Shewanella spp., which was wrongly reported as Pseudomonas spp.

Materials and Methods:

Clinical samples were cultured as per standard clinical laboratory procedure. We tested the non-lactose-fermenting colonies for oxidase positivity. Oxidase-positive colony was inoculated in triple sugar iron slant (TSI) to know the hydrogen sulfide production. Hydrogen sulfide positive colonies were further tested for citrate, urease, indole, and amino acid decarboxylation and acid and gas production from sugars.

Results:

Five isolates identified as Pseudomonas spp. during preliminary testing were proved to be Shewanella spp. on further testing.

Conclusions:

It will help in better understanding the epidemiology, pathogenesis and risk factors associated with these and prevention of the rare pathogenic organisms.

Enhanced anaerobic biotransformation of carbon tetrachloride in the presence of reduced iron oxides

Rates of anaerobic transformation of carbon tetrachloride (CT) by the facultative anaerobe Shewanella putrefaciens 200 were increased by the presence of Fe(III)-containing minerals. In batch reactors with amorphous, Fe(III)-hydroxide and S. putrefaciens, CT transformation rates could be modeled by a first-order expression in which the pseudo-first-order rate constant was linearly proportional to the initial concentration of Fe(III)-oxide. Subsequent measurement of soluble and acid-extractable Fe(II) showed that increased CT transformation rates were proportional to microbially reduced, surface-bound Fe(II), rather than soluble Fe(II). In biomimetic experiments using 20 mM dithiothreitol (DTT) as a reductant, rates of transformation of CT by DTT were low in the absence of Fe(III)-oxides. However, in the presence of iron oxides, DTT was able to transform CT at elevated rates. Results again strongly suggested that surface-bound Fe(II) was primarily responsible for the reductive transformation of CT. Results suggested that the surface area of the iron mineral determines the rate of CT transformation by affecting the extent of iron reduction. Chloroform (CF) was the only transformation product identified and production of CF was nonstoichiometric. In microbial and abiotic experiments with Fe(III) oxides, the percentage of the transformed CT recovered as CF decreased even though the rate and extent of CT transformation was increased. Overall, our results have important implications for an improved understanding of possible microbial and geochemical interactions in the environmental transformation of chlorinated organic pollutants and for modeling of CT transformation rates in anaerobic, iron-bearing sediments.