Shewanella decolorationis sp. nov., a dye-decolorizing bacterium isolated from activated sludge of a waste-water treatment plant

Shewanella goraebulensis sp. nov., isolated from sea water

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

Shewanella metallivivens sp. nov., a deep-sea hydrothermal vent tube worm endobiont capable of dissimilatory anaerobic metalloid oxyanion reduction

A polyphasic taxonomic study was carried out on a Gram-stain-negative and rod-shaped strain, ER-Te-42B-LightT, isolated from the tissue of a tube worm, Riftia pachyptila, collected near a deep-sea hydrothermal vent of the Juan de Fuca Ridge in the Pacific Ocean. This bacterium was capable of performing anaerobic respiration using tellurite, tellurate, selenite and orthovanadate as terminal electron acceptors. While facultatively anaerobic, it could aerobically resist tellurite, selenite and orthovanadate up to 2000, 7000 and 10000 µg ml-1, respectively, reducing each oxide to elemental forms. Nearly complete 16S rRNA gene sequence similarity related the strain to Shewanella, with 98.8 and 98.7 % similarity to Shewanella basaltis and Shewanella algicola, respectively. The dominant fatty acids were C16 : 0 and C16 : 1. The major polar lipids were phosphatidylethanolamine and phosphatidylglycerol and MK-7 was the predominant quinone. DNA G+C content was 42.5 mol%. Computation of average nucleotide identity and digital DNA-DNA hybridization values with the closest phylogenetic neighbours of ER-Te-42B-LightT revealed genetic divergence at the species level, which was further substantiated by differences in several physiological characteristics. Based on the obtained results, this bacterium was assigned to the genus Shewanella as a new species with the name Shewanella metallivivens sp. nov., type strain ER-Te-42B-LightT (=VKM B-3580T=DSM 113370T).

Recent advances in enrichment, isolation, and bio-electrochemical activity evaluation of exoelectrogenic microorganisms

Exoelectrogenic microorganisms (EEMs) catalyzed the conversion of chemical energy to electrical energy via extracellular electron transfer (EET) mechanisms, which underlay diverse bio-electrochemical systems (BES) applications in clean energy development, environment and health monitoring, wearable/implantable devices powering, and sustainable chemicals production, thereby attracting increasing attentions from academic and industrial communities in the recent decades. However, knowledge of EEMs is still in its infancy as only ~100 EEMs of bacteria, archaea, and eukaryotes have been identified, motivating the screening and capture of new EEMs. This review presents a systematic summarization on EEM screening technologies in terms of enrichment, isolation, and bio-electrochemical activity evaluation. We first generalize the distribution characteristics of known EEMs, which provide a basis for EEM screening. Then, we summarize EET mechanisms and the principles underlying various technological approaches to the enrichment, isolation, and bio-electrochemical activity of EEMs, in which a comprehensive analysis of the applicability, accuracy, and efficiency of each technology is reviewed. Finally, we provide a future perspective on EEM screening and bio-electrochemical activity evaluation by focusing on (i) novel EET mechanisms for developing the next-generation EEM screening technologies, and (ii) integration of meta-omics approaches and bioinformatics analyses to explore nonculturable EEMs. This review promotes the development of advanced technologies to capture new EEMs.

Feasibility and potential of laccase-based enzyme in wastewater treatment through sustainable approach: A review

The worldwide increase in metropolitan cities and rise in industrialization have resulted in the assimilation of hazardous pollutants into the ecosystems. Different physical, chemical and biological techniques have been employed to remove these toxins from water bodies. Several bioprocess applications using microbes and their enzymes are utilized to achieve the goal. Biocatalysts, such as laccases, are employed explicitly to deplete a variety of organic pollutants. However, the degradation of contaminants using biocatalysts has many disadvantages concerning the stability and activity of the enzyme. Hence, they are immobilized on different supports to improve the enzyme kinetics and recyclability. Furthermore, standard wastewater treatment methods are not effective in eliminating all the contaminants. As a result, membrane separation technologies have emerged to overcome the limitations of traditional wastewater treatment methods. Moreover, enzymes immobilized onto these membranes have generated new avenues in wastewater purification technology. This review provides the latest information on laccases from diverse sources, their molecular framework and their mode of action. This report also gives information about various immobilization techniques and the application of membrane bioreactors to eliminate and biotransform hazardous contaminants. In a nutshell, laccases appear to be the most promising biocatalysts for green and cost-efficient wastewater treatment technologies.

Shewanella shenzhenensis sp. nov., a novel Fe(III)-reducing bacterium with abundant possible cytochrome genes, isolated from mangrove sediment

A facultative anaerobic bacterium, designated as A25^T, was isolated from a mangrove sediment sample collected in Shenzhen, China. Cells of strain A25^T were found to be Gram-staining negative, rod-shaped, flagella-harboring, and oxidase- and catalase-positive. The isolate was able to grow at 4-40 °C (optimum 28 °C) and pH 5.0-9.0 (optimum pH 6.0), and in 0-10% NaCl concentration (w/v) (optimum 1%). Strain A25^T was capable of reducing Fe(III) citrate under anaerobic conditions. The major fatty acids of this strain was C_16:1ω7c/C_16:1ω6c (summed feature 3), C_17:1ω8c and iso-C_15:0. Results of phylogenetic analyses based on 16S rRNA gene sequences indicated that strain A25^T is affiliated with the genus Shewanella, showing the highest similarity to Shewanella seohaensis S7-3^T (98.4% similarity). The average nucleotide identity and digital DNA-DNA hybridization values between the genomes of strain A25^T and its closely related strains were ≤ 79.0% and ≤ 22.8%, respectively. Based on its phenotypic, phylogenetic properties and physiological and biochemical characteristics, strain A25^T (= JCM 34900^T = GDMCC 1.2731^T) was designated as the type strain of a novel species of the genus Shewanella, for which the name Shewanella shenzhenensis sp. nov. was proposed.

Engineering Shewanella carassii, a newly isolated exoelectrogen from activated sludge, to enhance methyl orange degradation and bioelectricity harvest

Electroactive microorganisms (EAMs) play important roles in biogeochemical redox processes and have been of great interest in the fields of energy recovery, waste treatment, and environmental remediation. However, the currently identified EAMs are difficult to be widely used in complex and diverse environments, due to the existence of poor electron transfer capability, weak environmental adaptability, and difficulty with engineering modifications, etc. Therefore, rapid and efficient screening of high performance EAMs from environments is an effective strategy to facilitate applications of microbial fuel cells (MFCs). In this study, to achieve efficient degradation of methyl orange (MO) by MFC and electricity harvest, a more efficient exoelectrogen Shewanella carassii-D₅ that belongs to Shewanella spp. was first isolated from activated sludge by WO₃ nanocluster probe technique. Physiological properties experiments confirmed that S. carassii-D₅ is a Gram-negative strain with rounded colonies and smooth, slightly reddish surface, which could survive in media containing lactate at 30 °C. Moreover, we found that S. carassii-D₅ exhibited remarkable MO degradation ability, which could degrade 66% of MO within 72 h, 1.7 times higher than that of Shewanella oneidensis MR-1. Electrochemical measurements showed that MFCs inoculated with S. carassii-D₅ could generate a maximum power density of 704.6 mW/m², which was 5.6 times higher than that of S. oneidensis MR-1. Further investigation of the extracellular electron transfer (EET) mechanism found that S. carassii-D₅ strain had high level of c-type cytochromes and strong biofilm formation ability compared with S. oneidensis MR-1, thus facilitating direct EET. Therefore, to enhance indirect electron transfer and MO degradation capacity, a synthetic gene cluster ribADEHC encoding riboflavin synthesis pathway from Bacillus subtilis was heterologously expressed in S. carassii-D₅, increasing riboflavin yield from 1.9 to 9.0 mg/g DCW with 1286.3 mW/m² power density output in lactate fed-MFCs. Furthermore, results showed that the high EET rate endowed a faster degradation efficient of MO from 66% to 86% with a maximum power density of 192.3 mW/m², which was 1.3 and 1.6 times higher than that of S. carassii-D₅, respectively. Our research suggests that screening and engineering high-efficient EAMs from sludge is a feasible strategy in treating organic pollutants.

Complete genome sequence of Shewanella algae strain 2NE11, a decolorizing bacterium isolated from industrial effluent in Peru

Shewanella is a microbial group with high potential to be applied in textile effluents bioremediation due to its ability to use a wide variety of substrates as a final electron acceptor in respiration. The present research aimed to describe a new strain, Shewanella algae 2NE11, a decolorizing bacterium isolated from industrial effluent in Peru. S. algae 2NE11 showed an optimal growth under pH 6-9, temperature between 30-40 °C, and 0-4 % NaCl. It can tolerate high concentrations of NaCl until 10% and low temperatures as 4 °C. It decolorizes azo and anthraquinone dyes with a decolorization rate of 89-97%. We performed next-generation sequencing (Pacific Bioscience®) and achieved its complete genome sequence with a length of 5,030,813bp and a GC content of 52.98%. Genomic characterization revealed the presence of protein-coding genes related to decolorization like azoreductase, dyp-peroxidase, oxidoreductases, and the complete Mtr respiratory pathway. Likewise, we identified other properties such as the presence of metal resistant genes, and genes related to lactate and N-acetylglucosamine metabolism. These results highlight its potential to be applied in the bioremediation of textile effluents and guide future research on decolorization metabolic pathways.

Molecular mechanism of zero valent iron-enhanced microbial azo reduction

Zero valent iron (ZVI)-microbe technology has an increasing application on the removal of organic pollution, yet the molecular mechanism of microbe respond to ZVI is still a mystery. Here, we established a successive ZVI-enhanced microbial system to remove azo dye (a typical organic pollutant) by Shewanella decolorationis S12 (S. decolorationis S12, an effective azo dye degradation bacterium) and examined the gene expression time course (10, 30, 60, and 120 min) by whole genome transcriptional analysis. The addition of ZVI to the microbial degradation system increases the rate of azo reduction from ~60% to over 99% in 16 h reaction, suggesting the synergistic effect of ZVI and S12 on azo dye degradation. Comparing with the treatment without ZVI, less filamentous cells were observed in ZVI treated system, and approximately 8% genes affiliated with 10 different gene expression profiles in S. decolorationis S12 were significantly changed in 120 min during the ZVI-enhanced azo reduction. Intriguingly, MarR transcriptional factor might play a vital role in regulating ZVI-enhanced azo reduction in the aspect of energy production, iron homeostasis, and detoxification. Further investigation showed that the induced [Ni-Fe] H₂ase genes (hyaABCDEF) and azoreductase genes (mtrABC-omcA) contributed to ZVI-enhanced energy production, while the reduced iron uptake (hmuVCB and feoAB), induced sulfate assimilation (cysPTWA) and cysteine biosynthesis (cysM) related genes were essential to iron homeostasis and detoxification. This study disentangles underlying mechanisms of ZVI-enhanced organic pollution biotreatment in S. decolorationis S12.

The first complete genome sequence of species Shewanella decolorationis, from a bioremediation competent strain Ni1-3

Shewanella decolorationis are Gram-negative γ-Proteobacteria with environmental bioremediation potential because they can perform anaerobic respiration using various types of pollutants as terminal electron acceptors. So far, three isolated and cultured strains of S. decolorationis have been reported. However, no complete S. decolorationis genome has been published yet, which limited exploring their metabolism and feasibility in application. Here, S. decolorationis Ni1-3 isolated from an electroplating wastewater treatment plant showed strong reduction capabilities on azo dyes and oxidized metals. In order to construct the complete genome, high-quality whole-genome sequencing of strain Ni1-3 were performed by using both Nanopore MinION and Illumina NovaSeq platforms, from which the first complete genome of S. decolorationis was obtained by hybrid assembly. The genome of strain Ni1-3 contains a megaplasmid and a circular chromosome which encodes more proteins than that of the strains LDS1 and S12 belonging to the same species. In addition, more Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs) are identified in strain Ni1-3 genome. Importantly, 32 cytochrome-c and AzoR azoreductase coding genes are identified in the genome, which make strain Ni1-3 competent to degrade the azo dyes and versatile to bioremediate some other environmental pollution. The complete genome sequence of strain Ni1-3 can expand our knowledge toward its metabolic capabilities and potential, meanwhile, provide a reference to reassemble genomes of other S. decolorationis strains.

Phylogenetically diverse bacteria isolated from tattoo inks, an azo dye-rich environment, decolorize a wide range of azo dyes

Purpose

There has been an interest in the microbial azo dye degradation as an optional method for the treatment of azo dye-containing wastes. Tattoo ink is an extremely unique azo dye-rich environment, which have never been explored in terms of microorganisms capable of degrading azo dyes. Previously, we isolated 81 phylogenetically diverse bacteria, belonging to 18 genera and 52 species, contaminated in tattoo inks. In this study, we investigated if these bacteria, which can survive in the azo dye-rich environment, have an ability to degrade azo dyes.

Methods

We conducted a two-step azo dye degradation (or decolorization) assay. In step 1, a high-throughput degradability assay was done for 79 bacterial isolates using Methyl Red and Orange II. In step 2, a further degradation assay was done for 10 selected bacteria with a representative of 11 azo dyes, including 3 commercial tattoo ink azo dyes. Degradation of azo dyes were calculated from measuring optical absorbance of soluble dyes at specific wavelengths.

Results

The initial high-throughput azo dye assay (step 1) showed that 79 isolates had a complete or partial degradation of azo dyes; > 90% of Methyl Red and Orange II were degraded within 24 h, by 74 and 20 isolates, respectively. A further evaluation of azo dye degradability for 10 selected isolates in step 2 showed that the isolates, belonging to Bacillus, Brevibacillus, Paenibacillus, and Pseudomonas, exhibited an excellent decolorization ability for a wide range of azo dyes.

Conclusions

This study showed that phylogenetically diverse bacteria, isolated from azo dye-rich tattoo inks, is able to degrade a diverse range of azo dyes, including 3 azo dyes used in commercial tattoo inks. Some of the strains would be good candidates for future studies to provide a systematic understanding of azo dye degradation mechanisms.

Deciphering the black box of microbial community of common effluent treatment plant through integrated metagenomics: Tackling industrial effluent

Identifying the microbial community and their functional potential from different stages of common effluent treatment plants (CETP) can enhance the efficiency of wastewater treatment systems. In this study, wastewater metagenomes from 8 stages of CETP were screened for microbial diversity and gene profiling along with their corresponding degradation activities. The microbial community displayed 98.46% of bacterial species, followed by Eukarya (0.10%) and Archaea 0.02%. At the Phylum level, Proteobacteria (28.8%) was dominant, followed by Bacteroidetes (16.1%), Firmicutes (11.7%), and Fusobacteria (6.9%) which are mainly capable of degrading the aromatic compounds. Klebsiella pneumoniae, Wolinella succinogenes, Pseudomonas stutzeri, Desulfovibrio vulgaris, and Clostridium sticklandii were the most prevalent species. The functional analysis further demonstrated the presence of enzymes linked with genes/pathways known to be involved in the degradation/metabolization of aromatic compounds like benzoate, bisphenol, 1,2-dichloroethane phenylalanine. This information was further validated with the whole genome analysis of the bacteria isolated from the CETP. We anticipate that integrating both shotgun and whole-genome analyses can reveal the rich reservoir for novel enzymes and genes present in CETP effluent that can contribute to designing efficient bioremediation strategies for the environment in general CETP system, in particular.

Comparative Metagenomics Reveals Microbial Signatures of Sugarcane Phyllosphere in Organic Management

Converting conventional farms to organic systems to improve ecosystem health is an emerging trend in recent decades, yet little is explored to what extent and how this process drives the taxonomic diversity and functional capacity of above-ground microbes. This study was, therefore, conducted to investigate the effects of agricultural management, i.e., organic, transition, and conventional, on the structure and function of sugarcane phyllosphere microbial community using the shotgun metagenomics approach. Comparative metagenome analysis exhibited that farming practices strongly influenced taxonomic and functional diversities, as well as co-occurrence interactions of phyllosphere microbes. A complex microbial network with the highest connectivity was observed in organic farming, indicating strong resilient capabilities of its microbial community to cope with the dynamic environmental stressors. Organic farming also harbored genus Streptomyces as the potential keystone species and plant growth-promoting bacteria as microbial signatures, including Mesorhizobium loti, Bradyrhizobium sp. SG09, Lactobacillus plantarum, and Bacillus cellulosilyticus. Interestingly, numerous toxic compound-degrading species were specifically enriched in transition farming, which might suggest their essential roles in the transformation of conventional to organic farming. Moreover, conventional practice diminished the abundance of genes related to cell motility and energy metabolism of phyllosphere microbes, which could negatively contribute to lower microbial diversity in this habitat. Altogether, our results demonstrated the response of sugarcane-associated phyllosphere microbiota to specific agricultural managements that played vital roles in sustainable sugarcane production.

Description of Shewanella salipaludis sp. nov., isolated from a salt marsh

A Gram-stain-negative and flagellated bacterial strain, SHSM-M6T, was isolated from salt marsh from Yellow Sea, Republic of Korea. Neighbor-joining phylogenetic tree of 16S rRNA gene sequences showed that strain SHSM-M6T belongs to the genus Shewanella. 16S rRNA gene sequence similarity values between strain SHSM-M6T and the type strains of Shewanella species were <98.0%. The average nucleotide identity and DNA-DNA hybridization values between genomic sequences of strain SHSM-M6T and the type strains of Shewanella species were <73.3 and 20.7%, respectively. Strain SHSM-M6T contained MK-6 as predominant menaquinone and Q-7 and Q-8 as the predominant ubiquinones. The novel strain contained C16:1ω7c and/or C16:1ω6c, iso-C15:0 and C16:0 as major fatty acids. Major polar lipids of strain SHSM-M6T were phosphatidylethanolamine, phosphatidylglycerol, one unidentified lipid, one unidentified aminolipid and one unidentified phospholipid. Differential phenotypic properties of strain SHSM-M6T, together with its phylogenetic and genetic distinctiveness, revealed that strain SHSM-M6T is separated from recognized Shewanella species. On the basis of the data presented, strain SHSM-M6T is considered to represent a novel species of the genus Shewanella, for which the name Shewanella salipaludis sp. nov. is proposed. The type strain is SHSM-M6T (=KACC 19901T = NBRC 113646T).

Shewanella insulae sp. nov., isolated from a tidal flat

A Gram-stain-negative, aerobic, non-spore-forming, motile by single polar flagellum and ovoid or rod-shaped bacterial strain, designated JBTF-M18^T, was isolated from tidal-flat sediment collected from the Yellow Sea, Republic of Korea. The neighbour-joining phylogenetic tree of 16S rRNA gene sequences showed that strain JBTF-M18^T fell within the clade comprising the type strains of Shewanella species. Strain JBTF-M18^T exhibited 16S rRNA gene sequence similarity values of 97.1-98.8 % to the type strains of S. loihica, S. aquimarina, S. waksmanii and S. marisflavi and of less than 96.9 % to the type strains of the other Shewanella species. The average nucleotide identity and digital DNA-DNA hybridization values between strain JBTF-M18^T and the type strains of S. waksmanii and S. loihica were 72.0 and 89.5% and 18.9 and 38.1 %, respectively. DNA-DNA relatedness values between strain JBTF-M18^T and the type strains of S. aquimarina and S. marisflavi were 14 and 19 %, respectively. The DNA G+C content of strain JBTF-M18^T from genomic sequence data was 52.9 %. Strain JBTF-M18^Tcontained MK-6 as the predominant menaquinone and Q-7 and Q-8 as the predominant ubiquinones. It had iso-C_15 : 0, summed feature 3 (C_16 : 1  ω7c and/or C_16 : 1  ω6c) and C_16 : 0 as the major fatty acids. The major polar lipids of strain JBTF-M18^T were phosphatidylethanolamine and phosphatidylglycerol. Distinguished phenotypic properties, along with the phylogenetic and genetic distinctiveness, revealed that strain JBTF-M18^T is separated from recognized Shewanella species. On the basis of the data presented, strain JBTF-M18^T is considered to represent a novel species of the genus Shewanella, for which the name Shewanella insulae sp. nov. is proposed. The type strain is JBTF-M18^T (=KACC 19869^T=NBRC 113583^T).

Isolation of two iron-reducing facultative anaerobic electricigens and probing the application performance in eutrophication water

Purpose

Sediment microbial fuel cell (SMFC) is a promising bioremediation technology in which microbes play an important role. Electricigens as the bio-catalysts have effect on pollution control and electricity generation. It is of great significance to screen the microorganisms with the ability of generating electricity.

Methods

The SMFC anode biofilm was used as microbiological source to study the feasibility of electricigens with iron-reducing property for eutrophication water treatment. Preliminarily, we isolated 20 facultative anaerobic pure bacteria and evaluated their cyclic voltammogram (CV) through the three-electrode system and electrochemical workstation. The power generation performance of strains was verified by air-cathode microbial fuel cells (AC-MFCs) under different single carbon sources.

Result

According to its morphological, physiological, and biochemical characteristics, along with phylogenetic analysis, the two strains (SMFC-7 and SMFC-17) with electrical characteristics were identified as Bacillus cereus. Compared with SMFC-7, SMFC-17 exhibited efficient NH4+-N and NO3−-N removal and PO43−-P accumulation from eutrophic solution with a removal rate of 79.91 ± 6.34% and 81.26 ± 1.11% and accumulation rate of 57.68 ± 4.36%, respectively.

Conclusion

The isolated bacteria SMFC-17 showed a good performance in eutrophic solution, and it might be a useful biocatalyst to enable the industrialized application of SMFC in eutrophic water treatment.

Lack of Periplasmic Non-heme Protein SorA Increases Shewanella decolorationis Current Generation

Bacterial extracellular electron transport (EET) plays an important role in many natural and engineering processes. Some periplasmic non-heme redox proteins usually coexist with c-type cytochromes (CTCs) during the EET process. However, in contrast to CTCs, little is known about the roles of these non-heme redox proteins in EET. In this study, the transcriptome of Shewanella decolorationis S12 showed that the gene encoding a periplasmic sulfite dehydrogenase molybdenum-binding subunit SorA was significantly up-regulated during electrode respiration in microbial fuel cells (MFCs) compared with that during azo-dye reduction. The maximum current density of MFCs catalyzed by a mutant strain lacking SorA (ΔsorA) was 25% higher than that of wild strain S12 (20 vs. 16 μA/cm2). Both biofilm formation and the current generation of the anodic biofilms were increased by the disruption of sorA, which suggests that the existence of SorA in S. decolorationis S12 inhibits electrode respiration. In contrast, disruption of sorA had no effect on respiration by S. decolorationis S12 with oxygen, fumarate, azo dye, or ferric citrate as electron acceptors. This is the first report of the specific effect of a periplasmic non-heme redox protein on EET to electrode and provides novel information for enhancing bacterial current generation.

The Shewanella genus: ubiquitous organisms sustaining and preserving aquatic ecosystems

The Gram-negative Shewanella bacterial genus currently includes about 70 species of mostly aquatic γ­-proteobacteria, which were isolated around the globe in a multitude of environments such as surface freshwater and the deepest marine trenches. Their survival in such a wide range of ecological niches is due to their impressive physiological and respiratory versatility. Some strains are among the organisms with the highest number of respiratory systems, depending on a complex and rich metabolic network. Implicated in the recycling of organic and inorganic matter, they are important components of organism-rich oxic/anoxic interfaces, but they also belong to the microflora of a broad group of eukaryotes from metazoans to green algae. Examples of long-term biological interactions like mutualism or pathogeny have been described, although molecular determinants of such symbioses are still poorly understood. Some of these bacteria are key organisms for various biotechnological applications, especially the bioremediation of hydrocarbons and metallic pollutants. The natural ability of these prokaryotes to thrive and detoxify deleterious compounds explains their use in wastewater treatment, their use in energy generation by microbial fuel cells and their importance for resilience of aquatic ecosystems.

Antibacterial and catalytic activity of biogenic gold nanoparticles synthesised by Trichoderma harzianum

This study reveals the antibacterial and catalytic activity of biogenic gold nanoparicles (AuNPs) synthesised by biomass of Trichoderma harzianum. The antibacterial activity of AuNPs was analysed by the means of growth curve, well diffusion and colony forming unit (CFU) count methods. The minimum inhibitory concentration of AuNPs was 20 µg/ml. AuNPs at 60 µg/ml show effective antibacterial activity as optical absorption was insignificant. The well diffusion and CFU methods were also applied to analyse the effect of various concentration of AuNPs. Further, the catalytic activity of AuNPs was analysed against methylene blue (MB) as a model pollutant in water. MB was degraded 39% in 30 min in the presence of AuNPs and sodium borohydrate and the rate constant (k) was found to be 0.2 × 10^-3 s^-1. This shows that the biogenic AuNP is an effective candidate for antibacterial and catalytic degradation of toxic pollutants.

Shewanella decolorationis LDS1 Chromate Resistance

The genus Shewanella is well known for its genetic diversity, its outstanding respiratory capacity, and its high potential for bioremediation. Here, a novel strain isolated from sediments of the Indian Ocean was characterized. A 16S rRNA analysis indicated that it belongs to the species Shewanella decolorationis It was named Shewanella decolorationis LDS1. This strain presented an unusual ability to grow efficiently at temperatures from 24°C to 40°C without apparent modifications of its metabolism, as shown by testing respiratory activities or carbon assimilation, and in a wide range of salt concentrations. Moreover, S. decolorationis LDS1 tolerates high chromate concentrations. Indeed, it was able to grow in the presence of 4 mM chromate at 28°C and 3 mM chromate at 40°C. Interestingly, whatever the temperature, when the culture reached the stationary phase, the strain reduced the chromate present in the growth medium. In addition, S. decolorationis LDS1 degrades different toxic dyes, including anthraquinone, triarylmethane, and azo dyes. Thus, compared to Shewanella oneidensis, this strain presented better capacity to cope with various abiotic stresses, particularly at high temperatures. The analysis of genome sequence preliminary data indicated that, in contrast to S. oneidensis and S. decolorationis S12, S. decolorationis LDS1 possesses the phosphorothioate modification machinery that has been described as participating in survival against various abiotic stresses by protecting DNA. We demonstrate that its heterologous production in S. oneidensis allows it to resist higher concentrations of chromate.IMPORTANCE Shewanella species have long been described as interesting microorganisms in regard to their ability to reduce many organic and inorganic compounds, including metals. However, members of the Shewanella genus are often depicted as cold-water microorganisms, although their optimal growth temperature usually ranges from 25 to 28°C under laboratory growth conditions. Shewanella decolorationis LDS1 is highly attractive, since its metabolism allows it to develop efficiently at temperatures from 24 to 40°C, conserving its ability to respire alternative substrates and to reduce toxic compounds such as chromate or toxic dyes. Our results clearly indicate that this novel strain has the potential to be a powerful tool for bioremediation and unveil one of the mechanisms involved in its chromate resistance.

Whole-Genome Sequencing Redefines Shewanella Taxonomy

The genus Shewanella encompasses a diverse group of Gram negative, primarily aquatic bacteria with a remarkable ecological relevance, an outstanding set of metabolic features and an emergent clinical importance. The rapid expansion of the genus over the 2000 s has prompted questions on the real taxonomic position of some isolates and species. Recent work by us and others identified inconsistencies in the existing species classification. In this study we aimed to clarify such issues across the entire genus, making use of the genomic information publicly available worldwide. Phylogenomic analyses, including comparisons based on genome-wide identity indexes (digital DNA-DNA hybridization and Average Nucleotide Identity) combined with core and accessory genome content evaluation suggested that the taxonomic position of 64 of the 131 analyzed strains should be revisited. Based on the genomic information currently available, emended descriptions for some Shewanella species are proposed. Our study establishes for the first time a whole-genome based phylogeny for Shewanella spp. including a classification at the subspecific level.

Adaptive Responses of Shewanella decolorationis to Toxic Organic Extracellular Electron Acceptor Azo Dyes in Anaerobic Respiration

Bacterial anaerobic respiration using an extracellular electron acceptor plays a predominant role in global biogeochemical cycles. However, the mechanisms of bacterial adaptation to the toxic organic pollutant as the extracellular electron acceptor during anaerobic respiration are not clear, which limits our ability to optimize the strategies for the bioremediation of a contaminated environment. Here, we report the physiological characteristics and the global gene expression of an ecologically successful bacterium, Shewanella decolorationis S12, when using a typical toxic organic pollutant, amaranth, as the extracellular electron acceptor. Our results revealed that filamentous shift (the cells stretched to fiber-like shapes as long as 18 μm) occurred under amaranth stress. Persistent stress led to a higher filamentous cell rate and decolorization ability in subcultural cells compared to parental strains. In addition, the expression of genes involved in cell division, the chemotaxis system, energy conservation, damage repair, and material transport in filamentous cells was significantly stimulated. The detailed roles of some genes with significantly elevated expressions in filamentous cells, such as the outer membrane porin genes ompA and ompW, the cytochrome c genes arpC and arpD, the global regulatory factor gene rpoS, and the methyl-accepting chemotaxis proteins genes SHD_2793 and SHD_0015, were identified by site-directed mutagenesis. Finally, a conceptual model was proposed to help deepen our insights into both the bacterial survival strategy when toxic organics were present and the mechanisms by which these toxic organics were biodegraded as the extracellular electron acceptors.IMPORTANCE Keeping toxic organic pollutants (TOPs) in tolerable levels is a huge challenge for bacteria in extremely unfavorable environments since TOPs could serve as energy substitutes but also as survival stresses when they are beyond some thresholds. This study focused on the underlying adaptive mechanisms of ecologically successful bacterium Shewanella decolorationis S12 when exposed to amaranth, a typical toxic organic pollutant, as the extracellular electron acceptor. Our results suggest that filamentous shift is a flexible and valid way to solve the dilemma between the energy resource and toxic stress. Filamentous cells regulate gene expression to enhance their degradation and detoxification capabilities, resulting in a strong viability. These novel adaptive responses to TOPs are believed to be an evolutionary achievement to succeed in harsh habitats and thus have great potential to be applied to environment engineering or synthetic biology if we could picture every unknown node in this pathway.

Parashewanella tropica sp. nov., a mesophilic bacterium isolated from a marine sponge from Chuuk lagoon, Federated States of Micronesia, and emended description of the genus Parashewanella

A mesophilic, straight-rod-shaped, non-flagellated bacterium, designated MEBiC05444^T, was isolated from a marine sponge collected from Chuuk lagoon, Federated States of Micronesia. The strain was Gram-negative, catalase- and oxidase-positive, and facultative anaerobic. The isolate aerobically grew at 8-38 °C (optimum, 24-32 °C), pH 4.0-10.0 (pH 7.0-7.5) with an absolute requirement for Na⁺ up to 6 % (w/v) NaCl (2 %). Phylogenetic analyses based on 16S rRNA gene sequences revealed that MEBiC05444^T belonged to the family Shewanellaceae, within the class Gammaproteobacteria. Strain MEBiC05444^T showed highest 16S rRNA gene sequence similarity to Parashewanella curva C51^T, followed by [Shewanella] irciniae UST040317-058^T and Parashewanella spongiae HJ039^T (98.9 %, 97.2 and 95.7 %, respectively). In the phylogenetic tree based on the 16S rRNA gene sequences, MEBiC05444^T formed a cluster with P. curva C51^T, but the average nucleotide identity value between the two strains was 82 %, thus confirming their separation at species level. The major fatty acids were iso-C_15 : 0 (19.7 %), summed feature 3 (composed of C_16 : 1 ω7c and/or C_16 : 1ω6c; 16.1 %) and C_17 : 1ω8c (10.2 %). The only detected respiratory quinone was ubiquinone Q-8. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, three unidentified aminoglycolipids, two unidentified glycolipids, an unidentified aminoglycophospholipid and an unidentified lipid. The genomic DNA G+C content of strain MEBiC05444^T was 40.8 mol%. Based on the results of polyphasic analysis, the strain represents a novel species of the genus Parashewanella, distinct from P. curva C51^T, [Shewanella]irciniae UST040317-058^T and P. spongiae HJ039^T for which the name Parashewanellatropica sp. nov. is proposed with type strain MEBiC05444^T (=KCCM 43304^T=JCM 16653^T).

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-S14^T, was Gram-stain-negative, motile and pale-yellow. NIO-S14^T 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-S14^T contained diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, two unidentified aminophospholipids and six unidentified lipids as polar lipids. The DNA G+C content of NIO-S14^T 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-S14^T was closely related to Shewanella coralliiwith a pair-wise sequence similarity of 99.26 %. On the basis of the sequence comparison, NIO-S14^T 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-S14^T and Shewanella corallii DSM 21332^Trevealed a relatedness of 35 %. Distinct morphological, physiological and genotypic differences from these previously described taxa supported the classification of NIO-S14^T 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-S14^T (=MTCC 12524^T=KCTC 52277^T=LMG 30752^T).

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.

Complete genome sequence of the dissimilatory azo reducing thermophilic bacterium Novibacillus thermophiles SG-1

With the isolation and identification of efficient azo-dye degradation bacteria, bioaugmentation with specific microbial strains has now become an effective strategy to promote the bioremediation of azo dye. However, Azo dye wastewater discharged at high temperature restricted the extensive application of the known mesophilic azoreducing microorganisms. Here we present the complete genome sequence of a bacterium capable of reducing azo dye under thermophilic condition, Novibacillus thermophiles SG-1 (=KCTC 33118^T =CGMCC 1.12363^T). The complete genome of strain SG-1 contains a circular chromosome of 3,629,225 bp with a G + C content of 50.44%. Genome analysis revealed that strain SG-1 possessed genes encoding riboflavin biosynthesis protein that would secrete riboflavin, which could act as electron shuttles to transport the electrons to extracellular azo dye in decolorization process. HPLC analysis showed that the concentration of riboflavin increased from 0.01 μM to 0.255 μM with the growth of strain SG-1 under azo dye reduction. Quantitative real-time PCR analysis further demonstrated that the gene encoding riboflavin biosynthesis protein would be involved in the azo dye decolorization. The results from this study would be beneficial to research the mechanism of anaerobic reduction of azo dye under thermophilic conditions.

Methods for identification and differentiation of different Shewanella spp. isolates for diagnostic use

Shewanella spp. are Gram-negative, rod-shaped, motile bacteria that are widely distributed in marine and freshwater environments. The bacteria are present in the physiological microflora of fish from temperate waters and are known as fish spoilage species. From clinically healthy fish and from fish with skin ulcerations, Shewanella spp. is regularly isolated, indicating a possible role as fish pathogen. In this study, 74 isolates of Shewanella spp. were analysed. For species identification, biochemical techniques, 16S rRNA sequencing, MALDI-TOF MS and the Sherlock Microbial Identification System (MIS) based on the composition of fatty acid ethyl esters were compared. The phylogenetic relationship, cytotoxicity in vitro and resistance against antibiotics were tested. The most reliable method for species identification was 16S rRNA sequencing. From diseased fish, clinically healthy fish and the aquatic environment, different Shewanella species were isolated. This indicates that Shewanella spp. is widespread in the aquatic milieu and acts as a secondary pathogen. The virulence of Shewanella spp. is probably not depending on the species but on the isolate itself. Many isolates of Shewanella spp. were showing multiresistances against antibiotic substances, especially in samples derived from retailers and in routine diagnostics, all Shewanella spp. should therefore be tested for resistances against antibiotic agents.

Electricity Generation by Shewanella decolorationis S12 without Cytochrome c

Bacterial extracellular electron transfer (EET) plays a key role in various natural and engineering processes. Outer membrane c-type cytochromes (OMCs) are considered to be essential in bacterial EET. However, most bacteria do not have OMCs but have redox proteins other than OMCs in their extracellular polymeric substances of biofilms. We hypothesized that these extracellular non-cytochrome c proteins (ENCP) could contribute to EET, especially with the facilitation of electron mediators. This study compared the electrode respiring capacity of wild type Shewanella decolorationis S12 and an OMC-deficient mutant. Although the OMC-deficient mutant was incapable in direct electricity generation in normal cultivation, it regained electricity generation capacity (26% of the wide type) with the aid of extracellular electron mediator (riboflavin). Further bioelectrochemistry and X-ray photoelectron spectroscopy analysis suggested that the ENCP, such as proteins with Fe–S cluster, may participate in the falvin-mediated EET. The results highlighted an important and direct role of the ENCP, generated by either electricigens or other microbes, in natural microbial EET process with the facilitation of electron mediators.

Azo dye decolorization by a halotolerant exoelectrogenic decolorizer isolated from marine sediment

Based on both capabilities of extracellular electron transfer and high salt tolerance, marine exoelectrogenic bacteria have the potential to serve as halotolerant/halophilic exoelectrogenic decolorizers (HEDs) for textile wastewater treatment. However, research in this area is still rare. In this study, we employed Shewanella marisflavi EP1 for this purpose. The results showed that EP1 could decolorize Xylidine Ponceau 2R (XP2R) under high NaCl concentrations up to 20%. Two different mechanisms were involved: degradation and bioflocculation. XP2R was decolorized by degradation in the range of 0-7.4% NaCl, by bioaugmented flocculation in 10-20% NaCl; and the range of 7.4-10% NaCl was the transition period from degradation to flocculation. Considering the property of flocculation by strain EP1, it is reasonable that XP2R was hard to penetrate into EP1 cells, thus it was an extracellular process of decolorization. The overall results further suggested that like EP1, marine exoelectrogenic bacteria might serve as a category of functional microbes (i.e., HEDs) for textile wastewater treatment.

Electron acceptor redox potential globally regulates transcriptomic profiling in Shewanella decolorationis S12

Electron acceptor redox potential (EARP) was presumed to be a determining factor for microbial metabolism in many natural and engineered processes. However, little is known about the potentially global effects of EARP on bacteria. In this study, we compared the physiological and transcriptomic properties of Shewanella decolorationis S12 respiring with different EARPs in microbial electrochemical systems to avoid the effects caused by the other physicochemical properties of real electron acceptor. Results showed that the metabolic activities of strain S12 were nonlinear responses to EARP. The tricarboxylic acid cycle for central carbon metabolism was down-regulated while glyoxylate shunt was up-regulated at 0.8 V compared to 0.2 and -0.2 V, which suggested that EARP is an important but not the only determinant for metabolic pathways of strain S12. Moreover, few cytochrome c genes were differentially expressed at different EARPs. The energy intensive flagella assembly and assimilatory sulfur metabolism pathways were significantly enriched at 0.8 V, which suggested strain S12 had stronger electrokinesis behavior and oxidative stress-response at high EARP. This study provides the first global information of EARP regulations on microbial metabolism, which will be helpful for understanding microorganism respiration.

Shewanella algicola sp. nov., a marine bacterium isolated from brown algae

A Gram-stain-negative, aerobic, rod-shaped bacterium motile by means of a single polar flagella, strain ST-6T, was isolated from a brown alga (Sargassum thunbergii) collected in Jeju, Republic of Korea. Strain ST-6T was psychrotolerant, growing at 4-30 °C (optimum 20 °C). Phylogenetic analysis based on 16S rRNA and gyrB gene sequences revealed that strain ST-6T belonged to a distinct lineage in the genus Shewanella. Strain ST-6T was related most closely to Shewanella basaltis J83T, S. gaetbuli TF-27T, S. arctica IT12T, S. vesiculosa M7T and S. aestuarii SC18T, showing 96-97 % and 85-70 % 16S rRNA and gyrB gene sequences similarities, respectively. DNA-DNA relatedness values between strain ST-6T and the type strains of two species of the genus Shewanella were <22.6 %. The major cellular fatty acids (>5 %) were summed feature 3 (comprising C16:1ω7c and/ or iso-C15:0 2-OH), C16:0, iso-C13:0 and C17:1ω8c. The DNA G+C content of strain ST-6Twas 42.4 mol%, and the predominant isoprenoid quinones were menaquinone MK-7 and ubiquinones Q-7 and Q-8. On the basis of its phenotypic properties and phylogenetic distinctiveness, strain ST-6T is considered to represent a novel species of the genus Shewanella, for which the name Shewanella algicola sp. nov. is proposed. The type strain is ST-6T (= KCTC 23253T = JCM 31091T).

From red to green: the propidium iodide-permeable membrane of Shewanella decolorationis S12 is repairable

Viability is a common issue of concern in almost all microbial processes. Fluorescence-based assays are extensively used in microbial viability assessment, especially for mixed-species samples or biofilms. Propidium iodide (PI) is the most frequently used fluorescence indicator for cell viability based on the membrane permeability. Our results showed that the accumulation of succinate from fumarate respiration could induce PI-permeability in Shewanella decolorationis biofilm cells. Confocal laser scanning microscope further showed that the PI-permeable membrane could be repaired in situ when the extracellular succinate was eliminated by switching fumarate respiration to electrode respiration. Simultaneously with the membrane repair, the electrode respiring capacity of the originally PI-permeable cells was recovered. Agar-colony counts suggested that a major portion of the repaired cells were viable but nonculturable (VBNC). The results evidenced that S. decolorationis S12 has the capacity to repair PI-permeable membranes which suggests a reevaluation of the fate and function of the PI-permeable bacteria and expanded our knowledge on the flexibility of bacterial survival status in harsh environments.

Shewanella mangrovi sp. nov., an acetaldehyde-degrading bacterium isolated from mangrove sediment

A taxonomic study was carried out on strain YQH10T, which was isolated from mangrove sediment collected from Zhangzhou, China during the screening of acetaldehyde-degrading bacteria. Cells of strain YQH10T were Gram-stain-negative rods and pale brown-pigmented. Growth was observed at salinities from 0 to 11 % and at temperatures from 4 to 42 °C. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain YQH10T is affiliated to the genus Shewanella, showing the highest similarity with Shewanella haliotis DW01T (95.7 %) and other species of the genus Shewanella (91.4–95.6 %). The principal fatty acids were iso-C15 : 0 and C17 : 1ω8c. The major respiratory quinone was Q-8. The polar lipids comprised phosphatidylethanolamine and phosphatidylglycerol. The genomic DNA had a G+C content of 48.3 mol%. Strain YQH10T can completely degrade 0.02 % (w/v) acetaldehyde on 2216E at 28 °C within 48 h. Based on these phenotypic and genotypic data, strain YQH10T represents a novel species of the genus Shewanella, for which the name Shewanella mangrovi sp. nov. is proposed. The type strain is YQH10T ( = MCCC 1A00830T = JCM 30121T).

Characterization of the enhancement of zero valent iron on microbial azo reduction

BACKGROUND

The microbial method for the treatment of azo dye is promising, but the reduction of azo dye is the rate-limiting step. Zero valent iron (Fe(0)) can enhance microbial azo reduction, but the interactions between microbes and Fe(0) and the potential mechanisms of enhancement remain unclear. Here, Shewanella decolorationis S12, a typical azo-reducing bacterium, was used to characterize the enhancement of Fe(0) on microbial decolorization.

RESULTS

The results indicated that anaerobic iron corrosion was a key inorganic chemical process for the enhancement of Fe(0) on microbial azo reduction, in which OH(-), H2, and Fe(2+) were produced. Once Fe(0) was added to the microbial azo reduction system, the proper pH for microbial azo reduction was maintained by OH(-), and H2 served as the favored electron donor for azo respiration. Subsequently, the bacterial biomass yield and viability significantly increased. Following the corrosion of Fe(0), nanometer-scale Fe precipitates were adsorbed onto cell surfaces and even accumulated inside cells as observed by transmission electron microscope energy dispersive spectroscopy (TEM-EDS).

CONCLUSIONS

A conceptual model for Fe(0)-assisted azo dye reduction by strain S12 was established to explain the interactions between microbes and Fe(0) and the potential mechanisms of enhancement. This model indicates that the enhancement of microbial azo reduction in the presence of Fe(0) is mainly due to the stimulation of microbial growth and activity by supplementation with elemental iron and H2 as an additional electron donor. This study has expanded our knowledge of the enhancement of microbial azo reduction by Fe(0) and laid a foundation for the development of Fe(0)-microbial integrated azo dye wastewater treatment technology.

Lysinibacillus varians sp. nov., an endospore-forming bacterium with a filament-to-rod cell cycle

Six Gram-stain-positive, motile, filamentous and/or rod-shaped, spherical spore-forming bacteria (strains GY32T, L31, F01, F03, F06 and F07) showing polybrominated diphenyl ether transformation were investigated to determine their taxonomic status. After spore germination, these organisms could grow more than one hundred microns long as intact single cells and then divide into rod cells and form endospores in 33 h. The cell-wall peptidoglycan of these strains was type A4α, the predominant menaquinone was MK-7 and the major fatty acids were iso-C16 : 0, iso-C15 : 0 and C16 : 1ω7C. Diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine were detected in the polar lipid profile. Analysis of the 16S rRNA gene sequences indicated that these strains should be placed in the genus Lysinibacillus and they were most closely related to Lysinibacillus sphaericus DSM 28T (99 % 16S rRNA gene sequence similarity). The gyrB sequence similarity and DNA–DNA relatedness between strain GY32T and L. sphaericus JCM 2502T were 81 % and 52 %, respectively. The G+C content of the genomic DNA of strain GY32T was 43.2 mol%. In addition, strain GY32T showed differences in nitrate reduction, starch and gelatin hydrolysis, carbon resource utilization and cell morphology. The phylogenetic distance from its closest relative measured by DNA–DNA relatedness and DNA G+C content, and its phenotypic properties demonstrated that strain GY32T represents a novel species of the genus Lysinibacillus , for which the name Lysinibacillus varians sp. nov. is proposed. The type strain is GY32T ( = NBRC 109424T = CGMCC 1.12212T = CCTCC M 2011307T).

Psychrobium conchae gen. nov., sp. nov., a psychrophilic marine bacterium isolated from the Iheya North hydrothermal field

A novel psychrophilic, marine, bacterial strain designated BJ-1(T) was isolated from the Iheya North hydrothermal field in the Okinawa Trough off Japan. Cells were Gram-negative, rod-shaped, non-spore-forming, aerobic chemo-organotrophs and motile by means of a single polar flagellum. Growth occurred at temperatures below 16 °C, with the optimum between 9 and 12 °C. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that the closest relatives of strain BJ-1(T) were Shewanella denitrificans OS-217(T) (93.5% similarity), Shewanella profunda DSM 15900(T) (92.9%), Shewanella gaetbuli TF-27(T) (92.9%), Paraferrimonas sedimenticola Mok-106(T) (92.1%) and Ferrimonas kyonanensis Asr22-7(T) (91.7%). The major respiratory quinone was Q-8. The predominant fatty acids were C(16:1)ω7c and C(16:0). The G+C content of the novel strain was 40.5 mol%. Based on phylogenetic, phenotypic and chemotaxonomic evidence, it is proposed that strain BJ-1(T) represents a novel species in a new genus, for which the name Psychrobium conchae gen. nov., sp. nov. is proposed. The type strain of Psychrobium conchae is BJ-1(T) ( =JCM 30103(T) =DSM 28701(T)).

Draft Genome Sequence of the Dye-Decolorizing and Nanowire-Producing Bacterium Shewanella xiamenensis BC01

Shewanella xiamenensis BC01 is an important biodecolorizing and nanowire-producing bacterium which was found in Xiamen, China. Here, we present the draft genome sequence consisting of 4,677,169 bp (GC content, 46.21%) and 3,999 coded proteins. This information boosts insight into and understanding of the genetic evolution of Shewanella species.

Physiological and electrochemical effects of different electron acceptors on bacterial anode respiration in bioelectrochemical systems

To understand the interactions between bacterial electrode respiration and the other ambient bacterial electron acceptor reductions, alternative electron acceptors (nitrate, Fe2O3, fumarate, azo dye MB17) were added singly or multiply into Shewanella decolorationis microbial fuel cells (MFCs). All the added electron acceptors were reduced simultaneously with current generation. Adding nitrate or MB17 resulted in more rapid cell growth, higher flavin concentration and higher biofilm metabolic viability, but lower columbic efficiency (CE) and normalized energy recovery (NER) while the CE and NER were enhanced by Fe2O3 or fumarate. The added electron acceptors also significantly influenced the cyclic voltammetry profile of anode biofilm probably via altering the cytochrome c expression. The highest power density was observed in MFCs added with MB17 due to the electron shuttle role of the naphthols from MB17 reduction. The results provided important information for MFCs applied in practical environments where contains various electron acceptors.

Recent advances in heterogeneous photocatalytic decolorization of synthetic dyes

During the process and operation of the dyes, the wastes produced were commonly found to contain organic and inorganic impurities leading to risks in the ecosystem and biodiversity with the resultant impact on the environment. Improper effluent disposal in aqueous ecosystems leads to reduction of sunlight penetration which in turn diminishes photosynthetic activity, resulting in acute toxic effects on the aquatic flora/fauna and dissolved oxygen concentration. Recently, photodegradation of various synthetic dyes has been studied in terms of their absorbance and the reduction of oxygen content by changes in the concentration of the dye. The advantages that make photocatalytic techniques superior to traditional methods are the ability to remove contaminates in the range of ppb, no generation of polycyclic compounds, higher speed, and lower cost. Semiconductor metal oxides, typically TiO₂, ZnO, SnO, NiO, Cu₂O, Fe₃O₄, and also CdS have been utilized as photocatalyst for their nontoxic nature, high photosensitivity, wide band gap and high stability. Various process parameters like photocatalyst dose, pH and initial dye concentrations have been varied and highlighted. Research focused on surface modification of semiconductors and mixed oxide semiconductors by doping them with noble metals (Pt, Pd, Au, and Ag) and organic matter (C, N, Cl, and F) showed enhanced dye degradation compared to corresponding native semiconductors. This paper reviews recent advances in heterogeneous photocatalytic decolorization for the removal of synthetic dyes from water and wastewater. Thus, the main core highlighted in this paper is the critical selection of semiconductors for photocatalysis based on the chemical, physical, and selective nature of the poisoning dyes.

Rapid isolation of a facultative anaerobic electrochemically active bacterium capable of oxidizing acetate for electrogenesis and azo dyes reduction

In this study, 27 strains of electrochemically active bacteria (EAB) were rapidly isolated and their capabilities of extracellular electron transfer were identified using a photometric method based on WO3 nanoclusters. These strains caused color change of WO3 from white to blue in a 24-well agar plate within 40 h. Most of the isolated EAB strains belonged to the genera of Aeromonas and Shewanella. One isolate, Pantoea agglomerans S5-44, was identified as an EAB that can utilize acetate as the carbon source to produce electricity and reduce azo dyes under anaerobic conditions. The results confirmed the capability of P. agglomerans S5-44 for extracellular electron transfer. The isolation of this acetate-utilizing, facultative EBA reveals the metabolic diversity of environmental bacteria. Such strains have great potential for environmental applications, especially at interfaces of aerobic and anaerobic environments, where acetate is the main available carbon source.

Draft Genome Sequence of Shewanella decolorationis S12, a Dye-Degrading Bacterium Isolated from a Wastewater Treatment Plant

Shewanella decolorationis is a valuable microorganism for degrading diverse synthetic textile dyes. Here, we present an annotated draft genome sequence of S. decolorationis S12, which contains 4,219 protein-coding genes and 86 structural RNAs. This information regarding the genetic basis of this bacterium can greatly advance our understanding of the physiology of this species.

Shewanella dokdonensis sp. nov., isolated from seawater

A novel bacterial strain, designated UDC329T, was isolated from a sample of seawater collected at Dong-do, on the coast of Dokdo Island, in the East Sea of the Republic of Korea. The Gram-staining-negative, motile, facultatively anaerobic, non-spore-forming rods of the strain developed into dark orange–yellow colonies. The strain grew optimally between 25 and 30 °C, with 1 % (w/v) NaCl and at pH 7. It grew in the absence of NaCl, but not with NaCl at >7 % (w/v). The predominant menaquinone was MK-7, the predominant ubiquinones were Q-7 and Q-8, and the major fatty acids were iso-C15 : 0 (33.52 %) and C17 : 1ω8c (11.73 %). The genomic DNA G+C content of strain UDC329T was 50.2 mol%. In phylogenetic analyses based on 16S rRNA and gyrB gene sequences, strain UDC329T was grouped with members of the genus Shewanella and appeared most closely related to Shewanella fodinae JC15T (97.9 % 16S rRNA gene sequence similarity), Shewanella indica KJW27T (95.0 %), Shewanella algae ATCC 51192T (94.8 %), Shewanella haliotis DW01T (94.5 %) and Shewanella chilikensis JC5T (93.9 %). The level of DNA–DNA relatedness between strain UDC329T and S. fodinae JC15T was, however, only 27.4 %. On the basis of phenotypic, genotypic and DNA–DNA relatedness data, strain UDC329T represents a novel species in the genus Shewanella , for which the name Shewanella dokdonensis sp. nov. is proposed. The type strain is UDC329T ( = KCTC 22898T = DSM 23626T).

Bio-current as an indicator for biogenic Fe(II) generation driven by dissimilatory iron reducing bacteria

Microbial reduction of insoluble iron minerals by dissimilatory iron reducing bacteria (DIRB) is an important environment process in the iron biogeochemical cycle. We reported that the bio-current generated from oxidation of organic matter by these bacteria in the presence of iron oxides can be used as an indicator for microbial dissolution of insoluble iron oxides. Bioelectrochemical experiments were conducted to investigate the effects of the specific bacteria and the phase identity of iron oxides on bio-current generation by recording the current response as a result of a poised constant potential. Experimental results indicated that the bio-current generation can be greatly enhanced by iron oxide addition under all the conditions varying in the type of pure culture or iron oxide. The increase in the bio-current was linearly correlated with the increased concentration of biogenic Fe(II) detected either by chemical analysis or cyclic voltammetry (CV) tests. This can be understood based on the proposed mechanism that the Fe(II)/Fe(III) couple functions as the electron mediator shuttling electrons from the microbes to the electrodes.

Differential biofilms characteristics of Shewanella decolorationis microbial fuel cells under open and closed circuit conditions

Biofilms formation capacities of Shewanella species in microbial fuel cells (MFCs) and their roles in current generation have been documented to be species-dependent. Understandings of the biofilms growth and metabolism are essential to optimize the current generation of MFCs. Shewanella decolorationis S12 was used in both closed-circuit and open-circuit MFCs in this study. The anodic S. decolorationis S12 biofilms could generate fivefold more current than the planktonic cells, playing a dominant role in current generation. Anodic biofilms viability was sustained at 98 ± 1.2% in closed-circuit while biofilms viability in open-circuit decreased to 72 ± 7% within 96 h. The unviable domain in open-circuit MFCs biofilms majorly located at the inner layer of biofilm. The decreased biofilms viability in open-circuit MFCs could be recovered by switching into closed-circuit, indicating that the current-generating anode in MFCs could serve as a favorable electron acceptor and provide sufficient energy to support cell growth and metabolism inside biofilms.