Flavobacterium arsenatis sp. nov., a novel arsenic-resistant bacterium from high-arsenic sediment

Emergence and mobilization of a novel lincosamide resistance gene lnu(I): From environmental reservoirs to pathogenic bacteria

Antimicrobial resistance remains an utmost concern in human and veterinary medicine, impacting humans, animals, and the environment while significantly influencing the principles of One Health. While Riemerella anatipestifer (R. anatipestifer) is recognized as a waterfowl pathogen with multidrug-resistant properties, the specifics of its lincosamide resistance mechanism are inadequately understood. In this study, we identified a novel lincosamide resistance gene, lnu(I), in R. anatipestifer RCAD0121, and investigated its potential origin, transfer mechanisms, and dissemination status through genomic epidemiology. This exhibited 74.80 % amino acid identity with a previously reported gene, lnu(H). PCR analysis revealed lnu(I) prevalence in at least 44 R. anatipestifer isolates collected from multiple provinces in China. Furthermore, genomic mining unveiled 56 lnu(I) sequences within publicly available databases, primarily originating from environmental sources. In addition, members of the family Flavobacteriaceae were the dominant (16/56, 28.57 %) bacteria carrying the lnu(I) gene, with Flavobacterium exhibiting a similar GC content as lnu(I). Notably, specific instances of the lnu(I) gene were linked to mobile genetic elements within human and animal pathogenic bacteria. These findings suggest that Flavobacterium species within the environment could serve as potential ancestral sources of the novel lnu(I) gene, which has undergone mobilization events toward pathogenic bacteria.

Flavobacterium potami sp. nov., a multi-metal resistance genes harbouring bacterium isolated from shallow river silt

Environmental pollution by heavy metals is becoming an increasing problem and has become a matter of great concern due to the adverse effects worldwide. In this study, we report a novel strain of multi-metal resistant bacteria. A Gram-stain-negative, strictly aerobic, non-motile, yellow, rod-shaped strain 17A^T, was isolated from the shallow silt of Fuyang River located in Longdian town, Hengshui city, Hebei province, China. Strain 17A^T grew at 20-35 °C (optimum, 30 °C), pH 5-10 (optimum, pH 7) and 0-2% (w/v) NaCl (optimum, 1%). Phylogenetic analyses of 16S rRNA gene sequences showed that strain 17A^T was closely related to members of the genus Flavobacterium, and had the highest 16S rRNA gene sequence similarity with 'Flavobacterium panacis' DCY106^T (97.5%), followed by Flavobacterium johnsoniae subsp. johnsoniae UW101^T (97.3%), Flavobacterium cutihirudinis E89^T (97.2%), Flavobacterium limi THG-AG6.4^T (97.2%), Flavobacterium hibisci THG-HG1.4^T (97.2%) and Flavobacterium johnsoniae subsp. aurantiacum DSM 6792^T (97.1%). The genome size of strain 17A^T was 5.4 Mb and the DNA G + C content was 34.0%. The average nucleotide identity, digital DNA-DNA hybridization and average amino acid identity values among strain 17A^T and reference strains were in the ranges of 79.8-86.1%, 24.1-31.4% and 80.5-88.6%, respectively, lower than the threshold values for species delineation. Strain 17A^T contained iso-C_15:0 and C_16:0 3-OH as the predominant fatty acids (≥ 10%). The main isoprenoid quinone of strain 17A^T was identified as MK-6. The polar lipids consisted of phosphatidylethanolamine, three unidentified aminolipids, two unidentified aminophospholipids and six unidentified lipids. Comparative genomics analysis between strain 17A^T and its reference type strains revealed that there are a number of metal-resistant genes in strain 17A^T, which are located in 15 gene clusters responsible for the copper homeostasis, cobalt-zinc-cadmium resistance, copper resistance, and arsenic/antimony resistance, with the copper resistance protein NlpE being unique to 17A^T. Combined data from phenotypic, phylogenetic and chemotaxonomic studies demonstrated that strain 17A^T is a representative of a novel species within the genus Flavobacterium, for which the name Flavobacterium potami sp. nov. is proposed. The type strain is 17A^T (= GDMCC 1.2723^T = JCM 34833^T).

Harnessing plant microbiome for mitigating arsenic toxicity in sustainable agriculture

Heavy metal toxicity has become an impediment to agricultural productivity, which presents major human health concerns in terms of food safety. Among them, arsenic (As) a non-essential heavy metal has gained worldwide attention because of its noxious effects on agriculture and public health. The increasing rate of global warming and anthropogenic activities have promptly exacerbated As levels in the agricultural soil, thereby causing adverse effects to crop genetic and phenotypic traits and rendering them vulnerable to other stresses. Conventional breeding and transgenic approaches have been widely adapted for producing heavy metal resilient crops; however, they are time-consuming and labor-intensive. Hence, finding new mitigation strategies for As toxicity would be a game-changer for sustainable agriculture. One such promising approach is harnessing plant microbiome in the era of 'omics' which is gaining prominence in recent years. The use of plant microbiome and their cocktails to combat As metal toxicity has gained widespread attention, because of their ability to metabolize toxic elements and offer an array of perquisites to host plants such as increased nutrient availability, stress resilience, soil fertility, and yield. A comprehensive understanding of below-ground plant-microbiome interactions and their underlying molecular mechanisms in exhibiting resilience towards As toxicity will help in identifying elite microbial communities for As mitigation. In this review, we have discussed the effect of As, their accumulation, transportation, signaling, and detoxification in plants. We have also discussed the role of the plant microbiome in mitigating As toxicity which has become an intriguing research frontier in phytoremediation. This review also provides insights on the advancements in constructing the beneficial synthetic microbial communities (SynComs) using microbiome engineering that will facilitate the development of the most advanced As remedial tool kit in sustainable agriculture.

Effects of in situ Remediation With Nanoscale Zero Valence Iron on the Physicochemical Conditions and Bacterial Communities of Groundwater Contaminated With Arsenic

Nanoscale Zero-Valent Iron (nZVI) is a cost-effective nanomaterial that is widely used to remove a broad range of metal(loid)s and organic contaminants from soil and groundwater. In some cases, this material alters the taxonomic and functional composition of the bacterial communities present in these matrices; however, there is no conclusive data that can be generalized to all scenarios. Here we studied the effect of nZVI application in situ on groundwater from the site of an abandoned fertilizer factory in Asturias, Spain, mainly polluted with arsenic (As). The geochemical characteristics of the water correspond to a microaerophilic and oligotrophic environment. Physico-chemical and microbiological (cultured and total bacterial diversity) parameters were monitored before and after nZVI application over six months. nZVI treatment led to a marked increase in Fe(II) concentration and a notable fall in the oxidation-reduction potential during the first month of treatment. A substantial decrease in the concentration of As during the first days of treatment was observed, although strong fluctuations were subsequently detected in most of the wells throughout the six-month experiment. The possible toxic effects of nZVI on groundwater bacteria could not be clearly determined from direct observation of those bacteria after staining with viability dyes. The number of cultured bacteria increased during the first two weeks of the treatment, although this was followed by a continuous decrease for the following two weeks, reaching levels moderately below the initial number at the end of sampling, and by changes in their taxonomic composition. Most bacteria were tolerant to high As(V) concentrations and showed the presence of diverse As resistance genes. A more complete study of the structure and diversity of the bacterial community in the groundwater using automated ribosomal intergenic spacer analysis (ARISA) and sequencing of the 16S rRNA amplicons by Illumina confirmed significant alterations in its composition, with a reduction in richness and diversity (the latter evidenced by Illumina data) after treatment with nZVI. The anaerobic conditions stimulated by treatment favored the development of sulfate-reducing bacteria, thereby opening up the possibility to achieve more efficient removal of As.

Seasonal variations in arsenic mobility and bacterial diversity: The case study of Huangshui Creek, Shimen Realgar Mine, Hunan Province, China

Rivers throughout the world have been contaminated by arsenic dispersed from mining activities. The biogeochemical cycling of this arsenic has been shown to be due to factors such as pH, Eh, ionic strength and microbial activity, but few studies have examined the effects of both seasonal changes and microbial community structure on arsenic speciation and flux in mining-affected river systems. To address this research gap, a study was carried out in Huangshui Creek, Hunan province, China, which has been severely impacted by long-term historic realgar (α-As₄S₄) mining. Water and sediment sampling, and batch experiments at different temperatures using creek sediment, were used to determine the form, source and mobility of arsenic. Pentavalent (AsO₄³) and trivalent arsenic (AsO₃^3-) were the dominant aqueous species (70-89% and 30-11%, respectively) in the creek, and the maximum concentration of inorganic arsenic in surface water was 10,400 μg/L. Dry season aqueous arsenic concentrations were lower than those in the wet season samples. The sediments contained both arsenate and arsenite, and relative proportions of these varied with season. 8.3 tons arsenic per annum were estimated to be exported from Huangshui Creek. Arsenic release from sediment increased by 3 to 5 times in high water temperature batch experiments (25 and 37 °C) compared to those carried out at low temperature (8 °C). Our data suggest that the arsenic-containing sediments were the main source of arsenic contamination in Huangshui Creek. Microbial community structured varied at the different sample sites along the creek. Redundancy analysis (RDA) showed that both temperature and arsenic concentrations were the main controlling factors on the structure of the microbial community. Protecbacteria, Bacteroidetes, Cyanobacteria, Firmicutes, Verrucomicrobia, and Planctomycetes were the stable dominant phyla in both dry and wet seasons. The genera Flavobacterium, Hydrogenophaga and Sphingomonas occurred in the most highly arsenic contaminated sites, which removed arsenic by related metabolism.Our findings indicate that seasonal variations profoundly control arsenic flux and species, microbial community structure and ultimately, the biogeochemical fate of arsenic.

Epidemiological and phylogenetic analysis reveals Flavobacteriaceae as potential ancestral source of tigecycline resistance gene tet(X)

Emergence of tigecycline-resistance tet(X) gene orthologues rendered tigecycline ineffective as last-resort antibiotic. To understand the potential origin and transmission mechanisms of these genes, we survey the prevalence of tet(X) and its orthologues in 2997 clinical E. coli and K. pneumoniae isolates collected nationwide in China with results showing very low prevalence on these two types of strains, 0.32% and 0%, respectively. Further surveillance of tet(X) orthologues in 3692 different clinical Gram-negative bacterial strains collected during 1994–2019 in hospitals in Zhejiang province, China reveals 106 (2.7%) tet(X)-bearing strains with Flavobacteriaceae being the dominant (97/376, 25.8%) bacteria. In addition, tet(X)s are found to be predominantly located on the chromosomes of Flavobacteriaceae and share similar GC-content as Flavobacteriaceae. It also further evolves into different orthologues and transmits among different species. Data from this work suggest that Flavobacteriaceae could be the potential ancestral source of the tigecycline resistance gene tet(X).

Emergence of tigecycline-resistance tet(X) genes is of concern. Here, the authors determine tet(X) prevalence in more than 6,000 clinical Gram-negative bacterial isolates collected between 1994 to 2019 in hospitals in China and suggest that Flavobacteriaceae could be the potential ancestral source of the tigecycline resistance genes.

Composition and predicted functions of the bacterial community in spouting pool sediments from the El Tatio Geyser field in Chile

The El Tatio Geyser Field (ETGF), located in Northern Chile, is the main geyser field in the southern hemisphere. Despite this, details of its microbial ecology are still unknown. Here, we briefly report on  the composition and predicted functions of the bacterial community in spouting pool sediments from the ETGF as revealed by high-throughput sequencing of 16S rRNA genes. Results of this analysis showed that while there were differences in richness and diversity between samples, bacterial communities were primarily dominated by the phyla Proteobacteria, followed Firmicutes, Bacteroidetes, Acidobacteria, and Chloroflexi. Analyses of predicted functional activity indicated that the functions were mostly attributed to chemoheterotrophy and aerobic chemoheterotrophy, followed by sulfur (respiration of sulfur compounds and sulfate) and nitrogen (nitrate reduction, respiration of nitrogen and nitrate) cycling. Taken together, our results suggest a high diversity in taxonomy and predictive functions of bacterial communities in sediments from spouting pools. This study provides fundamentally important  information on the structure and function  predictive functions of microbiota  communities in spouting pools. Moreover, since the ETGF is intensively visited and impacted by tens of thousands of tourists every year, our results can be used to help guide the design of sustainable conservation strategies.

Characterisation of hyper tolerant Bacillus firmus L-148 for arsenic oxidation

Groundwater arsenic pollution causes millions of deaths worldwide. Long term natural and anthropogenic activities have increased arsenic levels in groundwater causing higher threats of arsenic exposure. Arsenic hyper-tolerant Firmicute Bacillus firmus L-148 was isolated from arsenic limiting Lonar lake soil, which tolerated more than 3 M arsenic and could oxidize 75 mM arsenite [As(III)] in 14 days. It oxidized As(III) in presence of heavy metals and had unusual pH optima at 9.2. B. firmus L-148 was studied at the biochemical, protein, genomic and transcript level for understanding its arsenic oxidizing machinery. The proteomic and transcript analysis exhibited the presence of ars and aio operon and supported the inducible nature of ars operon. Robust, hyper-tolerant, fast As(III) oxidizing, least nutrient requiring and multi-metal resistance qualities of the strain were used in microcosm studies for bioremediation. Artificial groundwater mimicking microcosm with 75 mM As(III) was developed. Modulation of carbon source, iron and multi metals affected growth and As(III) oxidation rate. The As(III) oxidation was recorded to be 77% in 15 days in presence of sodium acetate and Fe ions. This microcosm study can be explored for bioremediation of arsenic contaminated water and followed by precipitation using other methods.

Flavobacterium riviphilum sp. nov., isolated from a freshwater creek

A novel bacterium, designated strain TAPY6^T, was isolated from a freshwater creek in Taiwan. The strain was Gram-stain-negative, strictly aerobic, motile-by-gliding, rod-shaped and formed translucent yellow colonies. Optimal growth occurred at 20-30 °C, pH 6 and in the absence of NaCl. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain TAPY6^T belonged to the genus Flavobacterium and was most closely related to Flavobacterium succinicans LMG 10402^T (97.3 % sequence similarity) and Flavobacterium glycines Gm-149^T (96.3 %). Strain TAPY6^T contained C15 : 0 and iso-C15 : 0 as the predominant fatty acids. The polar lipid profile consisted of phosphatidylethanolamine, five uncharacterized aminophospholipids, two uncharacterized phospholipids and one uncharacterized aminolipid. The major polyamine was homospermidine. The major isoprenoid quinone was MK-6. The DNA G+C content of the genomic DNA was 39.8 mol%. Phenotypic characteristics of the novel strain also differed from those of the closest related species of the genus Flavobacterium. On the basis of the genotypic, chemotaxonomic and phenotypic data, strain TAPY6^T represents a novel species in the genus Flavobacterium, for which the name Flavobacterium riviphilum sp. nov. is proposed. The type strain is TAPY6^T (=BCRC 81007^T=LMG 29728^T=KCTC 52444^T).

Flavobacterium chryseum sp. nov. and Flavobacterium psychroterrae sp. nov., novel environmental bacteria isolated from Antarctica

A group of rod-shaped, aerobic, Gram-stain-negative, gliding bacteria producing flexirubin-type pigment was isolated from environmental samples collected in Antarctica in 2009-2014. Phylogenetic analysis of the almost complete 16S rRNA gene sequences revealed two separated branches belonging to the genus Flavobacterium. Group I (n=8), represented by strain CCM 8826^T, shared the highest sequence similarity to Flavobacterium collinsii 983-08^T (98.8 %) and Flavobacterium saccharophilum DSM 1811^T (98.4 %), and group II (n=4) represented by strain CCM 8827^T shared the highest similarity to Flavobacterium aquidurense WB 1.1-56^T (99.6 %). High genetic homogeneity of both groups, separation from each other and from phylogenetically close Flavobacterium species was verified by the rep-PCR fingerprinting method. DNA-DNA hybridization confirmed low genomic relatedness between strain CCM 8826^T and F. collinsii 983-08^T and F. saccharophilum DSM 1811^T (18 and 28 %, respectively) and between strain CCM 8827^T and F. aquidurense WB 1.1-56^T (27 %). Chemotaxonomic analyses of strains CCM 8826^T and CCM 8827^T revealed the respiratory quinone to be MK-6, the major identified polar lipid was phosphatidylethanolamine and the predominant polyamine was sym-homospermidine. The common major fatty acids were C15 : 0 iso, C17 : 0 iso 3OH, C15 : 1 iso G, Summed Feature 3 (C16 : 1ω7c/C16 : 1ω6c), C15 : 0 iso 3OH and additionally, C15 : 0 anteiso among group II members. All analyses confirmed that strains of group I and II represent two novel species of the genus Flavobacterium, for which the names Flavobacterium chryseum sp. nov. (type strain CCM 8826^T=P3160^T=LMG 30615^T) and Flavobacterium psychroterrae sp. nov. (type strain CCM 8827^T=P3922^T=LMG 30616^T) are proposed.

Flavobacterium ureilyticum sp. nov., a novel urea hydrolysing bacterium isolated from stream bank soil

A novel bacterium designated S-42^T was isolated from stream bank soil. Cells were found to be aerobic, Gram staining-negative, oxidase-positive, catalase-negative, non-motile, non-spore-forming, rod-shaped, and yellow-pigmented. The strain can grow at 15-35 °C, pH 6.0-10.0, and at 0.5% (w/v) NaCl concentration. Urea was hydrolysed. Flexirubin-type pigments were absent. Phylogenetic analysis based on its 16S rRNA gene sequence revealed that strain S-42^T formed a lineage within the family Flavobacteriaceae of the phylum Bacteroidetes that is distinct from various species of the genus Flavobacterium, including Flavobacterium maotaiense T9^T (97.6% sequence similarity), Flavobacterium hibernum ATCC 51468^T (97.4%), and Flavobacterium granuli Kw05^T (97.1%). The 16S rRNA gene sequences identity between strain S-42^T and other members of the genus Flavobacterium were < 97.0%. Strain S-42^T contains MK-6 as sole respiratory quinone. The major polar lipids were identified as phosphatidylethanolamine and an unidentified aminolipid. The major cellular fatty acids were identified as iso-C_15:0, summed feature 3 (C_16:1ω7c and/or C_{16: 1}ω6c), C_16:0, anteiso-C_15:0, iso-C_17:0 3-OH, iso-C_15:0 3-OH, and iso-C_15:1 G. The DNA G + C content of the strain was 35.8 mol%. The polyphasic characterization indicated that strain S-42^T represents a novel species of the genus Flavobacterium, for which the name Flavobacterium ureilyticum sp. nov. is proposed. The type strain is S-42^T (= KEMB 9005-537^T = KACC 19115^T = NBRC 112683^T).

Flavobacterium zaozhuangense sp. nov., a new member of the family Flavobacteriaceae, isolated from metolachlor-contaminated soil

Strain ZZ-8^T, a Gram-negative, aerobic, non-spore-forming, non-motile, yellow-pigmented, rod-shaped bacterium, was isolated from metolachlor-contaminated soil in China. The taxonomic position was investigated using a polyphasic approach. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain ZZ-8^T is a member of the genus Flavobacterium and shows high sequence similarity to Flavobacterium humicola UCM-46^T (97.2%) and Flavobacterium pedocola UCM-R36^T (97.1%), and lower (< 97%) sequence similarity to other known Flavobacterium species. Chemotaxonomic analysis revealed that strain ZZ-8^T possessed MK-6 as the major respiratory quinone; and iso-C_15:0 (28.5%), summed feature 9 (iso-C_17:1 w9c/C_16:0 10-methyl, 22.9%), iso-C_17:0 3-OH (17.0%), iso-C_15:0 3-OH (8.9%), iso-C_15:1 G (8.6%) and summed feature 3 (C_16:1 w7c/C_16:1 w6c, 5.7%) as the predominant fatty acids. The polar lipids of strain ZZ-8^T were determined to be lipids, a glycolipid, aminolipids and phosphatidylethanolamine. Strain ZZ-8^T showed low DNA-DNA relatedness with F. pedocola UCM-R36^T (43.23 ± 4.1%) and F. humicola UCM-46^T (29.17 ± 3.8%). The DNA G+C content was 43.3 mol%. Based on the phylogenetic and phenotypic characteristics, chemotaxonomic data and DNA-DNA hybridization, strain ZZ-8^T is considered a novel species of the genus Flavobacterium, for which the name Flavobacterium zaozhuangense sp. nov. (type strain ZZ-8^T = KCTC 62315 ^T = CCTCC AB 2017243^T) is proposed.

Flavobacterium phocarum sp. nov., isolated from soils of a seal habitat in Antarctica

A Gram-stain-negative, yellow-pigmented, non-flagellated, gliding, rod-shaped, oxidase-negative and catalase-positive bacterium, designated SE14^T, was isolated from soil on King George Island, South Shetland Islands, Antarctica. Strain SE14^T grew at 4-25 °C (optimum, 20 °C), at pH 6.0-9.0 (optimum, pH 7.0-7.5) and with 0-3.0 % NaCl (optimum, 1.0-1.5 %), and could not produce flexirubin-type pigments. 16S rRNA gene sequence analysis showed the the isolate belonged to the genus Flavobacterium. Strain SE14^T had the highest 16S rRNA gene sequence similarity to Flavobacterium antarcticum, F. tegetincola and F. degerlachei with 95.8, 95.5 and 95.2 %, respectively. The strain SE14^T consisted of a clade with Flavobacteriumnoncentrifugens (16S rRNA gene sequence similarity 94.9 %) and F. qiangtangense (16S rRNA gene sequence similarity 94.2 %) and simultaneously formed a distinct phyletic lineage in the neighbour-joining phylogenetic tree. Polar lipids of the strain included phosphatidylethanolamine and four unidentified aminolipids. Strain SE14^T contained anteiso-C15 : 0, iso-C15 : 0 and a mixture of iso-C15 : 0 2-OH and/or C16 : 1ω7c as the main fatty acids, and the only respiratory quinone was menaquinone-6. The genomic DNA G+C content was 42.3 mol%. The polyphasic taxonomic study revealed that strain SE14^T belongs to a novel species within the genus Flavobacterium , and the name Flavobacterium phocarum sp. nov. is proposed. The type strain is SE14^T (=CCTCC AB 2017225^T=KCTC 52612^T).

Bacteria from the rhizosphere and tissues of As-hyperaccumulator Pteris vittata and their role in arsenic transformation

Arsenic (As)-resistant bacteria are abundant in the rhizosphere and tissues of As-hyperaccumulator Pteris vittata. However, little is known about their roles in As transformation and As uptake in P. vittata. In this study, the impacts of P. vittata tissue extracts with or without surface sterilization on As transformation in solutions containing 100 μg L^-1 AsIII or AsV were investigated. After 48 h incubation, the sterilized and unsterilized root extracts resulted in 45% and 73% oxidation of AsIII, indicating a role of both rhizobacteria and endobacteria. In contrast, AsV reduction was only found in rhizome and frond extracts at 3.7-24% of AsV. A total of 37 strains were isolated from the tissue extracts, which are classified into 18 species based on morphology and 16S rRNA. Phylogenic analysis showed that ∼44% isolates were Firmicutes and others were Proteobacteria except for one strain belonging to Bacteroidetes. While most endobacteria were Firmicutes, most rhizobacteria were Proteobacteria. All isolated bacteria belonged to AsV reducers except for an As-sensitive strain and one AsIII- oxidizer PVR-YHB6-1. Since As transformation was not observed in solutions after filtrating or boiling, we concluded that both rhizobacteria and endobacteria were involved in As transformation in the rhizosphere and tissues of P. vittata.

Functional genes and thermophilic microorganisms responsible for arsenite oxidation from the shallow sediment of an untraversed hot spring outlet

Hot Springs have unique geochemical features. Microorganisms-mediated arsenite oxidation is one of the major biogeochemical processes occurred in some hot springs. This study aimed to understand the diversities of genes and microorganisms involved in arsenite oxidation from the outlet of an untraversed hot spring located at an altitude of 4226 m. Microcosm assay indicated that the microbial community from the hot spring was able to efficiently oxidize As(III) using glucose, lactic acid, yeast extract or sodium bicarbonate as the sole carbon source. The microbial community contained 7 phyla of microorganisms, of which Proteobacteria and Firmicutes are largely dominant; this composition is unique and differs significantly from those of other described hot springs. Twenty one novel arsenite oxidase genes were identified from the samples, which are affiliated with the arsenite oxidase families of α-Proteobacteria, β-Proteobacteria or Archaea; this highlights the high diversity of the arsenite-oxidizing microorganisms from the hot spring. A cultivable arsenite-oxidizer Chelatococcu sp. GHS311 was also isolated from the sample using enrichment technique. It can completely convert 75.0 mg/L As(III) into As(V) in 18 days at 45 °C. The arsenite oxidase of GHS311 shares the maximal sequence identity (84.7%) to that of Hydrogenophaga sp. CL3, a non-thermotolerant bacterium. At the temperature lower than 30 °C or higher than 65 °C, the growth of this strain was completely inhibited. These data help us to better understand the diversity and functional features of the thermophilic arsenite-oxidizing microorganisms from hot springs.

Microbial communities involved in arsenic mobilization and release from the deep sediments into groundwater in Jianghan plain, Central China

It was shown that groundwater in Jianghan Plain was severely contaminated by arsenic; however, little is known about the mechanism by which the mineral arsenic was mobilized and released into groundwater from the high-arsenic sediments in this area. Here, we collected sediment samples from the depths of 5-230m in Jianghan Plain. Although all of the samples contain high contents of total arsenic, the soluble arsenic was only detectable in few of the shallow sediments, but was readily detectable in all of the deep sediments at the depths of 190-230m. Analysis of the genes of arsenate-respiring reductases indicated that they were not present in all of the shallow sediments from the depths of 5-185m, but were detectable in all of the deep sediments from the depths of 190-230m; all of the identified reductase genes are new or new-type, and they display unique diversity. Microcosm assay indicated that the microbial communities from the deep sediments were able to reduce As(V) into As(III) using lactate, formate, pyruvate or acetate as an electron donor under anaerobic condition. Arsenic release assay demonstrated that these microbial communalities efficiently catalyzed the mobilization and release of the mineral arsenic into aqueous phase. We also isolated a novel cultivable dissimilatory As(V)-respiring bacterium Aeromonas sp. JH155 from the sediments. It is able to completely reduce 2.0mM As(V) into As(III) in 72h, and efficiently promote the reduction and release of the mineral arsenic into aqueous phase. Analysis of the 16S rRNA genes indicated that the deep sediments contain diversities of microbial communities, which were shaped by the environmental factors, such as As, SO₄^2-, NO₃^-, Fe and pH value. These data suggest that the microorganisms in the deep sediments in Jianghan Plain played key roles in the mobilization and release of insoluble arsenic into the groundwater.

Flavobacterium jejuensis sp. nov., isolated from marine brown alga Ecklonia cava

A bacterial strain, designated EC11(T) was isolated from brown alga Ecklonia cava collected from Jeju Island, Korea. EC11(T) was identified as a Gram-negative, rod-shaped and yellow-pigmented bacterial strain. The strain EC11(T) grew over a temperature range of 10 °C to 30 °C (optimally at 25 °C), and a pH range of 6.0-10.5 (optimally at pH 7.5). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain EC11(T) belongs to the genus Flavobacterium. Strain EC11(T) shared close similarity with Flavobacterium jumunjinense HME7102(T) (96.4%), Flavobacterium dongtanense LW30(T) (95.8%), Flavobacterium haoranii LQY-7(T) (95.3%), and Flavobacterium urocaniciphilum (95.1%). The major fatty acids (> 5%) were iso-C17:0 3-OH (22.4%), iso-C15:0 3-OH (19.0%), C15:0 (12.4%), summed feature 3 (comprising C16:1 ω7c/ C16:1 ω6c; 9.78%), iso-C15:1 G (9.6%), and iso-C16:0 3-OH (9.0%). The DNA G+C content was 28.1 mol% and the strain contained MK-6 as the predominant menaquinone. The major polar lipids were phosphatidylethanolamine, two unknown aminolipids and three unknown polar lipids. Based on phenotypic, chemotaxonomic and phylogenetic analysis, strain EC11T represents a novel species of the Flavobacterium genus, for which the name Flavobacterium jejuensis sp. nov. is proposed. The type strain of F. jejuensis is EC11(T) (=KCTC 42149(T) = JCM 30735(T)).