Fervidicella metallireducens gen. nov., sp. nov., a thermophilic, anaerobic bacterium from geothermal waters

Microbially mediated iron redox processes for carbon and nitrogen removal from wastewater: Recent advances

Iron is the most abundant redox-active metal on Earth. The microbially mediated iron redox processes, including dissimilatory iron reduction (DIR), ammonium oxidation coupled with Fe(III) reduction (Feammox), Fe(III) dependent anaerobic oxidation of methane (Fe(III)-AOM), nitrate-reducing Fe(II) oxidation (NDFO), and Fe(II) dependent dissimilatory nitrate reduction to ammonium (Fe(II)-DNRA), play important parts in carbon and nitrogen biogeochemical cycling globally. In this review, the reaction mechanisms, electron transfer pathways, functional microorganisms, and characteristics of these processes are summarized; the prospective applications for carbon and nitrogen removal from wastewater are reviewed and discussed; and the research gaps and future directions of these processes for the treatment of wastewater are also underlined. This review is expected to give new insights into the development of economic and environmentally friendly iron-based wastewater treatment procedures.

A flavin-based extracellular electron transfer mechanism in diverse Gram-positive bacteria

Extracellular electron transfer (EET) describes microbial bioelectrochemical processes in which electrons are transferred from the cytosol to the exterior of the cell1. Mineral-respiring bacteria use elaborate haem-based electron transfer mechanisms2-4 but the existence and mechanistic basis of other EETs remain largely unknown. Here we show that the food-borne pathogen Listeria monocytogenes uses a distinctive flavin-based EET mechanism to deliver electrons to iron or an electrode. By performing a forward genetic screen to identify L. monocytogenes mutants with diminished extracellular ferric iron reductase activity, we identified an eight-gene locus that is responsible for EET. This locus encodes a specialized NADH dehydrogenase that segregates EET from aerobic respiration by channelling electrons to a discrete membrane-localized quinone pool. Other proteins facilitate the assembly of an abundant extracellular flavoprotein that, in conjunction with free-molecule flavin shuttles, mediates electron transfer to extracellular acceptors. This system thus establishes a simple electron conduit that is compatible with the single-membrane structure of the Gram-positive cell. Activation of EET supports growth on non-fermentable carbon sources, and an EET mutant exhibited a competitive defect within the mouse gastrointestinal tract. Orthologues of the genes responsible for EET are present in hundreds of species across the Firmicutes phylum, including multiple pathogens and commensal members of the intestinal microbiota, and correlate with EET activity in assayed strains. These findings suggest a greater prevalence of EET-based growth capabilities and establish a previously underappreciated relevance for electrogenic bacteria across diverse environments, including host-associated microbial communities and infectious disease.

Changes in microbial communities during volatile fatty acid production from cyanobacterial biomass harvested from a cyanobacterial bloom in a river

Volatile fatty acid (VFA) production, utilization of soluble organic compounds, and associated microbial consortia were investigated after different pretreatments (untreated, alkaline, and thermal-alkaline) using cyanobacterial biomass as a substrate. Compared to the untreated control, soluble carbohydrate concentrations were almost the same after alkaline and thermal-alkaline pretreatments, but soluble protein concentration was 1.58 times higher after alkaline pretreatment and 1.81 times higher after thermal-alkaline pretreatment. However, the highest degree of acidification was obtained after alkaline pretreatment (55.36 ± 3.00%). Microbial communities in the untreated control differed only slightly from those after thermal-alkaline pretreatment, but were clearly distinct from those after alkaline pretreatment. After alkaline pretreatment, protein-utilizing bacteria became relatively predominant. These results revealed the relationships between efficiency of VFA production and the shift in microbial community.

Orenia metallireducens sp. nov. Strain Z6, a Novel Metal-Reducing Member of the Phylum Firmicutes from the Deep Subsurface

A novel halophilic and metal-reducing bacterium, Orenia metallireducens strain Z6, was isolated from briny groundwater extracted from a 2.02 km-deep borehole in the Illinois Basin, IL. This organism shared 96% 16S rRNA gene similarity with Orenia marismortui but demonstrated physiological properties previously unknown for this genus. In addition to exhibiting a fermentative metabolism typical of the genus Orenia, strain Z6 reduces various metal oxides [Fe(III), Mn(IV), Co(III), and Cr(VI)], using H₂ as the electron donor. Strain Z6 actively reduced ferrihydrite over broad ranges of pH (6 to 9.6), salinity (0.4 to 3.5 M NaCl), and temperature (20 to 60°C). At pH 6.5, strain Z6 also reduced more crystalline iron oxides, such as lepidocrocite (γ-FeOOH), goethite (α-FeOOH), and hematite (α-Fe₂O₃). Analysis of X-ray absorption fine structure (XAFS) following Fe(III) reduction by strain Z6 revealed spectra from ferrous secondary mineral phases consistent with the precipitation of vivianite [Fe₃(PO₄)₂] and siderite (FeCO₃). The draft genome assembled for strain Z6 is 3.47 Mb in size and contains 3,269 protein-coding genes. Unlike the well-understood iron-reducing Shewanella and Geobacter species, this organism lacks the c-type cytochromes for typical Fe(III) reduction. Strain Z6 represents the first bacterial species in the genus Orenia (order Halanaerobiales) reported to reduce ferric iron minerals and other metal oxides. This microbe expands both the phylogenetic and physiological scopes of iron-reducing microorganisms known to inhabit the deep subsurface and suggests new mechanisms for microbial iron reduction. These distinctions from other Orenia spp. support the designation of strain Z6 as a new species, Orenia metallireducens sp. nov.

IMPORTANCE

A novel iron-reducing species, Orenia metallireducens sp. nov., strain Z6, was isolated from groundwater collected from a geological formation located 2.02 km below land surface in the Illinois Basin, USA. Phylogenetic, physiologic, and genomic analyses of strain Z6 found it to have unique properties for iron reducers, including (i) active microbial iron-reducing capacity under broad ranges of temperatures (20 to 60°C), pHs (6 to 9.6), and salinities (0.4 to 3.5 M NaCl), (ii) lack of c-type cytochromes typically affiliated with iron reduction in Geobacter and Shewanella species, and (iii) being the only member of the Halanaerobiales capable of reducing crystalline goethite and hematite. This study expands the scope of phylogenetic affiliations, metabolic capacities, and catalytic mechanisms for iron-reducing microbes.

Draft Genome Sequence of Fervidicella metallireducens Strain AeBT, an Iron-Reducing Thermoanaerobe from the Great Artesian Basin

The genome sequence of Fervidicella metallireducens strain AeB^T, a curved, heterotrophic, thermoanaerobic, and iron-reducing bacterium isolated from a gray microbial mat colonizing the free-flowing waters of a Great Artesian Basin (GAB) bore well located in outback Queensland, Australia, is reported here. The analysis of the 2.9-Mb sequence indicates that the attributes of the genome are consistent with its physiological and phenotypic traits.

Youngiibacter fragilis gen. nov., sp. nov., isolated from natural gas production-water and reclassification of Acetivibrio multivorans as Youngiibacter multivorans comb. nov

A taxonomic study employing a polyphasic approach was performed on a novel anaerobic bacterium isolated from natural gas production-water. The bacterium stained Gram-negative and consisted of non-motile, non-spore-forming, rod-shaped cells. Products of glucose or starch fermentation were ethanol, CO2, formate, acetate and H2. The predominant fatty acids were C16 : 0 ALDE and summed feature 3 comprising C16 : 1ω7c and/or C16 : 1ω6c. The DNA G+C content was 45.5 mol%. 16S rRNA gene sequence analysis demonstrated that the nearest phylogenetic neighbours of the novel strain were Acetivibrio multivorans DSM 6139T (98.5 %) and Proteiniclasticum ruminis JCM 14817T (95.4 %). The DNA–DNA hybridization value between the novel organism and Acetivibrio multivorans PeC1 DSM 6139T was determined to be only 30.2 %, demonstrating the separateness of the two species. Based on phylogenetic, phenotypic and chemotaxonomic evidence that clearly distinguished strain 232.1T from Proteiniclasticum ruminis and other close relatives, it is proposed that the novel isolate be classified as representing a novel species of a new genus within the family Clostridiaceae , Youngiibacter fragilis gen. nov., sp. nov. The type strain of the type species is 232.1T ( = ATCC BAA-2257T = DSM 24749T). In addition, Acetivibrio multivorans is proposed to be reclassified as Youngiibacter multivorans comb. nov.

Vanadate and acetate biostimulation of contaminated sediments decreases diversity, selects for specific taxa, and decreases aqueous V5+ concentration

Vanadium is a commercially important metal that is released into the environment by fossil fuel combustion and mining. Despite its prevalence as a contaminant, the potential for vanadium bioremediation has not been widely studied. Injection of acetate (as a carbon source) directly into an aquifer to biostimulate contaminated sediments in Colorado, United States, resulted in prolonged removal of aqueous vanadium for a period of at least two years. To further investigate this process, we simultaneously added acetate and vanadate (V(5+)) to columns that were packed with aquifer sediment and inserted into groundwater wells installed on the Colorado River floodplain. This allowed evaluation of the microbial response to amendments in columns that received an influx of natural groundwater. Our results demonstrate the removal of up to 99% of the added V(5+)(aq) and suggest microbial mediation. Most probable number measurements demonstrate up to a 50-fold increase in numbers of V(5+)-reducing cells in vanadium-amended columns compared to controls. 16S rRNA gene sequencing indicates decreased diversity and selection for specific taxa in columns that received vanadate compared to those that did not. Overall, our results demonstrate that acetate amendment can be an effective strategy for V removal, and that V bioremediation may be a viable technology.

Fonticella tunisiensis gen. nov., sp. nov., isolated from a hot spring

A strictly anaerobic, moderately thermophilic, halotolerant rod, designated BELH25T, was isolated from a water sample of a Tunisian hot spring. Cells were non-motile, 2–6 µm long and 0.4–0.6 µm wide, appearing singly or in pairs. The isolate grew at 45–70 °C (optimum 55 °C), at pH 6.2–8.0 (optimum pH 7.0) and with 0–4 % NaCl (optimum 0–2.0 %). Sulfate, thiosulfate, elemental sulfur, sulfite, nitrate and nitrite were not used as terminal electron acceptors. Strain BELH25T used cellobiose, fructose, galactose, glucose, maltose, mannose, sucrose, starch and yeast extract as electron donors. The main fermentation products from glucose metabolism were formate, acetate, ethanol and CO2. The predominant cellular fatty acids were iso-C15 : 0, iso-C17 : 0 and anteiso-C15 : 0. The DNA G+C content was 37.2 mol%. Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain BELH25T was most closely related to Caloramator viterbiensis JW/MS-VS5T and Fervidicella metallireducens AeBT (92.2 and 92.1 % sequence similarity, respectively), and the isolate was positioned approximately equidistantly between these genera. Based on phenotypic, phylogenetic and chemotaxonomic characteristics, strain BELH25T is proposed to be a member of a novel species of a novel genus within the order Clostridiales , family Clostridiaceae , for which the name Fonticella tunisiensis gen. nov., sp. nov. is proposed. The type strain of the type species is BELH25T ( = DSM 24455T = JCM 17559T).