Tatiana V. Khijniak

Reduction of uranium(VI) phosphate during growth of the thermophilic bacterium thermoterrabacterium ferrireducens

ABSTRACT The thermophilic, gram-positive bacterium Thermoterrabacterium ferrireducens coupled organotrophic growth to the reduction of sparingly soluble U(VI) phosphate. X-ray powder diffraction and X-ray absorption spectroscopy analysis identified the electron acceptor in a defined medium as U(VI) phosphate [uramphite; (NH4)(UO2)(PO4) · 3H2O], while the U(IV)-containing precipitate formed during bacterial growth was identified as ningyoite [CaU(PO4)2 · H2O]. This is the first report of microbial reduction of a largely insoluble U(VI) compound.

Reduction of pertechnetate by haloalkaliphilic strains of Halomonas.

Abstract It is shown for the first time that haloalkaliphilic bacteria, isolated from soda-lake environments were capable of reducing Tc(VII)O(4) (-) to the Tc(V), Tc(IV) and Tc(III) at pH 10 in carbonate medium, whereas no reduction took place without bacteria or in the presence of dead biomass. After 34 h of incubation, 55% remained as Tc(VII), 36% was found as Tc(IV) and 8% as Tc(V) and after 2 months 80% of the technetium was reduced. Technetium has a toxic effect on bacteria. Reduction of TcO(4) (-) was drastically decreased at concentration above 1.5 mM. The microbial reduction has been suggested as a potential mechanism for the removal of Tc from contaminated environments or waste streams.

Molybdenum-free nitrate reductases from vanadate-reducing bacteria

Two catalytically distinct molybdenum‐free dissimilatory nitrate reductases, a soluble periplasmic and a membrane‐bound one, were isolated from the vanadate‐reducing facultatively anaerobic bacterium Pseudomonas isachenkovii and purified to electrophoretic homogeneity. The enzymes did not contain molybdenum, the periplasmic enzyme contained vanadium, whereas the membrane‐bound enzyme was vanadium‐free. Both nitrate reductases lacked molybdenum cofactor. This fact was proved by reconstitution of the apoprotein of the nitrate reductase of Neurospora crassa nit‐1 mutant. This is the first demonstration of molybdenum‐free and molybdenum cofactor‐free nitrate reductases.

Halomonas chromatireducens sp. nov., a new denitrifying facultatively haloalkaliphilic bacterium from solonchak soil capable of aerobic chromate reduction

A heterotrophic bacterial strain AGD 8-3 capable of denitrification under extreme haloalkaline conditions was isolated from soda solonchak soils of the Kulunda steppe (Russia). The strain was classified within the genus Halomonas. According to the results of 16S rRNA gene sequencing, Halomonas axialensis, H. meridiana, and H. aquamarina are most closely related to strain AGD 8-3 (96.6% similarity). Similar to other members of the genus, the strain can grow within a wide range of salinity and pH. The strain was found to be capable of aerobic reduction of chromate and selenite on mineral media at 160 g/l salinity and pH 9.5–10. The relatively low level of phylogenetic similarity and the phenotypic characteristics supported classification of strain AGD 8-3 as a new species Halomonas chromatireducens.

Vanadate Reduction by Molybdenum‐Free Dissimilatory Nitrate Reductases from Vanadate‐Reducing Bacteria

Molybdenum‐ and molybdenum cofactor‐free nitrate reductases recently isolated by us from vanadate‐reducing bacteria Pseudomonas isachenkovii are likely to mediate vanadate reduction. During anaerobic growth of P. isachenkovii on medium supplemented with nitrate and vanadate, vanadate dissimilation was followed by nitrate consumption, and this process was associated with some structural reorganizations of nitrate reductases. The homogeneous membrane‐bound nitrate reductase of P. isachenkovii reduced vanadate with NADH as an electron donor.

Treatment of Alkaline Cr(VI)-Contaminated Leachate with an Alkaliphilic Metal-Reducing Bacterium.

ABSTRACT Chromium in its toxic Cr(VI) valence state is a common contaminant particularly associated with alkaline environments. A well-publicized case of this occurred in Glasgow, United Kingdom, where poorly controlled disposal of a cementitious industrial by-product, chromite ore processing residue (COPR), has resulted in extensive contamination by Cr(VI)-contaminated alkaline leachates. In the search for viable bioremediation treatments for Cr(VI), a variety of bacteria that are capable of reduction of the toxic and highly soluble Cr(VI) to the relatively nontoxic and less mobile Cr(III) oxidation state, predominantly under circumneutral pH conditions, have been isolated. Recently, however, alkaliphilic bacteria that have the potential to reduce Cr(VI) under alkaline conditions have been identified. This study focuses on the application of a metal-reducing bacterium to the remediation of alkaline Cr(VI)-contaminated leachates from COPR. This bacterium, belonging to the Halomonas genus, was found to exhibit growth concomitant to Cr(VI) reduction under alkaline conditions (pH 10). Bacterial cells were able to rapidly remove high concentrations of aqueous Cr(VI) (2.5 mM) under anaerobic conditions, up to a starting pH of 11. Cr(VI) reduction rates were controlled by pH, with slower removal observed at pH 11, compared to pH 10, while no removal was observed at pH 12. The reduction of aqueous Cr(VI) resulted in the precipitation of Cr(III) biominerals, which were characterized using transmission electron microscopy and energy-dispersive X-ray analysis (TEM-EDX) and X-ray photoelectron spectroscopy (XPS). The effectiveness of this haloalkaliphilic bacterium for Cr(VI) reduction at high pH suggests potential for its use as an in situ treatment of COPR and other alkaline Cr(VI)-contaminated environments.

Natronotalea proteinilytica gen. nov., sp. nov. and Longimonas haloalkaliphila sp. nov., extremely haloalkaliphilic members of the phylum Rhodothermaeota from hypersaline alkaline lakes

Two proteolytic bacterial strains, BSker2T and BSker3T, were enriched from sediments of hypersaline alkaline lakes in Kulunda Steppe (Altai, Russia) with chicken feathers as substrate, followed by pure culture isolation on hypersaline alkaline media with casein. The cells were non-motile, filamentous, flexible rods. The isolates were obligately aerobic heterotrophs utilizing proteins and peptides as growth substrates. Both were obligate alkaliphiles, but differed in their pH optimum for growth: pH 9.5-9.8 for Bsker2T and pH 8.5-8.8 for BSker3T. The salt range for growth of both isolates was between 2 and 4.5 M total Na+ with an optimum at 2.5-3 M. No organic osmolytes were detected in cells of BSker2T, but they accumulated high intracellular concentrations of K+. The polar lipid fatty acids were dominated by unsaturated C16 and C18 species. The 16S rRNA gene phylogeny indicated that both strains belong to the recently proposed phylum Rhodothermaeota. BSker2T forms a novel genus-level branch, while BSker3T represents a novel species-level member in the genus Longimonas. On the basis of distinct phenotypic and genotypic properties, strain BSker2T (=JCM 31342T=UNIQEM U1009T) is proposed to be classified as a representative of a novel genus and species, Natronotalea proteinilyticagen. nov., sp. nov., and strain BSker3T (=JCM 31343T=UNIQEM U1010T) as a representative of a novel species, Longimonas haloalkaliphila sp. nov.

Natronospira proteinivora gen. nov., sp. nov, an extremely salt-tolerant, alkaliphilic gammaproteobacterium from hypersaline soda lakes

Brine samples from Kulunda Steppe soda lakes (Altai, Russia) were inoculated into a hypersaline alkaline mineral medium with β-keratin (chicken feather) as a substrate. The micro-organisms dominating the enrichment culture were isolated by limiting serial dilution on the same medium with casein as a substrate. The cells of strain BSker1T were motile, curved rods. The strain was an obligately aerobic heterotroph utilizing proteins and peptides as growth substrates. The isolate was an obligate alkaliphile with a pH range for growth from pH 8.5 to 10.25 (optimum at pH 9.5), and it was extremely salt tolerant, growing with between 1 and 4.5 M total Na+ (optimally at 2-2.5 M). BSker1T had a unique composition of polar lipid fatty acids, dominated by two C17 species. The membrane polar lipids included multiple unidentified phospholipids and two aminolipids. According to phylogenetic analysis of the 16S rRNA gene sequence, the isolate forms a novel branch within the family Ectothiorhodospiraceae (class Gammaproteobacteria) with the highest sequence similarity to the members of this family being 91 %. On the basis of distinct phenotypic and genotypic properties, strain BSker1T (=JCM 31341T=UNIQEM U1008T) is proposed to be classified as a representative of a novel genus and species, Natronospira proteinivora gen. nov., sp. nov.

Draft Genome Sequence of “Halomonas chromatireducens” Strain AGD 8-3, a Haloalkaliphilic Chromate- and Selenite-Reducing Gammaproteobacterium

ABSTRACT Here, we report the complete genome sequence (3.97 Mb) of “Halomonas chromatireducens” AGD 8-3, a denitrifying bacterium capable of chromate and selenite reduction under extreme haloalkaline conditions. This strain was isolated from soda solonchak soils of the Kulunda steppe, Russian Federation.

Natronobiforma cellulositropha gen. nov., sp. nov., a novel haloalkaliphilic member of the family Natrialbaceae (class Halobacteria) from hypersaline alkaline lakes

Six strains of extremely halophilic and alkaliphilic euryarchaea were enriched and isolated in pure culture from surface brines and sediments of hypersaline alkaline lakes in various geographical locations with various forms of insoluble cellulose as growth substrate. The cells are mostly flat motile rods with a thin monolayer cell wall while growing on cellobiose. In contrast, the cells growing with cellulose are mostly nonmotile cocci covered with a thick external EPS layer. The isolates, designated AArcel, are obligate aerobic heterotrophs with a narrow substrate spectrum. All strains can use insoluble celluloses, cellobiose, a few soluble glucans and xylan as their carbon and energy source. They are extreme halophiles, growing within the range from 2.5 to 4.8 M total Na+ (optimum at 4 M) and obligate alkaliphiles, with the pH range for growth from 7.5 to 9.9 (optimum at 8.5–9). The core archaeal lipids of strain AArcel5T were dominated by C20–C20 dialkyl glycerol ether (DGE) (i.e. archaeol) and C20–C25 DGE in nearly equal proportion. The 16S rRNA gene analysis indicated that all six isolates belong to a single genomic species mostly related to the genera Saliphagus-Natribaculum-Halovarius. Taking together a substantial phenotypic difference of the new isolates from the closest relatives and the phylogenetic distance, it is concluded that the AArcel group represents a novel genus-level branch within the family Natrialbaceae for which the name Natronobiforma cellulositropha gen. nov., sp. nov. is proposed with AArcel5T as the type strain (JCM 31939T = UNIQEM U972T).