Sulfur-dependent respiration under extremely haloalkaline conditions in soda lake ‘acetogens’ and the description of Natroniella sulfidigena sp. nov.

Microbial sulfidogenesis is the main dissimilatory anaerobic process in anoxic sediments of extremely haloalkaline soda lakes. In soda lakes with a salinity >2 M of the total Na+ sulfate reduction is depressed, while thiosulfate- and sulfur-dependent sulfidogenesis may still be very active. Anaerobic enrichments at pH 10 and a salinity of 2-4 M total Na+ from sediments of hypersaline soda lakes with thiosulfate and elemental sulfur as electron acceptors and simple nonfermentable electron donors resulted in the isolation of two groups of haloalkaliphilic bacteria capable of dissimilatory sulfidogenesis. Both were closely related to obligately heterotrophic fermentative homoacetogens from soda lakes. The salt-tolerant alkaliphilic thiosulfate-reducing isolates were identified as representatives of Tindallia magadiensis, while the extremely natronophilic obligate sulfur/polysulfide-respiring strains belonged to the genus Natroniella and are proposed here as a novel species Natroniella sulfidigena. Despite the close phylogenetic relation to Natroniella acetigena, it drastically differed from the type strain phenotypically (chemolithoautotrophic and acetate-dependent sulfur respiration, absence of acetate as the final metabolic product). Apparently, in the absence of specialized respiratory sulfidogens, primarily fermentative bacteria that are well adapted to extreme salinity may take over an uncharacteristic ecological function. This finding, once again, exemplifies the importance of isolation and phenotypic investigation of pure cultures

<i>Tundrisphaera lichenicola</i> gen. nov., sp. nov., a psychrotolerant representative of the family <i>Isosphaeraceae</i> from lichen-dominated tundra soils

Two strains of aerobic, budding, pink-pigmented bacteria, P12T and P515, were isolated from a lichen-dominated peatland and a forested tundra soil of north-western Siberia, respectively. Cells of these isolates were represented by non-motile spheres that occurred singly or were arranged in short chains and aggregates. While growing on solid media, cells of strains P12T and P515 attached to the surface by means of holdfast-like appendages. These isolates were mildly acidophilic (optimum growth at pH 5.5–6.0), psychrotolerant bacteria, which displayed tolerance of low temperatures (4–15 °C), grew optimally at 15–22 °C and did not grow at temperatures above 28 °C. The preferred growth substrates were sugars and some heteropolysaccharides. The major fatty acids were C18 : 1ω9c, C16 : 0 and C14 : 0. Trimethylornithine lipid was the major polar lipid. The only quinone was MK-6, and the G+C content of the DNA was 61.2–62.2 mol%. Strains P12T and P515 possessed identical 16S rRNA gene sequences, which affiliated them with the family Isosphaeraceae , order Planctomycetales , and these displayed the highest similarity (93–94 %) to 16S rRNA gene sequences from members of the genus Singulisphaera . However, the signature fatty acid of species of the genus Singulisphaera , i.e. C18 : 2 ω6c,12c, was absent in cells of strains P12T and P515. They also differed from members of the genus Singulisphaera by substrate utilization pattern and a number of physiological characteristics. Based on these data, the novel isolates should be considered as representing a novel genus and species of planctomycetes, for which the name Tundrisphaera lichenicola gen. nov., sp. nov, is proposed. The type strain is P12T (=LMG 29571T=VKM B-3044T)

<i>Planctomicrobium piriforme</i> gen. nov., sp. nov., a stalked planctomycete from a littoral wetland of a boreal lake

An aerobic, budding, non-pigmented and rosette-forming bacterium was isolated from a littoral wetland of a boreal lake located in Valaam Island, northern Russia, and designated strain P3T.Ellipsoidal to pear-shaped cells of this bacterium were covered with crateriform pits and possessed stalks suggesting a planctomycete morphotype. 16S rRNA gene sequence analysis confirmed that strain P3T was a member of the order Planctomycetales and belonged to a phylogenetic lineage defined by the genus Planctomyces, with 89 and 86% sequence similarity to Planctomyces brasiliensis and Planctomyces maris, respectively. Strain P3T was a mildly acidophilic, mesophilic organism capable of growth at pH values between pH 4.2 and 7.1 (with an optimum at pH 6.0–6.5) and at temperatures between 10 and 30 o C (optimum at 20–28 o C).Most sugars, a number of polysaccharides and several organic acids were the preferred growthsubstrates. Compared with Planctomyces brasiliensis and Planctomyces maris, which require NaCl for growth, strain P3T was salt-sensitive and did not develop at NaCl concentrations above 0.5% (w/v). The major fatty acids were C16 : 0 and C16 : 1w7c; the cells also contained significant amounts of C18 : 1w7c and C18 : 0. The major intact polar lipids were diacylglycerol-O-(N,N,Ntrimethyl)homoserine (DGTS) lipids; the major neutral lipids were long-chain 1,(w-1)-diols andC31 : 9 hydrocarbon. The quinone was MK-6, and the G+C content of the DNA was 59.0 mol%.Strain P3T differed from Planctomyces brasiliensis and Planctomyces maris by cell morphology,substrate utilization pattern and a number of physiological characteristics. Based on these data,the novel isolate should be considered as representing a novel genus and species ofplanctomycetes, for which the name Planctomicrobium piriforme gen. nov., sp. nov., is proposed. The type strain is P3T (=DSM 26348T=VKM B-2887T)

Methylomonas paludis sp. nov., the first acid-tolerant member of the genus Methylomoas, from an acidic wetland

An aerobic methanotrophic bacterium was isolated from an acidic (pH 3.9) Sphagnum peat bog in north-eastern Russia and designated strain MG30T. Cells of this strain are Gram-negative, pale-pink-pigmented, non-motile, thick rods that are covered by large polysaccharide capsules and contain an intracytoplasmic membrane system typical of type I methanotrophs. They possess a particulate methane monooxygenase enzyme (pMMO) and utilize only methane and methanol. Carbon is assimilated via the ribulose-monophosphate pathway; nitrogen is fixed via an oxygen-sensitive nitrogenase. Strain MG30T grows in a pH range of 3.8-7.3 (optimum pH 5.8-6.4) and at temperatures between 8 and 30°C (optimum 20-25°C). The major cellular fatty acids are C16:1ω5t, C16:1ω8c, C16:1ω7c, and C14:0; the DNA G+C content is 48.5 mol%. The isolate belongs to the family Methylococcaceae of the class Gammaproteobacteria and displays 94.7-96.9% 16S rRNA gene sequence similarity to members of the genus Methylomonas. However, strain MG30T differs from all taxonomically characterized members of this genus by the absence of motility, the ability to grow in acidic conditions, and low DNA G+C content. Therefore, we propose to classify this strain as a novel, acid-tolerant species of the genus Methylomonas, Methylomonas paludis sp. nov. Strain MG30T (=DSM 24973T = VKM B-2745T) is the type strain.

Culturable diversity of lithotrophic haloalkaliphilic sulfate-reducing bacteria in soda lakes and the description of Desulfonatronum thioautotrophicum sp. nov., Desulfonatronum thiosulfatophilum sp. nov., Desulfonatronovibrio thiodismutans sp. nov., and Desulfonatronovibrio magnus sp. nov.

Soda lake sediments usually contain high concentrations of sulfide indicating active sulfate reduction. Monitoring of sulfate-reducing bacteria (SRB) in soda lakes demonstrated a dominance of two groups of culturable SRB belonging to the order Desulfovibrionales specialized in utilization of inorganic electron donors, such as formate, H2 and thiosulfate. The most interesting physiological trait of the novel haloalkaliphilic SRB isolates was their ability to grow lithotrophically by dismutation of thiosulfate and sulfite. All isolates were obligately alkaliphilic with a pH optimum at 9.5–10 and moderately salt tolerant. Among the fifteen newly isolated strains, four belonged to the genus Desulfonatronum and the others to the genus Desulfonatronovibrio. None of the isolates were closely related to previously described species of these genera. On the basis of phylogenetic, genotypic and phenotypic characterization of the novel soda lake SRB isolates, two novel species each in the genera Desulfonatronum and Desulfonatronovibrio are proposed.BiotechnologyApplied Science