Microbial communities of Kamchatka Peninsula terrestrial hot springs were studied using molecular, radioisotopic and cultural approaches. Analysis of 16S rRNA gene fragments performed by means of high-throughput sequencing revealed that aerobic autotrophic sulfur-oxidizing bacteria of the genus Sulfurihydrogenibium (phylum Aquificae) dominated in a majority of streamers. Another widely distributed and abundant group was that of anaerobic bacteria of the genus Caldimicrobium (phylum Thermodesulfobacteria). Archaea of the genus Vulcanisaeta were abundant in a high-temperature, slightly acidic hot spring, where they were accompanied by numerous Nanoarchaeota, while the domination of uncultured Thermoplasmataceae A10 was characteristic for moderately thermophilic acidic habitats. The highest rates of inorganic carbon assimilation determined by the in situ incubation of samples in the presence of C-labeled bicarbonate were found in oxygen-dependent streamers; in two sediment samples taken from the hottest springs this process, though much weaker, was found to be not dependent on oxygen. The isolation of anaerobic lithoautotrophic prokaryotes from Kamchatka hot springs revealed a wide distribution of the ability for sulfur disproportionation, a new lithoautotrophic process capable to fuel autonomous anaerobic ecosystems.
Extended_Data_Figur e_4.epsError bars represent standard deviations of independent radioisotopic measurement experiments (n = 3).Extended Data Fig.Genes related to sulphate reduction.
Extended_Data_Figur e_5.epsThe key sulphate reduction genes from genomes of selected sulphate reducing archaea ("Candidatus V. moutnovskia", Caldivirga sp. Obs2 and A. fulgidus) and bacteria (D. vulgaris Hildenborough and A. degensii) are shown, as well as from genomes of archaea not capable of sulphate reduction (V. distributa, V. souniana, Caldivirga sp. MU80, Ca. Methanodesulfokores washburnensis MDKW and unclassified Aigarchaeota JZ bin 15). Extended Data Fig. Proteomic analysis of the soluble fraction of cells in the binary culture. Extended_Data_Figur e_6.eps Dissimilatory sulphate reduction in archaeon Candidatus Vulcanisaeta moutnovskia sheds light on evolution of sulphur metabolism
An obligately anaerobic, sulfate-reducing micro-organism, strain 3127-1T, was isolated from geothermally heated soil (Oil Site, Uzon Caldera, Kamchatka, Russia). The new isolate was a moderately thermoacidophilic anaerobe able to grow with H2 or formate by respiration of sulfate or thiosulfate. The pH range for growth was 3.7-6.5, with an optimum at 4.8-5.0. The temperature range for growth was 37-65 °C, with an optimum at 55 °C. The G+C content of the genomic DNA was 33.7 mol%. The genome of strain 3127-1T contained two almost identical 16S rRNA genes, differing by a single nucleotide substitution. The closest 16S rRNA gene sequence of a validly published species belonged to Thermodesulfobium narugense Na82T (99.5 % similarity). However, the average nucleotide identity of the genomes of strain 3127-1T and T. narugense Na82T and the predicted DNA-DNA hybridization value (GGDC 2.1 blast+, formula 2) were as low as 86 and 32.5±2.5 %, respectively. This, together with phenotypic data, showed the new isolate to belong to a novel species, for which the name Thermodesulfobium acidiphilum sp. nov. is proposed. The type strain is 3127-1T (=DSM 102892T=VKM B-3043T).
The Calvin–Benson–Bassham (CBB) cycle assimilates CO2for the primary production of organic matter in all plants and algae, as well as in some autotrophic bacteria. The key enzyme of the CBB cycle, ribulose-bisphosphate carboxylase/oxygenase (RubisCO), is a main determinant of de novo organic matter production on Earth. Of the three carboxylating forms of RubisCO, forms I and II participate in autotrophy, and form III so far has been associated only with nucleotide and nucleoside metabolism. Here, we report that form III RubisCO functions in the CBB cycle in the thermophilic chemolithoautotrophic bacteriumThermodesulfobium acidiphilum,a phylum-level lineage representative. We further show that autotrophic CO2fixation inT. acidiphilumis accomplished via the transaldolase variant of the CBB cycle, which has not been previously demonstrated experimentally and has been considered unlikely to occur. Thus, this work reveals a distinct form of the key pathway of CO2fixation.
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