Application of Microbial Mats for the Isolation of Spore-Forming Prokaryotes from Deep Biosphere
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Application of Microbial Mats for the Isolation of Spore-Forming Prokaryotes from Deep Biosphere A. P. Lukinaa, M. R. Avakyana, E. V. Danilovab, and O. V. Karnachuka, * a bLaboratory
Department of Plant Physiology and Biotechnology, Tomsk State University, Tomsk, 634050 Russia of Microbiology, Institute of General and Experimental Biology, Siberian Branch, Russian Academy of Sciences, Ulan-Ude, 670047 Russia *е-mail: [email protected] Received April 27, 2020; revised May 22, 2020; accepted May 29, 2020
Abstract—Deep biosphere is an prolific source of novel prokaryotes. A phylogenetically distant lineage of Firmicutes was reported in 2019 as a new genus Thermoanaerosсeptrum. Ecology of this group remains uncertain, since the only known species, T. fracticalcis, gains energy from the use of fumarate, and the source of the latter in groundwater is not apparent. The organism is incapable of using any of the oxidized sulfur species (sulfate, sulfite, thiosulfate, or elemental sulfur) as an electron acceptor for respiration, although the proteins required for dissimilatory sulfate reduction are present in the genome. Research on T. fracticalcis ecology is complicated by the fact that the organism constitutes a minor component of the microbial community. The present work was aimed at the use of microbial mats formed at the head of a deep thermal borehole to obtain sporeforming sulfidogens. The isolated pure culture, Thermoanaerosсeptrum sp. BuN1, reduced sulfate and exhibited saccharolytic activity. It could grow within a broad pH range (3.5 to 9). Strain BuN1 was a moderate thermophile growing within the range from 37 to 60°C, with an optimum at 50°C. Keywords: deep biosphere, cultivation, microbial mats, Thermoanaerosceptrum DOI: 10.1134/S0026261720060120
According to various estimates, the carbon reservoir in underground aquifers reaches 14‒135 Pg (1 Pg = 1015 g), which is 2‒19% of the total biomass of the Earth (McMahon and Parnell, 2014). Our knowledge of underground microorganisms is largely based on the 16S rRNA gene sequences and, to a lesser extent, metagenome-assembled genomes (MAGs) and single amplified genomes (SAGs). The ratio of cultivated prokaryotes to the number known from molecular data is minimal for underground environments (Anantharaman et al., 2018). This is caused by the difficulties in collecting samples that are not contaminated with organisms from the surface and the difficulty of cultivating slow-growing underground forms (Karnachuk et al., 2019). Artesian boreholes, thermal springs associated with faults, and deep mines for the extraction of minerals are a kind of “windows” into the deep biosphere. Sampling from artesian boreholes, where water is supplied under pressure from deep aquifers, helps to avoid contamination by surface organisms. Underground aquifers in most cases are characterized by oligotrophic conditions, to which prokaryotes adapt by slow metabolism. In places where borehole water is ejected to the surface, specific thermal biotopes may form, where hi
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