Exploring the diversity of pathways of autotrophic carbon assimilation in thermophilic prokaryotes

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At least six different autotrophic pathways are involved in primary production, and further pathways are still awaiting their description, reflecting the diversity of the physicochemical parameters of the habitats and of the autotrophic organisms living in them. Thermophilic microorganisms developing at high temperatures are represented by various (including the most ancient) phylogenetic groups in the Archaea and Bacteria domains. Thermophiles are extraordinary diverse in their biochemical processes, being capable to use an unusually wide range of RedOx pairs in their catabolism as well as of CO2 fixation pathways. Being only scarcely explored yet highly metabolically varied physiological group, thermophiles are promising to study diversity of metabolism, in particular autotrophic carbon assimilation, which is the core expertise of the German partner of this joint project. The team of the Russian applicant gained huge expertise in the isolation and characterization of novel thermophiles and has at its disposal a large collection of phylogenetically and metabolically diverse autotrophic thermophilic prokaryotes. In this project, both teams will combine their expertise to explore the diversity of thermophilic autotrophic microorganisms and their pathways. We are going to • screen the available collection for the microorganisms with modified/novel autotrophic pathways,• analyze thermophilic communities of hot springs of Kamchatka, Kuriles and/or the Baikal rift zone using radioisotopic and omics techniques,• isolate novel thermophilic autotrophs from these environments, • determine their CO2 fixation pathways using the genomic analysis,• study the corresponding microorganisms and their pathways biochemically, • identify genomic determinants of the pathways and their modifications.For the organisms that do not possess genes for the known pathways, we will outline the pathway(s) of autotrophic CO2 fixation. The anticipated results are either detection of a novel pathway, or of a recently described reversed oxidative tricarboxylic acid (roTCA) cycle. This is an exciting alternative, as only two examples of this cryptic metabolic pathway are known to date.Our preliminary studies have identified organisms whose genomes lacked key genes of the known autotrophic pathways (Thermus sp., Deferribacter autotrophicus). These organisms will firstly be studied along with Desulfurella acetivorans, which is studied for the identification of genomic determinants of the roTCA cycle. The part of the project, devoted to analysis of environmental samples, will shed light onto the distribution of CO2 fixation pathways in nature as well as their impact. We expect that the work on this project will expand our knowledge about the autotrophic pathways in thermophiles, contribute to the understanding of biochemistry, ecology and evolution of the most important biological synthetic process, and may lead to the discovery of unknown autotrophic pathways/strategies.