Metagenomic insights into Thermus-mediated sulfur oxidation, nitrogen cycling, and thermoadaptation in thermophilic autotrophic denitrification bioreactors

Thermus species are widely recognized as a key group of heterotrophic denitrifiers mediating carbon, nitrogen, and sulfur cycling in geothermal habitats, and have attracted extensive research attention for their thermostable enzyme resources. However, their autotrophic denitrification potential remains poorly characterized, and the systems-level mechanisms underlying their thermal adaptation remain incompletely understood. This study presents three high-quality metagenome-assembled genomes (MAGs) of Thermus from autotrophic sulfur-based denitrification bioreactors. These MAGs encode the complete genetic potential for the Calvin-Benson-Bassham cycle, reductive tricarboxylic acid cycle, and 3-hydroxypropionate bicycle for inorganic carbon fixation. Thermus strains employ a distinct sulfide oxidation route: HS− is first oxidized to polysulfides or glutathione persulfide by fccAB, then condensed with sulfite to form thiosulfate via rhodanese, and finally completely oxidized to sulfate by complete sox cluster. T. scotoductus (MAG1) carries genes for nitrate reduction (narGHI) and dissimilatory nitrate reduction to ammonium (nrfA and nrfH). As conspecific strains, MAG2 and MAG3 harbor abundant denitrification genes (nar, nirK, norBC), indicating strong substrate-driven metabolic plasticity. A protein–protein interaction network further elucidated the systems-level thermoadaptive survival mechanisms of T. scotoductus, identifying chaperone-mediated protein homeostasis and DNA repair-dependent genomic stability as core adaptive strategies, alongside orphan nodes (e.g., aceE, lpd, nuoC) with potential independent functions. Collectively, these findings advance our understanding of Thermus’ metabolic plasticity, offer valuable thermostable resources for high-temperature wastewater treatment and industrial applications, and bridge critical knowledge gaps in the autotrophic metabolism and thermoadaptive regulation of thermophilic bacteria-laying a robust genomic foundation for the development and optimization of high-temperature biotechnological processes.