Discovery of Eremiobacterota withnifHhomologs in tundra soil

Abstract

We describe a population genome of Eremiobacterota (KWL-0264) recovered from tundra soil metagenomes that contains the minimal set of nif genes needed to fix atmospheric N2. Such putative diazotroph population would link for the first time Eremiobacterota and N2 fixation. The integrity of the genome and its nif genes are well supported by both environmental and taxonomic signals. KWL-0264 contains three nifH homologs and the complementary set of nifDKENB genes that are thought needed to assemble a functional nitrogenase. The putative role in N2 fixation of this Eremiobacterota population is also evidenced by the presence of other genes involved with the regulation of the N2 fixation activity as well as ammonia assimilation and amino acid metabolism. Like other Eremiobacterota, KWL-0264 also encodes the potential for atmospheric chemosynthesis. Interestingly, the presence of a N2O reductase indicates that this population could also play a role as a N2O sink in tundra soils. Due to the lack of activity data, it remains uncertain if this Eremiobacterota population is able to assemble a functional nitrogenase and participate in N2 fixation. Confirmation of this activity would be a testament to the great metabolic versatility of Eremiobacterota, which appears to underlie their ecological success in cold and oligotrophic environments.