Biology Seminar by Subhadeep Chowdhury Start date
SENG 113
Geneviee Kozak
gkozak@umassd.edu
Nitrogen availability regulates primary production and Earth's climate, yet the metabolic architectures of microorganisms mediating biological nitrogen fixation (BNF) and denitrification remain poorly understood. We mapped metabolic potential across cultured and uncultivated diazotrophs and denitrifiers by analyzing ~12,000 high-quality genomes. Here we demonstrate that nitrogen-cycling functions frequently extend beyond canonical guild boundaries. Strikingly, 11% of the combined set of diazotrophs and denitrifiers encoded BNF, denitrification, and nitrogen retention within a single genome. Further, 55% of diazotrophs and 51% of denitrifiers encode dissimilatory nitrate reduction to ammonium, indicating widespread nitrogen retention capacity. Beyond nitrogen metabolism, 59% of diazotroph and 24% of denitrifiers encoded at least one carbon fixation pathway, revealing widespread mixotrophic potential coupled to chemolithotrophic energy and organic-carbon metabolism. Carbon fixation strategies were phylogenetically partitioned and habitat-structured, with Wood-Ljungdahl pathway was 14-fold more abundant in diazotrophs than denitrifiers. In metabolic space, organisms capable of multiple nitrogen-cycling functions and mixotrophs occupied an intermediate region between canonical guilds, shifting the view of nitrogen-cycling organisms from taxonomy-defined guilds to pathway resolved metabolic understandings. Additionally, we separated true and pseudo diazotrophs (which carry only a fragment of the nitrogenase enzyme) and showed that the retained nitrogenase component have undergone neofunctionalization, with predicted roles in tetrapyrrole biosynthesis, sulfur scavenging and methanogenesis. These pathway-resolved genomic maps provide a framework for incorporating uncultivated nitrogen-cycling lineages and their metabolic plasticity into biogeochemical models of nitrogen and carbon flux under environmental change.