987 / 2024-09-19 23:43:00

Comammox Nitrospira clade B as a key nitrification driver in coastal Antarctica

Nitrification,DNA-SIP,Metagenomes,Comammox,Antarctica

Antarctica's remote coastal regions, largely isolated from anthropogenic nitrogen inputs, exhibit notably low nitrogen levels, yet the mechanisms driving the nitrogen cycle, particularly nitrate (NO₃^-) cycling, remain largely unexplored. This study delves into the microbial nitrogen cycling processes in these pristine environments, focusing on the biological origins of nitrate through detailed isotopic analyses and extensive metagenomic sequencing. By reconstructing 1,968 metagenome-assembled genomes across 29 microbial phyla from soil and lake sediments, we uncover the metabolic capacities for nitrogen fixation, nitrification, and denitrification, with a notable absence of anaerobic ammonium oxidation pathways. Our findings highlight the dominance of complete ammonia oxidizing (comammox) Nitrospira, which uniquely perform the entire nitrification process. Special adaptations such as trehalose synthesis for cold tolerance, high substrate affinity for efficient resource utilization, and alternative metabolic pathways for adaptation to nutrient-limited conditions are evident in these organisms. The pivotal role of comammox Nitrospira in autotrophic nitrification is further substantiated through ¹³C-DNA-based stable isotope probing, confirming their significant contribution to the nitrogen budget in coastal Antarctica. This research not only sheds light on the critical nitrification processes driven by comammox Nitrospira clade B but also enhances our understanding of microbial adaptations and ecosystem functioning under extreme conditions.