Novel arsenate-respiring bacteria drive arsenic biogeochemical cycling in Tibetan geothermal springs revealed by DNA-SIP based metagenomics

Arsenic (As) is a toxic element posing health risks globally, with geothermal environment as one of the hotspots. Arsenic biotransformation is mainly mediated by microorganisms which often employ diverse metabolic strategies for survival. However, the microorganisms responsible for As cycling and their survival strategies in geothermal environment in Tibet, the Third Pole, remain unclear. To address this knowledge gap, we investigated As biotransformation in representative geothermal springs using DNA-stable isotope probing (DNA-SIP) combined with metagenomic sequencing. As(V) reduction to the more toxic As(III) was found to be prevalent. Pseudomonas and Thermincola were identified as the dominant As(V)-reducing bacteria (AsRB). Metagenome-assembled genomes (MAGs) affiliated with AsRB contained abundant genes encoding As(V)-respiratory reductase (arrA, 1044.34 transcripts per million (TPM)), nitrate reduction pathway (e.g., narG), and Wood-Ljungdahl pathway (e.g., acsA), indicating their role as dissimilatory As(V)-reducing prokaryotes (DARPs) with diverse metabolic strategies. Here, Thermincola's potential of As(V) reduction via arrA and carbon fixation via Wood-Ljungdahl pathway was observed for the first time, which was found to be widespread in various ecosystems. Our study unravels the key players driving As biogeochemical cycle in Tibetan geothermal springs and provides insights into the genetic mechanisms enabling their survival in extreme environments.