Carbon monoxide oxidizers in soils of different ages from Piton de la Fournaise volcano.

Volcanic soils provide a unique environment for studying microbial colonization and succession due to their extreme conditions and distinct geochemical profiles. This study focused on carbon monoxide (CO)-oxidizing microbial communities in volcanic soils at Piton De La Fournaise, Réunion Island. Soil samples from three sites (corresponding to eruptions in 1401, 1559, and 2007) were analysed to assess microbial community structure using 16S rRNA gene sequencing and metagenomic analysis to identify functional genes involved in CO oxidation. Phylum-level analysis showed higher relative abundance of Acidobacteriota and Chloroflexota, lower abundances of Actinomycetota and Bacteroidota, and relatively stable levels of Pseudomonadota, while class-level patterns included rising Alphaproteobacteria and Acidobacteriia, with Ktenobacteria emerging in the 1401 site. CO dehydrogenase-related genes were found in 17 metagenome-assembled genomes across all sites. The CO consumption rate by microbes in soils was measured. CO-oxidizing microbes were present across soil ages, with detectable activity in the 2007 site and greatest activity in the 1401 site, suggesting that these microbes actively use CO as an energy source even in soils with primary vegetation, contrary to general understanding. The findings suggest intricate dynamics of microbial succession in volcanic soils and may challenge conventional expectations about community complexity over time.