Metagenomic insight into the diversity and biogeochemical functions of microbial communities in the maar tropical Lake Atexcac

Warm monomictic maar lakes in tropical regions represent dynamic systems where thermal stratification generates strong vertical gradients in oxygen availability and redox conditions, shaping microbial community structure and function. Lake Atexcac (Puebla, Mexico) undergoes seasonal stratification and episodic whiting events that provide a framework to examine microbial responses to changing hydrodynamic conditions. In this study, we applied deep shotgun metagenomic sequencing to characterize the taxonomic composition and functional potential of microbial communities across the epilimnion, metalimnion and hypolimnion during two contrasting stratification phases: early stratification associated with a whiting event and a later, well-established stratification period.Metagenomic profiles revealed a clear vertical organization of microbial communities, with samples clustering primarily according to thermal strata and the metalimnion displaying the highest genetic differentiation. Genome-resolved analyses enabled the recovery of a large number of metagenome-assembled genomes, with marked differences in their vertical distribution between hydrodynamic phases. The recovered genomes encompassed diverse metabolic pathways related to carbon, nitrogen and sulphur transformations, reflecting the heterogeneous redox conditions along the water column. Notably, sulphur-related metabolisms were widespread across strata, and <i>Chlorobiota</i>-affiliated genomes and metagenomic reads were consistently detected in suboxic layers. These organisms were found to harbour diverse thiosulphate disproportionation pathways and are thought to play an important role in the sulphur cycle that has not previously been reported in this type of lacustrine system.Overall, this study provides a genome-resolved perspective on microbial diversity and metabolic potential in a stratified tropical maar lake and establishes a baseline for future comparative and process-oriented studies integrating water column and sediment microbial communities.