Geomicrobiology of the Rincon de Parangueo maar crater: Exploring the link between an evolving extreme environment and its potential metabolic diversity

Rincon de Parangueo (RP) is a Quaternary maar crater located in the Michoacan-Guanajuato Volcanic Field in central Mexico. Like other volcanic craters in the region, the central part was occupied by an endorheic lacustrine system. As a consequence of extensive groundwater extraction, the perennial lake started a gradual desiccation process and now the remnant ponds host a highly saline-alkaline ecosystem. The stratigraphic record indicates an exceptional and long-term sedimentation of carbonate microbialites. Previous studies based on the 16S rRNA gene have shown that microbial communities have a widespread presence in the crater at the microbialites, the remaining saline ponds, superficial soils and below the surface. To understand the possible role of the microbial communities that generate these biogeological structures, novel analytical methods to resolve the amplicon datasets and their microbial metabolic potential were used.We describe in detail the relationship between the microbial communities, the evolution of physicochemical parameters, and carbonate morphology, in four micro-environments. A 16S rRNA gene sequencing dataset from previous publications was re-analysed using an ASV-based bioinformatic pipeline to identify new insights into the microbial assemblage. Finally, a taxon-based metabolic profile was used to predict the potential metabolic contribution of the prokaryotic community.Results indicated a refinement in terms of community composition using the ASV-based bioinformatic methods. Functional profiling through 16S rRNA gene-based analysis suggested metabolisms associated with carbonate precipitation, indicating a broad potential for microbially mediated carbonate precipitation (e.g., carbon fixation and photosynthesis). The possibility of biogenic methane gas production by methanogenic microorganisms was recognised, supporting the estimated flow of methane on the surface soils.The lacustrine evolution over the last years and the extreme physicochemical characteristics of RP have an impact on the microbial community structure. Prokaryotic community and metabolic potential results from RP coincide with the diversity and abundance of microbial communities and functional metabolisms reported from other microbialite-forming lakes along the Trans Mexican Volcanic Belt. The identification of important possible phylotypes involved in carbonate precipitation might be an important factor in considering RP microbialites as active calcifying entities.These findings provide novel insights into the potential key role of metabolic pathways driving the process of carbonate precipitation inside RP and evidence of its importance as a microbial biodiversity hotspot in Mexico.