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Depth Related Structure and Microbial Composition of Microbialites in a Karst Sinkhole, Cenote Azul, Mexico

Abstract:

Microbialites are sedimentary structures that represent modern models of the oldest life forms, stromatolites (<3.5 Ga), and are relevant for evolutionary and ecological studies. Cenote Azul is a deep (>90 m) karst sinkhole in the Yucatan peninsula characterized by microbialites that develop along its wall and hydrogeochemistry defined by the saturation of carbonate, sulfate and calcium ions. In this study, high throughput sequence analysis of 16S rRNA genes allowed characterization of the prokaryotic communities associated with microbialites in a depth profile. The most represented phyla were Proteobacteria (23.6–30.1%), Planctomycetes (11.6–13.8%), Cyanobacteria (9.7–16.5%), Acidobacteria (6.1–8.3%), Rokubacteria (4.1–7.8%), Chloroflexi (3.3–4.4%), Nitrospirae (3.5–4.6%), Actinobacteria (2.6–5%) Bacteroidetes (1.7–4.1%) and Thaumarchaeota (7.5–11.1%). Phylogenetic distance analyses described two distinct clusters of microbialites: Shallow (5 and 10 m) and Deep (20 and 30 m). The dominant diversity at the phylum level of the prokaryotic community described in this system is similar to that of other microbialites from different environments, but differences are reported at the classification level of order, family and genus. The mineral composition of the Cenote Azul microbialites has calcite as the main constituent mineral (∼97%). Finally, this work establishes a baseline on the presence of microbialites and its relation to depth in the sinkholes of the Yucatan peninsula and stimulates the monitoring of these communities as a tool for the conservation of sites with high tourism pressure.