Exploring Biogeochemistry and Microbial Diversity of Extant Microbialites in Mexico and Cuba

Abstract

Microbialites are modern analogs of ancient microbial consortia that date as far back as the Archaean Eon. Microbialites have contributed to the geochemical history of our planet through their diverse metabolic capacities that mediate mineral precipitation. These mineral-forming microbial assemblages accumulate major ions, trace elements and biomass from their ambient aquatic environments; their role in the resulting chemical structure of these lithifications needs clarification. We studied the biogeochemistry and microbial structure of microbialites collected from diverse locations in Mexico and in a previously undescribed microbialite in Cuba. We examined their structure, chemistry and mineralogy at different scales using an array of nested methods including 16S rRNA gene high-throughput sequencing, elemental analysis, X-Ray fluorescence (XRF), X-Ray diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS), Fourier Transformed Infrared (FTIR) spectroscopy and Synchrotron Radiation-based Fourier Transformed Infrared (SR-FTIR) spectromicroscopy. The resulting data revealed high biological and chemical diversity among microbialites and specific microbe to chemical correlations. Regardless of the sampling site, Proteobacteria had the most significant correlations with biogeochemical parameters such as organic carbon (Corg), nitrogen and Corg:Ca ratio. Biogeochemically relevant bacterial groups (dominant phototrophs and heterotrophs) showed significant correlations with major ion composition, mineral type and transition element content, such as cadmium, cobalt, chromium, copper and nickel. Microbial-chemical relationships were discussed in reference to microbialite formation, microbial metabolic capacities and the role of transition elements as enzyme cofactors. This paper provides an analytical baseline to drive our understanding of the links between microbial diversity with the chemistry of their lithified precipitations.

Rethinking the Coral Microbiome: Simplicity Exists within a Diverse Microbial Biosphere

“…These phylotypes belong to the classes Alphaproteobacteria , Betaproteobacteria , and Chloracidobacteria ; family Ellin6075, and orders EC94 and Kiloniellales . The family Ellin6075 (class Chloracidobacteria ) is unusual in the coral microbiome, but it has been previously found, with variable abundance, in microbialites ( 40 ) and soil ( 41 , 42 ). Members of this family possess a nitrifying capacity ( 43 ).…”

The microbiome of modern microbialites in Bacalar Lagoon, Mexico

“…All the microbialites analyzed in Bacalar Lagoon share mineral composition (CaCO 3 ,~97%). Valdespino et al, [23] reported a similar mineralogy for the microbialites of Bacalar Lagoon and Cuatro Cienegas Basin, which are water bodies of karstic origin. Bacalar Lagoon, which is located in the evaporative hydrogeochemical region [62], presents carbonate dissolution processes of the subterranean water tunnels that reach the lagoon and the walls (carbonate rock) of the cenotes within the lagoon, favoring the saturation of bicarbonates [37,72].…”

“…Depending on the chemistry of the water and the bacterial community, microbialites present a diverse range of minerals, although generally they have been reported in greater percentage aragonite, hydromagnesite, gypsum and calcite [23,73]. Cyanobacteria such as Pleurocapsales and Chroococcales and Alphaproteobacteria are associated with the formation of aragonite in microbialites from Lake Alchichica (Mexico), a Mg-rich hyperalkaline crater lake (pH 8.9), while in Cuatro Cienegas and Bacalar, a S-rich karstic system, filamentous cyanobacteria and Sulfate Reducing Bacteria (SRB) favor calcite precipitation [39].…”

“…Microbialites in the world maintain, regardless of their geographical region, a similar composition at the phylum level [8,23]. Actinobacteria, Bacteroidetes, Cyanobacteria and Proteobacteria [8,[37][38][39], are common components of microbialites.…”

“…The North-Center region also presented a higher diversity of Planctomycetes and Verrucomicrobia (~8.4% and~3.8%, respectively), both forming part of a taxonomic super phylum called PVC [85][86], described with a relative abundance between 7-12% in different microbialites of the world [8,86]. Recently, the presence of these bacteria was correlated in places where calcite crystals predominated [23]. Chloroflexi, an anoxygenic phototrophic phylum, which participates in the "alkaline machinery" which in combination with oxygenic photosynthesis by cyanobacteria and sulfate reduction, promote the precipitation of carbonated minerals [20,36], was also more abundant in the North-Center region.…”