Abstract
Vermelha Lagoon is a coastal hypersaline lagoon located in Rio de Janeiro state, Brazil, and it harbors both stromatolites and living microbial mats. Due to its remarkable geological, biological and paleontological attributes, determinations of the trophic state of this lagoon may highlight the importance of the environmental conditions that drive microbial mat processes over evolutionary and geological timescales. Analyses of nutrients, phytopigments, biopolymers, and viral and bacterial biomass revealed eutrophic conditions in both the water column and sediments. Accordingly, we classify Vermelha Lagoon as eutrophic. We observed biominerals deposited in microbial mat extracellular polymeric substances (EPS), associated with filamentous green bacteria. X-ray microtomography of microbial mats revealed dome-shaped layers of deposited minerals, both in the cyanobacteria and sulfate-reducing layers. SEM/EDS analysis showed biomineral deposition of carbonate-like CaMg dolomite at the sulfate-reducing zone of microbial mats. Virus-like particles (VLP) were found in high abundance, with Caudovirales being dominant. Bacterial abundance was two-fold higher than VLP at the water–sediment interface where microbial mats occur. Levels of salinity and eutrophication in Vermelha Lagoon allow EPS formation and biomineral deposition by microbial mats, and may influence the relationship between VLP and bacterial cells.
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