Metabarcoding reveals unique microbial mat communities and evidence of biogeographic influence in low-oxygen, high-sulfur sinkholes and springs

High-sulfur, low-oxygen environments formed by underwater sinkholes and springs create unique habitats populated by microbial mat communities. To explore the diversity and biogeography of these mats, samples were collected from three sites in Alpena, Michigan, one site in Monroe, Michigan, and one site in Palm Coast, Florida. Our study investigated previously undescribed eukaryotic diversity in these habitats and further explored their bacterial communities. Mat samples and water parameters were collected from sulfur spring sites during the spring, summer, and fall of 2022. Cyanobacteria and diatoms were cultured from mat subsamples to create a culture-based DNA reference library. Remaining mat samples were used for metabarcoding of the 16S and rbcL regions to explore bacterial and diatom diversity, respectively. Analyses of water chemistry, alpha diversity, and beta diversity articulated a range of high-sulfur, low-oxygen habitats, each with distinct microbial communities. Conductivity, pH, dissolved oxygen, temperature, sulfate, and chloride had significant influences on community composition but did not describe the differences between communities well. Chloride concentration had the strongest correlation with microbial community structure. Mantel tests revealed that biogeography contributed to differences between communities as well. Our results provide novel information on microbial mat composition and present evidence that both local conditions and biogeography influence these unique communities. Groundwater-fed underwater sinkholes and springs create habitats with high-sulfur, low-oxygen conditions. Multi-marker metabarcoding was used to describe microbial mat communities in these extreme aquatic habitats. Unique bacterial and diatom communities were found in five springs in Michigan and Florida, with water parameters and biogeography contributing to these differences.image