Metagenomic insights into ecosystem function in the microbial mats of Blue Holes, Shark Bay

Microbial mat ecosystems vary in complexity and structure depending on the environmental constraints placed by nature. Here, we describe in detail for the first time the community composition and functional potential of the microbial mats found in the supratidal, gypsum-rich, and hypersaline region of Blue Holes, Shark Bay. This was achieved via high throughput sequencing of total mat community DNA on the Illumina NextSeq platform. Mat communities were mainly comprised of Proteobacteria (29%), followed by Bacteroidetes/Chlorobi Group (11%), and Planctomycetes (10%). These mats were found to also harbor a diverse community of potentially novel microorganisms including members from the DPANN and Asgard archaea, Candidate Phyla Radiation (CPR) and other candidate phyla, with highest diversity indices found in the lower regions of the mat. Major metabolic cycles belonging to sulfur, carbon, nitrogen, and fermentation were detected in the mat metagenomes with the assimilatory sulfate reduction pathway being distinctly abundant. Critical microbial interactions were also inferred, and from 117 medium-to-high quality metagenome-assembled genomes (MAGs), viral defense mechanisms (CRISPR, BREX, and DISARM), elemental transport, osmoprotection, heavy metal and UV resistance were also detected in the mats. These analyses have provided a greater understanding of these distinct mat systems in Shark Bay, including key insights into adaptive responses.