Metagenomic profiling of Arctic microbial mat communities as nutrient scavenging and recycling systems

By way of metagenomics and high-throughput pyrosequencing, we addressed the hypothesis that cyanobacterial mats in polar aquatic ecosystems maintain a nutrient-rich microenvironment via decomposition and scavenging processes. Analysis of more than 592,554 genomic deoxyribonucleic acid (DNA) reads (total of 11.5 million base pairs) showed that the ribosomal and protein-coding genes of two High Arctic ice-shelf mat communities were dominated by Proteobacteria, not Cyanobacteria, which implies a broad range of bacterial decomposition and nutrient recycling processes in addition to phototrophy. Principal component analysis of genes for light-, nitrogen-, and phosphorus-related processes provided evidence of partitioning of mat function among taxonomically different constituents of the mat consortia. Viruses were also present (notably Alpha-, Beta-, Gammaproteobacteria phages and cyanophages), which likely contribute to cellular lysis and recycling, as well as other Bacteria, Archaea, and microbial eukaryotes. Nitrogen-related genes were dominated by ammonium-assimilation systems, implying that the microbial mats are sites of intense mineralization, but not N-oxidation, since nitrification genes were absent. Nutrient scavenging systems were detected, including genes for transport proteins and enzymes for converting larger molecules into more readily assimilated inorganic forms (allantoin degradation, cyanate hydrolysis, exophosphatases, phosphonatases). Metagenomic profiling results underscore the rich diversity of microbial life even in extreme polar habitats, and the capability of mat consortia to retain and recycle nutrients in the benthic microenvironment.