Awakening Ancient Polar Actinobacteria: Diversity, Evolution and Specialized Metabolite Potential

Polar and subpolar ecosystems are highly vulnerable to global climate change with consequences for biodiversity and community composition. As bacteria are directly impacted by future environmental change; it is essential to have a better understanding of microbial communities in fluctuating ecosystems. Exploration of Polar environments, specifically sediments, represent an exciting opportunity to uncover bacterial and chemical diversity and link this to ecosystem and evolutionary parameters. In terms of specialized metabolite production, the bacterial order actinomycetales, within the phyla Actinobacteria are unsurpassed, producing 10000 specialized metabolites accounting for over 45% of all bioactive microbial metabolites. Culture-dependant studies of 12 sediment cores from the Antarctic and sub-Arctic generated a culture collection of 39 strains belonging to rare actinomycetales genera including Microbacterium, Rhodococcus and Pseudonocardia. This study used a combination of nanopore sequencing and molecular networking to explore the community composition, culturable bacterial diversity, evolutionary relatedness and specialized metabolite potential of these strains. Metagenomic analyses using MinION sequencencing was able to detect the phylum Actinobacteria across polar sediment cores as an average of 13% of the total bacterial reads. The resulting molecular network consisted of 1652 parent ions and the lack of known metabolite identification supports the argument that Polar bacteria are likely to produce previously unreported chemistry.