Ancient and remote quartzite caves as a novel source of culturable microbes with biotechnological potential.

Quartzite caves located on table-top mountains (tepuis) in the Guyana Shield, are ancient, remote, and pristine subterranean environments where microbes have evolved peculiar metabolic strategies to thrive in silica-rich, slightly acidic and oligotrophic conditions. In this study, we explored the culturable fraction of the microbiota inhabiting the (ortho)quartzite cave systems in Venezuelan tepui (remote table-top mountains) and we investigated their metabolic and enzymatic activities in relation with silica solubilization and extracellular hydrolytic activities as well as the capacity to produce antimicrobial compounds. Eighty microbial strains were isolated with a range of different enzymatic capabilities. More than half of the isolated strains performed at least three enzymatic activities and four bacterial strains displayed antimicrobial activities. The antimicrobial producers Paraburkholderia bryophila CMB_CA002 and Sphingomonas sp. MEM_CA187, were further analyzed by conducting chemotaxonomy, phylogenomics, and phenomics. While the isolate MEM_CA187 represents a novel species of the genus Sphingomonas, for which the name Sphingomonas imawarii sp. nov. is proposed, P. bryophila CMB_CA002 is affiliated with a few strains of the same species that are antimicrobial producers. Chemical analyses demonstrated that CMB_CA002 produces ditropolonyl sulfide that has a broad range of activity and a possibly novel siderophore. Although the antimicrobial compounds produced by MEM_CA187 could not be identified through HPLC-MS analysis due to the absence of reference compounds, it represents the first soil-associated Sphingomonas strain with the capacity to produce antimicrobials. This work provides first insights into the metabolic potential present in quartzite cave systems pointing out that these environments are a novel and still understudied source of microbial strains with biotechnological potential.