MICROBIAL INFLUENCE ON ELEMENTAL SULFUR PRODUCTION AND CONSUMPTION IN A SULFIDIC CAVE SYSTEM

The Frasassi cave system (Italy) hosts microbial biofilms that thrive with little to no oxygen, no sunlight, and high levels of hydrogen sulfide. Sulfur-oxidizing bacteria are abundant in this ecosystem, and their metabolically generated sulfuric acid contributes to cave formation through carbonate dissolution. Elemental sulfur (S⁰), a poorly understood intermediate in sulfur oxidation, accumulates in biofilms with unknown production and consumption rates, possibly affecting cave formation. In order to investigate the microbial contributions to elemental sulfur production, biofilm samples were collected in situ. Community metagenome analysis revealed abundant sequences from the understudied group Epsilonproteobacteria. To understand the metabolic functions of these microbes, isolation and culturing experiments were conducted. Epsilonproteobacteria could not be isolated under oxic conditions, but successfully grew under anoxic conditions with nitrate and hydrogen. 16s rRNA gene sequencing confirmed two strains of Epsilonproteobacteria with close relatives to Sulfuricurvum kujiense and Sulfurospirillum, forming Frasassi-specific clades within these genera. Metagenomic sequencing and isolation experiments are ongoing in an attempt to understand each strain’s contribution to S⁰production, sulfuric acid production, and carbonate dissolution. Microbial influence on cave formation has relevance not only for our own subsurface, but also for the prospects of subsurface life beyond Earth.