Nullarbor Cave Slime: Looking at Life in the Dark
Beneath Australia’s large, dry Nullarbor desert lies an extensive underwater cave system, where microbial communities known as ‘slime curtains’ exist in complete darkness. In the absence of photosynthesis and other nutrient inputs from above, these microbial cave communities may derive their energy from the oxidation of inorganic compounds, such as ammonia, sulfate, nitrate and nitrite, which are relatively abundant in cave waters. We have carried out metagenomic sequencing to explore the diversity and metabolic potential of Nullarbor ‘cave slime’ from Weebubbie cave. Of particular interest was the finding that the dominant organism in this community was an archaea related to Nitrosopumilus maritimus. N. maritimus derives energy by oxidising ammonia to nitrite via the enzyme ammonia monooxygenase and is capable of growing at the very low concentrations of ammonia found in the open ocean. Putative ammonia monooxygenase encoding genes were recovered from this environment using metagenomic sequencing and PCR. Other genes involved in biological nitrogen cycling, including archaeal nitrite oxidoreductase were also observed in the metagenome. 16S ribosomal RNA surveys conducted to compare multiple bacterial communities from two cave systems, Warbla and Weebubbie, indicate that communities from different caves are distinct and harbor a wide range of microorganisms. We are presently carrying out Scanning Electron Microscopy and Fluorescence In Situ Hybridization to gain further insight into the structure of this unusual microbial slime community.