Microbial diversity and geochemical energy sources of Tutum Bay, Ambitle Island, Papua New Guinea, an arsenic-rich, shallow-sea hydrothermal system

I investigate the hydrothermal system located in Tutum Bay, Ambitle Island, Papua New Guinea, a shallow-sea system ∼5--10 meters below sea level that is arsenic-rich. Hydrothermal vents in the bay expel fluids with arsenite (AsIII) concentrations as high as 950 mug/L. To determine the role that Tutum Bay microorganisms might play in mediating As-redox reactions, three approaches were used: analyzing the geochemical environment for energy sources, characterizing the archaeal community composition of the sediments, and conducting culture-dependent As-cycling experiments. The second chapter of this dissertation discusses an energetic study of potential chemolithotrophic metabolic reactions, including As-redox reactions. Results show that under the environmental conditions present in Tutum Bay, significant amounts of energy for microbial metabolism could be gained from a number of reactions, including AsIII oxidizing reactions using oxygen and nitrate as terminal electron acceptors. In the third chapter, a 16S rRNA-based culture-independent investigation of the archaeal community structure of the As-rich sediments shows the presence of diverse uncultured archaea at sites both near and far from hydrothermal venting. The studies in these two chapters demonstrate that the Tutum Bay hydrothermal system provides an environment hospitable to metabolically and phylogenetically diverse microorganisms. Finally, in chapter four, evidence of functional genes related to both arsenate- and arsenite-redox were recovered from sediments examined via molecular screening. It was also shown that microbial consortia enriched from Tutum Bay sediments and porefluids were able to reduce arsenate (AsV) to arsenite when incubated at 30°C in an AsV-rich growth medium. These results demonstrate that As-redox microorganisms exist in shallow-sea hydrothermal environments and broaden our understanding of not only the types of microbial species that are capable of As-redox, but also the unique environmental niches in which life can exist and thrive.