Exploring the Microbial Ecology of Inferno Crater Lake, Waimangu Geothermal Valley, New Zealand; a Culture Independent Approach.

Abstract

Geothermal environments harbour communities of bacteria and archaea that are uniquely adapted to temperature and acidity ranges beyond those considered hospitable to other forms of life. The ecology of these extremophile microbial communities has previously been investigated for numerous reasons including bioprospecting for thermostable proteins, determining the physiological limits of life, and investigating potential sites of early biotic evolution. The microbial diversity of alkaline-neutral geothermal springs has been well studied but there is a paucity of studies focusing on acidic geothermal springs. Acidic geothermal studies, to date, have mostly used outdated and biased techniques that provide a limited representation of the true diversity of these systems. Furthermore, the field of microbial ecology is now shifting focus from site-specific descriptions of microbial diversity to the application of macro-ecological concepts that might explain how microbial communities assemble in space and over time. Inferno Crater Lake, within the Waimangu Geothermal Valley in New Zealand, is an ideal system in which to observe microbial community dynamics in an acidic environment, due to its unique monthly thermal cycle between 30oC and 80oC. This thesis presents the first investigation into the microbial ecology of this acid-sulphate spring, and how it responds to recurrent thermal perturbation over time, using next-generation sequencing and quantitative PCR methods. Quantitative PCR targeting 16S rRNA genes was used to measure the relative abundances of archaea and bacteria, with an aim to test the culture-based hypothesis that archaea have a higher temperature tolerance than bacteria, in acidic conditions. This was confirmed by a recurrent turnover between archaeal and bacterial abundances concurrent with the thermal cycle, with archaea dominating at high temperature stages. 454 pyrosequencing of amplified 16S rRNA genes was used to identify the taxa present in the Inferno Crater Lake microbial community at different temperature stages across two consecutive thermal cycles, with an aim to explore whether changes in the community were correlated with physicochemical variations. The hypothesis that acidic geothermal waters are dominated by chemotrophic microbes, due to the high availability of inorganic energy substrates, was confirmed by the high number of sequence reads assigned to sulphur- and hydrogen-oxidising taxa. Multivariate statistical methods further confirmed that changes in microbial community structure were highly correlated with temperature and sulphur based geochemistry. The results of this study confirm that the microbial ecology of Inferno Crater Lake is highly dynamic in response to cyclical temperature perturbation, and these dynamic changes correlate well with physicochemical change. The research described here adds significantly to our understanding of this highly unique geothermal system, and expands on a limited knowledge base of acidophiles in hot springs, both in New Zealand and worldwide.