Ecological roles of subsurface microbial taxa from Eastern Australian coal seams

Microbial communities in subsurface coal seams use fossilised organic matter as a key carbon source. Microbes have been introduced to these environments through either the influx of meteoric water or through movement of microbe-containing water from other aquifers via faulting or similar geological processes. These microbial communities are capable of catabolising complex recalcitrant organic matter derived from coal and converting it into simpler and more biologically accessible forms, namely biogenic methane gas which is both a valuable energy source and a potential environmental hazard (as a greenhouse gas). As a fuel source it has significant advantages over mined coal in that it has reduced environmental and human health impacts and, unlike coal, is a dispatchable source of energy. Despite the economic and environmental importance of biogenic methane, there is a dearth of knowledge associated with the ecological roles that microbial taxa play deep in coal seam environments. The current body of work aimed to improve our understanding of functional roles of microbes in the catabolism of coal to methane through various approaches and techniques. In summary, data in this thesis reveals for the first time that the adherence of microbes to the coal surface is a non-random process in some coals. Further, data generated here provide a new ecological model for which taxa may be involved in coal degradation in eastern Australian settings, providing a list of new taxa that require further investigation to determine their involvement in early coal degradation. Finally, this thesis used targeted strategies to culture, ‘sulfur-active’ taxa from the coal seams. These approaches resulted in the first enrichment culture of the most abundant and ubiquitous taxon from eastern Australian coal seams (Desulfuromonas sp. ‘CSMB_57’) and facilitated the further culturing of Desulfovibrio sp. ‘CSMB_222’. Genomics based analyses of these taxa revealed their possible roles in the coal seam environment which needs to be further explored, namely co-culturing with methanogens and acetogens to investigate any potential syntrophic relationships.