Baseline characterization of aerobic hydrocarbon degrading microbial communities in deep-sea sediments of the Great Australian Bight, Australia.

Exploratory drilling for deep-sea oil and gas resources is planned for the Great Australian Bight (GAB). There is scant knowledge of the region's benthic ecosystems and no baseline information of the region's indigenous oil degrading bacteria. To address this knowledge gap, we used next generation sequencing (NGS) of three marker genes (alkB, c23o and pmoA) to detect and characterize the microbial communities capable of aerobic hydrocarbon degradation. Unique, highly novel microbial communities capable of degrading hydrocarbons occur in surface sediments at depths between 200 and 2800 m. Clustering at 97% demonstrated differences in community structure with depth, changing most markedly between 400 and 1000 m depth on the continental slope, and identified putative functional 'ecotypes' related to depth. Observed differences in community structure showed strong correlations with temperature, other physicochemical properties of the overlying water column and are further modulated by differences in sediment grain size. This study provides important baseline data on hydrocarbon degrading microbial communities prior to the start of petroleum resource extraction. Our data will inform future ecological monitoring of the GAB deep-sea ecosystem.