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The aim of this study was to understand the microbial communities of deep terrestrial subsurface environments associated with high-organic-matter coal and lignite bearing strata. A sedimentary sequence from the Waikato Basin, New Zealand consisting of interbedded organic-rich layers, sandstones, siltstones and mudstones was drilled. Viable microbial communities were enumerated using most probable number (MPN) series with media selective for a) general heterotrophs b) sulfate-reducing bacteria c) iron(III)- and manganese(IV)-reducing bacteria d) acetogens e) methanogens and f) lignite-reducing bacteria. Subcultures were made from positive MPN enrichment cultures and representative strains were isolated from the sediments. Selected isolates were tested for their metabolic capabilities and physiological characteristics and Molecular genetic techniques were used to investigate the microbial diversity. Viable counts for active metabolic groups ranged from 104 to 105 cells gsed"1 and representatives from 5 bacterial phyla (Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes and Acidobacterid) were detected. Community size and diversity did not decrease with depth and viable microbes were present in deeply buried and previously heated and possibly sterilised sediments. A large and diverse set of isolates was obtained from the sediments. The collection included several genera previously detected in the deep terrestrial biosphere (Acetobacterium, Sporotalea, Microbacterium, Acidovorax, Sphingomonas) and also genera not typically associated with the deep biosphere (sulfurospirilium). Isolates had a wide range of metabolic capabilities and the collection includes both fermentative and respiring strains. There was also a good overlap between organisms detected using molecular genetic methods and cultivated organisms indicating that these may be important bacteria in situ. There is a substantial and diverse community of Bacteria inhabiting the sediments of the Waikato Basin. Although Archaea were detected in the sediments, none were isolated. The presence of these microbial communities implies that carbon and energy sources must persist within these sediments over millions of years. |
