A deep sleep in coal beds Deep below the ocean floor, microorganisms from forest soils continue to thrive. Inagaki et al. analyzed the microbial communities in several drill cores off the coast of Japan, some sampling more than 2 km below the seafloor (see the Perspective by Huber). Although cell counts decreased with depth, deep coal beds harbored active communities of methanogenic bacteria. These communities were more similar to those found in forest soils than in other deep marine sediments. Science , this issue p. 420 ; see also p. 376

Temporal changes in microbial community structures during methanogenesis were investigated in cultures of South Sumatra Basin (SSB) coalbed methane (CBM) formation water (SSB5) grown on three coals of different rank (Burung sub bituminous Rv 0.39%, Mangus sub bituminous Rv 0.5%, Mangus anthracite Rv 2.2%). Methane production accelerated from day 6, peaked around day 17 and then levelled off around day 20. The initial bacterial community from the SSB formation water was predominantly Acetobacterium, Acidaminobacter, Bacteriodes and Pelobacter species, while the archaeal community consisted of Methanosaeta, Methanosarcina and Methanobacterium members. A general pattern was observed in all cultures with the three coals.Over time the bacterial members decreased in proportion whereas the archaeal component increased. The increase in the proportion of archaeal methanogens corresponded with an increase in methane production yield. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTEnrichment cultures produced similar communities when grown on coals from the same seam (Mangus sub bituminous and Mangus anthracite), rather than from different seams of similar type (Burung sub bituminous and Mangus sub bituminous). Methanosaeta was the dominant methanogen species in the sub bituminous Burung coal culture, but was a lesser proportion in cultures of both Mangus sub bituminous and anthracite coals where Methanosarcina species were a greater proportion. Interestingly, obligate hydrogenotrophic methanogens from the genera of Methanobacterium, which were present at low levels in culture enrichment of all coal substrates, increased in proportion only in the absence of coal in the no-coal control enrichment cultures. These results suggest that the low rank Burung sub bituminous coal favours methane production by the obligate acetoclastic Methanosaeta members while both Mangus coals also favour metabolically versatile Methanosarcina members, and the absence of coal favours hydrogenotrophic methanogens. Despite the similarity of communities grown on coals from the same seam, greater quantities of methane were generated from the lower rank coals when compared to higher rank coals.

No abstract