Quantitative FluorescenceIn SituHybridization Analysis of Microbial Consortia from a Biogenic Gas Field in Alaska's Cook Inlet Basin
ABSTRACTFilter-collected production water samples from a methane-rich gas field in the Cook Inlet basin of Alaska were investigated using whole-cell rRNA-targeted fluorescencein situhybridization (FISH) and 16S rRNA tag pyrosequencing. Both techniques were consistent in determining the microbial community composition, including the archaeal or bacterial dominance of samples. The archaeal community is dominated by the obligate methylotrophic methanogen genusMethanolobusas well as the nutritional generalist methanogen genusMethanosarcina, which is capable of utilizing acetate, CO2, and methyl-bearing compounds. The most-abundant bacterial groups areFirmicutes, notably of theAcetobacteriumgenus, andCytophaga-Flexibacter-Bacteroidesspecies (CFBs) affiliated with the orderBacteroidales. We observed spatial variation among samples in both the percentage of members ofArchaeacompared to that of members ofBacteriaand the dominant members of the bacterial community, differences which could not be explained with the available geochemical data. Based upon the microbial community composition and the isotopic signature of methane associated with the Cook Inlet basin site, we propose a simplified reaction network beginning with the breakdown of coal macromolecules, followed by fermentation and methylotrophic and acetoclastic methane production.