Transformation of natural organic matter (NOM) is central to carbon and energy fluxes in the environment; however, little is known about the interplay between NOM and it’s turnover by microbial communities. Microbial activity changes NOM structure and properties, which influences further bioavailability of NOM, which in turn affects microbial community structure and function. We investigated the interactions between water soluble NOM and native microbial communities present in groundwater of Oak Ridge Field Research Center, TN.
Water-soluble NOM was extracted from sediment close to the groundwater well. The total organic carbon and inorganic carbon in these sediment samples were 0.071% and 0.011%, respectively. Water extracted 3.2% of the total organic carbon and 1.6% of the total inorganic carbon. The extracted NOM was then provided as the sole substrate to microbial inoculum from groundwater suspended in minimal nutrient media. Subsamples were harvested several times from these incubations during a 50-day study. 16S rRNA gene amplicon sequencing and Geochip were used to identify the changes of microbial communities and expression of functional genes during transformation of the NOM. Several advanced chemical techniques including FTICR-MS and NEXAFS were used to characterize the C pool (i.e., NOM metabolites and microbial byproducts) at several stages of transformation during the study. Our data clearly shows that microbial community responded to NOM, and shifted as different functional groups in NOM were transformed. Further detailed metabolite and gene-based analysis to elucidate these changes is currently being conducted.