Microbial carbon cycling in oligotrophic regional aquifers near the Tono Uranium Mine, Japan as inferred from C and C values of phospholipid fatty acids and carbon sources

Mills, C.*; Amano, Yuki   ; Slater, G.*; Dias, R.*; Iwatsuki, Teruki  ; Mandernack, K.*

The natural abundance delta C and C values of microbial membrane phospholipid fatty acids (PLFAs) were measured and used to assess the carbon sources of bacteria in sedimentary and granitic groundwaters sampled from three boreholes in the vicinity of the Tono Uranium Mine, Gifu, Japan. The most abundant PLFA structures in all waters sampled were heterotrophic bacteria. A PLFA biomarker for type II methanotrophs in sedimentary and granitic waters, sampled from the KNA-6 borehole. The delta C values determined for type II methanotroph PLFAs in the groundwaters were very similar to the delta C values of dissolved inorganic carbon in each water. This suggests that type II methanotrophs ultimately derive all their carbon from inorganic carbon, whether directly from DIC and/or from CH produced by the reduction of DIC. In contrast, C values of type II PLFAs in the groundwaters indicate that these organisms use different carbon assimilation schemes in each environment despite very similar delta C values for each water. Ancient delta C values of some PLFAs suggest that many heterotrophs utilize ancient organic matter, perhaps from lignite seams within the sedimentary rocks.