PLFA FROM MICROBIAL COMMUNITIES ASSOCIATED WITH FRACTURE WATERS WITHIN THE PRECAMBRIAN DEEP SUBSURFACE

The deep terrestrial subsurface is known to harbor microbial life at depths of up to several kilometers where, in some cases, organisms live independently from the photosphere and atmosphere. Ancient fracture fluids trapped within the crystalline basement of the Canadian Precambrian Shield have been shown to be preserved on geologic timescales (millions to billions of years). To characterize the PLFA from microbial communities associated with the fracture fluids from Kidd Creek Mine, in Timmins, Ontario, large volumes of water from two boreholes, 12261 and 12299, were passively filtered for 6-12 months to collect microbial biomass.

Membrane component phospholipid fatty acids (PLFA) representative of viable microbial cells were extracted and analyzed by gas chromatography – mass spectroscopy (GC – MS) and gas chromatography-isotope ratio mass spectroscopy (GC-IRMS). Abundant PLFA were present in all samples, indicating the presence of extant microbial communities. The geochemistry of the porewaters from each borehole were similar and are thought to be sourced from the same fracture system. However, while PLFA distributions were identical between replicates of each borehole, they were distinct between boreholes suggesting differences in the microbial communities detected. Individual PLFA biomarkers indicated the presence of sulphate-reducing bacteria associated with 12261, consistent with recent MPN results for this borehole, but this marker was absent from 12299. Carbon isotope analysis of lipids for 12261 shows heavier δ¹³C values for all PLFA, which was not observed for 12299, indicating the utilization of different metabolic pathways. Currently it is not known whether this difference is representative of microbial communities living within the fracture system, or a result of differential growth of communities within the filters over their deployment. Molecular genetic analysis is ongoing and will provide additional complementary insight into the community composition. Understanding the structure and function of microbial communities associated with fracture waters in Precambrian rock environments has the potential to provide new insights into the capabilities, limits and evolution of life.