MINERALOGIC CONTROL ON ABUNDANCE AND DIVERSITY OF SURFACE-ADHERENT MICROBIAL COMMUNITIES

In the subsurface microorganisms inhabit rock and mineral surfaces, potentially benefiting from attachment by accessing sorbed nutrients or by eluding predation. While attachment behavior of microbial communities has been studied in field and laboratory settings, it is still unknown how mineral composition impacts abundance and diversity of the attached microbial community. In this study, we investigated the role of P and Fe within minerals in defining microbial abundance and diversity in carbon-rich groundwater. Field colonization experiments of sterile mineral surfaces were combined with community structure characterization of the attached microbial population. Minerals containing varying concentrations of P and Fe were incubated in three different microbially-active zones within a petroleum-contaminated aquifer for 14 months. Upon retrieval the microbial community structure and biomass on minerals were analyzed using phospholipid fatty acid analysis (PLFA). Total lipid biomass determinations of the minerals demonstrated distinct trends depending on the environment of incubation. In the carbon-rich, aerobic groundwater attached biomass did not correlate to mineralogy. However, in the methanogenic groundwater, biomass was most abundant on the P-containing minerals. Similarly, in the Fe-reducing groundwater a distinct correlation between Fe-content and biomass was observed. Biomass measurements were equivalent for goethite [FeO(OH)], and a feldspar containing far less Fe (4.4 wt% Fe2O3) that occur as discrete oxide inclusions. Using PLFA characterization and identification of specific biomarkers for the dissimilatory Fe-reducing bacteria, Geobacter sp. was identified as the dominant organism attached to the Fe-containing minerals in the Fe-reducing environment. Our results demonstrate that the trace nutrient content of minerals affects both the abundance and diversity of surface-adherent microbial communities. This behavior may be a means to access limiting nutrients from the mineral, creating a niche for a particular microbial population. The implication is that microbial ecology, and, by extension, groundwater geochemistry can be significantly influenced by the aquifer mineralogy.