0149-0451 /01 $12.00 +.00 Silicates, Silicate Weathering, and Microbial Ecology

Mineralogy, microbial ecology, and mineral weathering in the subsurface are an inti-mately linked biogeochemical system. Although bacteria have been implicated indirectly in the accelerated weathering of minerals, it is not clear if this interaction is simply the coincidental result of microbial metabolism, or if it represents a speci c strategy of-fering the colonizing bacteria a competitive ecological advantage. Our studies provide evidence that silicate weathering by bacteria is sometimes driven by the nutrient re-quirements of the microbial consortium, and therefore depends on the trace nutrient content of each aquifer mineral. This occurrence was observed in reducing groundwa-ters where carbon is abundant but phosphate is scarce; here, even resistant feldspars are weathered rapidly. This suggests that the progression of mineral weathering may be in uenced by a mineral’s nutritional potential, with microorganisms destroying only bene cial minerals. The rock record, therefore, may contain a remnant mineralogy that re ects earlymicrobial destruction of biologically valuableminerals, leaving a residuum of “useless”minerals, where “value ” depends on the organism, its metabolic needs, and the diagenetic environment. Conversely, the subsurface distribution of microorganisms may, in part, be controlled by the mineralogy and by the ability of an organism to take advantage of mineral-bound nutrients. Keywords microbial geochemistry, phosphate, silicate weathering Interest in the microbial ecology of subsurface environments has grown tremendously in the past 10 years, and viable microorganisms have been recovered from a wide range o