Nutrient Silicates

Nutrient-Driven Colonization and Weathering of Silicates

ROGERS, J.R., BENNETT, P.C., HIEBERT, F.K., and CHOI, W.J.Department of Geological Sciences, The University of Texas at Austin, Austin, TX, 78712

The dynamics of microbial attachment to mineral surfaces is a complex combination of surface charge, solution and mineral composition, and the types of organisms present in the ground water. Another potential influence is the presence of limiting inorganic nutrients in the mineralogy of the aquifer, or conversely the presence of toxic metals. In this study we examined microbial colonization and weathering of silicate minerals using in situ field microcosms and controlled laboratory microcosms, as a function of mineral composition. We found that in environments where P is scarce, feldspars that contain micro-inclusions of P-minerals such as apatite are preferentially colonized over similar feldspars without P. Further, we found that colonization of mineral surfaces directly correlates to the degree of mineral weathering and weathering is only found near attached organisms. This suggests that colonizing organisms produce a reactive microenvironment at the mineral surface altering the mineral-water equilibria at that surface. Degradation of substrate in laboratory microcosms containing P-silicates was substantially faster than in those containing non P-silicates, suggesting that P released from silicates influences metabolism of the microbial community. We propose that colonization behavior can be influenced by the availability of P, and that native subsurface microorganisms preferentially colonize and weather silicates, which contain apatite. The implications of this interaction is that nutrient-bearing silicates will be colonized, and destroyed, while non P bearing silicates are uncolonized and unweathered. The dissolution of P-bearing silicates releases P to the colonizing organisms, offering them a competitive advantage over planktonic organisms or those colonizing non P-bearing silicates.