Patterns of Microbial Colonization on Silicates

By Jennifer Roberts Rogers, Philip C. Bennett, and Franz K. Hiebert

ABSTRACT

Several factors influence the attachment of microorganisms to mineral surfaces, such as surface charge, solution and mineral composition, and the types of organisms present in the ground water. In dilute groundwater systems inorganic nutrients can represent limiting components for growth of subsurface microorganisms and in these systems mineral composition may be an important factor in microbial colonization. In this study we examined microbial colonization of silicate minerals in situ using field microcosms, as well as in controlled laboratory microcosms. We found that in the petroleum-contaminated aquifer near Bemidji, MN where P is scarce, feldspars that contain inclusions of P-minerals such as apatite are preferentially colonized over similar feldspars without P. A microcline from S. Dakota, for example, which contains 1220 ppm P, was heavily colonized and deeply weathered after one year, while a similar microcline without detectable P was barren of attached organisms and completely unweathered. Anorthoclase (1050 ppm P) was very heavily colonized and weathered, whereas plagioclase specimens (<50 ppm) were uncolonized and unweathered. However, compositional differences in a limiting nutrient may not be the only controlling factor. In a stressed environment such as the aquifer near Bemidji, toxic elements may also influence colonization. Using silicate glasses, one with 4500 ppm Al and the other with 450 ppm Al, we found that Al appeared to be a deterrent to surface colonization, nor was olivine, with~3000 ppm Ni, colonized. Quartz however was sparsely colonized and is most likely the result of no positive or negative compositional effects. Quartz with an iron hydroxide coating was heavily colonized with microorganisms remaining even after the iron was utilized. We propose that colonization in this system is particularly sensitive to the availability of P, and the native subsurface microorganisms tend to colonize and weather silicates, which contain apatite. Colonization may also be increased when more than one scarce nutrient is present. The result of this interaction is that nutrient-bearing silicates will be colonized, and preferentially destroyed, as the subsurface microbial community scavenges a limiting nutrient, while colonization of non-nutrient bearing minerals are colonized based on surface charge and toxic elements effects.