Bacteria Affect Rock Weathering
In their effort to derive energy from iron, bacteria may set off a cascade of reactions that reduce rocks to soil and free biologically important minerals. These findings from a team at the Environmental Molecular Sciences Laboratory (EMSL) at Pacific Northwest National Laboratory are based on a model microbial community called the Straub culture, a lithotrophic culture or literally an “eater of rock,” that can turn non-carbon sources such as iron into energy. This energy is produced via a biochemical pathway driven by a series of electron exchanges, which, in the case of the Straub culture, is initiated by taking an electron from, or oxidizing, iron. To gain insight into how lithotrophs behave in the environment, the Straub culture was incubated with media containing fine particles of an iron-rich mica called biotite. After two weeks, Mössbauer spectroscopy was used to compare a biotite control to biotite incubated with the Straub culture to quantify how much iron exists in what oxidation states in the sample. In the biotite, Mössbauer confirmed that the microbes did oxidize iron from Fe(II) to Fe(III). Transmission electron microscopy revealed that this oxidation affected the biotite structure, leading to changes that resemble those observed in nature. This work offers new insight into the roles of microbes in soil production and in the biogeochemical cycling of minerals (e.g., iron oxidation) and suggests that microbes have a direct effect on rock weathering.
Shelobolina, E. S., H. Xu, H. Konishi, R. K. Kukkadapu, T. Wu, M. Blothe, and E. E. Roden. 2012. “Microbial Lithotrophic Oxidation of Structural Fe(II) in Biotite,” Applied and Environmental Microbiology 78(16), 5746–52. DOI: 10.1128/AEM.01034-12.