Stephanie Napieralski, University of Wisconsin-Madison, Madison, WI, USA, and colleagues have crushed drill cores from a quartz and diorite dominated rock bedrock in Puerto Rico and cultivated them in the dark for almost two and a half years. In parallel, samples of the same material were sterilized and kept under the same conditions. At the end of this period, Napieralski and her colleagues carried out chemical and physical analyses of the material.
In the unsterilized sample, many rock particles showed visible scoring and notching, indicating that mineral content had been released. At the same time, the analyses showed that the microbes present in the rock had multiplied and produced the high-energy molecule ATP. Because the samples contained only rock without any organic material, the bacteria must have fed on a purely inorganic diet.
The microbes had oxidized the iron contained in the quartz diorite and thus received the energy for their survival. They produce a protein that enables the iron oxidation without the bacteria having to take up the metal into their cells. The cells come into electrical contact with the minerals.
The stone eaters are mainly from the group of Betaproteobacteria. This is a group of bacteria from which some microbes with the ability to oxidize metal were known before.
According to the researchers, these results refute the assumption that microbes only become active for soil formation after chemical and physical weathering. Instead, chemolithotrophic Fe(II)-oxidizing bacteria also contribute to the decomposition of the rock into mineral trace substances. This discovery opens a completely new view of the oxidative weathering of iron-bearing silicate rock.
- Microbial chemolithotrophy mediates oxidative weathering of granitic bedrock,
Stephanie A. Napieralski, Heather L. Buss, Susan L. Brantley, Seungyeol Lee, Huifang Xu, Eric E. Roden,
Proceedings of the National Academy 2019.