Abstract
Microorganisms have long been recognized for their capacity to catalyze the weathering of silicate minerals. While the vast majority of studies on microbially mediated silicate weathering focus on organotrophic metabolism linked to nutrient acquisition, it has been recently demonstrated that chemolithotrophic ferrous iron [Fe(II)] oxidizing bacteria (FeOB) are capable of coupling the oxidation of silicate mineral Fe(II) to metabolic energy generation and cellular growth. In natural systems, complex microbial consortia with diverse metabolic capabilities can exist and interact to influence the biogeochemical cycling of essential elements, including iron. Here we combine microbiological and metagenomic analyses to investigate the potential interactions among metabolically diverse microorganisms in the near surface weathering of an outcrop of the Rio Blanco Quartz Diorite (DIO) in the Luquillo Mountains of Puerto Rico. Laboratory based incubations utilizing ground DIO as metabolic energy source for chemolithotrophic FeOB confirmed the ability of FeOB to grow via the oxidation of silicate-bound Fe(II). Dramatically accelerated rates of Fe(II)-oxidation were associated with an enrichment in microorganisms with the genetic capacity for iron oxidizing extracellular electron transfer (EET) pathways. Microbially oxidized DIO displayed an enhanced susceptibility to the weathering activity of organotrophic microorganisms compared to unoxidized mineral suspensions. Our results suggest that chemolithotrophic and organotrophic microorganisms are likely to coexist and contribute synergistically to the overall weathering of the in situ bedrock outcrop.
Highlights
The weathering of Earth’s continental crust involves a complex set of physical, geochemical, and biological reactions
As microorganisms are ubiquitous in soils and sedimentary environments, often preferentially associated with mineral surfaces (Hazen et al, 1991) they have vast potential to enhance mineral weathering impacting the cycling of bioessential elements between the lithosphere and the biosphere
By combining microbiological and metagenomic based approaches, Napieralski et al (2019) demonstrated that Fe(II)-oxidizing bacteria (FeOB) can dramatically accelerate the oxidation of silicate mineral bound Fe(II) via extracellular electron transfer (EET) coupled to cellular growth, and that the subsequent oxidative weathering of the minerals biotite and hornblende within granitic rocks resulted in subtle changes to the surface structure that rendered the mineral more susceptible to proton promoted dissolution via dilute acid
Summary
The weathering of Earth’s continental crust involves a complex set of physical, geochemical, and biological reactions. The Weathering Microbiome acids (Drever and Stillings, 1997; Uroz et al, 2009) as well as siderophores (Kalinowski et al, 2000; Liermann et al, 2000; Buss et al, 2007) have been extensively invoked when relating microbial activity to mineral weathering Redox active elements, such as Fe, are often present in igneous rocks. By combining microbiological and metagenomic based approaches, Napieralski et al (2019) demonstrated that FeOB can dramatically accelerate the oxidation of silicate mineral bound Fe(II) via extracellular electron transfer (EET) coupled to cellular growth, and that the subsequent oxidative weathering of the minerals biotite and hornblende within granitic rocks resulted in subtle changes to the surface structure that rendered the mineral more susceptible to proton promoted dissolution via dilute acid. The redox driven mineralogical transformations associated with FeOB activity should affect the efficiency at which organotrophic microorganisms are able to solubilize cations for nutritional purposes
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