pH Influences the Distribution of Microbial Rock-Weathering Phenotypes in Weathered Shale Environments

Microbial rock weathering of shale forms an important part of global biogeochemical cycling and soil formation. Culture-independent analyses have revealed diverse microbial communities in weathered shale environments, yet few studies have attempted to discern the functional ecology of such communities in relation to their rock weathering capabilities. In this study, phenotypic plate assays were used to determine the abundance of microbes with different rock weathering phenotypic traits in weathered shale environments. A physicochemical parameter (pH) is shown to influence the abundance of aerobic rock weathering microbes in weathered shale. Iron and manganese oxidizers were restricted to acidic environments while siderophore producing and alkaline phosphatase producing microbes were largely confined to pH neutral environments. Furthermore, a clear separation in the spatial distribution of aerobic-iron oxidizing and siderophore-producing microbes, as defined by a pH gradient across the sites sampled, was demonstrated. Phylogenetic analysis of isolates revealed that siderophore-producing and alkaline phosphatase producing bacteria belonged to commonly identified rock weathering genera including Arthrobacter, Pseudomonas, and Streptomyces. These results enhance our understanding of how physicochemical parameters can define the composition and rock weathering potential of microbial communities.