Method for Assessing Mineral Composition-Dependent Patterns in Microbial Diversity Using Magnetic and Density Separation

Abstract

This study introduces a new method for characterizing mineral-associated microbial diversity in sedimentary environments, a habitat that has been intrinsically challenging to study in regard to microbe-mineral interactions. Mineral components were enriched from bulk environmental samples by magnetic susceptibility or density separation techniques and used in subsequent molecular and microscopic analyses. Testing and optimization of the method was performed on geochemically-distinct sediment horizons from Eel River Basin methane seeps and pyrite and sphalerite-rich hydrothermal vent samples from the Lau Basin. Initial results show reproducible variations in microbial diversity between mineral fractions from marine sedimentary environments enriched in authigenic pyrite and/or transition metal-bearing clay minerals. Specifically, different archaeal clades associated with the anaerobic oxidation of methane and putative sulfate-reducing deltaproteobbacteria show preferential colonization patterns, suggesting potential ecophysiological differences between closely-related taxa. These results indicate that mineral colonization may influence the extent and distribution of microbial diversity throughout unconsolidated sediments of the marine subsurface. The combination of mineral separation and molecular analyses introduced here provide a new approach for revealing previously concealed patterns of mineral-associated microbial diversity across a wide range of environments, from hard rock habitats to fine-grained lithologies.