Kerogen-rich rocks influence growth and composition of an anaerobic microbial community.

Kerogen, insoluble macromolecular organic matter in sedimentary rocks, is the most abundant form of organic carbon on Earth and plays a role in deep biosphere processes. It is classified into four types (I–IV) based on origin and chemical composition, yet its influence on microbial communities and carbon cycling remains poorly understood. In this study, we examined how kerogen-rich shales and coals, each containing a distinct kerogen type, shape anaerobic microbial community development and activity. CFU counts showed that kerogen types I and II did not significantly alter overall microbial abundance, while type III-rich rocks inhibited growth, and type IV-rich rocks enhanced it. 16S rRNA gene sequencing revealed that type II-rich rocks selectively enriched for Burkholderiaceae, whereas type IV-rich rocks promoted the proliferation of Cellulomonadaceae and Pleomorphomonadaceae. Gas chromatography showed that CO2 production occurred only in the presence of type II-rich rocks, likely driven by Burkholderiaceae activity. These findings suggest that kerogen structure and geochemical properties drive microbial community assembly and organic matter mobilization in the deep subsurface. Beyond Earth, kerogen type IV-like material is widespread in extraterrestrial environments. Our results indicate the enhancement of the habitability of these environments, offering new insights into the potential for life.