Author name: Miguel Iniesto

This chapter describes the biological composition of modern microbialites, aiming at identifying the major microbial actors that may contribute to their mineralization and growth. Despite the vast diversity in community composition, environmental conditions, and dominant mineral phases, certain key components emerge as critical drivers of these processes. Additionally, the dominance of specific microbial populations can serve as a proxy for identifying key metabolisms involved in mineralization, such as oxygenic and anoxygenic photosynthesis, sulfate reduction, and methanogenesis. Finally, we discuss how these insights enhance our understanding of ancient microbialites, bridging the gap between modern observations and the geological record.