A novel iron biomineralization on basaltic rocks from the Challenger Deep, southern Mariana Trench

The habitability of the hadal zone is not well understood and how microbes survive and adapt to this extreme environment is still largely unknown. Here we report the discovery of microbial biofilm that experience extensive Fe-mineralization on the surface of rocks from the Challenger Deep in the southern Mariana Trench. We found microbial biofilms of abundant globules internally permineralized by acicular goethite. The EDS analyses, combined with SEM and TEM, show that the globules are enriched in carbon and phosphorus, potentially indicating their biological origin. Cross sections of globules reveal a bilayer structure consisting of an acicular nano-crystalline core and a colloidal envelope. Vibrational spectroscopy reveals that this colloidal envelope is composed of EPS (extracellular polymeric substances). This mineralization is completely different from Femineralization induced by all other known Fe-oxidizing bacteria, suggesting previously unknown interactions between Fe and microorganisms in hadal settings. Our findings highlight the significance of Fe-mineralization and its contributions to the ecosystem in hadal environments.