Nanomineral-fueled chemolithoautotrophy leads to substantial mercury emission

Elemental mercury (Hg⁰) is a pervasive pollutant of global concern. Recent research shows that global Hg⁰ emissions are significantly underestimated, but the additional sources contributing to this gap are unclear. Here, we demonstrate that chemolithoautotrophic microorganisms, such as sulfur-oxidizing and iron-oxidizing bacteria that are ubiquitous in diverse environments, utilize mercury sulfide (HgS) nanoparticles to support growth while releasing substantial amounts of Hg⁰. Unlike dissolved Hg(II) species, HgS nanoparticles (HgS_NP) are internalized into bacterial cells through an adenosine triphosphate (ATP)-independent, highly energy-efficient process. This enhanced internalization leads to rapid metabolism of HgS_NP via sulfur-oxidation, as well as the subsequent reduction of the released Hg(II) to Hg⁰ mediated by the mer operon, superoxide or cytochrome c. Our modeling results show that the annual emission flux of Hg⁰ from this previously unrecognized source can reach 272.44 ± 134.99 tonnes, equivalent to that of geogenic Hg⁰ emissions and matching that of the fourth largest anthropogenic source, cement production.