Nanomineral-fueled chemolithoautotrophy leads to substantial mercury emission

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ABSTRACT 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 (HgSNP) are internalized into bacterial cells through an adenosine triphosphate (ATP)-independent, highly energy-efficient process. This enhanced internalization leads to rapid metabolism of HgSNP 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.

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