Biomineralization of Cu ₂ S Nanoparticles by Geobacter sulfurreducens

Abstract

Biomineralization of Cu has been shown to control contaminant dynamics and transport in soils. However, very little is known about the role that subsurface microorganisms may play in the biogeochemical cycling of Cu. In this study, we investigate the bioreduction of Cu(II) by the subsurface metal-reducing bacterium, Geobacter sulfurreducens. Rapid removal of Cu from solution was observed in cell suspensions of G. sulfurreducens when supplied with Cu(II), while transmission electron microscopy (TEM) analyses showed the formation of electron dense nanoparticles associated with the cell surface. Energy-dispersive X-ray spectroscopy (EDX) point analysis and EDX spectrum image maps revealed the nanoparticles are rich in both Cu and S. This was confirmed by x-ray absorption near edge structure (XANES) and extended X-Ray absorption fine structure (EXAFS) analyses which identified the nanoparticles as Cu2S. Biomineralization of CuxS nanoparticles in soils has been reported to enhance the colloidal transport of a number of contaminants including Pb, Cd, and Hg. However, formation of these CuxS nanoparticles has only been observed under sulfate-reducing conditions and could not be repeated using isolates of implicated organisms. As G. sulfurreducens is unable to respire sulfate, and no reducible sulfur was supplied to the cells, these data suggest a novel mechanism for the biomineralization of Cu2S under anoxic conditions. The implications of these findings for the biogeochemical cycling of Cu and other metals as well as the green production of Cu catalysts are discussed. Importance Dissimilatory metal-reducing bacteria are ubiquitous in soils and aquifers and are known to utilize a wide range of metals as terminal electron acceptors. These transformations play an important role in the biogeochemical cycling of metals in pristine and contaminated environments and can be harnessed for bioremediation and metal bioprocessing purposes. However, relatively little is known about their interactions with Cu. As a trace element that becomes toxic in excess, Cu can adversely affect soil biota and fertility. In addition, biomineralization of Cu nanoparticles has been reported to enhance mobilization of other toxic metals. Here, we demonstrate that when supplied with acetate under anoxic conditions, the model metal-reducing bacterium, Geobacter sulfurreducens, can transform soluble Cu(II) to Cu2S nanoparticles. This study provides new insights into Cu biomineralization by microorganisms and suggests that contaminant mobilization enhanced by Cu biomineralization could be facilitated by Geobacter species and related organisms.

Global Grassland Diazotrophic Communities Are Structured by Combined Abiotic, Biotic, and Spatial Distance Factors but Resilient to Fertilization

“…In contrast, Geobacter and Skermanella reads were positively correlated with Cu in our study. Previously, a Geobacter species was shown to survive on Cu ( Kimber et al, 2020 ) and, a Skermanella strain resistant to the toxic metalloid antimony was isolated from a coal mine ( Luo et al, 2012 ), suggesting that Cu tolerance is plausible in these groups. Precipitation in the coldest quarter, a water-related factor, determined the relative abundance of Azorhizobium and an unclassified Burkholderia group.…”

Controlling pore-scale processes to tame subsurface biomineralization

“…5 ) produces calcite precipitation under anaerobic conditions only (Cui et al 2015 ). In the presence of dissolved metals, sulfate-reducing bacteria can also precipitate metal sulfides (Fortin et al 1995 ; Kimber et al 2020 ). In soils and aquifers, local redox conditions depend on oxygen diffusion, which is limited by hydration conditions (as oxygen transport is facilitated by the aqueous phase) and by the consumption of oxygen by plant roots and microorganisms.…”

Diversity of Microbial Metal Sulfide Biomineralization

“…Intracellular biomineralization of copper sulfide, in turn, has been recently reported in the culture of the metal‐reducing bacterium Geobacter sulfurreducens [102] . This microorganism is a sulfur‐reducing organism, and does not have genes to exert dissimilatory sulfate reduction for metal sulfide production.…”