Bacterial biofilms on gold grains—implications for geomicrobial transformations of gold

Abstract

The biogeochemical cycling of gold (Au), i.e. its solubilization, transport and re-precipitation, leading to the (trans)formation of Au grains and nuggets has been demonstrated under a range of environmental conditions. Biogenic (trans)formations of Au grains are driven by (geo)biochemical processes mediated by distinct biofilm consortia living on these grains. This review summarizes the current knowledge concerning the composition and functional capabilities of Au-grain communities, and identifies contributions of key-species involved in Au-cycling. To date, community data are available from grains collected at 10 sites in Australia, New Zealand and South America. The majority of detected operational taxonomic units detected belong to the α-, β- and γ-Proteobacteria and the Actinobacteria. A range of organisms appears to contribute predominantly to biofilm establishment and nutrient cycling, some affect the mobilization of Au via excretion of Au-complexing ligands, e.g. organic acids, thiosulfate and cyanide, while a range of resident Proteobacteria, especially Cupriavidus metallidurans and Delftia acidovorans, have developed Au-specific biochemical responses to deal with Au-toxicity and reductively precipitate mobile Au-complexes. This leads to the biomineralization of secondary Au and drives the environmental cycle of Au.

Comparative Insights Into the Complete Genome Sequence of Highly Metal Resistant Cupriavidus metallidurans Strain BS1 Isolated From a Gold–Copper Mine

“…The Czc determinant mediating resistance to Co, Zn, and Cd is encoded on pMOL30 in C. metallidurans CH34 (Getaneh and Alemayehu, 2006;Rea et al, 2016) starting from MgtC until CzcP from (Rmet_5985 -Rmet_5970). Duplication of this czcNICBADRSJE_czcP cluster in BS1 was shown to have led to one copy being present on chromid and pBS1, respectively, and generated by mobile elements as shown in Figure 7.…”

“…The environmental impacts of mining range from ecosystems destruction with accompanying loss of bio-diversity resources to the accumulation of heavy metals and other pollutants (Mergeay et al, 2003). Gold-rich environments, such as gold mining sites, weathering Au deposits, auriferous soils and sediments embody highly toxic mobile Au-complexes as well as a challenging assortment of transition metals (Mergeay et al, 2003;Rea et al, 2016;Wiesemann et al, 2017).…”

Editorial for Special Issue “Geomicrobiology and Biogeochemistry of Precious Metals”

“…The advent of suitable biomolecular tools in the 2000s combined with high-resolution micro-analytical techniques revealed that microbial biofilms play a critical role in gold and platinum mobility as well as placer particle transformation. The fundamental processes driving the cycling of these elements is now better understood than ever before [7][8][9]. This current issue builds upon previous research in precious metals by bringing together recent studies in the areas of geomicrobiology and biogeochemistry.…”

Reflecting on Gold Geomicrobiology Research: Thoughts and Considerations for Future Endeavors

“…A better understanding of Au-biogeochemical-cycling has been attained through a range of studies looking at the structure and chemistry of placer Au particles. Studies that have observed microbes on the surface of placer Au particles, as well as the detection of microbial communities, have provided additional insight into the biogeochemical cycling of Au [17,[61][62][63][64][65][66][67]. Gold derived from a primary source, (e.g., hydrothermal or epithermal, Au-rich porphyry or Au-rich-porphyry-Cu deposits) often occurs as an alloy with varying amounts of silver (Ag).…”

“…Additionally, secondary Au structures can be physically altered during mechanical re-shaping, which suggests a balance between (bio)geochemical and mechanical weathering processes. Therefore, secondary Au structures are relicts-physical evidence of past, biogeochemical processes that have transformed particle surfaces and have attributed, in part, to the activity of microbes [61,66,67,77,81], as shown in Figure 3. Interestingly, Au particles that exhibited a greater extent of transformation also contained biofilms with a more-specialized, metal-tolerant, microbial community [61,67].…”