Biogenic Cyanide Production Promotes Dissolution of Gold Nanoparticles in Soil

Area of Science:

• Environmental Science
• Nanotechnology
• Microbiology

Background:

• Gold nanoparticles (Au NPs) are frequently used to study nanomaterial behavior in natural environments.
• Au NPs are generally considered inert, but gold can be oxidized and dissolved by cyanide, a common environmental compound.

Purpose of the Study:

• To investigate the role of quorum-sensing-regulated cyanide production by soil bacteria in the dissolution of Au NPs.
• To determine the conditions under which biologically enhanced metal dissolution occurs in soil environments.

Main Methods:

• Incubation of Au NPs in soil inoculated with Chromobacterium violaceum at different pH levels.
• Comparison of Au NP dissolution in soils with and without bacterial inoculation (abiotic controls).
• Utilizing quorum-sensing-deficient mutants (CV026) and varying cell densities to confirm the role of quorum sensing and biogenic cyanide.

Main Results:

• Significant oxidative dissolution of Au NPs (up to 15% at pH 7.0 and 29% at pH 7.5) was observed in soil with C. violaceum after 7 days.
• No observable dissolution of Au NPs occurred in abiotic soil.
• Au NP dissolution was directly linked to quorum-sensing-regulated cyanide production, confirmed by experiments with mutants and varying bacterial concentrations.

Conclusions:

• Biologically produced cyanide from soil bacteria can lead to significant oxidative dissolution of Au NPs.
• Quorum sensing plays a critical role in regulating the cyanide production responsible for Au NP dissolution.
• These findings highlight the importance of microbial activity in the geochemical transformation of nanoparticles in soil, even for materials considered inert in abiotic conditions.