Engineering Shewanella-reduced graphene oxide aerogel biohybrid to efficiently synthesize Au nanoparticles.

• eCell-rGA biohybrid was constructed by integrating Au³⁺ adsorption and reduction. • eCell-rGA synthesized AuNPs (7.62 ± 2.82 nm) from 60 ppm of Au³⁺ solution. • AuNPs size was regulated via engineering eCell's extracellular electron transfer. • The required Au³⁺ ions concentration is reduced by one or two orders of magnitude. Biosynthesizing Au nanoparticles (AuNPs) from gold-bearing scraps provides a sustainable method to meet the urgent demand for AuNPs. However, it remains challenging to efficiently biosynthesize AuNPs of which the diameter is less than 10 nm from a trace amount of Au³⁺ concentration at the level of tens ppm. Here, we constructed an exoelectrogenic cell (eCell)-conductive reduced-graphene-oxide aerogel (rGA) biohybrid by assembling Shewanella sp. S1 (SS1) as living biocatalyst and rGA as conductive adsorbent, in which Au³⁺ at trace concentrations would be enriched by the adsorption of rGA and reduced to AuNPs through the extracellular electron transfer (EET) of SS1. To regulate the size of the synthesized AuNPs to 10 nm, the strain SS1 was engineered to enhance its EET, resulting in strain RS2 (pYYD-P tac - ribADEHC & pHG13-P bad - omcC in SS1). Strain RS2 was further assembled with rGA to construct the RS2-rGA biohybrid, which could synthesize AuNPs with the size of 7.62 ± 2.82 nm from 60 ppm Au³⁺ solution. The eCell-rGA biohybrid integrated Au³⁺ adsorption and reduction, which enabled AuNPs biosynthesis from a trace amount of Au³⁺. Thus, the required Au³⁺ ions concentration was reduced by one or two orders of magnitude compared with conventional methods of AuNPs biosynthesis. Our work developed an AuNPs size regulation technology via engineering eCell's EET with synthetic biology methods, providing a feasible approach to synthesize AuNPs with controllable size from trace level of gold ions. [Display omitted] [ABSTRACT FROM AUTHOR]