Solar-driven PHB synthesis from wastewater by engineered semiconductor-bacteria biohybrids

Semiconductor biohybrid systems leverage microbial enzymatic precision and semiconductor light harvesting for efficient solar-to-chemical conversion, offering sustainable alternatives to energy-intensive production. To overcome challenges associated with the synthesis of ecofriendly nanoparticles (NPs), we utilized wastewater pollutants to produce semiconductor biohybrids. We engineered sulfate-reducing bacteria [rSRB-polyhydroxybutyrate (PHB)] for the self-assembly of extracellular polymeric substance (EPS)-complexed NPs through microbial S^2--metal bonding. These semiconductor biohybrids drive sulfate reduction using photogenerated electrons, while simultaneously degrading pollutants through hole-mediated oxidation, thus establishing a self-reinforcing cycle that enhances PHB synthesis. Photoelectrons fuel the acetogenic Wood-Ljungdahl pathway (WLP) through c-type cytochromes, enabling solar-driven CO₂ fixation for acetyl-CoA and NADPH regeneration. Coupled photoredox reactions channel carbon flux into PHB biosynthesis, achieving a yield of 15.38 g/l. In addition, photoelectrons upregulate sulfate metabolism genes, stabilizing metal sulfide production. Thus, this system achieves solar-driven CO₂ reduction coupled with organic conversion into chemicals in wastewater bioreactors, providing a sustainable route for pollutant removal and carbon mitigation, advancing low-carbon wastewater treatment and a circular bioeconomy.