Electro-driven microbial conversion of waste carbon sources to polyhydroxyalkanoates: pathways, mechanisms, and...

Polyhydroxyalkanoates (PHA) are fully biodegradable polymers with potential to replace fossil-based plastics. While bioelectrochemical systems (BES)-driven PHA (BES-PHA) have emerged recently for valorizing waste carbon substrates, a massive productivity gap still exists between current BES-PHA prototypes and mature conventional fermentation systems, hindering industrial viability. Although reported electro-driven strategies can enhance PHA content by 18-30% compared to open-circuit conditions and increase yield by up to 4.2-fold over unmodified cathodes, unstable microbial performance, unclear redox response mechanisms, and limited electron transfer efficiency at the electro-microbial interface remain critical bottlenecks. This review systematically summarizes recent advances in electro-driven PHA synthesis and proposes methods for optimizing the performance of PHA-producing bacteria under this system. Three core effects are identified: external electron-induced redox ratio and nicotinamide adenine dinucleotide (phosphate) (reduced form) regeneration; electron-driven carbon flux redistribution and precursor generation; and activity regulation and expression response of key PHA synthetic enzymes. Through mechanistic analysis, promising enhancement strategies are summarized, including electroresponsive metabolic engineering, redox homeostasis regulation, and decoupling of synthetic modules. Finally, three-tier coupled model integrating energy input, electron flux allocation, and carbon flux utilization efficiency to explain PHA synthesis behavior under different bioelectrochemical system configurations, providing a theoretical framework for system scaling and performance prediction. This review aims to provide a systematic cognitive foundation and quantifiable regulatory reference for studying the mechanisms and industrialization pathways of electro-driven microbial PHA production.