Substrate determines a relay-type electron transfer metabolic pathway to effectively drive low-carbon mixed culture PHA production

The anoxic-famine mode can reduce the aeration energy consumption involved in mixed-culture PHA production, which was believed to better achieve the coupling of PHA recovery with wastewater treatment and reduced carbon emission. PHA-producers could form different metabolic pathways for using different substrate which will affect the process performance. This study was the first to analyze the effects and mechanisms of acetic acid (R1) and propionic acid (R2) on the operation of anoxic-famine PHA system. In the 329 days of operation, the Y_P/S and nitrate removal efficiency of R2 during anoxic-famine phase, which were 0.74 mg COD/mg COD and 80 %, respectively, both exceed those of R1. The enriched PHA-producer in R2 utilized a relay-type electron transfer metabolic pattern to supply sufficient electrons for cytoplasmic and periplasmic denitrification enzymes, thereby maintaining diverse denitrification enzyme activities during the famine phase. Compared to R1, this metabolic pattern induces a more thorough consumption of PHA in R2 during the anoxic-famine period. This helps R2 to synthesize PHA more efficiently during the feast period, promoting stronger environmental selective pressure and maintaining the stability of the PHA-producing microbial community. The study developed the optimal substrate strategy for anoxic-famine mode, providing technical support for efficient recovery of PHA from wastewater and denitrification coupling, which can be referenced by the construction of energy and resource-based wastewater treatment plants.