The high-value utilization of agricultural by-products is of great significance for the development of sustainable materials. HadACd and PhaC1Pa93 are key enzymes in the biosynthesis of polyhydroxyalkanoates (PHA), but their mechanisms have not been fully elucidated. In this study, engineered Escherichia coli strains co-expressing hadACd and phaC1Pa93, or its mutant phaC1Pa93(STQK), were cultivated using hydrolysates derived from edible fungi residues and other agricultural by-products as carbon sources. The PHA synthesis capability and substrate adaptability of these strains were systematically analyzed. Results showed that strains harboring hadACd and phaC1Pa93 efficiently synthesized PHB from (R)-3HB, 4HBZ, HPBA, and (R)-MA, while strains expressing phaC1Pa93(STQK) produced PHBV when 4HBZ and HPBA were used as substrates. Mechanistic studies indicated that HadACd converted endogenous or exogenous 3HB from the E. coli sugar metabolism pathway into 3HB-CoA, which was subsequently polymerized into PHA by PhaC1Pa93, thereby simplifying the biosynthetic pathway for biodegradable PHA. Co-expression of hadACd and phaC1Pa93(STQK) not only broadened the substrate spectrum but also significantly enhanced PHA yield. This study lays a foundation for the design of novel PHA biosynthetic pathways and demonstrates the great potential of agricultural by-products as sustainable and low-cost feedstocks for the production of biodegradable PHA.
