Microbial synergy between Rhodospirillum rubrum and Acetobacterium woodii enables anaerobic CO conversion to polyhydroxyalkanoates.

The high cost of traditional substrates has hindered the large-scale adoption of polyhydroxyalkanoates (PHAs) as sustainable alternatives to petrochemical plastics. One-carbon (C1) substrates like carbon monoxide (CO) offer a low-cost, sustainable feedstock, but efficient biocatalytic systems for their conversion to PHAs have been lacking. Here, we report the first successful anaerobic production of PHAs from CO using a synthetic co-culture of Rhodospirillum rubrum and Acetobacterium woodii. In this system, R. rubrum catalyzes the water-gas shift reaction, converting CO into H₂ and CO₂. A. woodii subsequently transforms these products into acetate, serving as an organic carbon source for PHA accumulation by R. rubrum. Neither organism, in monoculture, was able to grow on CO alone, underscoring the importance of the microbial synergy. While continuous cultivation in chemostats proved unstable, fed-batch cultivation achieved a PHA production rate of 58 ± 11 mg L_medium ^-1 day^-1 with a final PHA content of 38 ± 5% (dry weight). This study introduces a pioneering anaerobic route for PHA synthesis from CO, representing a significant advance toward sustainable PHA production from C1 substrates.