Small but Mighty: The Surprising Metabolic Range of a Bacterial Microcompartment

Bacterial microcompartments (BMCs) are protein-based metabolic modules increasingly investigated as potential intracellular nanoreactors. In this study, we engineered Escherichia coli by chromosomally integrating the propanediol utilization (pdu) operon from Citrobacter freundii and evaluated the metabolic versatility of the heterologously produced Pdu BMCs. The formation of well-assembled, operational Pdu BMCs was confirmed in cellula. Oxygen was found to inhibit 1,2-propanediol utilization, an effect alleviated under microaerobic conditions. The engineered E. coli strain assimilated a range of diols and triols, demonstrating that Pdu BMCs process both their native substrate and glycerol and linear diols up to 1,2-butanediol (C4). This substrate promiscuity was exploited to produce high value-added compounds and revealed previously unrecognized potential for plastic upcycling through ethylene glycol metabolism. In keeping with molecular dynamics simulations indicating that the Pdu BMC shell does not impose significant diffusion barriers for longer chain diols and triols, the range of amenable substrates was successfully extended to 1,2-pentanediol (C5) by mutating the diol dehydratase large subunit (PduC). Together, these findings establish heterologous Pdu BMCs as promiscuous and genetically tunable metabolic modules in E. coli, highlighting their potential as scalable platforms for synthetic biology and biotechnological applications.