Competitive Metabolism of Terephthalic Acid by a Consortium of Native and Engineered Bacteria

Microbial metabolism of polyethylene terephthalate (PET) monomers provides a basis for biological mitigation of PET waste. Recent studies have shown that both certain native microorganisms and engineered counterparts can metabolize terephthalic acid (TPA), a primary monomer of PET, raising the question of how their coculture shapes individual population structure and total TPA degradation. Here, we investigated the coculture dynamics of an engineered degrader (Pseudomonas putida strain Pp-TE) and a native degrader (Rhodococcus sp. strain RDK17) in the presence of TPA as the sole carbon and energy source. We observed that while both strains were able to utilize TPA at comparable rates in monocultures, Pp-TE consistently outcompeted RDK17 in batch and multitransfer coculture fermentations, even when RDK17 was inoculated at a significantly higher initial abundance. Subsequent assays revealed that the dominance of Pp-TE was primarily conferred by its type VI secretion system, which impaired the growth of RDK17 via contact-dependent inhibition, but was also shaped partially by the relative growth kinetics of the two species. Furthermore, antibiotic selection experiments demonstrated that chloramphenicol reinforces the dominance of Pp-TE, whereas gentamicin allowed RDK17 to prevail when it harbored a resistance marker. Meanwhile, when TPA metabolism was abolished in Pp-TE, it lost its dominance to RDK17. Together, these findings demonstrate that exploitative competition in TPA metabolism and interference competition through contact-dependent inhibition jointly determine the population dynamics and overall TPA degradation of the synthetic consortium. This study also highlights the importance of careful design of interspecies interaction and metabolic capability in ecosystem-based metabolic engineering.