Genetic redundancy of catechol 1,2-dioxygenase conferred the ability of Rhodococcus opacus PD630 for efficient catecholic compounds degradation

Lignin, a bountiful natural resource, presents challenges in degradation and conversion due to its complex structure. Microorganisms have evolved a “biofunnel” pathway in nature that offers novel insights into lignin valorization. Among the key intermediates in lignin metabolism is catechol, predominantly metabolized by catechol 1,2-dioxygenase (CatA) in these organisms. Understanding the catechol degradation mechanism is pivotal for efficient lignin utilization. Rhodococcus opacus PD630 emerges as a promising host for lignin bioconversion, yet the gene redundancy of catechol 1,2-dioxygenase genes (catA) in this strain is not well understood, hindering a comprehensive grasp of its aromatic compound degradation pathway. This study explores the regulatory mechanisms governing the expression of catA gene duplicates, LPD06568 (catA1) and LPD06742 (catA2), in R. opacus PD630. We compared the functions of the enzymes they encode and discovered that catA2 is responsible for the degradation of excess extracellular catechol in R. opacus PD630. More interestingly, our results also showed that both of the CatAs of R. opacus PD630 could catalyze various catecholic compounds, including those with large side chain groups. Furthermore, catA1 was heterologously expressed in Streptomyces coelicolor M145 and achieved a marked cis, cis-muconic acid production (1.97 g/L) from catechol.