Contribution of Uncharacterized Target Genes of MxtR/ErdR to Carbon Source Utilization by Pseudomonas putida KT2440

MxtR/ErdR and homologous two-component systems play important roles in the regulatory networks that control cell metabolism and influence bacterial-host interactions. Using the MxtR/ErdR two-component system of the plant growth-promoting soil bacterium Pseudomonas putida KT2440 as a model, this work elucidates the function of previously uncharacterized target genes of MxtR/ErdR and extends the knowledge of the physiological significance of the two-component system. ABSTRACT MxtR/ErdR is a two-component system that has been previously described as a regulator of the utilization of acetate in Vibrio cholerae and in some Pseudomonas species. Regulation is achieved by controlling the expression of the acs gene (acetyl-coenzyme A [CoA] synthetase). However, the physiological significance of other identified target genes is not fully understood. Here, we investigated the role of pp_0154 (scpC) and pp_0354/pp_0353 in the soil bacterium Pseudomonas putida KT2440. To this end, the genes were individually deleted and complemented in trans. Then, the growth of the resulting strains on different carbon sources was analyzed. To obtain information on protein function, a bioinformatic analysis was performed, and ScpC was purified and characterized in vitro. Our results indicated that scpC is important for P. putida KT2440 to cope with high concentrations of acetate. The encoded enzyme catalyzes the transfer of coenzyme A between acetate and succinate. On the contrary, pp_0353 and pp_0354 proved to be unimportant for the growth of the strain on acetate under our conditions. Extending the phenotypic analysis to other carbon sources led to the discovery that mxtR, erdR, and pp_0353 are important for the utilization of pyruvate as a carbon source. Taken together, the findings of this study expand the knowledge about the role of the MxtR/ErdR two-component system in carbon source utilization and about the specific functions of its target genes. IMPORTANCE MxtR/ErdR and homologous two-component systems play important roles in the regulatory networks that control cell metabolism and influence bacterial-host interactions. Using the MxtR/ErdR two-component system of the plant growth-promoting soil bacterium Pseudomonas putida KT2440 as a model, this work elucidates the function of previously uncharacterized target genes of MxtR/ErdR and extends the knowledge of the physiological significance of the two-component system. Our results suggest that the target gene scpC encodes an acetate:succinate CoA transferase that is involved in the detoxification of acetate when it is present in large amounts. Furthermore, it is shown that MxtR/ErdR controls the metabolism of not only acetate but also pyruvate. This control involves the target gene pp_0353 (putative exonuclease). These findings may facilitate the optimization of P. putida KT2440 as a chassis for biotechnological applications and may contribute to a better understanding of the regulatory network of pathogens like Pseudomonas aeruginosa.