Studying Differences in Pdu Microcompartment Expression in the Context of pdu Gene System Cloning/Transfer and PocR Activity

Metabolism of 1,2-propanediol (1,2-PD) in Salmonella enterica occurs via the activity of microcompartment (MCP) proteins encoded by the pdu gene system. In this report, we observed that Salmonella Typhimurium appears to display greater 1,2-PD metabolism compared to S. Arizonae and S. Enteritidis. We were interested in whether species/strain differences in 1,2-PD metabolism are also seen in respective pdu clones, as this could have implications for downstream studies and applications with these systems. We therefore cloned the 38-kb pdu/cob/cbi regions from S. Arizonae, S. Enteritidis, and other S. Typhimurium strains as part of a first-of-kind comprehensive comparison. Remarkably, we found no differences in expression of the various cloned pdu systems. However, we observed that the S. Arizonae and S. Enteritidis clones appear to display a greater dependence on the Crp regulator as compared to the S. Typhimurium clone, and this dependence could be alleviated by overexpressing the PocR regulator. We found that lack of functional expression in Pseudomonas putida could be alleviated via PocR overexpression, demonstrating that the roadblock is at the transcriptional level. In Pectobacterium carotovorum, substitution of the native pdu promoter with a strong heterologous promoter allowed expression. A reporter assay system showed that S. Typhimurium PocR displayed higher transcriptional activation compared to S. Arizonae and S. Enteritidis PocR. Overall, this work demonstrates the central importance of the PocR regulator/transcriptional level of pdu expression and provides strategies to overcome pdu expression issues in other bacterial hosts.