Characterization of a periplasmic peptidyl-prolyl cis-trans isomerase in Erwinia chrysanthemi.

The main determinant of the plant pathogen Erwinia chrysanthemi virulence is the production of extracellular enzymes, mainly pectate lyases. Adjacent to a pectate lyase encoding locus, we identified the gene rotA supposed to encode a folding catalyst. Overproduction of the protein and assay of activity using a synthetic substrate, confirmed that rotA encodes a periplasmic peptidyl-prolyl cis-trans isomerase. rotA disruption provokes no change in cell morphology, cell viability, growth rate or stability of the extracellular and periplasmic proteins. In addition, this mutation does not alter the activity of the pectate lyases, their stability in the periplasm during the transitory step of secretion or their recognition by the Out secretory system. rotA expression was followed using a rotA::uidA transcriptional fusion. Some environmental conditions, such as temperature variations and nitrogen starvation, modulate rotA expression. In contrast to the E. coli rotA gene, the E. chrysanthemi rotA possesses only one promoter and is not controlled by the CRP global regulator.