Nematicidal effects of 2-methyl-aconitate isomerase from the phytopathogen Pseudomonas syringae MB03 on the model nematode Caenorhabditis elegans.

The pathogenicity of a common phytopathogenic bacterium, Pseudomonas syringae, against animal model hosts, such as mice and Caenorhabditis elegans, has been recently revealed. However, most of the virulence determinants associated with pathogenesis remain elusive. In the current study, we performed predictive analysis of virulence factors against C. elegans in the genome of the wild-type P. syringae strain MB03. Nine predicted nematicidal proteins were expressed and purified in recombinant Escherichia coli strains and were evaluated to define their toxicity against C. elegans in liquid killing assays. Next, we focused on one essential 2-methyl citrate cycle protein, PrpF03, which showed the highest lethal activity against C. elegans compared to the other tested proteins with a half lethal concentration (LC) of 155.3 (123.4-176.6) µg mL and a half lethal time (LT) of 3.72 (1.64-4.85) days. Purified PrpF03 also caused adverse effects on the brood size, growth, and motility of C. elegans. Moreover, the PrpF03 protein exhibited pathological activity towards the intestinal tract of C. elegans. We surmise that the PrpF03 protein functions as a virulence factor when it blocks the average circulation of the 2-methyl citrate cycle of C. elegans by accumulating 2-methyl citrate in the gut of C. elegans, which damages and restrains the growth of intestinal tissues that ultimately kill C. elegans. The discovery of specific nematicidal activities of PrpF03 provides a better understanding of the mechanisms of phytopathogenic P. syringae against nematodes and could aid in developing nematode pest-controlling agents in agriculture.