The Nif3-Family Protein YqfO03 from Pseudomonas syringae MB03 Has Multiple Nematicidal Activities against Caenorhabditis elegans and Meloidogyne incognita

The nematicidal activity of the common plant-pathogenic bacterium Pseudomonas syringae against certain nematodes has been recently identified, but little is known about its virulence factors. In the current study, predictive analysis of nematode-virulent factors in the genome of a P. syringae wild-type strain MB03 revealed a variety of factors with the potential to be pathogenic against nematodes. One of these virulence factors that was predicted with a high score, namely, YqfO03, was a protein with structural domains that are similar to the Nif3 superfamily. This protein was expressed and purified in Escherichia coli, and was investigated for nematicidal properties against the model nematode Caenorhabditis elegans and an agriculturally important pest Meloidogyne incognita. Our results showed that YqfO03 exhibits lethal activity toward C. elegans and M. incognita worms, and it also caused detrimental effects on the growth, brood size, and motility of C. elegans worms. However, C. elegans worms were able to defend themselves against YqfO03 via a physical defense response by avoiding contact with the protein. Discovery of the diverse nematicidal activities of YqfO03 provides new knowledge on the biological function of a bacterial Nif3-family protein and insight into the potential of this protein as a specific means of controlling agricultural nematode pests.