Analysis of pathogenicity mutants of a bacteriocin producing Xanthomonas perforans

Since the initial discovery of Xanthomonas perforans on tomato in 1991, it has completely displaced Xanthomonas euvesicatoria as the bacterial spot of tomato pathogen in Florida. Previous research has shown that X. perforans produces at least three different bacteriocin-like compounds (BcnA, BcnB, BcnC) antagonistic toward X. euvesicatoria strains. In this study pathogenicity-attenuated, bacteriocin-producing mutants of X. perforans were created to determine their potential as biological control agents for control of X. euvesicatoria. Several candidate genes were chosen based on previous studies in which mutant phenotypes exhibited reduced virulence in either X. perforans (OpgH_Xcv) or the closely related X. euvesicatoria strain 85-10 (hpaB, hpaC, xopA, xopD, avrBs2 and gumD). Each candidate gene in X. perforans was amplified and PCR-assisted deletion mutagenesis was performed in the wild-type (wt) X. perforans strain to create potential attenuation mutants. Each mutant was tested for growth rate, disease severity and antagonism toward X. euvesicatoria strains. Three mutants, XopA, opgH, and gumD were significantly less pathogenic than the wild-type strain with the opgH mutant reaching significantly lower internal populations than all other mutants except hpaC. The opgH-strain was the most affected in its ability to grow internally in plant tissue while inhibiting X. euvesicatoria populations equal to or more than the other mutant strains. This mutant strain could potentially be used as part of an effective biological control strategy.