Proteomic and functional analyses of a novel porin-like protein in Xanthomonas oryzae pv. oryzae

Proteomic analysis is a useful technique for postulating and elucidating protein functions. In the present work, a shotgun proteomic analysis was used to identify functions of the PXO_03968 gene (previously known as the ax21) from Xanthomonas oryzae pv. oryzae (Xoo), a causal agent for bacterial blight disease in rice. Structural prediction performed on the protein sequence encoded by PXO_03968 reveals that it encodes a putative porin-like protein, possessing a β-barrel domain with 10 β-strands and a signal peptide at the N-terminus. We renamed the gene as an omp1X (outer membrane protein 1 in Xoo), generated its knock out mutant (XooΔomp1X), and compared the protein expression level in the mutant to that in the wild type. A total of 106 proteins displayed more than 1.5-fold difference in expression between the mutant and the wild type strains. COG analysis revealed that these proteins are involved in cell motility as well as signal transduction. In addition, phenotypic analysis demonstrated that motility and biofilm formation in XooΔomp1X are lower than the wild type. These results provide new insights into the functions of outer membrane proteins in Gram-negative bacteria.