The Gram-negative plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria strain 85-10 is the causal agent of bacterial spot disease on pepper. This work contributed to the annotation and bioinformatic analysis of the genome sequence of this pathogen. The genome comprises a 5.17 Mb chromosome with a G+C content of 64,75% and four plasmids, 2 kb, 19 kb, 38 kb, and 182 kb in size. The whole genome contains 4726 predicted protein coding sequences. Comparisons with other sequenced xanthomonads revealed a gene order that is similar to the citrus pathogen X. axonopodis pv. citri and X. campestris pv. campestris, which infects Brassicaceae. By contrast, the genome structure of the rice-pathogenic X. oryzae pv. oryzae strains was quite different from the other xanthomonads. Bioinformatic analyses identified a multitude of putative virulence factors in the genome of X. campestris pv. vesicatoria strain 85-10, e.g., all protein secretion systems so far described in Gram-negative bacteria. Among these systems a putative type IV secretion system was identified, which showed the highest similarity to the Icm/Dot system of human-pathogenic Legionella spp. and Coxiella spp.. The type III secretion system (TTSS) is an essential pathogenicity factor of X. campestris pv. vesicatoria. The main function of the TTSS is the translocation of type III effector proteins directly into the plant cell cytosol. In this work, seven type III effectors, designated as Xanthomonas outer proteins (Xops), could be verified, using the effector domain of AvrBs3 (AvrBs3Δ2) as reporter. The effector genes xopC, xopE1, xopE2, xopH, xopI, and xopJ are co-regulated with the TTSS, whereas xopG is constitutively expressed. The genes xopC, xopE2 and xopH are associated with similar putative mobile genetic elements, which are flanked by 62 bp inverted repeats on each side and consist of genes coding for a transposase and cointegrate resolution proteins. The presence of the element is indicative for the acquisition of the effector genes by horizontal gene transfer. Interestingly, the effectors XopE1 and XopE2 possess a putative N-terminal N-myristoylation signal. Confocal laser scanning microscopy analysis of XopE1 and XopE2 GFP fusion proteins showed localization to the plasma membrane of Nicotiana benthamiana cells. |