B-273. Functional Characterization and Role in Pathogenesis of the Oligopeptide Uptake (Opp) System among Xanthomonas Species

E. E. Oshiro1, N. P. Taschner1, C. F. Suzuki1, D. C. Pimenta2, J. C. F. Oliveira3, M. I. T. Ferro3, L. C. S. Ferreira1, R. C. C. Ferreira1;
1Univ. of Sao Paulo, Sao Paulo, BRAZIL, 2Inst. Butantan, Sao Paulo, BRAZIL, 3Univ. Federal de São Paulo, Sao Paulo, BRAZIL.

Genome sequencing projects have highlighted the diversity and functional roles of ABC transporters involved in the uptake of nutrients in different bacterial species. The Xanthomonas genus encompasses a ubiquitous group of plant pathogens including species of major economic interest such as those infecting rice, beans, orange, grape and soy. In the present report we investigated the occurence of the oligopeptide uptake system (Opp) among different Xanthomonas species and its role in the pathogenesis of X. axonopodis pv. Citri (Xac), the etiological agent of citrus canker. Screening of 9 different Xanthomonas species by southern and immuno blot analysis revealed that only two Xac strains (306 and 381) carried the the oppA gene and expressed the OppA protein, the soluble periplasmic nutrient-binding component of the system. Construction of a precise Xac oppA knockout mutant showed that uptake of a tetrapeptide (YPLG) was not impaired in the mutant strain when compared to the parental 306 strain. Moreover, induction of necrotic lessions in leaves of a sensitive citrus host (Citrus sinensis) clearly showed that deletion of the oppA gene did not affect pathogenesis. Similarly, the in vivo growth kinetics in host tissues was not reduced in the oppA mutant strain. The present results indicate that the Opp system has a restricted occurence among Xanthomonas species. Furthermore, the Opp system is apparently not functional in Xac, the only species in which the uptake system has been detected. Taken together these results suggest a recent evolutionary origin of the opp genes in the Xanthomonas genus and strongly suggest that alternative oligopeptide transport systems are present in these bacteria