Characterization of the two type II secretion systems in Xanthomonas axonopodis pv. citri and their role in pathogenicity, enzyme secretion, and biofilm formation

RAFAEL A HOMMEM; FLORENCIA MALAMUD; JULIANA BAPTISTA; ADRIAN A VOJNOV; MARCOS A MACHADO; ALEXANDRE M DO AMARAL

Gothenburg, Suecia

Congreso; FEMS, federation of european microbiological society; 2009

Citrus canker is a major threat to the citrus industry worldwide, especially where the citrus product plays an important role in employment and revenue, like Brazil and the United States. In the genome of the citrus canker causal agent, the bacterium Xanthomonas axonopodis pv. citri, two operons (xpsEFGHIJKLMND and xcsCDEFGHIJKLMN) that encompass 11 and 12 different proteins, respectively, for type two secretion systems (TIISS) were identified. However, the interaction between those systems, if any, is poorly understood. Objectives:In this study, the function of the operons and their activity during interaction with the plant host were analyzed. Methods:X. axonopodis TIISS mutants were analyzed in citrus leaves inoculation assays and colonization monitored by confocal laser microscopy of autofluorescent proteins.  Results:The analyses revealed that the bacterium uses both TIISS, with the xps operon highly active during contact with the leaf tissue. The TIISS operons were found to differentially degrade starch, carboxymethylcellulose, and proteins. Bacterial organization (biofilm formation) is influenced by both TIISS. Conclusions:These results provide the first clear evidence of the independent influence of both TIISS in the pathogenic process of X. axonopodis pv. citri. Here, we report what we believe is the first broad, simultaneous description of two TIISS present in a plant pathogenic bacterium.