Xanthan is not essential for pathogenicity in citrus canker but contributes to Xanthomonas epiphytic survival.

Arch Microbiol

Molecular Biology Division, IBR (Instituto de Biología Molecular y Celular de Rosario), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Argentina.

Published: August 2007

AI Article Synopsis

  • Researchers created xanthan-deficient mutants of the bacterium Xanthomonas axonopodis pv. citri, which causes citrus canker, by modifying the GumD glycosyltransferase gene.
  • The mutants, despite lacking xanthan production, were still able to infect citrus plants similarly to the wild-type bacteria, showing no significant differences in disease symptoms or bacteria growth within the plants.
  • Although the mutants had normal growth in various stress conditions, they struggled with oxidative stress during stationary phase and had reduced survival on citrus leaves, indicating that xanthan may enhance bacterial colonization efficiency on the host plant.

Article Abstract

Xanthan-deficient mutants of Xanthomonas axonopodis pv. citri, the bacterium responsible for citrus canker, were generated by deletion and marker exchange of the region encoding the carboxy-terminal end of the first glycosyltransferase, GumD. Mutants of gumD did not produce xanthan and remained pathogenic in citrus plants to the same extent as wild-type bacteria. The kinetics of appearance of initial symptoms, areas of plant material affected, and growth of bacteria inside plant tissue throughout the disease process were similar for both wild-type and mutant inoculations. Moreover, exopolysaccharide deficiency did not impair the ability of the bacteria to induce hypersensitive response on non-host plants. Apart from variations in phenotypic aspects, no differences in growth or survival under different stress conditions were observed between the xanthan-deficient mutant and wild-type bacteria. However, gumD mutants displayed impaired survival under oxidative stress during stationary phase as well as impaired epiphytic survival on citrus leaves. Our results suggest that xanthan does not play an essential role in citrus canker at the initial stages of infection or in the incompatible interactions between X. axonopodis pv. citri and non-host plants, but facilitates the maintenance of bacteria on the host plant, possibly improving the efficiency of colonization of distant tissue.

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Source
http://dx.doi.org/10.1007/s00203-007-0227-8DOI Listing

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