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

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.

Identification and characterization of biofilm formation-defective mutants of Xanthomonas citri subsp. citri

“…Three of them are defective in xanthan production (gumB, gumD and galU), reinforcing the importance of the EPS in biofilm formation (Rigano et al, 2007;Dunger et al, 2007;Guo et al, 2010). These facts contribute to validating the approach used here.…”

Systems and synthetic biology perspective of the versatile plant-pathogenic and polysaccharide-producing bacterium Xanthomonas campestris

“…Xanthan pyruvylation is essential for the virulence of Xcc [58]. Xanthan is not essential for the infection of citrus plants but it contributes to the epiphytic survival of the pathogen [59]. Xanthan secreted by Xcc suppresses the deposition of callose, a plant polysaccharide, and induces susceptibility to pathogenesis [60].…”

Genómica comparativa de cepas de Xanthomonas arboricola asociada a Prunus spp.: caracterización de los procesos de infección de la mancha bacteriana de frutales de hueso y almendro

“…Los residuos de manosa están acetilados y piruvilados en sitios específicos (Figura 1) (Dunger et al, 2007;Hamman, 2010). La síntesis, la polimerización y la secreción de este polisacárido extracelular se lleva a cabo mediante un operón conformado por 12 genes denominados genes gum (gumB-gumM), los cuales están altamente conservados entre las diferentes especies del género (Dunger et al, 2007).…”

“…La síntesis, la polimerización y la secreción de este polisacárido extracelular se lleva a cabo mediante un operón conformado por 12 genes denominados genes gum (gumB-gumM), los cuales están altamente conservados entre las diferentes especies del género (Dunger et al, 2007). Además, al igual que todas las bacterias Gram negativas contienen como parte de su membrana externa una capa de lipopolisacáridos, compuestos de un lípido A y un núcleo de polisacáridos que contiene en su extremo unidades de antígeno O (Hori & Matsumoto, 2010).…”