Modified Monosaccharides Content of Xanthan Gum Impairs Citrus Canker Disease by Affecting the Epiphytic Lifestyle of subsp. .

subsp. () is a plant pathogenic bacterium causing citrus canker disease. The gene encodes a phosphoglucomutase/phosphomannomutase protein that is a key enzyme required for the synthesis of lipopolysaccharides and exopolysaccharides in Xanthomonads. In this work, firstly we isolated a transposon mutant (::Tn5) and analyzed its phenotypes as biofilm formation, xanthan gum production, and pathogenesis on the sweet orange host. Moreover, to confirm the role in the impaired phenotypes we further produced a non-polar deletion mutant (Δ) and performed the complementation of both mutants. In addition, we analyzed the percentages of the xanthan gum monosaccharides produced by wild-type and mutant. The mutant strain had higher ratios of mannose, galactose, and xylose and lower ratios of rhamnose, glucuronic acid, and glucose than the wild-type strain. Such changes in the saccharide composition led to the reduction of xanthan yield in the deficient strain, affecting also other important features in , such as biofilm formation and sliding motility. Moreover, we showed that ::Tn5 caused no symptoms on host leaves after spraying, a method that mimetics the natural infection condition. These results suggest that plays an important role in the epiphytical stage on the leaves that is essential for the successful interaction with the host, including adaptive advantage for bacterial survival and host invasion, which culminates in pathogenicity.