Biological role of xanthomonadin pigments in Xanthomonas campestris pv. campestris

Previous studies have indicated that the yellow pigments (xanthomonadins) p roduced by phytopathogenic Xanthomonas bacteria are unimportant during path ogenesis but may be important for protection against photobiological damage . We used a Xanthomonas campestris pv, campestris parent strain, single-sit e transposon insertion mutant strains, and chromosomally restored mutant st rains to define the biological role of xanthomonadins, Although xanthomonad in mutant strains were comparable to the parent strain for survival when ex posed to UV light; after their exposure to the photosensitizer toluidine bl ue and visible light, survival was greatly reduced. Chromosomally restored mutant strains were completely restored for survival in these conditions. L ikewise, epiphytic survival of a xanthomonadin mutant strain was greatly re duced in conditions of high light intensity, whereas a chromosomally restor ed mutant strain was comparable to the parent strain for epiphytic survival . These results are discussed with respect to previous results, and a model for epiphytic survival of X, campestris pv, campestris is presented.