Biofilm formation and motility of Xanthomonas strains with different citrus host range

Xanthomonas citri subsp. citri (Xcc) strain A is the causal agent of citrus bacterial canker (CBC) on most Citrus spp. and close relatives. Two restricted host range strains of CBC, A^w and A*, from Florida and southwest Asia, respectively, infect Mexican lime. Several studies have linked biofilm formation by Xcc to bacterial colonization prior to and after plant ingress, but none have evaluated connections between biofilm formation and the behaviour of different strains of Xcc on citrus hosts and non‐hosts. In this study biofilm formation and swimming motility were evaluated for citrus pathogenic xanthomonads including wide and restricted host range strains of Xcc, X. alfalfae subsp. citrumelonis (Xac) (the causal agent of citrus bacterial spot) and X. campestris pv. campestris (Xc). Differential biofilm formation was observed in vitro and in planta among the Xanthomonas strains assayed. Minimal medium XVM2 increased biofilm formation, especially for those strains with a host range restricted to Mexican lime. In planta, strains produced more biofilm on leaves or fruits of their host than on non‐hosts. Scanning electron microscopy of biofilms on leaf and fruit surfaces revealed differences in structure of bacterial aggregates with respect to the strain's host range. In addition, swimming motility varied widely depending on the host range of the strain. It was concluded that biofilm formation in vitro and in planta for strains of Xcc and Xac was related to their host range, as these processes affect colonization at the early stages of the infection process.