Xanthoferrin, the α‐hydroxycarboxylate‐type siderophore of Xanthomonas campestris pv. campestris, is required for optimum virulence and growth inside cabbage

Summary Xanthomonas campestris pv. campestris causes black rot, a serious disease of crucifers. Xanthomonads encodes a siderophore biosynthesis and uptake gene cluster xss (Xanthomonas siderophore synthesis) involved in production of a vibrioferrin type of siderophore. However, little is known about the role of siderophore in iron uptake and virulence of X. campestris pv. campestris. In this study, we show that X. campestris pv. campestris produces an α-hydroxy carboxylate type of siderophore (named xanthoferrin), which is required for growth under low-iron condition and optimum virulence. A mutation in the siderophore synthesis xssA gene causes deficiency in siderophore production and growth under low-iron conditions. In contrast, the siderophore utilization ΔxsuA mutant was able to produce siderophore but exhibited a defect to utilize siderophore-iron complex. Our radiolabelled iron uptake studies confirmed that the ΔxssA and ΔxsuA mutants exhibited defects in ferric iron uptake. The ΔxssA mutant was able to utilize and transport exogenous xanthoferrin-Fe3+ complex, in contrast, the siderophore utilization or uptake mutant ΔxsuA exhibited defects in siderophore uptake. Expression analysis of xss operon using a chromosomal gusA fusion indicates that the xss operon is expressed during in planta growth and under low-iron conditions. Furthermore, exogenous iron supplementation in the cabbage leaves rescued the in planta growth deficiency of ΔxssA and ΔxsuA mutants. Our study reveals that the siderophore xanthoferrin is an important virulence factor of X. campestris pv. campestris which promote in planta growth by sequestering ferric iron. This article is protected by copyright. All rights reserved.