Adhesion and Fitness in the Bean Phyllosphere and Transmission to Seed of Xanthomonas fuscans subsp. fuscans

Abstract

Deciphering the mechanisms enabling plant-pathogenic bacteria to disperse, colonize, and survive on their hosts provides the necessary basis to set up new control methods. We evaluated the role of bacterial attachment and biofilm formation in host colonization processes for Xanthomonas fuscans subsp. fuscans on its host. This bacterium is responsible for the common bacterial blight of bean (Phaseolus vulgaris), a seedborne disease. The five adhesin genes (pilA, fhab, xadA1, xadA2, and yapH) identified in X. fuscans subsp. fuscans CFBP4834-R strain were mutated. All mutants were altered in their abilities to adhere to polypropylene or seed. PilA was involved in adhesion and transmission to seed, and mutation of pilA led to lower pathogenicity on bean. YapH was required for adhesion to seed, leaves, and abiotic surfaces but not for in planta transmission to seed or aggressiveness on leaves. Transmission to seed through floral structures did not require any of the known adhesins. Conversely, all mutants tested, except in yapH, were altered in their vascular transmission to seed. In conclusion, we showed that adhesins are implicated in the various processes leading to host phyllosphere colonization and transmission to seed by plant-pathogenic bacteria.

Transmission of Plant-Pathogenic Bacteria by Nonhost Seeds without Induction of an Associated Defense Reaction at Emergence

“…phaseoli var. fuscans and bean take place later on during the colonization of the phyllosphere (11,12), when nutrient availability is limiting for bacterial multiplication. In addition, our present work indicates that in leaves, X. citri pv.…”

“…phaseoli var. fuscans CFBP4834-R produces at least five adhesins, some of which are involved in attachment to seeds (11). E. coli adhesion to bean seeds strikingly contrasts with its high capacities for adhesion to polypropylene.…”

“…campestris (45) Bacterial adhesion to bean seeds. Bacterial adhesion to bean seeds was tested as previously described (11). Briefly, columns were filled with 6 g of bean seeds and fully saturated with 12 ml of the inoculum at 1 ϫ 10 5 CFU ml…”

“…fuscans genome are involved in floral transmission to bean seeds. Conversely, all of them are involved in transmission through the vascular pathway, limiting or enhancing transmission efficiency and associated bacterial population sizes (11).…”

“…Bacterial adhesion under static conditions was quantified by a crystal violet (CV) incorporation assay with 96-well polypropylene microtiter plates (Microwell; Nunc, Denmark) using a method described previously by O'Toole and Kolter (43), modified as described previously by Darsonval et al (11). Three wells per strain were filled with 200 l MME minimal medium [K 2 HPO 4 at 10.5 g liter (2) and inoculated with 1:20 dilutions of the inoculum calibrated at 1 ϫ 10 7 CFU ml Ϫ1 .…”