Changes in the composition of xanthan affect its structure and its role as virulence factor of Xanthomonas campestris

BIANCO, MI; TOUM, L; YARYURA, PM; MIELNICHUK, N ; ROESCHLIN, R; MARANO, MR; VOJNOV, AA

Congreso; 11th International Congress of Plant Molecular Biology; 2015

Xanthan is an important virulence factorof Xanthomonas that could be used astarget in the development of control biotechnological strategies against thesebacteria. Xanthan is composed by pentasaccharidic repetitive units substitutedwith acetyl and/or pyruvate groups. Our goal is to determine which component ofthe xanthan molecule is key for its function as virulence factor. We analyze fourmutants of Xanthomonas campestris (Xcc) that produce xanthan modified in its composition anda xanthan-defective strain. In vitroassays showed that bacterial adhession decreased 20-35% in mutants thatsynthetized xanthan without acetyl (XcF, XcG) or pyruvate (XcL) groups, 55% inmutant that produced polytetrasaccharide (XcI), and 86% in thexanthan-defective strain. We observed differencesbetween biofilms formed by all mutants. XcL formed a biofilm with similarthickness and biomass values than that formed by WT strain, but flatter, less heterogeneous, and more compact with low tendency to form micro-colonies and undefinedchannels. Similar results were observed in the biofilm formed by XcI. In Nicotianabenthamiana infections, XcL, XcI and Xc1231 failed in colonization of leaftissue, while WT strain reached a severe infection. Pretreatment with xanthan synthesized by WT strain and with xanthan from XcF and XcGrestored two to three orders the bacterial growth of all mutants, whilepretreatment with xanthan from XcL and from XcI, restored only one order thebacterial growth in all cases. Altogether, these results suggest that pyruvategroups and terminal mannose are important to the role of xanthan in the virulenceand pathogenicity of Xcc.