Mutation of the gene encoding a major outer-membrane protein in Xanthomonas campestris pv. campestris causes pleiotropic effects, including loss of pathogenicity.
Xanthomonas campestris pv. campestris (Xcc) is the phytopathogen that causes black rot in crucifers. The xanthan polysaccharide and extracellular enzymes produced by this organism are virulence factors, the expression of which is upregulated by Clp (CRP-like protein) and DSF (diffusible signal factor), which is synthesized by RpfF. It is also known that biofilm formation/dispersal, regulated by the effect of controlled synthesis of DSF on cell-cell signalling, is required for virulence. Furthermore, a deficiency in DSF causes cell aggregation with concomitant production of a gum-like substance that can be dispersed by addition of DSF or digested by exogenous endo-beta-1,4-mannanase expressed by Xcc. In this study, Western blotting of proteins from a mopB mutant (XcMopB) showed Xcc MopB to be the major outer-membrane protein (OMP); Xcc MopB shared over 97 % identity with homologues from other members of Xanthomonas. Similarly to the rpfF mutant, XcMopB formed aggregates with simultaneous production of a gummy substance, but these aggregates could not be dispersed by DSF or endo-beta-1,4-mannanase, indicating that different mechanisms were involved in aggregation. In addition, XcMopB showed surface deformation, altered OMP composition, impaired xanthan production, increased sensitivity to stressful conditions including SDS, elevated temperature and changes in pH, reduced adhesion and motility and defects in pathogenesis. The finding that the major OMP is required for pathogenicity is unprecedented in phytopathogenic bacteria.
Chen
Yih-Yuan
YY
Institute of Molecular Biology, National Chung Hsing University, Taichung 402, Taiwan, ROC.
Wu
Chieh-Hao
CH
Institute of Molecular Biology, National Chung Hsing University, Taichung 402, Taiwan, ROC.
Lin
Juey-Wen
JW
Institute of Biochemistry, National Chung Hsing University, Taichung 402, Taiwan, ROC.
Weng
Shu-Fen
SF
Institute of Molecular Biology, National Chung Hsing University, Taichung 402, Taiwan, ROC.
Tseng
Yi-Hsiung
YH
Institute of Microbiology, Immunology and Molecular Medicine, Tzu Chi University, Hualien 907, Taiwan, ROC.
D001422:Bacterial Adhesion; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D001937:Brassica / Q000382:microbiology; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology; D037521:Virulence Factors / Q000235:genetics* / Q000378:metabolism; D016959:Xanthomonas campestris / Q000145:classification / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology*
D001425:Bacterial Outer Membrane Proteins; D037521:Virulence Factors