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.
Institute of Molecular Biology, National Chung Hsing University, Taichung 402, Taiwan, ROC.
Yih-Yuan
YY
Chen
Institute of Molecular Biology, National Chung Hsing University, Taichung 402, Taiwan, ROC.
Chieh-Hao
CH
Wu
Institute of Biochemistry, National Chung Hsing University, Taichung 402, Taiwan, ROC.
Juey-Wen
JW
Lin
Institute of Molecular Biology, National Chung Hsing University, Taichung 402, Taiwan, ROC.
Shu-Fen
SF
Weng
Institute of Microbiology, Immunology and Molecular Medicine, Tzu Chi University, Hualien 907, Taiwan, ROC.
Yi-Hsiung
YH
Tseng
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