A LOCUS DETERMINING PATHOGENICITY OF XANTHOMONAS-CAMPESTRIS IS INVOLVED IN LIPOPOLYSACCHARIDE BIOSYNTHESIS

A pathogenicity locus in Xanthomonas campestris pv. campestris has bee n shown to comprise two genes which mediate biosynthesis of the bacter ial lipopolysaccharide (LPS) but not extracellular polysaccharide, Mut ants with Tn5 insertions in either gene showed alterations in the elec trophoretic patterns of both water-soluble and phenol-soluble LPS form s, which suggested defects in the biosynthesis of the core oligosaccha ride component, On gel chromatography, core oligosaccharides of the mu tants were of apparently lower molecular weight than those from the wi ld type, Furthermore, the content of mannose and glucose, sugars chara cteristic of the core oligosaccharide, were significantly lower in the water-soluble LPS of the mutants, Because of their role in LPS core b iosynthesis, the two genes were called rfaX and rfaY, rfaX mutants sho w altered behavior in a range of host and non-host plants such that th e number of recoverable bacteria drop within the first 24 h after inoc ulation, In contrast, the behavior of rfaY mutants only differed from the wild type in Datura, a nonhost plant in which the growth of the wi ld type is severely attenuated, The predicted protein RfaY showed sign ificant sequence homology to a sub-family of RNA polymerase sigma fact ors which are involved in extracytoplasmic functions.