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Lipopolysaccharides Lipopolysaccharides (LPS) are a major component of the cell surface of gram-negative bacteria and are typically thought to be a protective barrier against host defense molecules. Mutational analysis of a LPS biosynthesis gene (waaL) in Spiraeoideae-infecting strains of E. amylovora has shown LPS to be involved in virulence [1]. Comparison of the LPS biosynthetic gene cluster of E. amylovora has identified a multiple-gene substitution between Spiraeoideae-infecting and Rubus-infecting strains (CFBP 1430, EAMY_0089-0092 vs. ATCC BAA-2158, EAIL5_0082-0084) [2]. In Spiraeoideae-infecting strains, the core region of the LPS biosynthetic gene cluster contains genes encoding three glycosyltransferases and an LPS ligase (Spiraeoideae-type waaL), whereas only two glycosyltransferases and a different LPS ligase (Rubus-type waaL) are located in the same region in Rubus-infecting strains. These coding domains share little to no similarity at the amino acid level between Rubusand Spiraeoideae–infecting strains and this genotypic difference was confirmed by PCR analysis of the associated DNA region in 31 Rubusand Spiraeoideae-infecting strains [2].