Relative Effects on Virulence of Mutations in the sap, pel, and hrp Loci of Erwinia chrysanthemi

Abstract

We constructed strains of Erwinia chrysanthemi EC16 with múltiple mutations involving three virulence systems in this bacterium, namelypel (coding for the major pectate lyases pelABCE), hrp (hypersensitive response and pathogenicity), and sap (sensitivity to antimicrobial peptides). The relative effects on virulence of those mutations have been analyzed on potato tubers and chicory leaves. In potato tubers, the sap mutation (BT105) had a greater effect in the reduction of the virulence than the peí (CUCPB5006) and hrp (CUCPB5039) mutations. This reduction was similar to that observed in the pel-hrp double mutant (CUCPB5037). The analysis of the strains affected in Pel-Sap (BT106), Hrp-Sap (BT107), and Pel- Hrp-Sap (BT108) suggested that the effects of these mutations are additive. In chicory leaves, the mutation in the sap locus appeared to have a greater effect than in potato tubers. The competitive Índices of strains BT105, UM1005 (Peí"), CUCPB5039, and CUCPB5037 have been estimated in vivo and in vitro. These results indícate that the mutation in the hrp locus can be complemented in vivo by coinfection, whereas the mutations in peí and sap cannot.