Relative effects on virulence of mutations in the sap, pel, and hrp loci of Erwinia chrysanthemi

We constructed strains of Erwinia chrysanthemi EC16 with multiple mutations involving three virulence systems in this bacterium, namely pet (coding fo r the major pectate lyases pelABCE), hrp (hypersensitive response and patho genicity), and sap (sensitivity to antimicrobial peptides), The relative: e ffects on virulence of those mutations have been analyzed on potato tubers and chicory leaves, In potato tubers, the sap mutation (BT105) had a greate r effect in the reduction of the virulence:than the pet (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 th e effects of these mutations are additive. rn chicory leaves, the mutation in the sap locus appeared to have a greater effect than in potato tubers. T he competitive indices of strains BT105, UM1005 (Pel(-)), CUCPB5039, and CU CPB5037 have been estimated in vivo and in vitro. These results indicate th at the mutation in the hrp locus can be complemented in vivo by coinfection , whereas the mutations in pel and sap cannot.