Factors governing pectate lyase synthesis in soft rot and non-soft rot bacteria

Abstract

Regulation of pectate lyase synthesis was examined in Erwinia and Pseudomonas species. Soft rot bacteria produced 100- to 1000-fold more enzyme per cell under optimal conditions than did other bacterial pathogens or saprophytes. Among pseudomonads, only Pseudomonas marginalis and a few other fluorescent strains isolated from plant tissue synthesized pectate lyase. Constitutive synthesis was common in this group. In contrast, lyase synthesis in most Erwinia species examined was inducible. Polypectate and pectin were effective carbon sources for lyase induction in some Erwinia strains while other strains showed much higher inducible synthesis on pectin than on polypectate. Vegetable extracts had profound effects on lyase synthesis. Potato extract, which was previously reported as exerting a synergistic effect on induction of pectate lyase in Erwinia carotovora ATCC 8061 grown on pectin, repressed lyase synthesis in other Erwinia strains. At high concentrations, extracts of carrot, lettuce and onion severely repressed constitutive and inducible synthesis. At low concentrations, lettuce and onion extracts stimulated constitutive lyase synthesis in Pseudomonas marginalis. The wide variety of regulatory controls governing lyase synthesis and the repressive as well as synergistic effects of vegetable extracts on synthesis suggest that the etiology of bacterial soft rot diseases can be influenced by such regulatory mechanisms.