Digalacturonic acid uptake in Erwinia chrysanthemi

Erwinia chrysanthemi produces pectolytic hydrolases and lyases that attack the plant cell wall releasing monomers, saturated and unsaturated dimers, trimers, and oligomers of galacturonic acid that are subsequently catabolized by the pathogen. The uptake system for the dimer molecule, digalacturonic acid, in E. chrysanthemi EC16 was studied, Uptake was inducible with growth on galacturonic acid, digalacturonic acid, or a mixture of pectin plus polygalacturonic acid. Induction by the monomer was approximately 1.5-fold less than that by the dimer or polymer. Glycerol-grown cells possessed a basal uptake activity several-fold lower than cells grown on pectin or its derivatives while glucose-grown cells had negligible uptake activity. Uptake for the dimer displayed saturation kinetics, and was insensitive to inhibitors of ATP synthesis but sensitive to dissipators of the proton motive force. Unsaturated digalacturonic acid inhibited [³H]digalacturonic acid uptake in a competitive manner while galacturonic acid did not.