Relevance of the galacturonic acid uptake system to the virulence phenotype of Erwinia chrysanthemi EC16



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Texas Tech University


Erwinia chrysanthemi EC 16 is a plant pathogen responsible for soft-rot disease in many plant species. Pathogenicity appears to be chiefly due to pectolytic activity. Pectindegrading enzymes break down the plant cell wall into monomers, saturated and unsaturated dimers and oligomers of galacturonic acid (GA) as well as keto-deoxygluconates. The monomers and dimers are taken up by the bacterium to be utilized for carbon sources, energy, and pectinase induction. The uptake of these compounds must then play a cmcial role in the vimlence of the bacterium. A 3.4-kb EcoRV fragment of EC 16 DNA capable of complementing an exuT mutant was cloned into pUC19. Alkaline phosphatase gene fusions and complementation analysis suggest that the entire 3.4-kb are required for complementation of a GA uptake mutant.

EC 16 GA transport mutants were generated using marker exchange-eviction mutagenesis and assessed for their significance in pathogenicity. Utilizing an nptl-sacBsacR cartridge the exuT gene was inactivated and exchanged with the E. chrysanthemi genome. The cartridge was then evicted. The resulting mutants were exuT~containing a 1.7-kb deletion in the exuT gene. The mutants demonstrated lower transport activity for GA resulting in a reduced growth rate on GA as the sole carbon source. This phenotype did not reveal a significant difference in the vimlence phenotype.



Plant diseases, Plant cell walls