PATHOGENICITY OF MUTANTS OF ERWINIA-CAROTOVORA SUBSP CAROTOVORA DEFICIENT IN AEROBACTIN AND CATECHOLATE SIDEROPHORE PRODUCTION

Erwinia carotovora subsp. carotovora strain W3C105 produces the hydrox amate siderophore aerobactin and a catecholate metabolite, which previ ously was not known to function in iron acquisition by the phytopathog en. A region containing catechol biosynthesis genes (cbsEA(+)) of stra in W3C105 complements EntA(-) and EntE(-) mutants of Escherichia coli, which are deficient in biosynthesis of the catecholate siderophore en terobactin. Four plasmids containing the cbsEA region mutagenized with Tn3-Spice complemented either the EntA(-) or the EntE(-) mutant of E. coli but not both mutants. Two of the plasmids, in which insertions o f Tn3-Spice generated transcriptional fusions of the promoterless ice nucleation reporter gene (inaZ) to a cbs promoter(s), conferred iron-r egulated ice nucleation activity on E. coli. One of the Tn3-Spice inse rtions was introduced into the genome of W3C105 by marker-exchange mut agenesis to generate a mutant deficient in catechol biosynthesis (Cbs( -)). Introduction of the insertion into a previously-derived mutant of W3C105 deficient in aerobactin biosynthesis (Iuc(-)) resulted in a do uble mutant that produced neither the catechol nor aerobactin (Cbs(-) Iuc(-)). A catechol-producing mutant (Cbs(+) Iuc(-)) grew on a minimal medium containing higher concentrations of the iron-chelator 2,2'-dip yridyl than did a mutant producing neither siderophore (Cbs(-) Iuc(-)) , demonstrating that the catechol functions as a siderophore in strain W3C105. Wild-type W3C105 and an aerobactin-producing mutant (Cbs(-) I uc(+)), however, grew on a minimal medium containing higher concentrat ions of 2,2'-dipyridyl than did a mutant producing only the catechol ( Cbs(+) Iuc(-)), indicating that aerobactin was superior to the catecho late siderophore in competing with 2,2'-dipyridyl for iron. Mutants de ficient in the production of either or both siderophores did not diffe r from the wild-type strain in the capacity to macerate potato tuber t issue or cause aerial stem rot of potato.