VIEW ARTICLE

Molecular Plant Pathology

Pathogenicity of Mutants of Erwinia carotovora subsp. carotovora Deficient in Aerobactin and Catecholate Siderophore Production. Carolee T. Bull, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331; and Horticultural Crops Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, 3420 N.W. Orchard Ave., Corvallis, OR 97330, Current address: Horticultural Crops Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, 2021 South Peach Ave., Fresno, CA 93727; Susan R. Carnegie(2), and Joyce E. Loper(3). (2)(3)Department of Botany and Plant Pathology, Oregon Sate University, Corvallis 97331; and Horticultural Crops Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, 3420 N.W. Orchard Ave., Corvallis, OR 97330. Phytopathology 86:260-266. Accepted for publication 20 November 1995. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1996. DOI: 10.1094/Phyto-86-260.

Erwinia carotovora subsp. carotovora strain W3C105 produces the hydroxamate siderophore aerobactin and a catecholate metabolite, which previously was not known to function in iron acquisition by the phytopathogen. A region containing catechol biosynthesis genes (cbsEA⁺) of strain W3C105 complements EntA^- and EntE^- mutants of Escherichia coli, which are deficient in biosynthesis of the catecholate siderophore enterobactin. 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 of Tn3-Spice generated transcriptional fusions of the promoterless ice nucleation reporter gene (inaZ) to a cbs promoter(s), conferred iron-regulated ice nucleation activity on E. coli. One of the Tn3-Spice insertions was introduced into the genome of W3C105 by marker-exchange mutagenesis 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 double 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’-dipyridyl 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^- Iuc⁺), however, grew on a minimal medium containing higher concentrations of 2,2’-dipyridyl than did a mutant producing only the catechol (Cbs⁺ Iuc^-), indicating that aerobactin was superior to the catecholate siderophore in competing with 2,2’-dipyridyl for iron. Mutants deficient in the production of either or both siderophores did not differ from the wild-type strain in the capacity to macerate potato tuber tissue or cause aerial stem rot of potato.