Role of crl in avian pathogenic Escherichia coli: A knockout mutation of crl does not affect hemagglutination activity, fibronectin binding, or curli production

This study determined the role of crl in the production of curli by, the hemagglutination activity of, and fibronectin binding by avian pathogenic Escherichia coli χ7122. Curli, an extracellular structure that binds fibronectin, was recently described (A. Olsen, A. Jonsson, and S. Normark, Nature [London] 338:652-655, 1989). The crl gene product was hypothesized to be the subunit monomer of curli and to bind fibronectin. E. coli HB101, which does not contain crl, binds fibronectin and produces curli when harboring a plasmid containing the crl gene. We show that HB101 hemagglutinates chicken erythrocytes when harboring the crl gene and that χ7122 hemagglutinates chicken erythrocytes, binds fibronectin, and produces curli. Hemagglutination activity, fibronectin binding, and curli production are best expressed by χ7122 and HB101 harboring the crl gene when the bacteria are grown on colonization factor antigen agar at 26°C. The expression of hemagglutination activity, fibronectin binding, and curli production by both strains is decreased by growth on this agar at an increased temperature, of an increased osmolarity, or in an anaerobic atmosphere. This result indicates that the crl gene plays a role in the expression of the three phenotypes in HB101 and possibly in χ7122 as well. We inactivated crl in χ7122 by allele replacement in the expectation of abolishing hemagglutination activity, fibronectin binding, and curli production. The mutation was verified by Southern blot analysis and by a polymerase chain reaction, and there was no evidence of a second crl gene in χ7122. However, the mutant of χ7122 lacking crl hemagglutinated chicken erythrocytes, bound fibronectin, and produced curli at wild-type levels. This result indicates that crl plays a nonessential role in the expression of these three phenotypes in χ7122.