Transmission of lac by the sex factor E in Erwinia strains from human clinical sources

Abstract

Lactose-utilizing (Lac(+)) strains of Erwinia spp. from human clinical material transfer lac by conjugation to plant strains of Erwinia herbicola and Erwinia amylovora, to other Erwinia strains from human clinical sources, and also to Escherichia coli, Paracolobactrum arizonae, Salmonella typhimurium, and Shigella dysenteriae. The frequency of this transfer varies with the donor and recipient strains employed. The lac genes appear stable in these exconjugants, and they are not cured by acridine orange. The Lac(+) exconjugants transfer lac to an Escherichia coli F(-) Lac(-) strain; the frequency of this transfer is high with E. herbicola and S. typhimurium exconjugants and relatively low with other exconjugants. The most studied Erwinia donor strain from human clinical material (EH133) and its Lac(+) exconjugants are insensitive to the F-specific phage, M13. P1-mediated transduction of lac, by using a Lac(+) exconjugant of E. coli as the donor and an E. coli F(-) Lac(-) strain as the recipient, revealed that all 50 Lac(+) transduced clones tested also inherited donor ability, suggesting a close linkage between the Erwinia sex factor (designated as E) and the lac genes. The E. coli culture harboring E-lac (E and the lac genes linked to it) does not restrict phages T1, T7, and lambdavir. E-lac is compatible with F'his, R100 drd-56 (F-like), and R64 drd-11 (I-like); cells harboring F'his or one of the R factors do not show super-infection immunity to the incoming E-lac, and E-lac plus one of the other plasmids can coexist stably in the same cell. The fertility of cells harboring F'his or R100 drd-56-as determined by the frequency of conjugal transfer of his or of the resistance determinant (Tet(r) in case of R100 drd-56) and also by sensitivity to F-specific phage (M13)-is not altered by the presence of E-lac, and this suggests that the sex factor E might belong to the fi(-) class.