Expression of R-plasmid functions during anaerobic growth of an Escherichia coli K-12 host

Abstract

The normal habit of enteric bacteria is largely anaerobic. Expression of the 3 characteristic properties of R-plasmids, drug resistance, vegetative replication and fertility, was therefore studied in E. coli K-12 during anaerobiosis. Replication and drug resistance functions were not altered in the 45 R-plasmids studied, but the expression of fertility varied considerably among different R-plasmids during anaerobiosis. The R-plasmids could be divided into 3 groups, one showing a strong, the 2nd a moderate and the 3rd little or no reduction of fertility by anaerobiosis. Plasmid-determined sensitivity to F-, N- and I-specific phage, respectively, was well, although not absolutely, correlated with each of the 3 groups mentioned. Anaerobiosis-aerobiosis appears to change the fertility of type F R-plasmids by influencing the degree of repression of their fertility functions, such as the formation of sex pili. Although the minimum inhibitory concentrations of ampicillin, chloramphenicol, streptomycin and tetracycline were unaltered by anaerobiosis, sulfonamide was 4 to 8-fold less active under this condition in resistant and sensitive strains. A surprisingly high frequency and uniformity of minimal inhibitory concentrations was observed for R-plasmid-mediated resistance to streptomycin and chloramphenicol.