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

The normal habitat of enteric bacteria is largely anaerobic. Expression of the three characteristic properties of R-plasmids, drug resistance, vegetative replication, and fertility, was therefore studied in Escherichia coli K-12 during anaerobiosis. Replication and drug resistance functions were not altered in the 45 R-plasmids studies, whereas the expression of fertility varied considerably among different R-plasmids during anaerobiosis. The R-plasmids could be divided into three groups, one showing a strong, the second a moderate, and the third 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 three 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 found to be four- to eightfold less active under this condition in both 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.