Lack of expression of RP4-specified beta-lactamase in Azospirillum brasilense.

Plasmid RP4, which normally confers resistance to ampicillin (Apr), tetracycline (Tcr), and kanamycin (Kmr) to its hosts, failed to express enhanced Apr when transferred from Escherichia coli to Azospirillum brasilense which has its own intrinsic beta-lactamase. Even in a beta-lactamase-deficient mutant, A. brasilense RG-D16, no increase in beta-lactamase or significant Apr appeared following transfer of RP4. However, A. brasilense RG (RP4) and A. brasilense RG-D16 (RP4) did exhibit Tcr Kmr. When RP4 was transferred back from A. brasilense to E. coli all three drug resistances and beta-lactamase activity were fully expressed.