Abstract
The OXA-2 beta-lactamase gene was first found on a conjugative plasmid R46 from a clinical isolate of Salmonella typhimurium. To test the expression and secretion of OXA-2 beta-lactamase in Streptomyces lividans a shuttle plasmid (pSU101) was created by fusing an Escherichia coli plasmid (pSU8) carrying the OXA-2 beta-lactamase gene with the S. lividans vector pLJ61. The OXA-2 beta-lactamase gene specified by the hybrid plasmid PSU101 was expressed in S. lividans, although at a lower level than in coli. Almost all the beta-lactamase activity was found in the culture supernatant of S. lividans, whereas in E. coli the enzyme was almost wholly cell associated. The identity of the enzyme was established by substrate specificity and isoelectric focusing. The stability and integrity of the plasmid pSU101 in both E. coli and lividans was determined, in comparison with that of pSU8 and pLJ61 plasmids. The promoter regions of the OXA-2 beta-lactamase gene were identified by using promoter-probe plasmid vectors; and by S1 mapping of the transcriptional start-sites coupled to the DNA sequencing of the OXA-2 beta-lactamase gene. Multiple transcriptional start sites were found in both hosts, with the origin of transcription apparently different in the two organisms. Part of this work has been published as a scientific paper which is appended.