otrA resembles elongation factor G (EF-G) and is considered to be an oxytetracycline (OTC)-resistance determinant in Streptomyces rimosus. In order to determine whether otrA also conferred resistance to OTC and other aminoglycosides to Streptomyces coelicolor, the otrA gene from S. rimosus M527 was cloned under the control of the strong ermE* promoter. The resulting plasmid, pIB139-otrA, was introduced into S. coelicolor M145 by intergeneric conjugation, yielding the recombinant strain S. coelicolor M145-OA. As expected S. coelicolor M145-OA exhibited higher resistance levels specifically to OTC and aminoglycosides gentamycin, hygromycin, streptomycin, and spectinomycin. However, unexpectedly, S. coelicolor M145-OA on solid medium showed an accelerated aerial mycelia formation, a precocious sporulation, and an enhanced actinorhodin (Act) production. Upon growth in 5-L fermentor, the amount of intra- and extracellular Act production was 6-fold and 2-fold higher, respectively, than that of the original strain. Consistently, reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that the transcriptional level of pathway-specific regulatory gene actII-orf4 was significantly enhanced in S. coelicolor M145-OA compared with in S. coelicolor M145.
Keywords: otrA gene; Streptomyces coelicolor; Actinorhodin; Morphological differentiation; actII-orf4.