Expression of an heterologous gene activating actinorhodin biosynthesis in Streptomyces lividans and Streptomyces coelicolor

Cloning and analysis of a DNA fragment stimulating avermectin production in various Streptomyces avermitilis strains

To isolate a gene for stimulating avermectin production, a genomic library of Streptomyces avermitilis ATCC 31267 was constructed in Streptomyces lividans TK21 as the host strain. An 8.0-kb DNA fragment that significantly stimulated actinorhodin and undecylprodigiosin production was isolated. When wild-type S. avermitilis was transformed with the cloned fragment, avermectin production increased approximately 3.5-fold. The introduction of this fragment into high-producer (ATCC 31780) and semi-industrial (L-9) strains also resulted in an increase of avermectin production by more than 2.0- and 1.4-fold, respectively. Subclones were studied to locate the minimal region involved in stimulation of pigmented-antibiotic and avermectin production. An analysis of the nucleotide sequence of the entire DNA fragment identified eight complete and one incomplete open reading frame. All but one of the deduced proteins exhibited strong homology (68 to 84% identity) to the hypothetical proteins of Streptomyces coelicolor A3(2). The orfX gene product showed no significant similarity to any other protein in the databases, and an analysis of its sequence suggested that it was a putative membrane protein. Although the nature of the stimulatory effect is still unclear, the disruption of orfX revealed that this gene was intrinsically involved in the stimulation of avermectin production in S. avermitilis.

Activation of the actinorhodin biosynthetic pathway in Streptomyces lividans

Production of the antibiotic actinorhodin was activated in Streptomyces lividans under conditions in which it is not normally produced when transformed with an activator gene from S. lividans. The gene encodes a 86-nucleotide transcript, responsible for the actinorhodin production phenotype, which is homologous to the 132 nucleotide transcript from S. fradiae, thought to act as a putative antisense RNA.