We report a system for the efficient removal of a marker flanked by two loxP sites in Streptomyces coelicolor, using a derivative of the temperate phage φC31 that expresses Cre recombinase during a transient infection. As the test case for this recombinant phage (called Cre-phage), we present the construction of an in-frame deletion of a gene, pglW, required for phage growth limitation or Pgl in S.coelicolor. Cre-phage was also used for marker deletion in other strains of S.coelicolor.

Streptomyces species strain GK18, isolated in Iran, induced deep-pitted lesions on potato tubers, lesions different from the raised lesions induced by the usual scab-causing phytotoxin, thaxtomin. In addition, neither thaxtomin production nor hybridization to its biosynthetic probe was detected for strain GK18, suggesting the production of a different phytotoxin. The active component was extracted with ethyl acetate from culture filtrate of strain GK18, purified by gel filtration and silica gel chromatography, and identified as an 18-membered macrolide, borrelidin, by spectroscopic analysis. The purified borrelidin induced necrosis on potato tuber slices and inhibited the growth of shoots and roots of radish seedlings. This is the first report on the phytotoxicity of borrelidin as a possible causative compound of potato scab disease.

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