A novel Streptomyces gene, samR, with different effects on differentiation of Streptomyces ansochromogenes and Streptomyces coelicolor

A 1.4-kb DNA fragment from Streptomyces ansochromogenes accelerated mycelium formation of S. ansochromogenes when present on a multicopy plasmid. The DNA fragment contains one complete open reading frame, designated samR, encoding a protein with 213 amino acids that contains a likely DNA-binding helix-turn-helix motif close to its N-terminus. The deduced SamR protein resembles the product of the hppR gene, which is involved in the regulation of catabolism of 3-(3-hydroxyphenyl) propionate in Rhodococcus globerulus. A samR disruption mutant was constructed that presented a bald phenotype and failed to form aerial hyphae and spores. We suggest that samR plays an important role in the emergence of aerial hyphae from substrate mycelium. An almost identical gene of Streptomyces coelicolor was also subjected to gene disruption. Surprisingly, the mutant was able to develop an aerial mycelium, but it remained white and deficient in sporulation instead of forming gray spores.