Developmental regulator RamR controls both morphological development and lincomycin biosynthesis in Streptomyces lincolnensis.

Aims: Assessing the role of ramR , a gene absent in a lincomycin over-producing strain, in the regulation of morphological development and lincomycin biosynthesis in Streptomyces lincolnensis.

Methods And Results: The gene ramR was deleted from the wild-type strain NRRL 2936 and the ΔramR mutant strain was characterized by a slower growth rate and a delayed morphological differentiation compared to the original strain NRRL 2936. Furthermore, the ΔramR produced 2.6-fold more lincomycin than the original strain, and consistently the level of expression of all lincomycin cluster located genes was enhanced at 48 and 96 h in the ΔramR. Complementation of ΔramR with an intact copy of ramR restored all wild-type features, whereas the over-expression of ramR led to a reduction of 33% of the lincomycin yield. Furthermore, the level of expression of glnR, bldA and SLCG_2919, three of known lincomycin biosynthesis regulators, was lower in the ΔramR than in the original strain at the early stage of fermentation and we demonstrated, using electrophoretic mobility shift assay and XylE reporter assay, that glnR is a novel direct target of RamR.

Conclusions: Altogether, these results indicated that, beyond promoting the morphological development, RamR regulates negatively lincomycin biosynthesis and positively the expression of the nitrogen regulator GlnR.

Significance And Impact Of The Study: We demonstrated that RamR plays a negative role in the regulation of lincomycin biosynthesis in S. lincolnensis. Interestingly, the deletion of this gene in other antibiotic-producing Streptomyces strains might also increase their antibiotic-producing abilities.