Three pathway-specific regulators control streptolydigin biosynthesis in Streptomyces lydicus.

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Streptolydigin is a complex polyketide antibiotic produced by *Streptomyces lydicus*.
• Understanding the genetic regulation of secondary metabolite biosynthesis is crucial for optimizing production.

Purpose of the Study:

• To elucidate the regulatory network controlling the streptolydigin biosynthetic gene cluster in *Streptomyces lydicus*.
• To identify key regulatory genes and their roles in streptolydigin production.

Main Methods:

• Gene inactivation and ectopic expression of putative regulatory genes (slgR1, slgR2, slgY).
• Reverse transcription PCR (RT-PCR) for gene expression analysis.
• Quantification of streptolydigin production via HPLC or similar methods.

Main Results:

• Inactivation of slgR1 or slgR2 abolished streptolydigin production, indicating their essential role as positive regulators.
• A hierarchical regulatory cascade was identified: SlgY controls slgR2, which in turn regulates structural genes and slgR1. SlgR1 controls downstream biosynthetic genes.
• Ectopic expression of slgR1, slgR2, and slgY led to significant increases in streptolydigin yields (18-, 11-, and 8.5-fold, respectively).
• Ectopic expression of slgY in an slgR1 mutant restored streptolydigin C production, highlighting SlgY's role in regulating this specific pathway.

Conclusions:

• The streptolydigin biosynthetic gene cluster is under a complex hierarchical regulation involving SlgY, SlgR2, and SlgR1.
• These regulatory genes are key targets for metabolic engineering to enhance streptolydigin production.