Expression of Multiple Copies of the Lon Protease Gene Resulted in Increased Antibiotic Production, Osmotic and UV Stress Resistance in <i>Streptomyces coelicolor</i> A3(2)

The genus Streptomyces is a group of gram-positive bacteria that exhibit a distinctive growth pattern characterised by elongated, branched hyphae. Streptomyces coelicolor A3(2), which produces at least five different antibiotics, is a model organism that is widely used in genetic studies. There are very few studies in Streptomyces on the ATP-dependent Lon protease, which has very important functions in every organism and is particularly responsible for protein homeostasis. The aim of this study was to construct and characterize a recombinant S. coelicolor strain expressing the lon gene on a multicopy plasmid. For this purpose, the lon gene was first cloned in Escherichia coli under the control of the glycerol-inducible promoter of pSPG, and its expression in S. coelicolor A3(2) cells was demonstrated by RT-qPCR. In contrast with the initial hypothesis, increased lon expression did not affect cell growth seriously. Instead, it increased the cell's tolerance to osmotic and UV stress and led to a significant increase in antibiotic production. The recombinant strain produced 27 times more actinorhodin and 43 times more undecylprodigiosin than the wild-type strain after 120 h of fermentation. To our knowledge, this is the first study to demonstrate the effects of expression of the lon gene on a high copy number plasmid in Streptomyces.