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Carotenoid synthesis in Streptomyces setonii ISP5395 is induced by the gene crtS, whose product is similar to a sigma
1Department of Microbiology, School of Pharmaceutical Sciences, Toho University, Chiba, Japan.
Abstract:
In many species of actinomycetes, carotenogenesis can be photoinduced. The capacity to respond to photoinduction is, however unstable and, in various strains of Streptomyces, is lost at a relatively high frequency. In Streptomyces setonii ISP5395, which normally produces no carotenoids, carotenoid-producing mutants can be obtained following protoplast regeneration. We report here the characterization of a gene, crtS, which was isolated from one such mutant and can confer on wild-type S. setonii ISP5395 cells the capacity to synthesize carotenoids. Sequence analysis of crtS reveals an open reading frame, which shows homology to genes that encode alternative sigma factors in Bacillus subtilis. We propose that crtS encodes a sigma factor which is necessary for the expression of a cryptic gene(s) for carotenoid biosynthesis in S. setonii ISP5395.
Insights
Carotenoid production in Streptomyces can be unstable. A newly identified gene, crtS, enables wild-type Streptomyces setonii to synthesize carotenoids, suggesting it activates a cryptic biosynthesis pathway.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Carotenogenesis in actinomycetes, particularly Streptomyces, is often photoinduced but can be unstable.
- The ability to produce carotenoids is frequently lost in various Streptomyces strains.
- Mutants of Streptomyces setonii ISP5395 that produce carotenoids arise spontaneously after protoplast regeneration.
Purpose of the Study:
- To characterize a gene responsible for conferring carotenoid production in Streptomyces setonii.
- To investigate the genetic basis of carotenoid biosynthesis regulation in Streptomyces.
- To identify the molecular mechanism underlying the activation of carotenoid production.
Main Methods:
- Isolation and characterization of a carotenoid-producing gene (crtS) from a mutant strain.
- Genetic complementation experiments to confer carotenoid synthesis capacity to wild-type S. setonii.
- Sequence analysis of the crtS gene and homology searches against known gene databases.
Main Results:
- A gene, designated crtS, was isolated and shown to confer carotenoid synthesis ability to wild-type S. setonii ISP5395.
- Sequence analysis revealed that crtS encodes an open reading frame with homology to alternative sigma factors.
- The crtS gene appears to activate previously unexpressed genes for carotenoid biosynthesis.
Conclusions:
- The crtS gene encodes a novel alternative sigma factor in Streptomyces setonii.
- This sigma factor is essential for the expression of cryptic carotenoid biosynthesis genes.
- The discovery of crtS provides insights into the regulation of secondary metabolite production in Streptomyces.