Uptake of chitosan-derived D-glucosamine oligosaccharides in Streptomyces coelicolor A3(2)

The csnR gene, localized at the beginning of an operon, csnR–K, which organization is conserved through many actinomycete genomes, was previously shown to repress the transcription of the chitosanase gene csnA in Streptomyces lividans. However, knowledge on the function of the whole csnR–K operon in the metabolism of chitosan (an N-deacetylated derivative of chitin) remained limited. Mutants of S. coelicolor A3(2) harboring partial or total deletions of the csnR–K operon were analyzed for their capacity to uptake glucosamine oligosaccharides (GlcN)n. The csnR–K operon was autoregulated by CsnR repressor and its transcription was inducible by GlcN oligosaccharides. The operon controlled the uptake of GlcN oligosaccharides in S. coelicolor A3(2), with a minor contribution to the consumption of monomeric GlcN but not chitin-related N-acetylated derivatives. The deletion of the whole operon abolished the uptake of GlcN oligosaccharides. The CsnEFG transporter encoded by this operon is the front door for the assimilation of chitosan-derived hydrolysis products in S. coelicolor A3(2). The ATP-binding component MsiK was essential for CsnEFG transport function. Also, deletion of msiK abolished the induction of csnA transcription by GlcN oligosaccharides. The ABC transporter CsnEFG, member of an operon highly conserved in streptomycetes, is shown to be essential for the uptake of chitosan hydrolysis products in Streptomyces coelicolor.