Disruption of ste23 gene affects composition profile and bioactivity of exopolysaccharide produced by Streptomyces sp. 139

AIMS: To study the function of the gene ste23 involved in the biosynthesis of Ebosin. METHODS AND RESULTS: In search of databases, the deduced product of the gene ste23 showed high homology to dTDP-4-dehydrorhamnose 3,5-epimerases. ste23 was replaced by a kanamycin resistance gene through double crossover. Compared with Ebosin, an exopolysaccharide (EPS) produced by wild-type Streptomyces sp. 139, the EPS produced by the ste23 mutant (designated EPS1) had a remarkably different monosaccharide composition and significantly diminished rhamnose content, though the molecular mass of EPS1 was similar to that of Ebosin. In addition, EPS1 lost the interleukin 1 (IL-1) antagonist activity in vitro. CONCLUSIONS: ste23 may be involved in the Ebosin biosynthesis in S. sp. 139. and its bioactivity. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first genetic work investigating functions of genes involved in EPS production in streptomyces by gene replacement of the pathway genes.