Abstract:A putative type Ⅲ polyketide synthase (PKS) gene orf18 found in genome sequence of Streptomyces sahachiroi ATCC 33158 was cloned and analyzed functionally.Bioinformatics and phylogenetic analyses revealed that orf18 was highly homologous to rppA-like type Ⅲ PKS gene.RT-PCR result demonstrated that orf18 can be transcribed into mRNA in wild-type S.sahachiroi.HPLC and LC-MS analyses verified that Orf18 catalyzes the 1,3,6,8-tetrahydroxynaphthalene (THN) biosynthesis by heterologously expressing in S.lividans.Moreover,brownish red pigments could be produced by heterologous expression of orf18 in Gram-negative bacteria Pseudomonas stutzeri.Experimental results demonstrated that Orf18 belongs to the RppA-like type Ⅲ PKS family and catalyzes THN formation,which could be further oxidized and then polymerized to produce red pigments.