Strain Identification And The Effects Of Type Ⅱ Polyketide Pathway Disruption On Streptolydigin Production

A Streptomyces strain was isolated from soil, which has the ability to produce a compound with strong biological activities of anti-gram-positive bacteria, anti-gram-negative bacteria and Cox virus. Privious precursors-adding and isotope labeling experiments showed that this compound is a complex polyketide produced by a typeⅠpolyketide synthesis pathway. However, the low yield of this strain is a disadvantage for compound identification and further biosynthesis research.On the basis of physiological and biochemical characters, the classification of this strain was studied with molecular taxonomy in this paper. A pair of 16S rDNA general primers for actinomycetes was used to clone 1454bp nucleotides, nearly complete sequence of 16S rDNA sequence from Streptomyces lydicus AS4.2501 chromosome. The result of Blast revealed that the target strain was highly conserved in 16S rDNA with Streptomyces lydicus DSM40461. Only two nucleotides were different between the 16S rDNA of the two Streptomyces strains. But one P450 monooxynase cloned from the chromosome of Streptomyces 099 was found to be only 94% identity with the corresponding gene from Streptomyces lydicus DSM40461, and some differences existed between the two strains in biological and biochemical characters. Further research indicated that they could both produce the secondary metabolite of streptolydigin. The target strain was named as a var. strain of Streptomyces named Streptomyces lydicus AS4.2501.Streptomyces lydicus can produce a lot of important secondary metabolites, including streptolydigin and streptomycin. Among them, streptolydigin was a polyketide compound synthesized by typeⅠpolyketide pathway, which shares same or similar precursors with the typeⅡpolyketide pathways. And they also have some connections in gene evolution point of view. So typeⅠpolyketide synthesis pathway has a certain relation with typeⅡpolyketide synthesis pathway for metabolism. Streptolydigin produced by Streptomyces lydicus AS4.2501 was used as an example to study the effects of typeⅡpolyketide pathway diruption on streptolydigin production. Partial sequence of KSαgene from typeⅡpolyketide synthesis pathway was disrupted using pKC1139. HPLC and HPLC-MS were used to analysis the metabolites of mutant. Preliminary result indicated no obvious differences existed between the two strains in biological and biochemical characters. But streptolydigin yield increased by 50% after typeⅡpolyketide synthesis pathway disruption.However, further researches should be conducted to reveal the full picture.