Study Of Biosynthetic Pathway Of Secondary Metabolites Of Xyloketal B And 1403C From Marine Fungi And Effects Of Lights

Xylaria sp. (No.2508) and Halorosellinia sp. (No.1403) are two mangrove endophytic fungi isolated from mangrove in the Sounth China Sea. Xyloketal B is a novel ketal compound produced by Xylaria sp. (No.2508), and 1403C, a novel anthraquinone, is produced by Halorosellinia sp. (No.1403). It was proven that xyloketal B could be a potential compound for further evaluation in the treatment of atherosclerosis, and 1403C showed significant anti-tumor activity against several kinds of cancer cell lines with milder effect on human normal cells. In this study, the biosynthestic pathways of xyloketal B and 1403C were first clarified, and then effects of different lights on the development of these two fungi and production of xyloketal B and 1403C were studied.In order to elucidate the biosynthestic pathway of xyloketal B, adding enzyme inhibitor and precursors feeding experiments were carried out. The production of xyloketal B was completely inhibited by 0.2 mmol/L iodoacetamide. It suggested that biosynthesis of xyloketal B was involved in polyketide pathway, and malonate was indicated as the precursor of xyloketal B by feeding experiments which increased the production to 43 mg/L from 5 mg/L. However lower concentration acetate had insensible effect on xyloketal B while 0.5 mmol/L acetate inhibited the yield markedly. It was supposed that acetyl-CoA carboxylase was the limiting enzyme of the flux. Then, citric acid, a activiting compound of acetyl-CoA carboxylase, was added to the culture. It improved xyloketal B production about 13 times, which proved the above hypothesis.[1,2,3-13C3]malonate and [2-13C]malonate were used as the labled precursors to study the origin of the carbon skeleton. The patterns of13C-enrichment reavealed that 15 carbon atoms of 1403C were derived from labeled malonate, among which 7 were labeled from the carboxylic group of malonate and the other 8 were from the methylene. Meanwhile, one carbon atom was derived from the reaction of O-methylation as well as a reaction of decarboxytion occureded at C-6. It also proved that PKS of Halorosellinia sp. (No.1403) used malonyl-CoA for both chain priming and chain elongation, loading malonate with decarboxylation to form acetyl starter unit.The effects of light on the development of Xylaria sp. (No.2508) and production of xyloketal B was investigated in this study. We found that blue light can induced Xylaria sp. (No.2508) to form stroma. The production of xyloketal B was increased by red light in contrast to white light. However, blue light had no effects on the production of xyloketal B. It may mean that Xylaria sp. (No.2508) has other light responses. It was also found that red light increased the production of 1403C while white and blue light could induce Halorosellinia sp. (No.1403)’s growth on plate and decrease the production of 1403C and its reduced compounds 1403B and 1403R in fermentation.