ABSTRACT
The main goal of this work was to investigate the biosynthetic origin of diterpenes in gorgorian Pseudopterogorgia acerosa and to investigate the possibility of diterpenes production by the coral associated bacteria. Live coral Pseudopterogorgia acerosa was treated with different antibiotics, specific for different bacterial groups. The treated coral homogenate was prepared and assayed for conversion of radiolabeled terpenes precursor geranyl genranyl diphosphate [3H-GGPP] into radiolabled diterpenes. Mixed bacterial cultures were started from different coral tissues. Cell free extract were prepared from the isolated mixed culture and assayed for radiolabeled diterpenes biosynthesis. Production of diterpenes by the mixed bacterial cultures was investigated using LC-MS analysis. Investigation of the effect of different antibiotics on live coral demonstrated that the biosynthetic capability of diterpenes by the coral homogenate, from 3H-GGPP, was reduced by the effect of antibiotics mixture which suggested bacterial origin of this diterpene in P. acerosa. Furthermore, coral treated with nalidixic acid [gram negative bacterial inhibitor] resulted in about three fold increase of the biosynthesis of the radiolabled diterpes by the coral homogenate which suggested that the diterpenes producer may be gram positive bacteria. The cell free extract of mixed bacterial cultures isolated from the coral tissues was able to convert the radiolabled diterpenes precursor, 3H-GGPP, into pseudopterolide. Furthermore, mixed bacterial culture, isolated from the coral, showed low level production of diterpenes using diluted marine broth medium The results provided strong evidences that the diterpenes biosynthesis in P. acerosa is due to bacterial symbionts rather than the coral tissues