Detection and Expression of Biosynthetic Genes in Actinobacteria ...

BERVANAKIS, G.Chapter 4: DISCUSSIONA) B)Figure 37. The chemical structure of A) Actinomycin D (Adapted from theChapman and Hall DNP, 1982-2001), B) Candicidin D an example of a heptaenemacrolide, containing 21 carbon bonds (Hu et al., 1994).RP-HPLC analysis of extract A2381 indicated the presence of several compounds,with different chromophores. However antibacterial activity was only detected againstgram positive bacteria from peaks collected between 14 to 18 mins. This region of theUV-chromatogram revealed only minor constituents. However, the LC/MS showedthe presence of several compounds in the non-polar region of the chromatogram.Peaks 1 and 2 from the chromatogram clearly showed in the ESI-MS trace that theywere two compounds with molecular ions in the negative ion mode at m/z 385.3 andm/z 425.5 respectively. A search of the Chapman and Hall DNP with MW from 425to 427, and MW from 386 – 387 revealed several possible candidates for theclassification of these compounds which included; antibiotic YL 01869P,actinopyrones, antibiotic WP 3688-5 or derivatives of trichostatin, all thesecompounds are known to be produced by streptomycete species.Actinopyrone and trichostatin A are polyene antibiotics (Figure 38a and b), modularPKS are involved in the formation of the polyene chain structures (Katz, 1998). PCRscreening detected a modular PKS gene in isolate A2381, indicating that it could beresponsible for the formation of the polyene structure._____________________________________________________________________131