Detection and Expression of Biosynthetic Genes in Actinobacteria ...

BERVANAKIS, G.Chapter 4: DISCUSSIONreveal any extra sequences that may have been indicative of the amplification of morethan one DNA segment.4.4 Adaptation of cultivation conditions for secondarymetabolite screening4.4.1 Solid Substrate FermentationsThe metabolic pattern of extracted metabolites from SSF as determined by TLC,showed that barley and whole oats supplemented with water produced the highestnumber of TLC bands though the EtAc extracts showed no antibacterial activity. Thisresult showed that the type of screening is crucial in determining the bioactivemetabolite producing capabilities of microorganisms, often combining a number ofscreens provides a comprehensive approach (Bérdy, 1989). In addition, it was shownthat minimal supplementation with the use of distilled water only of the solidsubstrates can produce a complex metabolic pattern, however when substrates wheresupplemented with additional mineral or trace elements a less complex pattern wasevident. The interpretation of these results supports the notion that under nutrientdeprived conditions variable expression of SM is produced, whereas cultures exposedto nutrient rich conditions only produce certain types or a decreased number ofcompounds.Altering cultivation conditions and diversifying substrates in SM screening can inducebioactive compounds and benefit screening efforts. A novel approach to cultivatingactinobacteria using solid-state fermentation (SSF) for SM production, has beenshown to posses many attractive advantages over conventional liquid fermentationsthese include; minimal energy input, higher yields in shorter durations of antibioticproduction and decreased production costs have made this technology a attractive andeconomical approach for SM screening groups (Yang &Ling, 1989., Robinson et al.,2001). SSF involves incorporating heterogeneous natural solid substrates having lowmoisture contents (12 %) (Barrios-González & Mejía, 1996., Jermini & Demain,1989). In the current study, environmental isolates exhibiting low antimicrobialactivity on agar media were subjected to SSF using various natural substrates todetermine if enhanced production could be achieved. Cultivation of the low yieldingisolates on SSF varied in their response in comparison to that of liquid fermentations_____________________________________________________________________126