Detection and Expression of Biosynthetic Genes in Actinobacteria ...

BERVANAKIS, G.Chapter 1: INTRODUCTIONSection 1: General Aspects of Actinobacteria1.1.1 Description of the genetic, biochemical and morphologicalfeatures of ActinobacteriaActinomycetes now referred to as actinobacteria, are Gram-positive, spore-formingsoil bacteria, belonging to the order Actinomycetales (Goodfellow, 1988),characterised by the formation of substrate and aerial mycelium on solid media andpossessing a high guanine plus cytosine content of DNA (60-70 mol %).Actinobacteria contain circular genomes that transcribe 3300 or more genes. Amajority of these genes encode large coding sequences which are utilised duringcomplex morphological differentiation and secondary metabolite biosynthesis(Hopwood et al., 1985). In addition to circular plasmids, actinobacteria possess linearplasmids which are large extrachromosomal DNA elements, implicated in the transferof secondary metabolite biosynthetic genes and antibiotic resistance genes (Kinashi,1994).1.1.2 Industrial Relevance of ActinobacteriaThe plethora of chemical diversity generated from microbial products has been themain contribution to the discovery of bioactive compounds in industrial screeningprograms (Bérdy, 1992). Actinobacteria are a major group of microorganisms that areprolific producers of secondary metabolites (SM), many of which are bioactivecompounds. They are major sources of these compounds and provide over two-thirdsof naturally occurring antibiotics (Bérdy, 1995), with a diverse range ofpharmacologic and agricultural uses (Lechevalier, 1988; Sanglier, 1993).The versatility of actinobacteria is reflected in their biotechnological applicationswhich has seen their use in 1) production of commercially important enzymes(Peczynska-Czoch & Mordarski, 1988), 2) bioremediation of industrial wastes(Lacey, 1988) and more recently 3) in the production of recombinant (human)proteins (Binnie et al., 1997).The high cost of discovering novel microbial compounds has lead to commercialattention focusing on efforts to reduce these costs by screening novel groups ofactinobacteria, and re-screening existing culture collections for a multitude of new_____________________________________________________________________1