Microorganisms grow in unique and extreme habitats, they may
have the capability to produce unique and unusual metabolites.
Generally, the reason why they produce such metabolites is not
known, but it is believed that many of these metabolites may act as
chemical defense of microbes competing for substrates [1]. Although
several hundreds of compounds with antibiotic activity have been
isolated from microorganisms over the years, but only a few of them
are clinically useful [2]. The outstanding role of microorganisms in
the production of antibiotics is notorious. At present, with 1% of the
microbial world having been explored, the advances in techniques
for microbial cultivation and extraction of nucleic acids from soil and
marine habitats are allowing access to a vast untapped reservoir of
genetic and metabolic diversity [3].
It has been known that cultivation parameters are critical to the
secondary metabolites produced by microorganisms. Even small
changes in the culture medium may not only impact the quantity of
certain compounds but also the general metabolic profile of
microorganisms [4]. In particular, in the field of antibiotics, much
effort was directed toward optimizing production rates and directing
the product spectrum. Manipulating nutritional or environmental
factors can promote the biosynthesis of secondary metabolites and
thus facilitate the discovery of new natural products [5].
It is well known that 30-40% of the production cost of antibiotics is
taken up by the cost of growth medium [6]. Carbon and nitrogen
sources together with fermentation time have been reported to play
significant roles in the determination of the final morphology of the
culture [7]. However, the production of antimicrobial substances
depends upon the substrate medium for their optimal growth,
temperature, pH and the concentration of nutrients in the medium
[8]. A balanced ingredient in the medium as nutrition for bacterial