What is Actinomycetes ?

Actinomycetes were originally considered to be an intermediate group between bacteria and fungi but are now recognized as prokaryotic. The gram-positive bacteria include two major branches: the low G+C organisms, containing genera such as Bacillus, Closdridium, Staphylococcus and Streptococcus; and the high G+C (> 55%) organisms referred to as the actinomycetes. The majority of the actinomycetes are free living, saprophytic bacteria found widely distributed in soil, water and colonizing plants. Actinomycetes population has been identified as one of the major group of soil population, which may vary with the soil type (Küster, 1968).
Actinomycetes belong to the order Actinomycetales (Superkingdom: Bacteria, Phylum: Firmicutes, Class: Actinobacteria, Subclass: Actinobacteridae). According to Bergey's Manual actinomycetes are divided into eight diverse families: Actinomycetaceae, Mycobacteriaceae, Actinoplanaceae, Frankiaceae, Dermatophilaceae, Nocardiaceae, Streptomycetaceae, Micromonosporaceae (Holt, 1989) and comprise 63 genera (Nisbet and Fox, 1991).
All members of the Streptomycetaceae family have a complex life cycle. They contain specific menaquinones, incorporate LL-diaminopimelic acid (a diagnostic amino acid) into their peptidoglycan, but lack a diagnostic sugar (Schrempf, 2006). An enormous number (>800) of Streptomyces species has been described by numerical taxonomy (Goodfellow et al., 1990). Streptomyces are aerobic, filamentous soil bacteria known for the production of secondary metabolites and biologically active materials (Stackebrandt et al., 1991).
Among microorganisms, actinomycetes are one of the most attractive sources of all types of bioactive metabolites that have important applications in human medicine (Watve et al., 2001). Streptomycetes and related actinomycetes continue to be useful sources of novel secondary metabolites with a range of biological activities that may ultimately find application as anti-infectives, anti-cancer agents or other pharmaceutically useful compounds (Bibb, 2005). Members of Streptomyces are a rich source of bioactive compounds, notably antibiotics, enzymes, enzyme inhibitors and pharmacologically active agents (Yamanaka et al., 2005; Sanglier et al., 1993). About 75 % of the known commercially and medically useful antibiotics are produced by Streptomyces (Sujatha et al., 2005; Takano, 2006).
Antibiotics are antimicrobial compounds produced by living microorganisms. These compounds were used therapeutically and some times prophylactically in the control of infectious diseases. Many antibiotics were produced by microorganisms as secondary metabolites (Ahmed, 2007). Most of the known antibiotics were isolated from some species belonging to actinomycetes and many of them were isolated from genus Streptomyces (Waskman, 1959a) for example 4-methylaeruginoic was isolated from Streptomyces sp. (Henriksen et al., 1998).
The screening programs for new Streptomyces and for their antibiotics are still proceeding at a very rapid pace. There is a need for the development of new antibiotics to overcome the problems associated with toxicity of some used antibiotics and the increase of resistant pathogenic bacteria. To discover the new antibiotics it will be necessary to continue the use of conventional screening programs. Different soils all over the world had been exploited in search of bioactive Streptomyces (Abdelghani et al., 2009; Laidi et al., 2008).