Basic Concept of Biotechnology 23

  Antibiotics   Antibiotics are a group of natural or synthetic compounds that destroy bacteria (bactericidal) or inhibit their growth (bacteriostatic). Antibiotics that are sufficiently nontoxic to the host are used as chemotherapeutic agents in the treatment of infectious diseases of humans, and animals. Nature produces an amazing variety and number of products. In this section we will concentrate on antibiotics and its natural sources. About 100,000 secondary metabolites of molecular weight less than 2500 have been characterized, which are mainly produced by microbes and plants (Roessner and Scott, 1996); Out of which around 50,000 are from microorganisms (Fenical and Jensen, 1993; Berdy, 1995). The selective action exerted on pathogenic bacteria and fungi by microbial secondary metabolites ushered in the antibiotic era, and for 50 years we have been benefited from this remarkable property of “wonder drugs” such as penicillins, cephalosporins, tetracyclines, aminoglyco side...

  Antibacterial agents The fight against bacterial infection is one of the great success stories of medicinal chemistry. During that latter half of the nineteenth century, scientists such as Koch were able to identify the microorganismsresponsible for diseases such as tuberculosis, cholera, and typhoid. Methods such as vaccination for fighting infections were studied. Research was also carried out to try and find effective antibacterial agents or antibiotics. However, the scientist who can lay claim to be the father of chemotherapy the use of chemicals against infection was Paul Ehrlich. Ehrlich spent much of his career studying histology, then immunochemistry, and won a Nobel prize for his contributions to immunology. However, in 1904 he switched direction and entered a field which he defined as chemotherapy. Ehrlich's 'Principle of Chemotherapy' was that a chemical could directly interfere with the proliferation of microorganisms, at concentrations tolerated by the host. ...

  Actinomycetes The phylum actinomycetes are one of the largest groups in the domain bacteria largely consists of environmental bacteria and the denizens of many varied habitat soils such as the rhizosphere, marine and extreme arid environments. Actinomycetes typically have elevated guanosine-cytosine contents (65-75% G + C) and their genome sizes range from 2.5-Mb skin commensal  Micrococcus luteus  to the 9.7-Mb environmental strain Rhodococcusjostii . Since the discovery of antibiotics in the 1940s, the actinomycetes have received a great deal of attention, and  Streptomyces  species in particular have become renowned as the principal sources of therapeutic pharmaceuticals. There have beenseveral good reviews on actinomycetes of late, notably that by Ventura  et al . (2007) on evolutionary and genomic aspects, as well as occasionalarticles focusing on specific genera. However, other genera, including  Rhodococcus , are beginning to excite more inter...

Marine actinomycetes Actinomycetes represent a ubiquitous group of microbes widely distributed in natural ecosystems around the world and especially significant for their role in the recycling of organic matter (Srinivasan  etal ., 1991). Actinomycetes are abundant in terrestrial soils, a source ofmost isolates shown to produce bioactive compounds. Goodfellow and Haynes (1984) reviewed the literature on the isolation of actinomycetes from marine sediments and suggested that this source may be valuable for the isolation of novel actinomycetes with the potential to yield useful new products. Earlier studies (Weyland, 1981; Helmke and Weyland, 1984) considered actinomycetes to be part of an indigenous marine microflora. Others saw them primarily as wash in components that nearly survived in marine and littoral sediments as spores (Goodfellow and Williams, 1983). Jensen  et al . (1991) and Takizawa  et al . (1993) reported a bimodal distribution of actinomycetes in near shore...

  Streptomyces The search for new antibiotics or new antibiotic producing microbial strains continues to be of utmost importance in research programs around the world because of the increase of resistant pathogens and toxicity of some used chemical antibiotics. Among actinomycetes a large number of antibiotics were obtained from the genus Streptomyces (Alan and James, 2007; Lyudmila  et al ., 2008; Junker  et al ., 2009; Koch and Loffler, 2009).  Streptomyces  are widely recognizedas industrially important microorganisms because of their ability to produce many kinds of novel secondary metabolites including antibiotics (Williams  et al ., 1983). Indeed, different Streptomyces species produce about 75% of commercially and medically useful antibiotics (Miyadoh, 1993). Streptomyces species are distributed widely in marine and terrestrial habitats (Pathomaree et al ., 2006) and are of commercial interest due to their unique capacity to produce novel metabolites...

  Identification of actinomycetes The traditional methods used for the identification of the aerobic filamentous actinomycetes are laborious, time consuming and oftenrequire a series of specialized tests (Steingrube et al ., 1995; Wilson  et al ., 1998; Harvey  et al ., 2001). Chemical criteria, such as the isomer of diaminopimelic acid (DAP) present in the cell wall and the diagnostic sugar(s) present in the whole-cell hydrolysate, have been used to separate the actinomycete genera into broad chemotaxonomic groups. However, determination of these characteristics is time-consuming and, in most cases, cannot identify an isolate to a single genus (Lechevalier, 1989). PCR-based methods have provided a rapid and accurate way to identify these bacteria (Gurtler et al ., 1991; Kohler  et al ., 1991; Beyazova and Lechevalier, 1993; Telenti et al ., 1993; Soini et al ., 1994; Mehling etal ., 1995; Steingrube et al ., 1997; Wilson  et al ., 1998; Laurent  et al .,19...

  Metabolite production by marine Streptomyces Actinomycetes comprise about 10% of the bacteria colonizing marine aggregates and can be isolated from various marine sources. Many actinomycete isolates from the depths of the oceans contain non-ribosomal polyketide synthase (NRPS) and polyketide synthase (PKS) pathways, the hallmarks of secondary metabolite production (Li and Piel, 2002; Salmon  et al ., 2003). Terrestrial soils have hitherto been the predominant and widely exploited source, and investigations on marine Streptomyces are few and inconclusive, though they are the important sources for new bioactive compounds (Okami, 1984). About 23,000 antibiotics have been discovered from microorganisms. It has been estimated that approximately 10,000 of them were isolated from actinomycetes (Okami and Hotta, 1988). Actinomycetes, mainly the genus Streptomyces, have the ability to produce a wide variety of secondary metabolites as bioactive compounds, including antibiotics. The n...