Antibiotic Production by Rhizospheric Soil Microflora - a Review

The rhizosphere represents the thin layer of soil surrounding plant roots and the soil occupied by the roots, supports large active groups of microorganisms. The vast organic compounds (amino acids, sugars etc.) secreted by plant roots in the rhizosphere provide a food source for microorganisms increasing microbial biomass and their activity in the rhizosphere. Antibiotics are antimicrobial compounds produced by living microorganism as secondary metabolites. These compounds are used therapeutically and sometimes prophylactically in the control of infectious diseases. The isolation of antibiotics from microorganisms is relatively easy as compared to chemical synthesis of antimicrobial agents. The isolation of antibiotics from microorganisms improved the discovery of novel antibiotics that could act as better chemotherapeutic agents. With the increased population pressure, costs and side effects and the development of resistance of pathogens to drugs for infectious diseases, there is an urgent need to explore microbes for development of new antimicrobial metabolites. As microorganisms grow in unique and extreme habitats, they may have the capability to produce unique and unusual metabolites. So rhizospheric soil gives an excellent option as a source for search of some new alternative medicines. This review highlights the recent developments in the production of antimicrobial compounds from rhizospheric soil microflora. INTRODUCTION: Rhizosphere is a soil around a plant root which is inhabited by a diverse population of microbes, comprising bacteria, fungi, actinomycetes and algae affected by the chemicals which are released from the roots of plant 1 . The organic materials from roots provide the driving force for the development of active microbial biomass around the root than in the bulk soil 2 . The different compounds secreted by plant roots into the rhizosphere perform multiple functions. QUICK RESPONSE CODE DOI: 10.13040/IJPSR.0975-8232.7(11).4304-14 Article can be accessed online on: www.ijpsr.com DOI link: http://dx.doi.org/10.13040/IJPSR.0975-8232.7 (11).4304-14 For example, Allelochemicals can inhibit the growth of other microorganisms in the rhizosphere, so plant microbes interactions are very complex 3 . The rhizosphere is divided into three zones which on the basis of their relative proximity to, and thus influence from, the root. Endorhizosphere includes parts of the endodermis and cortex where microbes and cations can occupy the “free space” between cells, rhizoplane is the medial zone which is directly adjacent to the root and includes the root epidermis and the mucilage and the outermost zone called the ectorhizosphere extends from the rhizoplane out into the bulk soil 4 . Populations of microbes can boom or reduce in the space in response to the changes in soil conditions i.e. moisture, temperature or substrates like carbon.