Detection and Identification of Bacterial Biological Control Agents

Abstract

Bacteria, classifi ed as prokaryotes, are much simple in structure and smaller in size. They have less complex structural features compared to the fungi (placed under eukaryotes) which have well defi ned thallus composed of different asexual and sexual structures bearing various spore forms at different stages of their life cycle. Most of the bacterial species are strictly saprophytic and they are involved in the decomposi-tion organic materials present in the soil and water, dead plants and animals. They are useful in denaturing large quantities of organic wastes from industries and oil spill occurring in the sea water. Some of them cause diseases in plants, humans and animals. Many bacterial species are benefi cial to human beings, as they help build up nutritional levels of the soil and have potential for reducing the activity of or inhibiting the development of bacterial plant pathogens. The morphological charac-teristics of bacterial cells are less variable and hence biological, biochemical, physi-ological, immunological and genomic characteristics have to be determined for reliable and precise identifi cation and meaningful classifi cation of the bacterial bio-control agents that are to be employed for the management of crop diseases caused by microbial plant pathogens (Narayanasamy 2002 , 2011). Taxonomic characteristics and guidelines for identifi cation of bacterial species are described in the Bergey's Manual of Systematic Bacteriology (Kreig and Holt 1984). Bacterial species obtained from different habitats are cultivated in appropri-ate media that favor their development. Cultural characteristics such as colony mor-phology, production of enzymes, toxins and other metabolites, pattern of utilization of carbon sources, pH and temperature optima for growth and other nutrient require-ments are determined. As the variations in the cultural characteristics are inadequate for discriminating closely related species/strains of a bacterial species, immunologi-cal properties of bacterial cell surface proteins have been used as the basis for detec-tion, differentiation and quantifi cation of bacteria. Nucleic acid-based techniques have been shown to be more sensitive, precise, specifi c and reliable, in addition to their ability to provide results rapidly. Various methods that have been employed for the detection and identifi cation of the bacterial biocontrol agents are discussed, indicating the advantages and disadvantages of different procedures applied.