**2.1 Importance of soil microorganisms**

Biological fertility of the soil comprises of the soil microbes which greatly influence the structure and functioning of the soil ecosystem. The maintenance of the physical fertility and chemical fertility is driven by the metabolic repertoire of the soil microorganisms. Soil microbes are part of a very complex food web that occurs in soil. Soil biota is indispensable for key soil function such as decomposition of soil organic matter, nutrient cycling and formation of soil aggregates and billions of microbes reside in a single gram of soil [2]. The most numerous microbes in soil are the bacteria, followed in decreasing numerical order the fungi, soil algae and soil protozoa. The work that is turned out by bacteria does benefit the plants and other living organisms. Plants are unable to absorb the nutrition from the soil without microbes working in the soil. Although microbes tend to receive more attention for the diseases they cause, they are likely to be more significant for their role in maintaining the health of the plants by protecting them from other microorganisms, providing vitamins, nutrients and influencing the developmental processes [3]. The microbial activity in the rhizosphere is essential for plant functioning as it assists the plant in nutrient uptake and offers protection against pathogen attack [4]. Rhizosphere, a region of soil which is influenced by the plant roots, a microenvironment where a great microbial diversity thrives in close association with plant roots where in various abiotic and biotic interactions take place. Abiotic factors influence the structure of microbial communities which have evolved mechanisms to deal with occupation of the space that allows them to obtain nutrients excreted by the plant roots. The organism diversity of the bulk-soil or the rhizospheric soil of different plants has been extensively studied; most studies have reported a wide range of organisms from those soil portions [5]. Surprisingly, a soil sample could contain up to 4 × 106 different taxa [6]. This suggests that soil is a large reservoir for the discovery of several compounds that may have applications in agriculture, human health or industry. The relevant insights of the studies related to soil are that each of them has shown different aspects to study and analyze. In some cases, they have provided innovative views of the microbial ecology on extreme environments for the development of life. At the same time, others have found novel biocatalysts, new antibiotics, personalized medicine, bioremediation and other potential applications in biotech industry [7].

Microbiological studies in the soil environment are hampered by the fact that the largest proportion of soil bacteria as yet cannot be cultured [8], and the microbes found using common culture methods are rarely abundant in any environmental niche from which they were cultured. The microbes isolated from the soil mostly belong to the four major phyla namely *Proteobacteria*, *Actinobacteria*, *Firmicutes* and *Bacteroidetes*, as those minute organisms are easily cultivable under laboratory conditions. Such information suggests that there is the need of molecular techniques which overcomes the need to isolate and study each organism for in depth characterization. However with the development in metagenomics a more complete picture of the rhizosphere microbiome can be unearthed [9] and many new microbial players in the rhizosphere are on their way to be discovered.
