Bacilli are the most abundant organism in the rhizosphere and can produce endospores which aid them to survive under adverse conditions. They are Gram positive, aerobic, rod shape, sporulating bacteria that are ubiquitous in nature. Some species have different PGPR capacities (Barriuso and Solano, 2008). There are numerous metabolites that are produced and released by these strains, which can affect the environment positively though the increase of nutrient availability for the plants (Barriuso and Solano, 2008). Bacillus spp play significant t role in the agroecosystems and this bacterium aid in improving nutrient assimilation and plant growth (Ramirez and Kloepper, 2010).
Bacillus spp have been reported to have the potential to increase the yield, growth and nutrition of raspberry plant under organic growing conditions. Several In vitro tests have been carried out on Bacillus cereus and Bacillus polymyxa and they were found to solubilise phosphate. Bacillus megaterium from tea rhizosphere is also able to solubilize phosphate, improving different root parameters (rooting performance, dry matter content of root and root length) in mint (Kaymak et al., 2008). Studies show that Bacillus licheniformis when inoculated on pepper and tomato gives favorable colonization and this can be used as biofertiliser without harmful effects in the environment. Bacillus megaterium var. phosphaticum, phosphorus solubilizing bacteria and Potassium Solubilising Bacteria (KSB) Bacillus mucilaginosus showed that rock materials such as Phosphorus and potassium rocks and both bacterial strains consistently increase mineral availability, uptake, increase growth of pepper, tomatoes and cucumber when inoculated in nutrient limited soil. (Han et al., 2009).PGPR play a major role in the biocontrol of plant pathogens in the rhizosphere. They provide protection and suppress a broad spectrum of bacterial, fungal, viral and nematode diseases. PGPR is a potential tool as biocontrol agent for agricultural benefit (Sivasakthi et al., 2013). Pseudomonades is a major group of rhizobacteria with potential for biological control. Pseudomonas sp. is ubiquitous bacteria in agricultural soils and it possesses many characteristics of PGPR that make them well suited as biocontrol and biofertilizers. Some of them have the ability to (i) grow rapidly in vitro and to be mass produced; (ii) colonize and multiply in the rhizosphere and spermosphere environments and in the interior of the plant; (iii) Rapid production of wide spectrum of bioactive metabolites (i.e., antibiotics, siderophores, volatiles, and growth-promoting substances); (iv) Utilization of root exudates and seed; (v) Aggressive compete with other microorganisms; and (vi) Adaptation to environmental stresses (Beneduzi et al., 2012).
Fluorescent Pseudomonas spp. has been studied and reported for their plant growth-promoting effects by effective suppression of soil borne plant diseases. Fluorescent pseudomonads posses multiple mechanisms for plant growth promotion, biocontrol of plant pathogens and production of antibiotics, chitinolytic enzymes, HCN and catalase, siderophores, and can solubilize phosphorous and potassium . Bacillus megaterium KL39 is one of the biocontrol agents of red-pepper Phytophthora blight disease; it produces an antifungal antibiotic active against a broad range of phytopathogenic fungi in the soil. Bacillus subtilis is a widely recognized powerful biocontrol agent that has the ability to form endospores in the soil and also produces different biologically metabolites with a broad spectrum of activity. Bacillus cereus UW 85 and Azotobacter vinelandii MAC 259 can produce siderophores and are employed as PGPR to enhance the crop yield (Saharan and Nehra, 2011). Bacillus thuringiensis (kurstaki) and Bacillus sphaericus have the ability to control lepidopteron pests. Azospirillum Brasilense have the capabilities of biocontrolling crown gall-producing Agrobacterium, bacterial leaf/vascular tomato diseases and bacterial leaf blight of mulberry. These antibacterial activities from Azospirillum Brasilense could result from the production of bacteriocins, siderophores and phenylacetic acid (PAA), an auxin-like molecule with antimicrobial activity (Somers et al., 2005).