Bacillus and Paenibacillus spp. are known to have wide PGPR potentials; in the
rhizosphere, they are involved in nitrogen fixation, soil phosphorus solubilisation,
the production of antibiotics, chitinase, hydrolytic enzymes, and exopolysaccharides
and in the enhancement of soil porosity. Numerous Bacillus and Paenibacillus strains
express these activities which promote plant growth and suppress soilborne plant
pathogens. A number of these strains already have been developed commercially as
plant growth promoters and biocontrol agents (Table 3) and their use in agriculture
has recently been reviewed (Lacey et al. 2001; Paulitz and Belanger 2001). Similarly,
many strains of Paenibacillus were isolated and characterized functionally (Table 4)
for their potential use in agriculture as plant growth promoters (Timmusk and Wagner
1999; Timmusk et al. 2003; Senthilkumar et al. 2007a). Improvements in plant
growth and productivity by the applications of Bacillus and Paenibacillus spp. are
mediated by three different ecological mechanisms: promotion of host plant nutrition
and growth, antagonism against plant pathogens and insect pests, and stimulation of
plant host defense mechanisms.