Doumbou et al. (2002) reported two general ways, direct and indirect ways, by which the plant growth-promoting rhizobacteria (PGPR), including actinomycetes,improve plant growth. They stated that indirect promotion occurs when PGPR prevent the harmful effects of one or more deleterious microorganisms. This is chiefly attained through biocontrol, or the antagonism of soil plant pathogens. While the direct way occurs when PGPR supply the plant with a compound that was synthesised by its own or when PGPR facilitates plant uptake of soil nutrients. Nitrogen fixation, siderophore synthesis, phytohormone synthesis, and solubilisation of minerals to make them available for plant uptake and use all are examples for the direct promotion of the plant growth by PGPR.