In fact, plants secrete both high and low-molecular weight compounds from their roots, termed as root exudates. These compounds may act as signal molecules for microbial attraction or be used as carbon sources for microbial nutrition (Antoun and Prevost, 2006). The role of root exudates as signaling molecules has been recently addressed by Rudrappa and associates, who showed that root-secreted malic acid recruits the beneficial soil bacteria Bacillus subtilis to the root and this interaction plays a role in plant protection against the foliar pathogen Pseudomonas syringae. The release of carbon compounds from plants into the rhizosphere increases microbial biomass and activity (Bashan and de-Bashan, 2005). In the first step, the bacteria multiply near the root and then adhere to it. This allows the bacteria to colonise and enter the root. The bacteria may enter directly through points on the root surface (Bashan and de-Bashan, 2005; Gnanamanickam, 2006). This method depends on the type of plant.