Antimicrobials compounds from extreme environment Rhizosphere organisms for plant growth

Rhizosphere microorganisms are a heterogenous group of bacteria, including plant growth promoting bacteria, which can improve extent or quality of plant growth direct and indirect. Generally large array of bacteria, including species of Pseudomonas, Azospirillum, Azotobacter, Klebsiella, Enterobacter, Alcaligenes, Arthrobacter, Burkholderia, Bacillus and Serratia have been reported to enhance plant growth (Ahmad et al., 2008; Barrie et al., 2008; Baudoin et al., 2010). PGP bacteria can exhibit a variety of characteristics responsible for influencing plant growth. The exact mechanisms by which PGP bacteria promote plant growth, are not fully understood, but are thought to include: (i) the ability to produce or change the concentration of plant growth regulators like IAA, gibberellic acid, cytokinins and ethylene (Arshad and Frankenberger, 1993; Glick 1995); (ii) N2 fixation (Boddey and Dobereiner, 1995); (iii) antagonism against pathophytogenic micro-organisms by production of siderophores (Scher and Baker, 1982), antibiotics (Shanahan et al., 1992) and cyanide (Flaishman et al., 1996) and (iv) solubilization of mineral phosphates and other nutrients (for 1990; De Freitas et al., 1997).