The induction of plant growth promoting microbiomes (PGPM) in agricultural and horticultural field crops considered an environmental friendly biofertilizers, an alternative to chemical fertilization. The PGPM in extreme environments are halophiles, acidophiles, thermophiles, psycrophiles and metal resistant microorganisms are mainly inoculated onto seeds, roots and soil. PGPEM improve plant growth by enhancing the availability of nutrients, the regulation of phytohormones, and by increasing plant tolerance against biotic and abiotic stresses. These PGPM colonize the rhizosphere of plants inducing the accumulation of osmolytes, antioxidants, upregulation or down regulation of stress responsive genes and alteration in root morphology in acquisition of tolerance under adverse environmental conditions. The PGPM have been reported from all three domain archaea, bacteria and eukarya of different groups such as Actinobacteria, Ascomycota, Bacteroidetes, Basidiomycota, Crenarchaeota, Euryarchaeota, Firmicutes and Proteobacteria. The microbes possess the diverse plant growth promoting features and these efficient and potential microbes may be applied as biofertilizers for crops improvements and soil health for sustainable agriculture. In order to survive under the biotic and abiotic stress conditions, these PGPM, have developed adaptive features which permits them to grow optimally under one or more environmental extremes, while poly-extremophiles grow optimally under multiple conditions. In this chapter compile the research progress in PGPM will promise on the development of molecular approaches to increase our knowledge of PGPM and to achieve an integrated management of plant growth promoting extremophiles.
Key words: PGPM, soil, acidity, alkalinity, archaea, bacteria, eukarya