Abstract
Survival of every organism on earth depends on its interactions with other organisms. For example, animals form associations with the intestinal microflora, while plants develop symbiotic associations with neighboring plants, microflora, and microfauna. Most of the associations between plants and microorganisms are mediated by organic compounds released by the plant. The plant root system acts as a factory and exudes enormous amount of chemicals to effectively communicate with the surrounding soil organisms. Bacteria on roots and in the rhizosphere can also utilize these organic compounds as a source of nutrients and enhance their population size and metabolic activities. In return, plant-associated bacteria improve plant growth and development by different mechanisms including nitrogen fixation, provision of nutrients, and mediating resistance against pathogens. Although plant–bacterial partnerships have been found effective to enhance biomass production, their importance and relevance in agricultural systems are still underestimated. A better understanding of beneficial interactions between plant, soil, and bacteria could be exploited to improve growth and health of food and feed crops. Plant growth-promoting mechanisms of bacteria might enhance biomass production in a more sustainable manner, even on marginal land. Furthermore, plant growth-promoting and/or pollutant-degrading activities of bacteria could be exploited to improve the efficiency of phytoremediation of organic and inorganic pollutants from the soil and water or to protect the food chain by decreasing the concentrations of pollutants in food crops.