Use of nitrogen-fixing bacteria to improve agricultural productivity

Nitrogen-fixing, plant-growth promoting bacteria are arguably the biotechnological tool of highest potential to improve agricultural productivity in short term. Nitrogen fixation and phytohormone production by these bacteria have been considered the most important factors for plant growth promotion. However, the underlying mechanisms responsible for productivity increases by associative bacteria are not clear. Moreover, the intensity of the plant growth promotion, including transfer of the fixed nitrogen from the bacteria to the plant, depends on an efficient interaction of the plant genotype and bacterial species. Azospirillum spp. are nitrogen-fixing, plant growth promoting bacteria that can associate with several cereals such as maize, rice and wheat, and also biofuel crops such as sugar cane and Pennisetum. Azospirillum brasilense is one of the most used plant growth promoting bacteria (PGPB), being used in Brazil, Argentina, Mexico, India and Europe. Analyses of field experiments have shown a success rate of inoculation with Azospirillum ranging from 60 to 70%, with statistically significant increases in yield varying from 5 to 30% [1]. The regulation of nitrogen metabolism in A. brasilense has been extensively studied. Here we will review nitrogen fixation regulation in this bacterium and advances in the understanding of aspects of interaction with cereal plants obtained by transcriptomic analyses.