Diversity and importance of diazotrophic bacteria to agricultural sustainability in the tropics

Abstract

The N2-fixing (diazotrophic) bacteria reduce atmospheric nitrogen (N2) into NH3 by means of the enzymatic complex of the nitrogenase and proliferate in a broad range of environments with different lifestyles. Considering their strategies in agricultural systems, diazotrophic bacteria are classified in four groups: Soil free- living, rhizospheric associative, endophytic, and symbiotic nodule-formers. The soil free-living group plays a key role in the soil organic matter cycling. The asso- ciative (living on root surfaces) and endophytic (living in inner plant parts) groups establish reciprocal relationships with plants, usually resulting in plant growth pro- motion. The nodule-forming bacteria, with an emphasis on rhizobia that associate with legumes, represent the most effective group in supplying N to agricultural systems. However, despite significant advances in our understanding of the diversity of diazotrophic bacteria achieved in the last decades, it is true to say that the use of these microorganisms to improve agriculture sustainability is still poorly explored in view of their great potential.