Genetic and Phenotypic Diversity of Plant Growth Promoting Bacilli

Abstract

Bacilli are aerobic or facultatively anaerobic, Gram-positive or variable, endospore-forming bacteria that exhibit resistance to environmental stress and produce peptide antibiotics, peptide signal molecules, and extracellular enzymes. Bacillus and Paenibacillus genera include the best knowing nitrogen-fixing species. Another characteristic of bacilli is their great potential in producing substances that promote direct plant growth by the production of phytohormones (mainly indolic compounds), low-molecular-weight iron-binding molecules with a high affinity for Fe3+ (siderophores), and phosphate solubilization. It is well known that many species of Bacillus and Paenibacillus can contribute to plant growth and health in many ways, and most commercially developed PGPR are species of Bacillus which form endospores that confer population stability during formulation and storage of products. The identification and the isolation of PGP bacilli from soils, which combine the ability to fix nitrogen with the production of substances capable of promoting plant growth, could also significantly increase the productivity of many grain crops around the world.