The natural condition of plants closely interacts with endophytic microorganisms. Endophytes help in increasing crop yields, removing contaminants, inhibiting pathogens, and producing fi xed nitrogen or novel substances. The repertoire of their effects and functions in plants has not been comprehensively defi ned. The challenge and goal is to be able to manage microbial communities to favour plant colonization by benefi cial bacteria. This would be possible when more knowledge on endophyte ecology and their molecular interaction is attained. The contributions of this research fi eld may have economic and environmental impacts. The most extensively studied mutualistic bacteria interacting with plants are Gram-negative because they are readily isolated from plant tissues, easily handled, amenable to genetic approaches and because they include the symbiotic nitrogen fi xing microorganisms, namely, rhizobia. However, the impact of Gram-positive bacteria on plants is more important