Bacterial Endophytes of Plants: Diversity, Invasion Mechanisms and Effects on the Host

Plant inner tissues are colonized by bacterial organisms known as endophytes. The relatively recent application of culture independent and molecular high throughput techniques allowed the description of a large diversity of endophytic bacterial taxa. These microorganisms can be found in any plant organ, including fruits and legume nodules. Some endophytic bacteria benefit the host by several mechanisms, and their application to economically important crops represents an interesting alternative to the use of agrochemicals. However, more studies are required to clearly assess their effects on the hosts (especially in co-inoculation with other beneficial bacteria) and the molecular events that lead to the interaction between plants and endophytic microorganisms. In this chapter, we focus on bacterial endophytes from legumes and non-legumes plants, analyzing their diversity and effects on the hosts. We also discuss the endophytic colonization of legume nodules, with emphasis on the endophytic bacterial diversity, the mechanisms involved in the nodule invasion and their effects on the hosts.