Interactions of Gramineous Plants with Azoarcus spp. and Other Diazotrophs: Identification,Localization, and Perspectives to Study their Function

Nitrogen-fixing bacteria colonize the roots of many gramineous plants from different geographic regions. The discovery that diazotrophs can be isolated from surface-sterilized roots or other plant material led to studies of their potential to inhabit plant tissue. For some diazotrophs, their endophytic character has been documented. This review summarizes current methods to identify endophytes and to characterize the colonization of plants by endophytic bacteria. Taxonomy, occurrence, diversity, and mechanisms of plant infection of Azoarcus spp. is discussed in relation to Herbaspirillum spp. and Acetobacter diazotrophicus. Perspectives how to study their functions and metabolism in association with plants are discussed.