Rhizobia are a diverse group of bacteria that engage in symbioses with the roots of leguminous host plants. Once established as symbionts, these bacteria reduce dinitrogen to a form the plant can use for growth. Symbiotic bacteria contribute significantly to an ecologically-sound and cost-efficient nitrogen supply. Most rhizobia belong to families in the order of the Rhizobiales within the alpha-proteobacteria subdivision (alpha-rhizobia). Many rhizobia are capable of inducing the formation of nodules on the roots of their leguminous host plants. These specialized plant organs are invaded by the bacteria which fix nitrogen in an endosymbiotic bacteroid state within the plant cell. This process involves specific recognition and coordinated differentiation of both bacterial and host cells.
Xanthomonas species which have adopted a plant-associated and usually plant pathogenic lifestyle group to the gamma-proteobacteria. Xanthomonads are pathogens of diverse groups of cultivated plants. We study Xanthomonas campestris as pathogen of cruciferous plants. Based on their specific host ranges, strains of Xanthomonas campestris were differentiated into over 140 pathovars.
Xanthomonas species are able to produce the acidic exopolysaccharide xanthan gum. Because of its physical properties it is widely used as a viscosifier, thickener, emulsifier or stabilizer in both food and non-food industries.