Chemotaxis of Rhizobium sp.S2 towards Cajanus cajan root exudate and its major components.

The chemotactic response of Rhizobium sp. S2, a slow-growing Cajanus cajan isolate, towards its host root exudate was examined. Two classes of mutants, one nonchemotactic towards nutrients (amino acids and sugars) and signal compounds like flavonoids and the other, nonchemotactic towards amino acids and sugars but positive towards naringenin, the flavonoid present in Cajanus cajan root exudate, were obtained. The plasmid-cured derivative of the parent showed positive response towards amino acids and sugars but was nonchemotactic towards naringenin. A possible presence of dual chemotaxis pathways, one towards nutrients and the other for sensing signal compounds, was thus demonstrated. The possible involvement of naringenin as a chemoattractant in the preliminary stages of this Rhizobium-legume interaction was also established.