Expression of the ACC deaminase gene from Enterobacter cloacae UW4 in Azospirillum brasilense

The ACC deaminase structural gene (acdS) from Enterobacter cloacae UW4 was cloned in the broad host range plasmid pRK415 under the control of the lac promoter and transferred into Azospirillum brasilense Cd and Sp245. A. brasilense Cd and Sp245 transformants showed high ACC deaminase activity, similar to that observed in Enterobacter cloacae UW4. The expression of ACC deaminase improved the existing growth promoting activity of Azospirillum. The roots of tomato and canola seedlings were significantly longer in plants inoculated with A. brasilense Cd transformants than those in plants inoculated with the nontransformed strains of the same bacterium. In the case of wheat seedlings, inoculation with A. brasilense Cd transformants did not promote root growth. The difference in plant response (canola and tomato versus wheat) is attributed to the greater sensitivity of canola and tomato plants to ethylene as compared to wheat plants.