MONOCHLOROACETATE DEHALOGENASE ACTIVITIES OF BACTERIAL STRAINS ISOLATED FROM SOIL

Seven bacterial strains capable of utilizing monochloroacetate (MCA) a t a concentration of 50 mM as the sole carbon source were isolated fro m soil and displayed MCA dehalogenase activity. Three of them were ide ntified as Pseudomonas spp., and the remaining four strains as Alcalig enes sp., Agrobacterium sp., Arthrobacter sp., and Azotobacter sp. Thi s latter is the first reported example of a bacterium fixing atmospher ic nitrogen under aerobic conditions that also uses a chloro-organic c ompound as sole source of carbon and energy. MCA dehalogenase activity in these strains was found to be inducible under different growth con ditions. Crude extracts from all seven isolated strains also displayed dehalogenating activity with a relatively wide range of halogenated o rganic compounds (aliphatic acids, ketones, alcohols, alkanes, and aro matics), which, depending on the strain, were dehalogenated to differe nt extents. The estimated K-m values for MCA were used to classify the dehalogenase activities into three groups: high affinity (30-40 mu M) in Alcaligenes and Agrobacterium species, medium affinity (100-180 mu M) in Pseudomonas and Azotobacter species, and low affinity (100 mM) in Arthrobacter sp. Both the optimal pH range for MCA dehalogenase act ivity (between pH 8 and 10) and the pH profile of stability (in the ne utral-basic range) were found to be similar in all strains, whereas th e thermal stability profiles were variable.