Monochloroacetate dehalogenase activities of bacterial strains isolated from soil

Abstract

Seven bacterial strains capable of utilizing monochloroacetate (MCA) at a concentration of 50 mM as the sole carbon source were isolated from soil and displayed MCA dehalogenase activity. Three of them were identified as Pseudomonas spp., and the remaining four strains as Alcaligenes sp., Agrobacterium sp., Arthrobacter sp., and Azotobacter sp. This latter is the first reported example of a bacterium fixing atmospheric nitrogen under aerobic conditions that also uses a chloro-organic compound as sole source of carbon and energy. MCA dehalogenase activity in these strains was found to be inducible under different growth conditions. Crude extracts from all seven isolated strains also displayed dehalogenating activity with a relatively wide range of halogenated organic compounds (aliphatic acids, ketones, alcohols, alkanes, and aromatics), which, depending on the strain, were dehalogenated to different extents. The estimated Kmvalues for MCA were used to classify the dehalogenase activities into three groups: high affinity (30–40 μM) in Alcaligenes and Agrobacterium species, medium affinity (100–180 μM) in Pseudomonas and Azotobacter species, and low affinity (100 mM) in Arthrobacter sp. Both the optimal pH range for MCA dehalogenase activity (between pH 8 and 10) and the pH profile of stability (in the neutral–basic range) were found to be similar in all strains, whereas the thermal stability profiles were variable.Key words: dehalogenase, halohydrolase, monochloroacetate, soil.