Batch and continuous mode degradation of monochloroacetic acid used as a sole carbon and energy source in the concentration range of 0.9-48.4 mM by pure culture of Xanthobacter autotrophicus GJ10 was investigated. The substrate was completely degraded in each flask in batch system. Partial substrate inhibition occurred at the concentrations exceeding 25.4 mM. Temporary accumulation of glycolic acid in the medium indicated that dehalogenation was undergoing faster than further utilization of glycolate. Three different carbon substrates were used for inoculum preparation--1,2-dichloroethane, tri-sodium citrate and a nutrient broth. The fastest growth on monochloroacetate occurred for 1,2-dichloroethane-grown inoculum. The assays of haloacid dehalogenase in crude extract indicated that the bacteria grown on 1,2-dichloroethane possessed higher level of the enzyme. The response of the GJ10 culture towards spikes of 20 mM monochloroacetate was tested in 2.5-1 continuously stirred tank fermentor. The substrate was readily utilized within 7-8 h. Continuous degradation of monochloroacetate in the fermentor was demonstrated for monochloroacetate concentration of 20 mM and dilution rate 0.016 h(-1). Quantitative agreement between the amount of monochloroacetate introduced and chloride released was found. The results demonstrated that the strain X. autotrophicus GJ10 might be suitable for biodegradation of monochloroacetate contaminated media.

The conversion of and toxic effects exerted by several mono- and dihalogenated C1 and C2 compounds on cultures of Xanthobacter autotrophicus GJ10 growing on 1,2-dichloroethane were investigated. Bromochloromethane, dibromomethane and 1-bromo-2-chloroethane were utilized by strain GJ10 in batch culture as a cosubstrate and sole carbon source. The rate of degradation of dihalomethanes by whole cells was lower than that of 1,2-dichloroethane, but a significant increase of the rate of dihalomethane biodegradation was observed when methanol or ethanol were added as a cosubstrate. Products of the degradation of several tested compounds by haloalkane dehalogenase were analyzed and a new metabolic pathway based on hydrolytic conversion to formaldehyde was proposed for the dihalomethanes. Strain GJ10 growing on 1,2-dichloroethane converted 2-fluoroethanol and 1-chloro-2-fluoroethane to 2-fluoroacetate, which was tolerated up to a concentration of 2.5 mM. On the basis of the results from batch cultures an inert (dichloromethane), a growth-supporting (dibromomethane) and a toxic (1,2-dibromoethane) compound were selected for testing their effects on a continuous culture of strain GJ10 growing on 1,2-dichloroethane. The compounds were added as pulses to a steady-state chemostat and the response of the culture was followed. The effects varied from a temporary decrease in cell density for dibromomethane to severe toxicity and culture washout with 1,2-dibromoethane. Our results extend the spectrum of halogenated C1 and C2 compounds that are known to be degraded by strain GJ10 and provide information on toxic effects and transformation of compounds not serving as a carbon source for this bacterium.