Aerobic cometabolism of chloroform by butane-grown microorganisms: long-term monitoring of depletion rates and isolation of a high-performing strain

The focus of this microcosm study was to monitor the performances of 17 butane-utilizing microcosms during a long-term (100-250 days) aerobic cometabolic depletion of chloroform (CF). The depletion of the contaminant began after a lag-time variable between 0 and 23 days. All microcosms quickly reached a pseudo steady-state condition, in terms of biomass concentration (with an average of 9.3·10^6 CFU/ml), chloroform depletion rate (0.005 mmol/(l d)) and butane utilization rate (0.73 mmol/(l d)). After about 100 days of CF depletion, a sudden 5- to 7-fold increase of the chloroform rate was observed in 2 microcosms, where the highest amount of contaminant had been depleted. In one of these high-performing microcosms, an experiment of chloroform depletion in the absence of butane resulted in the depletion of a surprisingly high amount of contaminant (0.765 mmolCF/kg of dry soil in 2 months) and in a marked selection of a single bacterial strain. Bioaugmentation assays conducted with the biomass selected in this microcosm and with a pure culture of the selected strain immediately resulted in very high chloroform depletion rates. Preliminary results of a study conducted with resting cells of the selected strain indicated that it can degrade chloroform concentrations up to 0.119 mM (14.2 mg/l) without any sign of substrate toxicity, and that it is able to transform vinyl chloride and 1,1,2-trichloroethane.