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

Abstract

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 × 10⁶ CFU ml⁻¹), chloroform depletion rate (5 μmol l⁻¹ d⁻¹) and butane utilization rate (730 μmol l⁻¹ d⁻¹). After about 100 days of CF depletion, a sudden 5- to 7-fold increase of the chloroform rate was observed in two 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 (765 μmol _CF kg ⁻¹_{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 119 μM (14.2 mg l⁻¹) without any sign of substrate toxicity, and that it is able to transform vinyl chloride and 1,1,2-trichloroethane.