Abstract: A novel saline-tolerant bacterium Bacillus circulans WZ-12 was evaluated for its potential to degrade four chlorinated hydrocarbons under saline conditions. CH₂Cl₂ was effectively degraded by Bacillus circulans WZ-12 cells in the medium containing NaCl concentrations ranging from 5 g·L^-1 to 10 g·L^-1, and the maximum degradation efficiency (85%) was achieved at NaCl concentration of 10 g·L^-1. Similarly, Bacillus circulans WZ-12 was able to degrade CH₂BrCl, C₂H₄Cl₂, and C₂H₂Cl₂ in the presence of 10 g NaCl per liter within 24 h. Cells of Bacillus circulans WZ-12 grown in minimal salt medium contained low levels of glycine betaine (GB), but GB levels were 3- to 5-fold higher in cells grown in media with high salt. Kinetic analysis revealed that biodegradation of the four chlorinated hydrocarbons was concentration dependent and a linear inverse correlation (R² 0.85-0.94) was observed between the rate of biodegradation (V) and salt concentration from 5 g·L^-1 to 60 g·L^-1. The growing cells (in minimal salt medium) degraded approximately 50% of the CH₂Cl₂ within 24 h, whereas the resting cells (in physiological saline) degraded only 25% of the CH₂Cl₂ within 24 h and were inactive after 36 h cultivation. Biodegradation could be repeatedly performed for more than 192 h with more than 50% removal efficiency. Bacillus circulans WZ-12 grows well in an aqueous/oil system, hence, it is effective for the treatment of industrial effluents that contain chlorinated hydrocarbons with high salt concentrations.

Key words: chlorinated hydrocarbons, biodegradation, Bacillus circulans WZ-12, salinity

摘要： A novel saline-tolerant bacterium Bacillus circulans WZ-12 was evaluated for its potential to degrade four chlorinated hydrocarbons under saline conditions. CH₂Cl₂ was effectively degraded by Bacillus circulans WZ-12 cells in the medium containing NaCl concentrations ranging from 5 g·L^-1 to 10 g·L^-1, and the maximum degradation efficiency (85%) was achieved at NaCl concentration of 10 g·L^-1. Similarly, Bacillus circulans WZ-12 was able to degrade CH₂BrCl, C₂H₄Cl₂, and C₂H₂Cl₂ in the presence of 10 g NaCl per liter within 24 h. Cells of Bacillus circulans WZ-12 grown in minimal salt medium contained low levels of glycine betaine (GB), but GB levels were 3- to 5-fold higher in cells grown in media with high salt. Kinetic analysis revealed that biodegradation of the four chlorinated hydrocarbons was concentration dependent and a linear inverse correlation (R² 0.85-0.94) was observed between the rate of biodegradation (V) and salt concentration from 5 g·L^-1 to 60 g·L^-1. The growing cells (in minimal salt medium) degraded approximately 50% of the CH₂Cl₂ within 24 h, whereas the resting cells (in physiological saline) degraded only 25% of the CH₂Cl₂ within 24 h and were inactive after 36 h cultivation. Biodegradation could be repeatedly performed for more than 192 h with more than 50% removal efficiency. Bacillus circulans WZ-12 grows well in an aqueous/oil system, hence, it is effective for the treatment of industrial effluents that contain chlorinated hydrocarbons with high salt concentrations.

关键词: chlorinated hydrocarbons, biodegradation, Bacillus circulans WZ-12, salinity