Motility-enhanced bioremediation of carbon tetrachloride-contaminated aquifer sediments

Pseudomonas stutzeri KC is an aquifer isolate capable of denitrification and cometabolic transformation of carbon tetrachloride (CT) under anoxic conditions. Capillary experiments established that strain KC is chemotactic toward nitrate. A model aquifer column was used to evaluate the effects of motility in the presence of groundwater flow, and a second column was used to isolate motility in the absence of flow. Both columns contained CT-saturated sediments and groundwater containing CT and nitrate. The flow column was inoculated near its upstream end with strain KC, base, acetate, and phosphate and flushed continuously thereafter with contaminated groundwater. Cells migrated through the column at a velocity exceeding that of the groundwater, removing both aqueous and sorbed CT. The no-flow column was inoculated near its midpoint and maintained as a static incubation. Motile KC cells migrated over a 0.3 m distance within 5 days, giving a cell velocity of >5 cm/day. Over 94% of the CT in the column was removed in 26 days. The results support the hypothesis that localized depletion of nitrate during denitrification creates nitrate gradients that trigger a chemotactic response. The results also indicate that motile KC cells can degrade CT.