Mineralization of pentachlorophenol in a contaminated soil by Pseudomonas sp UG30 cells encapsulated in κ-carrageenan

A contaminated soil from Ontario, Canada containing 350–370 ppm pentachlorophenol (PCP) and 21000 ppm total petroleum hydrocarbons (TPH) was inoculated with PCP-degrading Pseudomonas sp UG30 cells either encapsulated in κ κ-carrageenan or as free cells. Uninoculated control soil produced 18.8 ± 3.9% of ¹⁴CO₂ from 100000 dpm [U-¹⁴C]-PCP after 30 weeks incubation at 22°C. Addition of phosphate increased PCP mineralization, whereas addition of nitrogen inhibited mineralization almost completely in soil not inoculated with UG30 cells. No enhancement of mineralization was observed in soil with the addition of 10⁸ CFU g⁻¹ dry soil free UG30 cells. κ κ-Carrageenan-encapsulated UG30 cells at the same inoculum density mineralized 64.7 ± 0.3% PCP in soil after 26 weeks. Repeated inoculations with encapsulated UG30 cells up to six times over 6 weeks resulted in 64.8 ± 1.9% mineralization of radiolabelled PCP within 9 weeks, although by 12 weeks all treatments with encapsulated cells had mineralized to this level. Addition of sterile beads (controls) led to less than 16.6 ± 9.2% mineralization within 16 weeks. Varying initial inoculum densities of encapsulated cells were compared to determine effects on PCP mineralization. Cells grown inside the beads, and higher initial cell densities exhibited greater mineralization activity in the first weeks, but by 20 weeks PCP mineralization was approximately 70.0 ± 8.0% and was not significantly different between all soil treatments. Our results show encapsulation can enhance pollutant mineralization in a chemically contaminated soil.