Interactions of earthworms with indigenous and bioaugmented PCB-degrading bacteria

Abstract

Partial bioremediation of polychlorinated biphenyl (PCB)-contaminated soils has been achieved using bioaugmentation with PCB-degrading bacteria and earthworms. To further study the contribution of earthworms to bioremediation, an experiment was conducted in which the changes in indigenous and bioaugmented PCB-degrading bacteria were analyzed during treatment of contaminated soil using earthworms (Pheretima hawayana) alone or in combination with the PCB-degrading bacteria, Ralstonia eutrophus and Rhodococcus sp. ACS. Bacteria used for bioaugmentation were induced with carvone and salicylic acid in culture and were repeatedly applied every 3-4 days to the surface of unmixed, 20-cm long soil columns containing 100 ppm Aroclor 1242. After 9 weeks of treatment, the soil bacterial communities were analyzed using PCR primers for the bph genes. Results showed that approximately 50% of the PCBs were removed in the top 9 cm using a combination of earthworms and bioaugmentation, whereas bioaugmentation or earthworms applied alone were effective only for removing PCBs from the top 3 cm of the soil columns. Enhanced removal of PCBs caused by earthworms was associated with an increase in the population size of culturable, indigenous biphenyl-degrading bacteria, and an increase in the level of the bphA and bphC genes. The results suggest that earthworms facilitate PCB bioremediation by enhancing the dispersal of PCB-degrading bacteria in bioaugmented columns, as well as providing environmental conditions that favor the growth and activity of indigenous PCB-degrading bacteria.

Effects of two ecological earthworm species on atrazine degradation performance and bacterial community structure in red soil

“…The consumption of humic acid and humin by earthworms in this study therefore releases atrazine from soil aggregates and consequently accelerates its biodegradation. Our findings are consistent with Luepromchai's work that the enhanced removal of polychlorinated biphenyl (PCB) in vermicomposting is attributed to the increasing PCB availability and the abundance of PCB-degraders (Luepromchai et al, 2002).…”

Electrical stimulation of microbial PCB degradation in sediment

“…One possibility is that 1.5 V indirectly stimulates the PCB degradation of microaerophilic or aerobic microorganisms by promoting the movement of aquatic worms, which would actively mix O 2 into the sediment. Such worms have been reported to respond to electric stimuli (Satchell, J.E., 1955) and to stimulate indigenous or bioaugmented biphenyl-degrading bacteria and improve PCB bioremediation (Luepromchai, E. et al, 2002; Singer, A.C. et al, 2001). We observed that worms moved more actively to the surface of sediment in SBRs with the added voltage ( e.g .…”

Impact of the plant rhizosphere and augmentation on remediation of polychlorinated biphenyl contaminated soil

“…The eluted DNA products were stored at Ϫ20ЊC prior to analysis. DNA from each soil sample was subjected to polymerase chain reaction and DGGE as previously described [24].…”