Effect of earthworm egg capsule microbiota on degradation of 2,4-dichlorophenoxyacetic acid

Lori L. Daane and Max M. Häggblom

Biotechnology Center for Agriculture and the Environment

Rutgers, The State University of New Jersey

59 Dudley Road, New Brunswick, NJ 08901-8520, USA

There have been few investigations which have assessed the influence of earthworm egg capsule microbiota on degradation of toxic chemicals and on egg capsule (cocoon) viability. Earthworm cocoons may contain total culturable bacteria up to 10⁶ colony forming units (CFU) per cocoon, but there is little information on how this microbiota influences the fate of toxic chemicals. Earthworms may have some capability to control the bacteria associated with them. Specifically, cocoons may acquire bacteria from the environment in which they are produced. Of particular interest is the consistent recovery of Ralstonia eutropha (pJP4) from Eisenia fetida cocoons formed in inoculated soil. Plasmid pJP4 contains the genes necessary for 2,4-D and 2,4-dichlorophenol (2,4-DCP) degradation. We were interested in determining whether the presence of this bacterium within the developing earthworm cocoon can influence the degradation and toxicity of 2,4-D and 2,4-DCP. Cocoons were collected after 1, 2 and 3 weeks from soil-earthworm microcosms inoculated with 10⁹ cells of R. eutropha (pJP4) per gram and contained mean concentrations of 10⁵, 10⁴ and 10³ CFU per cocoon, respectively. 2,4-DCP toxicity studies were performed using viable cocoons with and without R. eutropha. Results showed that cocoons containing R. eutropha were able to tolerate higher levels of 2,4-DCP. The biodegradation of 2,4-D and 2,4-DCP by R. eutropha may be the mechanism contributing to toxicity reduction. These results suggest that the microbiota may influence the survival of developing earthworms exposed to toxic chemicals.