Earthworm egg capsules as vectors for the environmental introduction of biodegradative bacteria

Earthworm egg capsules (cocoons) may acquire bacteria from the environment in which they are produced. We found that Ralstonia eutropha (pJP4) can be recovered from Eisenia fetida cocoons formed in soil inoculated with this b acterium. Plasmid pJP4 contains the genes necessary for 2,4-dichlorophenoxy acetic acid (2,4-D) and 2,4-dichlorophenol (2,4-DCP) degradation. In this s tudy we determined that the presence of R. eutropha (pJP4) within the devel oping earthworm cocoon can influence the degradation and toxicity of 2,4-D and 2,4-DCP, respectively. The addition of cocoons, containing R. eutropha (pJP4) at either low or high densities (10(2) or 10(5) CFU per cocoon, resp ectively) initiated degradation of 2,4-D in nonsterile soil microcosms. Los s of 2,4-D was observed within the first week of incubation, and respiking the soil with 2,4-D showed depletion within 24 h. Microbial analysis of the soil revealed the presence of approximately 10(4) CFU R. eutropha (pJP4) g (-1) of soil. The toxicity of 2,4-DCP to developing earthworms was tested b y using cocoons with or without R. eutropha (pJP4). Results showed that coc oons containing R. eutropha (pJP4) were able to tolerate higher levels of 2 ,4-D(SP. Our results indicate that the biodegradation of 2,4-DCP by R. eutr opha (pJP4) within the cocoons may be the mechanism contributing to toxicit y reduction. These results suggest that the microbiota may influence the su rvival of developing earthworms exposed to toxic chemicals. In addition, co coons can be used as inoculants for the introduction into the environment o f beneficial bacteria, such as strains with biodegradative capabilities.