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Title: INFLUENCE OF EARTHWORM ACTIVITY ON GENE TRANSFER FROM PSEUDOMONAS FLUORESCENS TO INDIGENOUS SOIL BACTERIA

Author
item DAANE, LORI - UNIVERSITY OF MINNESOTA
item MOLINA, JEAN - UNIVERSITY OF MINNESOTA
item Berry, Edwin
item SADOWSKY, MICHAEL - UNIVERSITY OF MINNESOTA

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The release of microorganisms into the environment as a means to improve agriculture or remediate environmental hazards has raised concern about the dispersal of the organisms within the soil. There is a need to determine how the presence and activity of other soil-dwelling organisms influence the dispersal of microorganisms in the soil. We conducted studies to determine the role of earthworms in the dispersal of bacteria within the soil. Earthworm activity increases the vertical distribution of bacteria. Earthworm casts and cocoons may contain bacteria and may act as potential carriers for the dispersal of bacteria. The more we understand the relationship among soil organisms, the better we can develop risk assessments for releasing other microorganisms in the soil.

Technical Abstract: A model system has been developed to assess the influence of earthworm activity on the transfer of plasmid PJP4 from an inoculated donor bacterium, Pseudomonas fluorescens C5t(PJP4), to indigenous soil microorganisms. Three earthworm species (Lumbricus terrestris, L. rubellus and Apporectodea trapezoides), each with unique burrowing, casting and feeding behaviors, were individually evaluated. Soil columns were inoculated on the surface with 10**8 cells/g soil of the donor bacterium and after a two-week incubation period, donor, transconjugant and total bacteria were enumerated at 5 cm depth intervals. Transconjugants were confirmed by using colony hybridization with a mer gene probe. In situ gene transfer of plasmid PJP4 from P. fluorescens C5t to indigenous soil bacteria was detected in all inoculated microcosms. In the absence of earthworms the depth of recovery was limited to the top 5 cm of the column, with approximately 10**3 transconjugants/g soil. However, the total number of transconjugants recovered from soil was significantly greater in microcosms containing either L. rubellus or A. trapezoides, with levels reaching about 10**5 CFU/g soil. In addition, earthworms distributed donor and transconjugant bacteria throughout the microcosm columns, with the depth of recovery dependent on the burrowing behavior of each earthworm species. Donor and transconjugant bacteria were also recovered from earthworm casts and inside developing cocoons. Transconjugant bacteria from the indigenous soil microflora were classified as belonging to Acidovorax spp., Acinetobacter spp., Agrobacterium spp., Pasteurella spp., Pseudomonas spp. and Xanthomonas spp.