Affiliation:
1. Department of Microbiology and Immunology1 and
2. Department of Soil, Water, and Environmental Science,2 University of Arizona, Tucson, Arizona 85721
Abstract
ABSTRACT
Prior to gene transfer experiments performed with nonsterile soil, plasmid pJP4 was introduced into a donor microorganism,
Escherichia coli
ATCC 15224, by plate mating with
Ralstonia eutropha
JMP134. Genes on this plasmid encode mercury resistance and partial 2,4-dichlorophenoxyacetic acid (2,4-D) degradation. The
E. coli
donor lacks the chromosomal genes necessary for mineralization of 2,4-D, and this fact allows presumptive transconjugants obtained in gene transfer studies to be selected by plating on media containing 2,4-D as the carbon source. Use of this donor counterselection approach enabled detection of plasmid pJP4 transfer to indigenous populations in soils and under conditions where it had previously not been detected. In Madera Canyon soil, the sizes of the populations of presumptive indigenous transconjugants were 10
7
and 10
8
transconjugants g of dry soil
−1
for samples supplemented with 500 and 1,000 μg of 2,4-D g of dry soil
−1
, respectively. Enterobacterial repetitive intergenic consensus PCR analysis of transconjugants resulted in diverse molecular fingerprints. Biolog analysis showed that all of the transconjugants were members of the genus
Burkholderia
or the genus
Pseudomonas
. No mercury-resistant, 2,4-D-degrading microorganisms containing large plasmids or the
tfdB
gene were found in 2,4-D-amended uninoculated control microcosms. Thus, all of the 2,4-D-degrading isolates that contained a plasmid whose size was similar to the size of pJP4, contained the
tfdB
gene, and exhibited mercury resistance were considered transconjugants. In addition, slightly enhanced rates of 2,4-D degradation were observed at distinct times in soil that supported transconjugant populations compared to controls in which no gene transfer was detected.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
64 articles.
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