Gene Transfer of PIB-Type ATPases among Bacteria
Isolated from Radionuclide- and Metal-Contaminated Subsurface
Robert J. Martinez,1 Yanling
Wang,2 Melanie A. Raimondo,1 Jonna M.
Tamar Barkay,4 and Patricia A. Sobecky1*
School of Biology, Georgia Institute of Technology, 311
Ferst Drive, Atlanta, GA 30332-0230.
Aerobic heterotrophs were isolated from subsurface
soil samples obtained from the U.S. Department of Energy’s
(DOE) Field Research Center (FRC) located at Oak Ridge,
Tenn. The FRC represents a unique, extreme environment
consisting of highly acidic soils with cooccurring heavy
metals, radionuclides, and high nitrate concentrations.
Four hundred isolates obtained from contaminated soil
were assayed for heavy metal resistance, and a smaller
subset was assayed for tolerance to uranium. The vast
majority of the isolates were gram-positive bacteria
and belonged to the high-G+C- and low-G+C-content genera
Arthrobacter and Bacillus, respectively.
Genomic DNA from a randomly chosen subset of 50 Pb-resistant
(Pbr) isolates was amplified with PCR primers
specific for PIB-type ATPases (i.e., pbrA/cadA/zntA).
A total of 10 pbrA/cadA/zntA loci exhibited
evidence of acquisition by horizontal gene transfer.
A remarkable dissemination of the horizontally acquired
PIB-type ATPases was supported by unusual
DNA base compositions and phylogenetic incongruence.
Numerous Pbr PIB-type ATPase-positive
FRC isolates belonging to the genus Arthrobacter
tolerated toxic concentrations of soluble U(VI) (UO22+)
at pH 4. These unrelated, yet synergistic, physiological
traits observed in Arthrobacter isolates residing
in the contaminated FRC subsurface may contribute to
the survival of the organisms in such an extreme environment.
This study is, to the best of our knowledge, the first
study to report broad horizontal transfer of PIB-type
ATPases in contaminated subsurface soils and is among
the first studies to report uranium tolerance of aerobic
heterotrophs obtained from the acidic subsurface at
the DOE FRC.
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