The Y-12 plant in Oak Ridge, TN, which manufactured nuclear weapons during World War II and the Cold War, contaminated East
Fork Poplar Creek with heavy metals. The multimetal resistant bacterial strain,
Stenotrophomonas maltophilia Oak Ridge strain O2 (
S. maltophilia O2), was isolated from East Fork Poplar Creek. Sequence analysis of 16s rDNA suggested that our working strain of
S. maltophilia O2 was a strain of
Enterobacter. Phylogenetic tree analysis and biochemical tests confirmed that it belonged to an
Enterobacter species. This new strain was named
Enterobacter sp. YSU. Using a modified R3A growth medium, R3A-Tris, the Hg(II), Cd(II), Zn(II), Cu(II), Au(III), Cr(VI), Ag(I), As(III),
and Se(IV) MICs for a confirmed strain of
S. maltophilia O2 were 0.24, 0.33, 5, 5, 0.25, 7, 0.03, 14, and 40 mM, respectively, compared to 0.07, 0.24, 0.8, 3, 0.05, 0.4, 0.08, 14,
and 40 mM, respectively, for
Enterobacter sp. YSU. Although
S. maltophilia O2 was generally more metal resistant than
Enterobacter sp. YSU, in comparison to
Escherichia coli strain HB101,
Enterobacter sp. YSU was resistant to Hg(II), Cd(II), Zn(II), Au(III), Ag(I), As(III), and Se(IV). By studying metal resistances in these
two strains, it may be possible to understand what makes one microorganism more metal resistant than another microorganism.
This work also provided benchmark MICs that can be used to evaluate the metal resistance properties of other bacterial isolates
from East Fork Poplar Creek and other metal contaminated sites.