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Appl. Environ. Microbiol., Dec 1997, 4713-4720, Vol 63, No. 12
JP O'Gara, M Gomelsky and S Kaplan
The ability of the facultative photoheterotroph Rhodobacter sphaeroides to
tolerate and reduce high levels of tellurite in addition to at least 10
other rare earth metal oxides and oxyanions has considerable potential for
detoxification and bioremediation of contaminated environments. We report
the identification and characterization of two loci involved in high-level
tellurite resistance. The first locus contains four genes, two of which,
trgAB, confer increased tellurite resistance when introduced into the
related bacterium Paracoccus denitrificans. The trgAB-derived products
display no significant homology to known proteins, but both are likely to
be membrane- associated proteins. Immediately downstream of trgB, the cysK
(cysteine synthase) and orf323 genes were identified. Disruption of the
cysK gene resulted in decreased tellurite resistance in R. sphaeroides,
confirming earlier observations on the importance of cysteine metabolism
for high-level tellurite resistance. The second locus identified is
represented by the telA gene, which is separated from trgAB by 115 kb. The
telA gene product is 65% similar to the product of the klaB (telA) gene
from the tellurite-resistance-encoding kilA operon from plasmid RK2. The
genes immediately linked to the R. sphaeroides telA gene have no similarity
to other components of the kilA operon. R. sphaeroides telA could not
functionally substitute for the plasmid RK2 telA gene, indicating
substantial functional divergence between the two gene products. However,
inactivation of R. sphaeroides telA resulted in a significant decrease in
tellurite resistance compared to the wild- type strain. Both cysK and telA
null mutations readily gave rise to suppressors, suggesting that the
phenomenon of high-level tellurite resistance in R. sphaeroides is complex
and other, as yet uncharacterized, loci may be involved.
Copyright © 1997, American Society for Microbiology
Identification and molecular genetic analysis of multiple loci contributing to high-level tellurite resistance in Rhodobacter sphaeroides 2.4.1
Department of Microbiology and Molecular Genetics, University of Texas Medical School, Houston 77030, USA.
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