Author(s): D. F. Ackerley , C. F. Gonzalez , M. Keyhan , R. Blake III
& A. Matin
Cr(VI) (chromate) is a widespread environmental pollutant, and a constant threat
to drinking water supplies.
It is soluble, toxic and carcinogenic.
remediate it by reducing it to insoluble Cr(III).
Chromate, however, is toxic also
to the remediating bacteria, hampering their effectiveness; this and other
problems can be addressed through bio-molecular engineering.
ChrR, a soluble
chromate-reducing flavoenzyme of Pseudomonas putida, is a promising target
for engineering studies.
Gene knockout and enzyme overproduction studies show
that ChrR protects against chromate toxicity.
Stopped flow spectrophotometry
indicates that ChrR-catalyzed reduction of Cr(VI) to Cr(III) passes via a highly
reactive Cr(V) intermediate; and consistent with this, reduction of chromate by
ChrR in vitro generates reactive oxygen species (ROS).
generated lower levels of ROS than another soluble flavoenzyme, lipoyl
dehydrogenase; this and many other cellular enzymes are single electron
chromate reducers, and are a major cause of chromate toxicity to bacteria.
propose that ChrR may minimize this toxicity by diverting chromate away from
the one-electron reducers; and that by enhancing this activity it might be possible
to generate a strain that not only transforms chromate at a greater rate, but is also
more resistant to chromate’s toxic effects.
hexavalent chromium, bioremediation, reactive oxygen species,
Chromium(III), the most common form of chromium found in natural
environments, is an important material resource and essential micronutrient.
Size: 638 kb
Paper DOI: 10.2495/WRM050271
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