Chromium is a first row transition metal, but its interactions
with biological systems are very different from that of its
neighbors in the Periodic Table such as manganese and iron.
The latter metals often serve as enzyme cofactors. Chromium,
however, is largely substitution inert and serves poorly
in enzyme catalysis. Chromium will replace other metals in
biological systems with toxic effects
(ToxFAQs: Chromium). Chromium(VI) is a known human carcinogen.
In this context, most studies on prokaryotes and chromium
involve reduction of chromium(VI) to less toxic and less mobile forms such
Chromium(III) is an essential trace element in humans, where it enhances
insulin function. However, no beneficial function of chromium has been
described in microorganisms.
Microbial chromium(VI) reduction has been observed most often under aerobic conditions, but can also occur under anaerobic conditions (reviewed by Wang and Shen, 1995). Cytochromes of type c and b have been implicated in chromium reduction,
but the mechanisms of chromium bioreduction have not been completely determined (reviewed by Lovley, 1993). Chromium(VI) reduction is likely a detoxification mechanism, but
bacterial chromium resistance is also mediated by non-reductive plasmid-based systems that appear to exclude chromium (as chromate ions) from
the cell (reviewed by Silver, 1998). Chromium resistance has also been described in fungi and algae, and some of these organisms
can immobilize soluble chromium via bioaccumulation and biosorption (reviewed by Cervantes et al, 2001). Chromate influx is known to occur via sulfate uptake systems in some microorganisms
For more information:
Medline for chromium metabolism AND bacteria
Nkhalambayausi-Chirwa EM, Wang YT. Simultaneous chromium(VI)
reduction and phenol degradation in a fixed-film coculture
bioreactor: reactor performance. Water Res. 2001 Jun;35(8):1921-32.