|
Cesium is the rarest of the alkali metals, but the radioactive isotope 137Cs (a product of nuclear reactors and
nuclear weapons tests) is of concern as an environmental pollutant (ToxFAQs:
Cesium).
No essential biological function for cesium has been identified, but research has explored cesium transport and accumulation in microorganisms, and the
ability of Cs+ to replace K+ in growth and enzyme activation (reviewed by Avery, 1995).
In bacteria, Cs+ uptake occurs via monovalent cation transport systems, but not all bacteria are capable of Cs+
uptake (Johnson et al, 1991). Cs+ transport in Eschericia coli was shown to occur via the Kup K+ uptake system, but with
reduced affinity (Bossemeyer et al, 1989). The monovalent cation uptake system in the cyanobacterium Synechocystis was shown to transport
Cs+ with equal or higher
affinity than K+ (Avery et al, 1991), and Cs+ and NH4+ were found to have common transport systems
in Anabaena variabilis (Avery et al, 1992a) and Nostoc mucorum (Singh et al, 1994).
Both external ion concentration and pH have been shown to influence rates of Cs+ uptake in bacteria (Perkins and Gadd,
1995). In Saccharomyces cerevisiae, Cs+ uptake is mediated by monovalent cation transporters, but Cs+ is
imported with lower affinity than are K+, Rb+, and NH4+ (Borst-Pauwels, 1981)
The fraction of accumulated Cs+ present in the cytoplasm and vacuoles of yeasts varies among species (Perkins and Gadd, 1993).
Growth of Rhodopseudomonas capsulata in the absence of K+ could be stimulated by 1 mM Cs+ (Jasper, 1978).
Cs+ has been shown to replace K+ in the activation of acyl-coenzyme A caroboxylase in Streptomyces erythraeus
(Hunaiti and
Kolattukudy, 1982) and ribokinase in E. coli (Andersson
and Mowbray, 2002). Studies with unicellular algae have demonstrated that inhibition of growth resulting from Cs+ uptake is due to an
associated reduction in cellular K+ and not to direct action of Cs+ (Avery et al, 1992b).
For More Information:
Search
Medline for cesium metabolism AND bacteria
Avery SV, Codd GA, Gadd GM. Caesium accumulation and interactions with other monovalent cations in the cyanobacterium
Synechosystis PCC 6803. J Gen Microiol. 1991;137:405-413.
Avery SV, Codd GA, Gadd GM. Caesium transport in the cyanobacterium Anabaena variabilis: kinetics and evidence for uptake via
ammonium transport system(s). FEMS microbiol Lett. 1992a;95:253-258.
Avery SV, Codd GA, Gadd GM. Replacement of cellular potassium by caesium in Chlorella emersonii: differential
sensitivity of photoautotrophic and chemoheterotrophic growth. J Gen Microbiol. 1992b;138:69-76.
Heinrich G. Uptake and transfer factors of 137Cs by mushrooms.
Radiat Environ Biophys 1992;31(1):39-49.
Johnson EE, O'Donnell AG, Ineson P. An autoradiographic technique for selecting Cs-137-sorbing microorganisms from soil. J
Microbiol Meth. 1991;13:293-298.
Perkins J, Gadd GM, Caesium toxicity, accumulation, and intracellular localization in yeasts. Mycol Res. 1993;97:717-724.
|
