MICROBIAL INTERACTIONS WITH CESIUM - IMPLICATIONS FOR BIOTECHNOLOGY

The continuing release of caesium isotopes into the environment has hi ghlighted the necessity for efficient removal of Cs from industrial wa ste effluents prior to discharge. Existing technologies, e.g. zeolite ion-exchange for Cs removal, can be expensive and microbial metal adso rption/accumulation may represent a cheap alternative. The distinct ch emical properties of Cs+, which dictate a high degree of metabolism-de pendent uptake via monovalent cation transport systems, indicate that different approaches are required for biological Cs removal to those w hich are generally adopted for other metals/radionuclides. The low tox icity of Cs+ eliminates one potential problem in the use of live cells for Cs removal. High levels of Cs+ accumulation have been reported in a number of microorganisms, but uptake levels vary markedly in differ ent organisms and are strongly influenced by a number of physico-chemi cal and mechanical parameters, e.g. the use of batch or continuous-flo w systems, biomass immobilization (which tends to increase Cs adsorpti on at the expense of metabolism-dependent accumulation), pH and partic ularly the prevalence of other monovalent cations such as K+ and Na+ I nherent differences in Cs+ uptake capacities of different microorganis ms appear to be largely attributable to differences in the affinity of monovalent cation transport systems for Cs+. The application of rigor ous screening procedures involving the use of autoradiography has grea t potential for isolation of microorganisms with particularly high aff inities for Cs+. Alternatively, manipulation of the physiological stat us of microorganisms can dramatically alter the transport of Cs+ and o ther monovalent cations. Hyper- and hypo-osmotic shock, respectively, have so far proved to be the most successful treatments for stimulatin g Cs removal and recovery. Other manipulations, at both the cellular a nd molecular level, which are known to influence K+ fluxes but have ye t to be characterized for Cs+, are outlined here.