Replacement of cellular potassium by caesium in Chlorella emersonii: differential sensitivity of photoautotrophic and chemoheterotrophic growth

Abstract

Photoautotrophic growth of Chforeffu emersonii in the presence of 1 mM-CsC1 resulted in a 34% increase in cell doubling time and an 83 % reduction in the final cell yield as compared to growth in the absence of Cs+. In contrast, the presence of 1 mM-Cs+ had no effect on chemoheterotrophic growth in the dark with glucose. These observations were correlated with the stage of growth at which Cs+-induced cellular K+ loss was evident. For photoautotrophically growing cells this occurred during the exponential growth phase (after 4 d); for chemoheterotrophically growing cells this was during stationary phase (after 10 d). Inhibition of chemoheterotrophic cell division occurred after 2 d in 50 mM-CS+ or 5 d in 20 mM-CS+, and coincided with a decline in intracellular K+ to -2 nmol (lo6 cells)-'. Accumulation of Cs+ ceased after 2 d in both of these cases. Cell doubling times during chemoheterotrophic growth remained approximately constant at internal K+ levels between 7 and 28 nmol (lo6 cells)-l. In contrast, a decline in intracellular K+, from 42 to 19 nmol (lo6 cells)-I , after 4 d photoautotrophic growth in the presence of Cs+, was concurrent with the 34% increase in cell doubling times. Photosynthesizing cells accumulated approximately 2-fold more Cs+ than respiring cells after incubation for 12 h in HEPES buffer, pH 8. Culture age and intracellular K+ levels had little effect on the ability of C. emersonii to accumulate Cs+. Externally supplied K+ inhibited Cs+ accumulation to a greater extent in photosynthesizing cells (75% inhibition at 10 mM-K+, 1 mM-Cs+) than in respiring cells (50% inhibition at 10 mM-K+, 1 mM-CS+). Greatly elevated Na+ concentrations (50 mM) were required to inhibit Cs+ accumulation in both cases. Incubation of cells in buffer in the light in the absence and presence of 10 mM-CS+ resulted in decreases in cellular K+ of 44% and 77% respectively and a concomitant 66% reduction in the rate of photosynthesis in both cases. A Cs+-induced K+ loss of 71 yo from respiring cells had no effect on the rate of respiration. These results indicate that it is not the presence of Cs+ in cells that is growth inhibitory, but rather the resulting loss of K+ and that photosynthesis and photoautotrophic growth are more sensitive to this K+ loss than respiration and chemoheterotrophic growth.

Novel classes of mutants of the cyanobacterium Nostoc muscorum showing absolute requirement of Cs+ or Rb+ for diazotrophy

“…Therefore, it is desirable to investigate the biological consequences of caesium (Cs ϩ ) pollution on such primary producers. Recent studies on Cs ϩ -toxicity to cyanobacteria and algae have shown that it results from replacement of cellular K ϩ by Cs ϩ associated with the inability of Cs ϩ to substitute functionally for K ϩ (Avery et al, 1991) and that such Cs ϩ -toxicity is known to be reversible with K ϩ , Na ϩ , or NH 4 ϩ (Avery et al, 1992a(Avery et al, , b, 1993Singh et al, 1994). A preliminary physiological and mutational study on Cs ϩ -toxicity in the cyanobacterium Nostoc muscorum suggest that in heterocystous, diazotrophic forms its toxicity is diazotrophic specific and, like diazotrophic itself, NH 4 ϩ -repressible (Singh et al, 1994).…”

The effects of K+ growth conditions on the accumulation of cesium by the bacterium Thermus sp. TibetanG6

“…However, in the K + -deficient cells that were induced by the absence of K + in the culture medium, the storage of K + was very limited. Na + and Cs + could enter into cells by replacing K + , due to their physical and chemical similarity to K + [20] . This may explain the results from the pH experiment: the quantity of cesium accumulated by strain TibetanG6 was much higher in the K + -deficient cells than that in the K + -sufficient cells.…”

Uptake of cobalt and cesium by microalgal- and cyanobacterial-clay mixtures

“…It conformed to a Freundlich isotherm [16] and was dependent on metal concentration. The second phase was slower, absent in the dark and in the presence of CCCP, and comprised energy-dependent uptake of cesium and cobalt by the cells [5,6,18]. Over a 4 h incubation period, the majority of metal taken up was via the first phase, although over a longer time period, the second, energy-dependent phase could become more significant.…”