Caesium accumulation by microorganisms: uptake mechanisms,cation competition,compartmentalization and toxicity

Summary The continued release of caesium radioisotopes into the environment has led to a resurgence of interest in microbe-Cs interactions. Caesium exists almost exclusively as the monovalent cation Cs⁺ in the natural environment. Although Cs⁺ is a weak Lewis acid that exhibits a low tendency to form complexes with ligands, its chemical similarity to the biologically essential alkali cation K⁺ facilitates high levels of metabolism-dependent intracellular accumulation. Microbial Cs⁺ (K⁺) uptake is generally mediated by monovalent cation transport systems located on the plasma membrane. These differe widely in specificity for alkali cations and consequently microorganisms display large differences in their ability to accumulate Cs⁺; Cs⁺ appears to have an equal or greater affinity than K⁺ for transport in certain microorganisms. Microbial Cs⁺ accumulation is markedly influenced by the presence of external cations, e.g. K⁺, Na⁺, NH₄ ⁺ and H⁺, and is generally accompanied by an approximate stoichiometric exchange for intracellular K⁺. However, stimulation of growth of K⁺-starved microbial cultures by Cs⁺ is limited and its has been proposed that it is not the presence of Cs⁺ in cells that is growth inhibitory but rather the resulting loss of K⁺. Increased microbial tolerance to Cs⁺ may result from sequestration of Cs⁺ in vacuoles or changes in the activity and/or specificity of transport systems mediating Cs⁺ uptake. The precise intracellular target(s) for Cs⁺-induced toxicity has yet to be clearly defined, although certain internal structures, e.g. ribosomes, become unstable in the presence of Cs⁺ and Cs⁺ is known to substitute poorly for K⁺ in the activation of many K⁺-requiring enzymes.     

Scrapie I. Transmission and Pathogenesis

Homogenized brain, extracts, and residues of brain from normal and scrapie sheep were inoculated into 116 sheep. Of 72 sheep inoculated with scrapie material 27 developed the disease, whereas four of 44 inoculated with ;normal' brain material showed symptoms similar to those of scrapie. The scrapie agent survived extraction for 18 hours with diethyl ether followed by water for 24 hours. Similarly the agent survived extraction in a Soxhlet apparatus with 95 per cent ethanol containing 2.0 per cent 4 M HC1 for 24 hours. There was no evidence of demyelination in sections of brain and spinal cord supporting the view that allergic encephalomyelitis is not responsible for the scrapie symptoms. Liver function, as measured by the bromsulfalein test, remained normal until just before death. These results preclude that liver dysfunction contributes to the disease but do not exclude the possibilities of other metabolic derangements.     

Effect of pre-incubation pH on the growth characteristics of Aeromonas hydrophila at 5°C, as assessed by two methods

Two strains of Aeromonas hydrophila (the type strain ATCC 7966 and a food-derived strain JAH4) were pre-incubated at 5°C in Brain Heart Infusion (BHI) broth with pH adjusted to 6.0 or 7.0, and then incubated at the same temperature in BHI broth with pH adjusted to 6.0, 6.5, 7.0 and 7.5. Growth kinetics during incubation were determined by two methods: viable count (VC) and measurement of optical density (O.D.). Pre-incubation at different pH values did not significantly affect the maximum specific growth rates of the strains during incubation, but the lag phases were shorter after pre-incubation at pH 6.0 than at pH 7.0. The VC method was more sensitive than O.D. measurements for assessing lag phase.     

Prognosis in giant-cell arteritis.

In a study to assess the natural history of giant-cell arteritis, 90 patients with proved disease were followed up from the time of diagnosis. Early mortality was low and most commonly due to vertebral arteritis, but cerebral infarction did not appear to be a late complication. High maintenance dose steroids and visual loss were associated significantly with a shortened life span (p=0.0003 and p=0.0024). One-third of the patients developed chronic relapsing disease, but serious late complications were not encountered. After the initial attack has been controlled steroid dosage should be reduced to the minimum needed to alleviate symptoms.     

Differences between ATP-mediated cytotoxicity and cell-mediated cytotoxicity.

There has been considerable recent interest in the possible role of extracellular ATP in cell-mediated cytotoxicity. To investigate the similarities and differences between ATP-mediated lysis and CTL-mediated lysis, we studied in detail the ATP-mediated lysis of EL-4 cells, which are highly susceptible to lysis by extracellular ATP. ATP-mediated lysis was time and concentration dependent; most lysis occurred within 4 to 6 h of incubation. The kinetics of ATP- and cell-mediated lysis were similar. However, in contrast to CTL-mediated lysis, ATP-mediated lysis of EL-4 cells did not appear to be accompanied by characteristic chromosomal degradation (apoptosis). In order to compare these cytotoxic processes in greater detail, ATP-resistant clones were derived by growing EL-4 cells continuously in the presence of high concentrations of ATP. These cloned EL-4 lines showed marked resistance to ATP-mediated cytotoxicity across a wide range of concentrations but were as susceptible as the parent EL-4 cells to cell-mediated cytotoxicity by an alloreactive effector population from a MLC. Thus, there appear to be a number of differences between ATP-mediated and cell-mediated cytotoxicity in this system; most notable is the identification of cell lines that are resistant to ATP but susceptible to CTL-mediated lysis.     

The effect of aphidicolin on the rate of DNA replication and unscheduled DNA synthesis of Bloom syndrome and normal fibroblasts

Summary Ultraviolet radiation induced more unscheduled DNA synthesis (UDS) in ten Bloom syndrome (BS) fibroblast strains than in control cells, but this difference could be suppressed by aphidicolin treatment in at least nine BS strains. Aphidicolin, 1 and 5 g/ml, were required to inhibit by 30% the UDS of BS and control cells respectively, but the DNA replication of BS cells did not prove abnormally sensitive to such an inhibitor. These findings are discussed in relation to current knowledge of the action of aphidicolin and hypotheses of the metabolic defect in BS.     

Effects of caffeine-pretreatment on SCE and chromosome aberrations induced by monofunctional- and bifunctional-mitomycin C in bloom syndrome lymphocytes

Bloom syndrome (BS) lymphocytes, which are characterized by a high incidence (75.4 per cell) of SCE, were treated with caffeine (CAF) during the first cell cycle and with monofunctional-(M-MC) and bifunctional-(MC)mitomycin C during the second cycle. The effect on the SCE level was synergistic. The CAF-pretreated cells in combination with M-MC and MC post-treatments, had significantly higher (SCE values 152.5 and 167.9 SCE per cell, resp.) than those treated with M-MC or MC alone during the second cycle (101.1 and 116.4 SCE per cell, resp.). M-MC and MC in the presence of BrdU (without CAF) for 2 cell cycles increased SCE to 157.6 and 169.4 per cell (about twice the control level). M-MC + CAF and MC + CAF treatments for 2 cell cycles did not produce a synergistic effect on the SCE frequency in BS cells; the SCE level was not significantly greater than that with M-MC or MC alone. Normal cells treated with MC and CAF for 2 cycles had a maximum SCE frequency of 156 per cell. This suggests that cells with SCE frequencies above this level may not be able to survive, i.e., this is the “saturation” level of SCE. However, CAF alone had almost no effect on SCE in either BS or normal cells and did not produce multiple chromosome aberrations. The lack of CAF effect on BS cells suggests that the lesions in DNA strands of BS cells which lead to SCE are double-strand lesions. In normal cells CAF is known to significantly slow down DNA-chain growth; the reduced rate of DNA-chain growth in BS is an inherent defect of the cells. Therefore, though CAF enhanced SCE and chromosome aberrations (shattered chromosomes) in combination with alkylating agents, CAF alone did not significantly increase the SCE rate in either BS cells or in normal cells. Thus, processes which may induce SCE are not only related to retarded rate of DNA-chain growth, but also to breaks in the template strand permitting double-strand exchanges to occur.