Iron requirements and aluminum sensitivity of an hydroxamic acid-requiring strain of Bacillus megaterium

Bacillus megaterium strain ATCC 19213 secretes a ferric-chelating secondary hydroxamic acid, whereas a mutant (strain SK11) derived from it cannot produce a hydroxamate. Strain SK11 could be cultivated in a sucrose-mineral salts medium (treated with Chelex 100 to reduce trace metals) in the absence of added hydroxamate, if the inoculum was high. The lowest iron supplements necessary for maximal growth of both strains were equivalent (0.01 to 0.04 mug of iron per ml). Addition of either aluminum (0.5 mug/ml) or chromium (0.1 mug/ml) to the medium prevented full growth of strain SK11 at the minimal iron concentration, although elevated iron (1 mug/ml) reversed this inhibition. The iron-free secondary hydroxamate, Desferal, also abolished aluminum and chromium inhibition of strain SK11, producing maximal population densities at the low iron concentration. Growth of the hydroxamate-producing strain 19213 was not altered significantly by the aluminum or chromium levels which inhibited strain SK11. However, strain 19213 responded to these metals by increasing its secretion of a secondary hydroxamate. It was concluded that aluminum and chromium interfered with iron incorporation, either directly or by formation of nonutilizable aggregates with iron. The secondary hydroxamates may have overcome this interference by solubilization of iron for delivery to a single uptake process, or the ferric-hydroxamate chelate may enter the cell by an alternate route.

Antibody induced lysis of PPD-coated chicken erythrocytes by spleen cells of non-immunized guinea pigs

Chicken erythrocytes coated with PPD were labelled with ⁵¹Cr. When incubated with spleen cells from non-immunized animals in the presence of heat inactivated serum from immunized guinea pigs, the red cells were lysed as assessed by isotope release. The reaction was highly specific and required direct contact between target cells and spleen cells. Cytotoxicity of normal spleen cells was observed after preincubation of the PPD-coated erythrocytes, or when immune serum was present in the incubation mixture. Spleen cells pretreated with immune serum exhibited an activity of low degree. Sera from animals injected with tubercle bacilli or with PPD in incomplete Freund’s adjuvant were active, whereas sera from animals immunized with alum precipitated PPD were of weak or doubtful activity. The stimulating activity of sera increased with the intensity of immunization. Cytotoxicity inducing activity and haemagglutinating antibody titers were roughly correlated in animals injected with PPD but not in animals immunized with tubercle bacilli.

Dependence of acetylcholine desensitization on the membrane potential of frog muscle fibre and on the ionic changes in the medium

1. The rate of desensitization of the post-synaptic membrane to prolonged action of acetylcholine was investigated during (a) potassium depolarization of the frog muscle fibre, (b) artificial changes of the membrane potential and (c) in the presence of some multivalent cations and of caffeine.2. Depolarization of the muscle fibre by 15 mM-K(+) led to a slowing down in the development of desensitization by 80%. This effect on desensitization produced by membrane potential changes could account for the previously described effect of increased K(+) concentration.3. Electrotonically produced depolarization of the muscle fibre membrane resulted in a decrease, hyperpolarization in an increase of the rate of desensitization.4. Several multivalent cations can be, according to their ability to increase rate of desensitization, arranged in the following series: [Formula: see text]5. Caffeine in a concentration of 1.5 mM does not affect the rate of desensitization.6. A hypothesis is presented suggesting that desensitization is not only restricted to the receptor level but that it also occurs, at least partly, at the terminal stages of the activation system.

Adjuvant arthritis in the rat. Effect of intraperitoneal injections of either whole dead mycobacteria or tuberculin

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