Scanning and transmission electron microscopy evidence of the cytological effect of pyrrolnitrin on ‘Microsporon audouinii’ Gruby CBS 313-54 ‘in vitro’

Scanning and transmission electron microscopy showed that a ceiling quantity (1.56 mcg) of antifungal antibiotic Pyrrolnitrin caused heavy damage to dermathophyteMicrosporon audouinii Gruby CBS 313-54in vitro. Suitable preparation technique made it clear that the changes involved consisted of hyphal collapse on the edge of the culture, with loss of euplasmic organelles identity and cell autolysis. The cell wall, however, was apparently undamaged. These findings fit in with the suggestion that the mode of action of the antibiotic leads to generalised lipoproteic membranes damage. They must, however, be considered as representing the result of the terminal phase of cell distress.     

Role of sodium in determining alternate pathways of aerobic citrate catabolism in Aerobacter aerogenes

In contrast to the absolute Na(+) requirement for anaerobic growth of Aerobacter aerogenes on citrate as sole carbon source, aerobic growth of this microorganism did not require the presence of Na(+). However, Na(+) (optimal concentration, 10 mm) did increase the maximal amount of aerobic growth by 60%, even though it did not change the rate of growth. This increase in growth was specifically affected by Na(+), which could not be replaced by K(+), NH(4) (+), Li(+), Rb(+), or Cs(+). Enzyme profiles were determined in A. aerogenes cells grown aerobically on citrate in media of varying cationic composition. Cells grown in Na(+)-free medium possessed all the enzymes of the citric acid cycle including alpha-ketoglutarate dehydrogenase, which is repressed by anaerobic conditions of growth. The enzymes of the anaerobic citrate fermentation pathway, citritase and oxalacetate decarboxylase, were also present in these cells, but this pathway of citrate catabolism was effectively blocked by the absence of Na(+), which is essential for the activation of the oxalacetate decarboxylase step. Thus, in Na(+)-free medium, aerobic citrate catabolism proceeded solely via the citric acid cycle. Addition of 10 mm Na(+) to the aerobic citrate medium resulted in the activation of oxalacetate decarboxylase and the repression of alpha-ketoglutarate dehydrogenase, thereby diverting citrate catabolism from the (aerobic) citric acid cycle mechanism to the fermentation mechanism characteristic of anaerobic growth. The further addition of 2% potassium acetate to the medium caused repression of citritase and derepression of alpha-ketoglutarate dehydrogenase, switching citrate catabolism back into the citric acid cycle.     

Stereospecificity of citrate synthetase in relation to glutamate biosynthesis by extracts of Chloropseudomonas ethylicum

The synthesis of citric and glutamic acids by extracts of Chloropseudomonas ethylicum was studied with labeled precursors. When acetyl-coenzyme A-1-(14)C was used as substrate, only 0.1% of the total radioactivity was found in the C-5 position of citric acid; whereas, with oxalacetate-4-(14)C as substrate, 100% of the total radioactivity was found in C-5. These results demonstrated that the Chloropseudomonas citrate synthetase had an absolute stereospecificity, identical to that of the pig heart synthetase. The distribution of radioactivity in the glutamic acid synthesized from acetyl-coenzyme A-1-(14)C was 0% in C-1 and 94.0% in C-5; whereas the glutamic acid formed from oxalacetate-4-(14)C contained 89.6% in C-1 and 0.5% in C-5. This distribution is entirely consistent with the biosynthesis of glutamic acid from citric acid via aconitase, d(s)-isocitrate, and l-glutamate dehydrogenases. The presence of l-glutamate dehydrogenase in extracts was demonstrated. The stereospecificity of the citrate synthetase and the pattern of glutamate labeling further establish that the aconitase of Chloropseudomonas is completely stereospecific.