- Volume 88, Issue 2, 1975

The effect of various solubilizing agents on the release of the dextranase from whole Cytophaga bacteria or washed envelopes is described. Among the proteolytic enzymes tested, only α-chymotrypsin solubilized the dextranase very efficiently with retained enzymic activity even after prolonged exposure. Among the snake venoms tested, that of Hemachatus haemachates showed the highest selectivity and efficiency. Non-ionic detergents with hydrophilic-lipophilic balance values of about 13 to 15 also effectively and selectively solubilized the membrane-bound enzyme. Organic solvents, urea, guanidine hydrochloride, glycine, chaotropic ions, pH variations and mechanical disruption (including osmotic shock) were ineffective.

SUMMARY: Enzymes of glycolysis, pentose phosphate pathway, gluconeogenesis, tricarboxylate acid cycle, glyoxylate by-pass and fatty-acid biosynthesis were assayed in extracts from Candida 107 grown continuously on glucose under carbon limitation, nitrogen limitation and on n-alkanes. The yeast was therefore either in a lipogenic or lipolytic state. Phosphofructokinase was absent under all conditions whereas enzymes of gluconeogenesis, including fructose 1,6-bisphosphatase and the pentose phosphate cycle, were all present. Glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were specific for NADP+ and were inhibited in a non-competitive manner by NADPH and NADH. Phosphoenolpyruvate, citrate, ATP and acetyl CoA had no inhibitory effects. Thus glucose metabolism appears to be by the pentose phosphate pathway which will rapidly produce NADPH. This can readily be consumed during fatty-acid biosynthesis and, as there appears to be no inhibition of the flow of carbon from glucose to acetyl CoA, fatty-acid synthesis can continue for as long as there is a supply of glucose. These results help to explain the probable causes of fat build-up to high concentrations (about 40% of the cell dry weight) in this and other organisms. In alkane-grown cells, lipogenesis is repressed and carbon is able to flow from the alkanes via acetyl CoA, oxaloacetate and pyruvate into pentoses and hexoses in a unidirectional manner, because of the strong repression of pyruvate kinase and the increased activities of phosphoenolpyruvate kinase and fructose 1,6-bisphosphatase under these conditions. Although there was little change in the total activity of the TCA cycle enzymes under the various growth conditions, isocitrate lyase was induced under lipolytic conditions.

SUMMARY: Incorporation of [1-14C]acetate and [2-14C]malonate into aflatoxins by resting mycelia of Aspergillus parasiticus resuspended in different buffers was studied. A decrease in pH from 5·8 to 2·8, as well as addition of EDTA, markedly stimulated the incorporation of malonate but the effect on acetate incorporation was less pronounced. Mycelia took up comparatively more acetate than malonate, but more malonate (4·3%) entering mycelia was incorporated into aflatoxins than was acetate (1·6%). Furthermore, the addition of unlabelled acetate reduced the incorporation of label from [1-14C]acetate by 75 % but from [2-14C)malonate by only 25 %. These results suggest that malonate is an intermediate in aflatoxin synthesis and that it can be incorporated without prior conversion to acetate.

SUMMARY: Rhodospirillum rubrum was investigated electronmicroscopically after freeze-etching. Indentations on the convex faces of cytoplasmic membranes and protuberances on the concave faces were interpreted to represent sites of invaginations for intracytoplasmic membranes. The number of such invagination sites/μm2 of membrane face increased as the cellular bacteriochlorophyll content increased, but no defined proportionality between these parameters could be established.

SUMMARY: An antigenic determinant isolated from a strain of the Gram-negative bacterium Butyrivibrio fibrisolvens reacted with specific antisera to the polyglycero-phosphate backbone of membrane teichoic acids of lactobacilli. It gave a reaction of identity with membrane glycerol lipoteichoic acid and glycerol teichoic acid preparations from lactobacilli, and with phenol extracts of other Gram-positive bacteria. The antigen-antibody reaction was strongly inhibited by glycerol-phosphoryl-glycerol-phosphoryl-glycerol and the chemical composition was consistent with glycerol teichoic acid. It was concluded that this Gram-negative bacterium contained a glycerol teichoic acid whose polyglycerophosphate backbone was acting as antigenic determinant. Extracts of 33 out of 52 other strains of butyrivibrios examined gave similar reactions.

SUMMARY: Cultures of the blue-green alga Anacystis nidulans were synchronized with respect to DNA synthesis as well as cell division. Application of ethyl methane-sulphonate at different stages of replication resulted in a peak of mutation frequency for different genetic markers; this peak can be accounted for in terms of the involvement of repair processes. A temporal map of 19 markers has been constructed by this method. Comparison of gene position obtained by temporal mapping indicates that either bidirectional replication or unidirectional replication from more than one origin occurs.

SUMMARY: dl-Norvaline inhibits growth of wild-type Bacillus subtilis. A number of mutants resistant to growth inhibition by this analogue were isolated and studied. Cross-feeding experiments and paper chromatography of culture supernatants indicated that the mutants excreted leucine and possibly valine and glutamate. Enzymic analysis indicated that the mutants were derepressed for acetohydroxy-acid synthetase and α-isopropylmalate synthetase; however, no derepression of threonine deaminase, dihydroxyacid dehydrase or transaminase B was observed.

SUMMARY: Properties of a transducing system with a phage able to transduce a kanamycin-resistance marker of the T compatibility group plasmid R394 at a frequency of 2 × 10−2/plaque-forming unit adsorbed are described. The phage was detected in Providence strain P29 transduced to kanamycin resistance by Providence phage PL25 grown on this strain harbouring the R factor. Four P29 transductants, specially selected at the lowest multiplicities of infection of the high frequency transducing (HFT) phage, were defective lysogens. They plated PL25 with an efficiency of 1 and only one liberated low-titre phage spontaneously or on u.v. induction. The defect in maturation function could be corrected by introduction of a wild PL25 prophage. The transducing phage was serologically identical to PL25. It could transduce in single infection, but transduction frequency was increased by the simultaneous presence of homologous non-transducing phage. Transductants did not transfer the kanamycin-resistance marker by conjugation, and produced kanamycin-sensitive segregants at a moderate rate. These segregants could be transduced to kanamycin resistance by the HFT phage. Irradiation of HFT lysates by u.v. produced an exponential fall in transduction frequency. It was concluded that the defective phage transduced by lysogenization. Kanamycin-resistant transductants could themselves be transduced to streptomycin resistance by PL25 reared on a streptomycin-resistant mutant. Lysogenic transductants produced by the HFT phage did not always liberate HFT phage on u.v. induction. Possible explanations are considered.

SUMMARY: The killing of Pasteurella septica by horse antiserum has features not previously associated with serum bactericidal reactions. The present work showed that lowering the pH from 7·4 to 6·8 abolished the action of antiserum. The bactericidal effect and the degradation of RNA seen when antiserum is added to P. septica growing in horse serum, were abolished at pH 6.8 in much the same way as when haem compounds were added to the system. Addition of chloramphenicol, rifampicin or puromycin to P. septica growing apparently normally in antiserum at pH 6·8 or in antiserum containing haem compounds led to rapid killing of the bacteria and to degradation of their RNA. Addition of these antibiotics to P. septica growing in normal serum produced only bacteriostasis and did not induce RNA breakdown. In contrast, nalidixic acid, although inhibiting growth, did not induce rapid killing and RNA breakdown under the same conditions. These findings were unexpected and led to a reassessment of ideas concerning the mechanism of action of specific antiserum on P. septica. Although iron compounds clearly abolish the bactericidal effects of antiserum, an explanation of the antibacterial action of such antiserum based simply on an interference with bacterial iron supply is no longer sufficient. The process is more complex and must involve other factors.

SUMMARY: 2,2-Dichloro-3,3-dimethyl-cyclopropane carboxylic acid (WL 28325) is a systemic fungicide highly specific for the rice leaf ‘blast’ disease caused by Piricularia oryzae Cav. Antifungal activity in vitro of WL 28325 against P. oryzae was dependent on the composition of the growth medium, growth being unaffected in two complex non-defined media but inhibited in a medium of defined composition. The antifungal effects of WL 28325 are probably not related to its activity as a rice ‘blast’ fungicide. Its intrinsic fungitoxicity was low. The ability of various di-chlorocyclopropanes of similar structure to WL 28325 to inhibit growth of P. oryzae in vitro did not correlate with their ability to prevent ‘blast’ on rice. Also, despite the high degree of pathogen specificity of WL 28325 as a disease protectant, WL 28325 inhibited the growth of several plant pathogens in culture.

No evidence was obtained to suggest that WL 28325 is converted, after its application to the rice plant, to a derivative of higher intrinsic fungitoxicity. These compounds may act by stimulating the disease-resistance mechanisms of the rice plant.

SUMMARY: Mycoplasma mycoides subsp. capri was grown in different media. The amounts of the lipids in these media were varied, resulting in altered lipid compositions of the cells. Lowering the amounts of cholesterol in the media resulted in less cholesterol incorporation into the cell lipid, with a concomitant decrease in the amount of phospholipid. The changes in the phospholipid/cholesterol ratio in the mycoplasmas were very small compared with the large changes in the amount of cholesterol which occurred when the cholesterol content in the medium was altered. Changes in the amounts of glycolipid and glyceride in the cell lipid also resulted from alterations of the cholesterol concentration in the media. Under these conditions cells with reduced cholesterol contents were more sensitive to lysis by digitonin. No changes were observed in the polyacrylamide gel electrophoretic pattern of cellular or membrane proteins when the cholesterol was replaced by other sterols.