摘要:

The timing and degree of gas vesicle production inMicrocyclus aquaticuswas affected by nutritional conditions. If 50 μgL-lysine/ml was added to a glucose – mineral salts medium (DM), the organism did not form gas vesicles. This effect was specific forL-lysine, as neitherD-lysine normeso-diaminopimelic acid prevented gas vesicle production. Cells grown in the presence ofL-lysine did not contain any immunologically detectable gas vesicle protein, which indicates thatL-lysine affects expression of the structural gene for the gas vesicle protein rather than assembly of the protein into gas vesicles. The addition ofL-lysine to cultures in DM did not immediately decrease the rate of gas vesicle assembly, nor did the removal of cells from DM plusL-lysine to DM result in immediate gas vesicle production. Gas vesicle production was also affected by the addition ofL-threonine orL-cysteine to culture media or by an increase in the medium's ionic strength. These results are discussed in relation to the aspartic acid pathway of amino acid biosynthesis and effects upon the intracellularL-lysine concentration.

ISSN:0008-4166    

DOI:10.1139/m77-054

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The physiological conditions for the excretion of staphylococcal enterotoxin B (SEB) by nongrowing cells have been determined. In general, SEB excretion appears to be best when amino acids serve as sources of carbon, nitrogen, and energy. Little toxin was produced in a nitrogen-free medium with glucose as the sole carbon source. Inhibitor studies have shown that most of the toxin excreted by nongrowing cells was the result ofde novoprotein synthesis. Optimum toxin excretion was also obtained under conditions of aeration, and at or near optimum growth temperature, those conditions at which the cells are metabolically and biosynthetically most active. Levels of cell-associated SEB decreased during toxin excretion. However, these levels of toxin could not account for the high levels of toxin released during excretion. Glucose and several other rapidly fermentable carbohydrates inhibited toxin excretion by as much as 80% under conditions of uncontrolled decrease in pH; however, when the pH was kept at either 6.2 or 7.5 a stimulation of toxin excretion was observed. Protoplast studies have suggested that SEB production does not take place in the absence of an intact cell wall.

ISSN:0008-4166    

DOI:10.1139/m77-055

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Effect of cyclic AMP (cAMP) onPhycomyces blakesleeanuswas studied by growing sporangiospores on glucose–asparagine agar or liquid medium containing three different levels of cAMP (10, 20 and 40 μM) in addition to the control (no cAMP added). The response ofPhycomycesto the exogenous cAMP concentration in the medium is as follows: (1) the time required for germ tube emergence is reduced; (2) the diameter of the mycelium is increased (sometimes more than 10 times) and frequency of branching is also increased; (3) the cell wall of the mycelium is thickened (in some cases more than 5 times); (4) the glycogen in the cytoplasm is decreased as visualized in thin sections and also demonstrated in biochemical quantitation; and (5) the distribution of intercalated membranous particles (Imp) on plasma membrane is altered and this can be easily detected in freeze-fractured replica. Such a change in Imp is seen in the formation of small clusters of aggregated particles on the plasmic half (PF) and craters on the complementary exoplasmic half(EF)of the plasma membrane. Although the mechanism of cAMP action requires further exploration, it is possible that the addition of cAMP to the culture medium leads to degradation of glycogen and enhancement of chitin synthesis since the cell wall is largely composed of chitin. The alteration in Imp may be related to a change in the activity of chitin synthetase which is a plasma membrane-bound enzyme.

ISSN:0008-4166    

DOI:10.1139/m77-056

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Growth and enterotoxin B (SEB) formation byStaphylococcus aureus14458 and its membrane mutant can be depressed or stimulated by addition of graded amounts of saturated or unsaturated fatty acid mixtures. Under some conditions depression of SEB formation is separable from growth inhibition. Individual fatty acids most active in altering growth and (or) SEB production have been identified. Small amounts of unsaturated fatty acid mixture not only antagonize some effects of saturated fatty acid mixtures, but also appear to potentiate inhibition of growth and SEB formation by the saturated fatty acid mixture. 2-Adamantanone, a compound which increases cell membrane fluidity, strongly suppresses SEB formation while stimulating growth. The results are discussed in relation to possible effects of exogenous fatty acids on the composition of membrane phospholipids and attendant changes in SEB production.

ISSN:0008-4166    

DOI:10.1139/m77-057

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Three isolates, one from each species ofCandida krusei,C.parakrusei, andC.tropicalis, obtained from infected patients, were more tolerant of significantly higher concentrations of polyene antibiotics than the corresponding reference wild types. The resistant strains isolated had the same sterols as their wild-type counterparts but in lower concentrations.

ISSN:0008-4166    

DOI:10.1139/m77-058

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

An obligate methyltrophMethylomonas methylovoraoxidized methylamine, formaldehyde, and formate. Enzymes oxidizing these substrates were detected in a cell-free system. Phenazine methosulfate-linked methylamine dehydrogenese was purified 21-fold. The enzyme had optimum activity at pH 7.5 and was stable at 60 °C for 5 min. The enzyme activity was inhibited by parachloromercuric benzoate, isonicotinic acid hydrazide, mercuric chloride, and sodium borate.

ISSN:0008-4166    

DOI:10.1139/m77-059

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Spores transferred to germination medium incorporated exogenous lysine into protein within 20 min but required 2–3 h to begin incorporation of exogenous proline or alanine. During this time considerable uptake of amino acids into the intracellular pool occurred. Cycloheximide added to the germination medium inhibited incorporation of lysine into protein but did not lessen its accumulation in the pool. Spore germination was inhibited by cycloheximide.

ISSN:0008-4166    

DOI:10.1139/m77-060

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Eight species of bacteria representing rod, coccus, gram-positive, and gram-negative forms were tested for their sensitivity to sodium chloride during freezing and thawing. Six of the eight species tested were salt-sensitive, though to different degrees, whileLactobacillus caseiandStreptococcus faecaliswere resistant.Escherichia coligrown anaerobically exhibited only 38% of the salt sensitivity of aerobically grown cells. Analysis of cytochrome pigments in the organisms revealed that the six sensitive organisms all contained these pigments but in varying amounts, while the two resistant ones were devoid of them. Anaerobically grownE.colicontained 50% of the cytochromes of aerobically grown cells. A relationship between cytochrome content of the organisms and salt sensitivity during freezing and thawing was demonstrated with a correlation coefficient of 0.76 (P < 0.05); the higher the cytochrome content, the more salt-sensitive the organism. This indicated that 58% of the salt sensitivity was due to the cytochrome content.Using a model organism,E.coli, the effect of salt during freezing and thawing on the respiratory activity was examined. Freezing and thawing in water or saline decreased the respiration by whole cells of substrates expected to be NAD-linked while NADH-stimulated respiration was increased. In cell-free extracts derived from unfrozen cells or those frozen and thawed in water or saline, the respiration of ascorbate plusN,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) was constant. The respiration of NADH, succinate, and lactate in cell-free extracts derived from cells frozen and thawed in saline was reduced compared with those extracts derived from unfrozen cells or cells frozen and thawed in water. Studies withE.colishowed that the decreased respiratory activity caused by disruptions in the electron-transport chain could not account for the salt sensitivity on freezing and thawing. More likely, salt sensitivity is related to the presence of bonds between cytochromes and other membrane components which are disrupted by sodium chloride on freezing and thawing. This would then result in loss of membrane integrity and function.

ISSN:0008-4166    

DOI:10.1139/m77-061

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The partial purification of two intracellular proteinases from the protozoan parasiteEntamoeba histolyticais reported. One of these enzymes is an acid proteinase exhibiting maximum activity at pH 3.5 (hemoglobin substrate), is little affected by a range of inhibitors or activators, and is presumed to be similar to cathepsin D. Also present is a neutral proteinase exhibiting optimum activity at pH 6.0 (azocasein) but only poorly hydrolyzing either hemoglobin or serum albumen. This latter enzyme displayed no metal ion requirement, but was markedly inhibited by thiol-blocking agents and activated by free sulfhydryl-containing compounds.

ISSN:0008-4166    

DOI:10.1139/m77-062

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Recommended concentrations of paraquat alone and its combination with each of linuron, diuron, atrazine, simazine, and simazine plus diuron exerted little effect on total populations of bacteria, actinomycetes, and fungi in Fox sandy loam under laboratory and simulated field conditions in 66 and 77 days, respectively. Respiration of the total microbiota in soil suspension was affected by the combinations as well as individual herbicides in various concentrations. Yet, the inhibition of the O2uptake by any of these herbicides, including some extreme concentrations, was not permanent, indicating adaptation, or suppression of specific organisms. Only linuron in concentrations up to 20 μg/ml stimulated respiration of the soil.

ISSN:0008-4166    

DOI:10.1139/m77-063

出版商:NRC Research Press    

年代:1977

数据来源: NRC