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21.
A method is presented for the rapid enzymatic determination of acetate in spent bacterial culture supernatants. The assay is based on a previously published assay for acetate kinase [Bergmeyer et al. (1974) in Methods of Enzymatic Analysis (Bergmeyer, H. V., ed.), Vol. 1, pp. 425-426, Verlag Chemie-Academic Press, New York/London], and is sufficiently sensitive to detect acetate levels of 50 microM. The assay is cheaper than commercially available assays and is particularly useful for occasional use by laboratories not equipped for routine acetate analysis using gas chromatography. The application of the assay to the measurement of acetate in bacterial cultures is described, though it should also be applicable to other biological fluids and foodstuffs. 相似文献
22.
J M Pages 《Biochimie》1983,65(10):531-541
Bacterial protein synthesis takes place in the cytoplasm, thus periplasmic and outer membrane proteins pass through the cytoplasmic membrane during their dispatch to the cell envelope. The exported proteins are synthesized as precursor that contains an extra amino-terminal sequence of amino-acids. This sequence, termed "signal sequence", is essential for transport of the envelope proteins through the inner membrane and is cleaved during the exportation process. Various hypotheses for the mechanism have been presented, and it is likely that no signal model will be suitable to the export of all cell envelope proteins. This review is focused on the relationship between the cytoplasmic membrane and the precursor form. The physiological state of the membrane - fluidity, membrane potential for instance - is the strategic requirement of exportation process. Precursors can be accumulated in whole cells with various treatments which alter the cytoplasmic membrane. This inhibition of processing is obtained by modification of unsaturated to saturated fatty acids ratio or with phenylethyl alcohol which perturbs the membrane fluidity, with uncoupler agents such as carbonyl cyanide m-chlorophenyl hydrazone which dissipate the proton motive force, or with hybrid proteins which get jamming in the membrane. However, little is known about the early steps of translocation process across the cytoplasmic membrane ; for instance, it is not clear yet whether energy is required for either or both of the first interaction membrane-precursor and the crossing through the membrane. Several studies have recently shown the presence of exportation sites and of proteins which might play a prominent role in the export process, but the mechanism of discrimination between outer membrane proteins and periplasmic proteins is unknown. Considerable work has been done by genetic or biochemical methods and we have now the first lights of the expert mechanism. 相似文献
23.
24.
通过对治疗前后腹泻羔羊粪便细菌检查及临床观察,以查明两种抗菌药物对腹泻羔羊肠道细菌的影响。结果表明,腹泻羔羊治疗前粪便中的革兰氏阳性杆菌,革兰氏阳性球菌及革兰氏阴性杆菌的比例分别为20%、10%和70%。用敌菌净治疗的效果显著,其羔羊肠道细菌的比例接近健康羔羊。用庆大霉素治疗的羔羊,部分出现不良反应,其肠道细菌出现失调状态。 相似文献
25.
Column chromatography of the Escherichia coli mannitol permease (mannitol-specific enzyme II of the phosphotransferase system) in the presence of deoxycholate has revealed that the active permease can exist in at least two association states with apparent molecular weights consistent with a monomer and a dimer. The monomeric conformation is favored by the presence of mannitol and by the phosphoenolpyruvate (PEP)-dependent phosphorylation of the protein. The dimer is stabilized by inorganic phosphate (Pi), which also stimulates phospho-exchange between mannitol and mannitol 1-phosphate (a partial reaction in the overall PEP-dependent phosphorylation of mannitol). Kinetic analysis of the phospho-exchange reaction revealed that Pi stimulates phospho-exchange by increasing the Vmax of the reaction. A kinetic model for mannitol permease function is presented involving both conformations of the permease. The monomer (or a less-stable conformation of the dimer) is hypothesized to be involved in the initial mannitol-binding and PEP-dependent phosphorylation steps, while the stably associated dimer is suggested to participate in later steps involving direct phosphotransfer between the permease, mannitol and mannitol 1-phosphate. 相似文献
26.
In anoxic salt marsh sediments of Sapelo Island, GA, USA, the vertical distribution of CH4 production was measured in the upper 20 cm of surface sediments in ten locations. In one section of high marsh sediments,
the concentration and oxidation of acetate in sediment porewaters and the rate and amount of14C acetate and14CO2 incorporation into cellular lipids of the microbial population were investigated. CH4 production rates ranged from <1 to 493 nM CH4 gram sediment−1 day−1 from intact subcores incubated under nitrogen. Replacement with H2 stimulated the rate of methane release up to nine fold relative to N2 incubations. Rates of lipid synthesis from CO2 averaged 39.2 ×10−2nanomoles lipid carbon cm3 sediment−1 hr−1, suggesting that CO2 may be an important carbon precursor for microbial membrane synthesis in marsh sediments under anoxic conditions. Qualitative
measurements of lipid synthesis rates from acetate were found to average 8.7 × 10−2 nanomoles. Phospholipids were the dominant lipids synthesized by both substrates in sediment cores, accounting for an average
of 76.6% of all lipid radioactivity. Small amounts of ether lipids indicative of methanogenic bacteria were observed in cores
incubated for 7 days, with similar rates of synthesis for both CO2 and acetate. The low rate of ether lipid synthesis suggests that either methanogen lipid biosynthesis is very slow or that
methanogens represent a small component of total microbial lipid synthesis in anoxic sediments.
present address: The University of Maryland,, Chesapeake Biological Laboratory, Box 38, Solomons, MD 20688, USA 相似文献
27.
From among 125 strains of fluorescent and 52 strains of nonfluorescent bacteria initially screened in the laboratory for their
antibiosis towards the bacterial wilt pathogen, Pseudomonas solanacearum, strain Pfcp of Pseudomonas fluorescens and strains B33 and B36 of Bacillus spp., were chosen and evaluated further in greenhouse and field tests. Pfcp treated banana (Musa balbisiana), eggplant and tomato plants were protected from wilt upto 50, 61 and 95% in greenhouse and upto 50, 49 and 36% respectively
in field. Protection afforded by the Bacillus strains was lower. In bacteria-treated plants which were subsequently inoculated
with P. solanacearum plant height and biomass values increased and were close to those of nontreated and noninoculated control plants. 相似文献
28.
Three post-emergence herbicides (2,4-D, picloram and glyphosate) were applied to samples of an Alberta agricultural soil at
concentrations of 0, 2, 20, and 200 μg g−1. The effects of these chemicals on certain microbial variables was monitored over 27 days. All herbicides caused enhancement
of basal respiration but only for 9 days following application, and only for concentrations of 200 μg g−1. Substrate-induced respiration was temporarily depressed by 200 μg g−1 picloram and 2,4-D, and briefly enhanced by 200 μg g−1 glyphosate. It is concluded that because changes in microbial variables only occurred at herbicide concentrations of much
higher than that which occurs following field application, the side-effects of these chemicals is probably of little ecological
significance. 相似文献
29.
Cholesterol as a target for toxins 总被引:2,自引:0,他引:2
B. de Kruijff 《Bioscience reports》1990,10(2):127-130
A mechanism is proposed for the way in which cholesterol facilitates channel formation by polyene antibiotics and bacterial protein toxins. Central elements of the model are: (i) interactions between the ring system of the sterol and rigid elements of the polyene or toxin molecule, and (ii) the specific orientation of cholesterol within the membrane. 相似文献
30.
Hurricane Danny resulted in the rapid deposition of 10cm of oxidized, acidic sediment in the Contrary Creek arm of Lake Anna, Virginia. Several biological and geochemical parameters were monitored with time to ascertain how long it took the newly-deposited lake sediments to attain the anaerobic, circumneutral, actively sulfate-reducing state normally observed in this portion of the lake. The sediment platinum-electrode potential dropped from 350 mV to 100 mV within the first week after the storm. The pH of the pore water increased from 4.5 to 5.8 within three weeks, and titratable alkalinity was detected within two weeks and three weeks at 3 cm and 1 cm depths, respectively. Accumulation of reduced products of sulfate reduction (acid volatile sulfide) began by three to four weeks after the storm event. Both methanogens and sulfate reducers were present in high and approximately equal numbers in the freshly deposited material. The rapid neutralization of the acidity in the fresh sediment prior to the onset of sulfate reduction suggests that reactions other than sulfate reduction caused the initial increase in pH and alkalinity in this system. 相似文献