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131.
Influence of Plumbing Materials on Biofilm Formation and Growth of Legionella pneumophila in Potable Water Systems 总被引:6,自引:1,他引:5
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Julie Rogers A. B. Dowsett P. J. Dennis J. V. Lee C. W. Keevil 《Applied microbiology》1994,60(6):1842-1851
A two-stage chemostat model of a plumbing system was developed, with tap water as the sole nutrient source. The model system was populated with a naturally occurring inoculum derived from an outbreak of Legionnaires' disease and containing Legionella pneumophila along with associated bacteria and protozoa. The model system was used to develop biofilms on the surfaces of a range of eight plumbing materials under controlled, reproducible conditions. The materials varied in their abilities to support biofilm development and the growth of L. pneumophila. Elastomeric surfaces had the most abundant biofilms supporting the highest numbers of L. pneumophila CFU; this was attributed to the leaching of nutrients for bacterial growth from the materials. No direct relationship existed between total biofouling and the numbers of L. pneumophila CFU. 相似文献
132.
Julie Turgeon Paul D. N. Hebert 《Evolution; international journal of organic evolution》1994,48(6):1855-1865
Freshwater ostracodes show both an exceptionally high incidence of transitions to unisexuality and, in some cases, an extraordinary level of clonal diversity. There is no understanding of the agents promoting these transitions to thelytoky, although it has been suggested that their frequency may set the stage for sexual taxa to infuse clonal diversity into unisexuals. This study examines the nature and origins of clonal diversity in the unisexual ostracode Cyprinotus incongruens. A combination of allozyme and cytogenetic studies revealed the presence of two diploid clones of this species at three temperate sites and ten clones at one arctic site including three diploids, five triploids, and two tetraploids. The low heterozygosity (0%–20%) of its diploid clones suggests that parthenogenesis has arisen spontaneously in C. incongruens rather than through hybridization, as in vertebrate asexuals. Polyploid clones appear to owe their origin to genome additions from sexual taxa, although subsequent mutational divergence has played a role in further enhancing diversity. Two triploid clones have apparently originated from the incorporation of a haploid genome from the sexually reproducing C. glaucus, as evidenced by their high heterozygosity and possession of alleles otherwise found only in that species. Other polyploid clones have likely arisen as a result of interbreeding between bisexual and unisexual C. incongruens. These results suggest that both the incidence of spontaneous transitions to clonality and the frequency of interbreeding with relatives may be the key processes that govern clonal diversity in unisexual ostracodes. 相似文献
133.
The effects of prolonged emersion and submersion by tidal manipulation on marine macrobenthos 总被引:3,自引:3,他引:0
Hummel Herman Fortuin Anne W. Bogaards Roelof H. Meijboom Andre de Wolf Lein 《Hydrobiologia》1994,282(1):219-234
Effects of tidal manipulation, resulting in prolonged periods of emersion and submersion or in protracted tidal cycles, on estuarine benthic animals are reviewed.Prolonged submersion periods did not show effects on mortality of most benthic animals tested, with the exception of the crumb-of-bread sponge Halichondrea panicea, which, at low water-flow rates, was covered with a layer of bacteria and subsequently died.Protracted low-water periods of 18 hours during several weeks hardly caused any mortality. However, protracted low-water periods of 30 hours during some weeks or emersion during several days caused a strong increase in mortality, depending on: the duration of emersion, temperature, condition of the animals, species and age. At temperatures below –1 °C and above 24 °C mortality was generally high. Animals with a low glycogen content were more sensitive to emersion than those with a high content. Species with a shell and those that are relatively big were less sensitive than those without a shell or of small size.The reproductive cycle of benthic animals could be delayed or accelerated by both emersion and submersion. 相似文献
134.
135.
S. John Gatley Ding-Wei Yu Joanna S. Fowler Robert R. MacGregor David J. Schlyer Stephen L. Dewey Alfred P. Wolf Thomas Martin Colleen E. Shea Nora D. Volkow 《Journal of neurochemistry》1994,62(3):1154-1162
Abstract: The psychostimulant drug of abuse, cocaine (benzoylecgonine methyl ester), is rapidly metabolized by cleavage of its two ester groups, to give benzoylecgonine (BE) and ecgonine methyl ester, and by N-demethylation, to give N-norcocaine (NC). The recent use of [N-methyl-11CH3]cocaine to image brain cocaine binding sites with positron emission tomography (PET) raises the question of whether PET images partially reflect the distribution and kinetics of labeled cocaine metabolites. We prepared [O-metty/-11CH3]cocaine by methylation of the sodium salt of BE with [11C]CH3l, and showed that PET baboon brain scans, as well as regional brain kinetics and plasma time-activity curves corrected for the presence of labeled metabolites, are nearly identical to those seen with [N-methyl-11CH3]cocaine. This strongly suggests that 11C metabolites do not significantly affect PET images, because the metabolite pattern is different for the two labeled forms of cocaine. In particular, nearly half the 11C in blood plasma at 30 min was [11C]CO2 when [N-methy/-11CH3]cocaine was administered, whereas [11C]CO2 was not formed from [O-methy/-11CH3]cocaine. Only a trace of [11C]NC was detected in plasma after [O-methyl-11CH3]cocaine administration. Nearly identical brain PET data were also obtained when 4′-[N-methy/-11CH3]fluorococaine and 4′-[18F]fluoro-cocaine (prepared by nucleophilic aromatic substitution from [18F]fluoride-and 4′-nitrococaine) were compared with [N-methy/-11CH3]cocaine. In vitro assays with rat brain membranes showed that cocaine and 4′-fluoroco-caine were equipotent at the dopamine reuptake site, but that 4′-fluorococaine was about 100 times more potent at the 5-hydroxytryptamine reuptake site. The studies with positron-emitting 4′-fluorococaines thus support the lack of significance of labeled metabolites or of binding to 5-hydroxytryptamine reuptake sites to PET images taken with [N-methy/-11CH3]cocaine. [11C]NC prepared by O-methylation of norbenzoylecgonine gave PET images with preferential uptake in striatum, but slower clearance from all brain regions than [O-methy/-11CH3]cocaine. [11C]BE prepared by N-methylation of norbenzoylecgonine did not show brain uptake. 相似文献
136.
Non-photochemical fluorescence quenching and the diadinoxanthin cycle in a marine diatom 总被引:7,自引:0,他引:7
Miguel Olaizola Julie La Roche Zbigniew Kolber Paul G. Falkowski 《Photosynthesis research》1994,41(2):357-370
The diadinoxanthin cycle (DD-cycle) in chromophyte algae involves the interconversion of two carotenoids, diadinoxanthin (DD) and diatoxanthin (DT). We investigated the kinetics of light-induced DD-cycling in the marine diatom Phaeodactylum tricornutum and its role in dissipating excess excitation energy in PS II. Within 15 min following an increase in irradiance, DT increased and was accompanied by a stoichiometric decrease in DD. This reaction was completely blocked by dithiothreitol (DTT). A second, time-dependent, increase in DT was detected 20 min after the light shift without a concomitant decrease in DD. DT accumulation from both processes was correlated with increases in non-photochemical quenching of chlorophyll fluorescence. Stern-Volmer analyses suggests that changes in non-photochemical quenching resulted from changes in thermal dissipation in the PS II antenna and in the reaction center. The increase in non-photochemical quenching was correlated with a small decrease in the effective absorption cross section of PS II. Model calculations suggest however that the changes in cross section are not sufficiently large to significantly reduce multiple excitation of the reaction center within the turnover time of steady-state photosynthetic electron transport at light saturation. In DTT poisoned cells, the change in non-photochemical quenching appears to result from energy dissipation in the reaction center and was associated with decreased photochemical efficiency. D1 protein degradation was slightly higher in samples poisoned with DTT than in control samples. These results suggest that while DD-cycling may dynamically alter the photosynthesis-irradiance response curve, it offers limited protection against photodamage of PS II reaction centers at irradiance levels sufficient to saturate steady-state photosynthesis.Abbreviations CAP
chloramphenicol
- D1
PS II reaction center protein
- DD
diadinoxanthin
- DD
cycle-diadinoxanthin cycle
- DT
diatoxanthin
- DTT
dithiothreitol
- FCP
fucoxanthin chlorophyll a-c protein
- Fm
maximum fluorescence yield in the dark-adapted state
- Fo
minimum fluorescence yield in the dark-adapted state
- Fm and Fo
maximum and minimum fluorescence yields respectively in some light adapted state
- Fv
maximum variable fluorescence yield in the dark-adapted state
- Ik
Irradiance at the intercept of the initial slope of the photosynthesis-irradiance curve and the maximum photosynthetic rate
- kD
first order rate constant for nonradiative de-excitation of excitions in the PS II antenna
- kd
first order rate constant for non-radiative de-excitation of excitons in the PS II reaction center
- kF
first order rate constant for fluorescence
- kT
first order rate constant for exciton transfer to the reaction center
- kt
first order rate constant for exciton transfer from the reaction center to the antenna
- Rubisco
ribulose bisphosphate carboxylase
- SVm
Stern-Volmer quenching coefficient of the maximum fluorescence yield
- SVo
Stern-Volmer quenching coefficient of the miniximum fluorescence yield
- PS II
apparent absorption cross-section of PS II
- arr
average interval between exciton arrival to the PS II reaction center (ms)
- rem
average interval between electron turnover during photosynthesis in the PS II reaction center (ms)
- d
the probability that an exciton is non-radiatively dissipated in the reaction center
- T
the probability that an exciton in the antenna is transferred to the reaction center
- t
the probability that an exciton is transferred back from the reaction center to the antenna 相似文献
137.
Julie Y. H. Chan Hsing-Fei Tsai Terry B. J. Kuo Samuel H. H. Chan 《Regulatory peptides》1994,50(3):247-257
We evaluated possible modulation by angiotensin III (AIII) of the interactive effect of noxious stimuli and elevation in systemic arterial pressure on the responsiveness of neurons in the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata. Combined extracellular single-neuron recording and microiontophoresis were carried out on male, adult Sprague-Dawley rats anesthetized with pentobarbital sodium. The responsiveness of NRGC neurons to nociception (tail clamp) and/or transient hypertension elicited by phenylephrine (5 μg/kg, i.v.), in the absence or presence of AIII, was used as the experimental index. Microiontophoretic application of the heptapeptide suppressed the responses of spontaneously active NRGC neurons to individually delivered nociception or hypertension. Interestingly, the preferential reduction in responsiveness to tail clamp upon simultaneous elevation in arterial pressure was reversed to one that favored nociception in the presence of AIII. These actions of the heptapeptide appeared to be receptor-specific, since they were discernibly blocked by its selective antagonist, Ile7-angiotensin III. Our results reveal that neuropeptides such as AIII may differentially modulate neuronal responsiveness according to the prevailing physiologic input(s) to the central nervous system of the animal. 相似文献
138.
Multiple mechanisms of membrane anchoring of Escherichia coli penicillin-binding proteins 总被引:3,自引:0,他引:3
Abstract: The major penicillin-binding proteins (PBPs) of Escherichia coli play vital roles in cell wall biosynthesis and are located in the inner membrane. The high M r PBPs 1A, 1B, 2 and 3 are essential bifunctional transglycosylases/transpeptidases which are thought to be type II integral inner membrane proteins with their C-terminal enzymatic domains projecting into the periplasm. The low M r PBP4 is a DD-carboxypeptidase/endopeptidase, whereas PBPs 5 and are DD-carboxypeptidases. All three low M r , PBPs act in the modification of peptidoglycan to allow expansion of the sacculus and are thought to be periplasmic proteins attached with varying affinities to the inner membrane via C-terminal amphiphilic α-helices. It is possible that the PBPs and other inner membrane proteins form a peptidoglycan synthesizing complex to coordinate their activities. 相似文献
139.
Abstract: Plants and the fission yeast Schizosaccharomyces pombe synthesize small cadmium-binding peptides, called phytochelatins, in response to cadmium. Derived from glutathione (GSH: λ-Glu-Cys-Gly), they have the general structure (λ-Glu-Cys) n Gly, where n is 2–11. In order to study the biosynthesis of phytochelatins, we used the mutagen N -methyl- N '-nitro- N nitrosoguanidine (MNNG) to select mutants with a lowered GSH content. GSH-deficient mutants show a Cd-sensitive phenotype, whereas resistance to Cu is only slightly influenced. These Cd-sensitive mutants contain 2–15% of the wild-type GSH level. For three mutants a lowered activity of λ-glutamylcysteine synthetase was measured. One of the mutants was transformed to Cd-resistance and the complementing fragment was analyzed further. The complementing fragment hybridized with chromosome III. In the transformants, GSH content was restored up to wild-type levels, whereas the activity of λ-glutamylcysteine synthetase was significantly increased compared with the wild-type. Possible mechanisms for Cd-resistance in the transformants are discussed. 相似文献
140.
Bioluminescent Salmonella typhimurium provides a rapid assay for measuring the efficacy of freeze-drying suspension media 总被引:1,自引:1,他引:0
A strain of Salmonella typhimurium , transformed to a bioluminescent phenotype, was used to compare three freeze-drying suspension media: inositol serum broth with and without added gelatin and sterile skimmed milk. Recovery and growth studies performed by measuring changes in bioluminescence demonstrated that of the three media tested, the routinely used inositol serum broth was the most effective freeze-drying suspension medium. 相似文献