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Nanosilver inhibits nitrification and reduces ammonia‐oxidising bacterial but not archaeal amoA gene abundance in estuarine sediments 下载免费PDF全文
Jessica Beddow Björn Stolpe Paula A. Cole Jamie R. Lead Melanie Sapp Brett P. Lyons Ian Colbeck Corinne Whitby 《Environmental microbiology》2017,19(2):500-510
Silver nanoparticles (AgNPs) enter estuaries via wastewater treatment effluents, where they can inhibit microorganisms, because of their antimicrobial properties. Ammonia‐oxidising bacteria (AOB) and archaea (AOA) are involved in the first step of nitrification and are important to ecosystem function, especially where effluent discharge results in high nitrogen inputs. Here, we investigated the effect of a pulse addition of AgNPs on AOB and AOA ammonia monooxygenase (amoA) gene abundances and benthic nitrification potential rates (NPR) in low‐salinity and mesohaline estuarine sediments. Whilst exposure to 0.5 mg L?1 AgNPs had no significant effect on amoA gene abundances or NPR, 50 mg L?1 AgNPs significantly decreased AOB amoA gene abundance (up to 76% over 14 days), and significantly decreased NPR by 20‐fold in low‐salinity sediments and by twofold in mesohaline sediments, after one day. AgNP behaviour differed between sites, whereby greater aggregation occurred in mesohaline waters (possibly due to higher salinity), which may have reduced toxicity. In conclusion, AgNPs have the potential to reduce ammonia oxidation in estuarine sediments, particularly where AgNPs accumulate over time and reach high concentrations. This could lead to long‐term risks to nitrification, especially in polyhaline estuaries where ammonia‐oxidation is largely driven by AOB. 相似文献
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Kung-Jong Lui Duane Steffey Jamie K. Pugh 《Biometrical journal. Biometrische Zeitschrift》1993,35(6):677-688
Calculating the required sample size for a desired power at a given type I error level, we often assume that we know the exact time of all subject responses whenever they occur during our study period. It is very common, however, in practice that we only monitor subjects periodically and, therefore, we know only whether responses occur or not during an interval. This paper includes a quantitative discussion of the effect resulting from data grouping or interval censoring on the required sample size when we have two treatment groups. Furthermore, with the goal of exploring the optimum in the number of subjects, the number of examinations per subject for test responses, and the total length of a study time period, this paper also provides a general guideline about how to determine these to minimize the total cost of a study for a desired power at a given α-level. A specified linear cost function that incorporates the costs of obtaining subjects, periodic examinations for test responses of subjects, and the total length of a study period, is assumed, primarily for illustrative purpose. 相似文献
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Seymour Kaufman 《Neurochemical research》1991,16(9):1031-1036
Tetrahydrobiopterin and the folate coenzymes can reciprocally interact in ways that would be useful to the metabolic pathways subserved by both of these coenzymes. Thus, through one of the reactions catalyzed by methylene tetrahydrofolate reductase, 5-CH3-H4-folate can regenerate BH4 from q-BH2 and q-BH2 can provide an escape from the methyl trap.Special issue dedicated to Dr. Louis Sokoloff 相似文献
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In Canis and Ursus the largest proportion of attachments of muscles of the shoulder and brachium on the scapula and humerus is direct; fewer attachments are aponeurotic or tendinous. In both genera most attachments can be associated with superficial osteological features (scars or delimitable surfaces); attachments that lack such features are direct. Most aponeurotic attachments are associated with rugose scarring whereas tendinous attachments are often associated with smooth surfaces. Although most attachments can be associated with osteological features the areal extent of attachment is often not inferrable from the bone. The inference of muscle size or functional significance from osteological features is problematic. The amount of myological information that can be deciphered from the osteology in Canis and Ursus is greater than that reported for particular members of other vertebrate groups which suggests that there may be differences in the degree to which muscles can be reconstructed from superficial osteology alone. Nonetheless, even in mammals such as the Carnivora, detailed muscular reconstructions in extinct taxa cannot be achieved without reference to the musculature of extant relatives. Such reconstructions rely on assumptions, that often have not been adequately tested, regarding the similarity of musculature in closely related taxa. This testing and well corroborated hypotheses of phylogenetic relationship are essential for the evaluation of the accuracy of reconstructions of the musculature in fossil vertebrates. 相似文献
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The thermal inactivation of Salmonella thompson, Escherichia coli, Staphylococcus aureus, Clostridium perfringens, Candida zeylanoides, Enterococcus faecium and E. faecalis was accelerated by the addition of sodium isoascorbate (1 mmol/l) to phosphate-buffer heating medium but not to complex food mixtures. The lethal effect of isoascorbate was nullified by heating under anaerobic conditions or by the addition of catalase. The scavengers of hydroxyl radicals, mannitol and formate were not protective whereas histidine was. Histidine may have protected by slowing the rate of isoascorbate autoxidation, a property common to other amino acids tested. Superoxide dismutase was not protective. Dehydroascorbic acid also enhanced heat killing and its action was also reversed by catalase. The bactericidal effects of mild heat plus isoascorbate or dehydroascorbic acid both apparently depend on oxidative processes but their relative effectiveness was not related to their respective rates of oxygen consumption or peroxide production. We speculate that site-specific redox reactions, involving amino-carbonyl intermediates are involved in the inactivation mechanism. 相似文献
9.
Moira L. Steyn-Ross D. Alistair Steyn-Ross Jamie W. Sleigh 《Cognitive neurodynamics》2012,6(3):215-225
During slow-wave sleep, general anesthesia, and generalized seizures, there is an absence of consciousness. These states are
characterized by low-frequency large-amplitude traveling waves in scalp electroencephalogram. Therefore the oscillatory state
might be an indication of failure to form coherent neuronal assemblies necessary for consciousness. A generalized seizure
event is a pathological brain state that is the clearest manifestation of waves of synchronized neuronal activity. Since gap
junctions provide a direct electrical connection between adjoining neurons, thus enhancing synchronous behavior, reducing
gap-junction conductance should suppress seizures; however there is no clear experimental evidence for this. Here we report
theoretical predictions for a physiologically-based cortical model that describes the general anesthetic phase transition
from consciousness to coma, and includes both chemical synaptic and direct electrotonic synapses. The model dynamics exhibits
both Hopf (temporal) and Turing (spatial) instabilities; the Hopf instability corresponds to the slow (≲8 Hz) oscillatory
states similar to those seen in slow-wave sleep, general anesthesia, and seizures. We argue that a delicately balanced interplay
between Hopf and Turing modes provides a canonical mechanism for the default non-cognitive rest state of the brain. We show
that the Turing mode, set by gap-junction diffusion, is generally protective against entering oscillatory modes; and that
weakening the Turing mode by reducing gap conduction can release an uncontrolled Hopf oscillation and hence an increased propensity
for seizure and simultaneously an increased sensitivity to GABAergic anesthesia. 相似文献