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Potential Bottlenecks (potential + bottleneck)
Selected AbstractsConsumer body composition and community structure in a stream is altered by pHFRESHWATER BIOLOGY, Issue 3 2010A. LARRAÑAGA Summary 1.,Low pH inhibits microbial conditioning of leaf-litter, which forms the principal energy input to many headwater streams. This reduces food quality and availability for the shredder assemblage, thereby creating a potential bottleneck in the flux of energy and biomass through acidified food webs. 2.,We explored the consequences of acidity on the well-characterised community of Broadstone Stream in southeast England, by quantifying the physiological condition (protein and lipid content) of three dominant shredder species (Leuctra nigra, L. hippopus and Nemurella pictetii) and relating this to changes in the numerical abundance and biomass of invertebrates across a longitudinal pH gradient (5.3,6.5). 3.,Total taxon richness increased with pH, as did shredder diversity. The acid-tolerant stonefly, L. nigra, exhibited a positive correlation between pH and protein content, but its abundance was suppressed in the less acid reaches. These results suggest that the impacts of environmental stressors might be manifested differently at the population (i.e. numerical and biomass abundance) versus the physiological (i.e. protein content of individuals) levels of organisation. Body composition of L. hippopus and N. pictetii did not exhibit any significant relationship with stream pH in the field. 4.,The survey data were corroborated with a laboratory rearing experiment using N. pictetii, in which survival rate, growth rate, and protein and lipid content of individuals were measured in stream water of differing pH and acid versus circumneutral microbial conditioning regimes. Acid-conditioned leaves were associated with increased mortality and reduced protein content in consumers' tissues, with acid water also having the latter effect. 5.,Our results suggest that biochemical constraints within key taxa might create energy flux bottlenecks in detrital-based food webs, and that this could ultimately determine the productivity of the entire system. Hence assays of the body composition of macroinvertebrates could be an effective new tool that complements population level studies of the impacts of stressors in fresh waters. [source] Modelling congestion in closed queueing networksINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 4-5 2000P.K. Pollett Abstract We will consider the problem of identifying regions of congestion in closed queueing networks with state-dependent service rates. A particular queue will be called a bottleneck if the number of customers in that queue grows without bound as the total number of customers in the network becomes large. We will review methods for identifying potential bottlenecks, with a view to controlling congestion. We will see that the problem of identifying bottlenecks can be reduced to one of finding them in an isolated subnetwork with suitably modified routing intensities. Several special cases will be studied, illustrating a range of behaviour. For example, it is possible for a subnetwork to be congested, yet each queue in that subnetwork is not strictly a bottleneck. [source] Endocytic uptake of fluorescence labelled DNA in yeastJOURNAL OF BASIC MICROBIOLOGY, Issue 1 2010Sean-Patrick Riechers Abstract After dispiriting results using viral vectors in gene therapy, by which a number of patients acquired cancer as a result of the use of retroviral vector constructs, the percentage of non-viral approaches has increased over recent years. To elucidate potential bottlenecks in the non-viral transfection process we here introduce a novel method to directly visualize endocytic non-viral DNA uptake in a transfection approach. This novel method allows for the first time to monitor the location of DNA which is taken up by endocytosis in yeast (Saccharomyces cerevisiae) wild type and mutant strains. More specifically it enables drawing conclusions about conditions favouring non-viral gene transfection. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Metabolic control analysis of an enzymatic biofuel cellBIOTECHNOLOGY & BIOENGINEERING, Issue 6 2009Doris J. Glykys Abstract Metabolic control analysis (MCA) is an analytical technique that aims to quantify the distribution of control that enzymes exhibit over the steady-state fluxes through a metabolic network. In an enzymatic biofuel cell, the flux of interest is the electrical current generated by the system. Regardless of transport limitations and other constraints, kinetic limitations can become potential bottlenecks in the operation of a biofuel cell. We have used an indirect approach to MCA to investigate a common osmium-mediated glucose oxidase/laccase enzymatic biofuel cell. The results of the analysis show that the control of the electron flux strongly depends on the total mediator concentrations and the extent of polarization of the individual electrodes. The effect of varying oxygen concentrations is also examined, as oxygen is required for the cathode, but it participates in a non-productive reaction at the anode. Under normal operating conditions the electrodes will be highly polarized and will both contain high mediator concentrations. This configuration will result in a dominant FCC at the anode, and the conditions that are needed for balanced flux control between the anode and cathode are explored. As increasingly complex bioelectrocatalytic systems and architectures are envisioned, MCA will be a valuable framework to facilitate their design and subsequent operation. Biotechnol. Bioeng. 2009;102: 1624,1635. © 2008 Wiley Periodicals, Inc. [source] Precursor Balancing for Metabolic Engineering of Lycopene Production in Escherichia coliBIOTECHNOLOGY PROGRESS, Issue 1 2001William R. Farmer One issue that must be addressed in the rational design of metabolic pathways is the elimination of potential bottlenecks in the upstream pathways. We have reconstructed the isoprenoid pathway to overproduce the carotenoid lycopene in Escherichia coli. Here we show that the distribution between pyruvate and glyceraldehyde 3-phosphate (G3P), the originating precursors of the isoprenoid pathway, is a major factor that can limit isoprenoid production yields in E. coli. In particular, alterations in the central metabolism that redirect flux from pyruvate back to G3P enhance lycopene production, while alterations that channel carbon flux away from the G3P pool have the opposite effect. These results suggest that G3P may be limiting in the biosynthesis of lycopene, and modifications that achieve a more equitable distribution between the two precursors are able to increase the lycopene yield in metabolically engineered E. coli. [source] | ||||||||||