Gas treatment in trickle-bed biofilters: biomass, how much is enough?

The objective of this article is to define and validate a mathematical model that desribes the physical and biological processes occurring in a trickle-bed air biofilter for waste gas treatment. This model considers a two-phase system, quasi-steady-state processes, uniform bacterial population, and one limiting substrate. The variation of the specific surface area with bacterial growth is included in the model, and its effect on the biofilter performance is analyzed. This analysis leads to the conclusion that excessive accumulation of biomass in the reactor has a negative effect on contaminant removal efficiency. To solve this problem, excess biomass is removed via full media fluidization and backwashing of the biofilter. The backwashing technique is also incorporated in the model as a process variable. Experimental data from the biodegradation of toluene in a pilot system with four packed-bed reactors are used to validate the model. Once the model is calibrated with the estimation of the unknown parameters of the system, it is used to simulate the biofilter performance for different operating conditions. Model predictions are found to be in agreement with experimental data. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 583-594, 1997.     

Lipid screening: is it enough to measure total cholesterol concentration?

OBJECTIVES--To determine whether measurement of total cholesterol concentration is sufficient to identify most patients at lipoprotein mediated risk of coronary heart disease without measurement of triglyceride and high density lipoprotein (HDL) cholesterol concentrations. DESIGN--Cross sectional screening programme. SETTING--Six general practices in Oxfordshire. PATIENTS--1901 Men and 2068 women aged 25-59. MAIN OUTCOME MEASURE--Cardiovascular risk as assessed by fasting venous plasma concentrations of total cholesterol, triglyceride, and HDL cholesterol. RESULTS--2931 Patients (74% of those screened) had a total cholesterol concentration of less than 6.5 mmol/l. If the triglyceride concentration had not been measured in these patients isolated hypertriglyceridaemia (greater than or equal to 2.3 mmol/l) would have remained undetected in 185. Among these 185 patients, however, 123 were overweight or obese and only 18 (0.6% of those screened) had an increased risk associated with both a raised triglyceride concentration (greater than or equal to 2.3 mmol/l) and a low HDL cholesterol concentration (less than 0.9 mmol/l). Conversely, in the 790 patients with predominant hypercholesterolaemia (cholesterol concentration greater than or equal to 6.5 mmol/l and triglyceride concentration less than 2.3 mmol/l) measurement of HDL cholesterol concentration showed that 348 (9% of those screened) had only a moderately increased risk with a ratio of total to HDL cholesterol of less than 4.5 and 104 had a low risk with a ratio of less than 3.5. CONCLUSIONS--Fasting triglyceride and HDL cholesterol concentrations identify few patients at increased risk of coronary heart disease if the total cholesterol concentration is less than 6.5 mmol/l. HDL cholesterol and triglyceride concentrations should, however, be measured in patients with a total cholesterol concentration exceeding this value. Total cholesterol concentration alone may overestimate risk in a considerable number of these patients, and measurement of HDL cholesterol concentration allows a more precise estimate of risk. Measurement of the triglyceride concentration is required to characterise the lipoprotein abnormality. A patient should not be started on a drug that lowers lipid concentrations without having had a full lipoprotein assessment including measurement of HDL cholesterol concentration.     

Hsp70 and larval thermotolerance in Drosophila melanogaster: how much is enough and when is more too much?

Heat shock proteins (Hsps) and other molecular chaperones perform diverse cellular roles (e.g., inducible thermotolerance) whose functional consequences are concentration dependent. We manipulated Hsp70 concentration quantitatively in intact larvae of Drosophila melanogaster to examine its effect on survival, developmental time and tissue damage after heat shock. Larvae of an extra-copy strain, which has 22 hsp70 copies, produced Hsp70 more rapidly and to higher concentrations than larvae of a control strain, which has the wild-type 10 copies of the gene. Increasing the magnitude and duration of pretreatment increased Hsp70 concentrations, improved tolerance of more severe stress, and reduced delays in development. Pretreatment, however, did not protect against acute tissue damage. For larvae provided a brief or mild intensity pretreatment, faster expression of Hsp70 in the extra-copy strain improved survival to adult and reduced tissue damage 21h after heat shock. Negative effects on survival ensued in extra-copy larvae pretreated most intensely, but their overexpression of Hsp70 did not increase tissue damage. Because rapid expression to yield a low Hsp70 concentration benefits larvae but overexpression harms them, natural selection may balance benefits and costs of high and low expression levels in natural populations.     

Cost effectiveness of incremental programmes for lowering serum cholesterol concentration: is individual intervention worth while?

OBJECTIVE--To evaluate the relative cost effectiveness of various cholesterol lowering programmes. DESIGN--Retrospective analysis. SETTING--Norwegian cholesterol lowering programme in Norwegian male population aged 40-49 (n = 200,000), whose interventions comprise a population based promotion of healthier eating habits, dietary treatment (subjects with serum cholesterol concentration 6.0-7.9 mmol/l), and dietary and drug treatment combined (serum cholesterol concentration greater than or equal to 8.0 mmol/l). MAIN OUTCOME MEASURE--Marginal cost effectiveness ratios--that is, the ratio of net treatment costs (cost of treatment minus savings in treatment costs for coronary heart disease) to life years gained and to quality of life years (QALYs) saved. RESULTS--The cost per life year gained over 20 years of a population based strategy was projected to be 12 pounds. For an individual strategy based on dietary treatment the cost was about 12,400 pounds per life year gained and 111,600 pounds if drugs were added for 50% of the subjects with serum cholesterol concentrations greater than or equal to 8.0 mmol/l. CONCLUSIONS--The results underline the importance of marginal cost effectiveness analyses for incremental programmes of health care. The calculations of QALYs, though speculative, indicate that individual intervention should be implemented cautiously and within more selected groups than currently recommended. Drugs should be reserved for subjects with genetic hypercholesterolaemia or who are otherwise at very high risk of arteriosclerotic disease.     

Neuroscience: how is three-dimensional space encoded in the brain?

A recent study in the rat has shown that hippocampal place cells and entorhinal grid cells exhibit vertically-elongated firing fields, indicating that the rat's brain may encode the animal's elevation less accurately than its horizontal position.     

The Mastodon in the room: how Darwinian is neo-Darwinism?

Failing to acknowledge substantial differences between Darwinism and neo-Darwinism impedes evolutionary biology. Darwin described evolution as the outcome of interactions between the nature of the organism and the nature of the conditions, each relatively autonomous but both historically and spatially intertwined. Furthermore, he postulated that the nature of the organism was more important than the nature of the conditions, leading to natural selection as an inevitable emergent product of biological systems. The neo-Darwinian tradition assumed a creative rather than selective view of natural selection, with the nature of the organism determined by the nature of the conditions, rendering the nature of the organism and temporal contingency unnecessary. Contemporary advances in biology, specifically the phylogenetics revolution and evo-devo, underscore the significance of history and the nature of the organism in biology. Darwinism explains more biology better, and better resolves apparent anomalies between living systems and more general natural laws, than does neo-Darwinism. The "extended" or "expanded" synthesis currently called for by neo-Darwinians is Darwinism.     

Grades in neural complexity: how large is the span?

The span of complexity in brains, between the simplest flatworms and the most advanced mammals is exceedingly great, measured by the number of different anatomical parts, physiological processes, sensory discriminations, and behavioral alternatives in the repertoire. Most evolution of brains has been adaptive radiation within the same grade of complexity. Distinct grades of complexity have appeared a dozen or more times and quite often in the retrograde direction. Advancement has not been inevitable or obviously advantageous in survival value but has happened-long before primates or mammals or vertebrates. Compare cuttlefish and the most advanced gastropods, bees and the best brine shrimp, primates and the most advanced reptiles known-all twigs with common branches. This repeated achievement of evolution has had all too little study in respect of the detailed listing of differences between major taxa of distinct grades of complexity. Connectivity at the level now known for the mammalian cortex is much needed in other classes, with estimates of reciprocity, intrinsic differentiation, dendritic parcellation and afferent and efferent connections, both locally and projecting to other centers, each done quantitatively to permit comparison. Physiological system organization, personality properties of neurons and circuits, proclivities and emergent phenomena at several integrative levels are sketchily known only for parts of a few systems. Examples are given of opportunities for new research that can more adequately characterize grades of brains.     

Local translation in neuronal compartments: how local is local?

Efficient neuronal function depends on the continued modulation of the local neuronal proteome. Local protein synthesis plays a central role in tuning the neuronal proteome at specific neuronal regions. Various aspects of translation such as the localization of translational machinery, spatial spread of the newly translated proteins, and their site of action are carried out in specialized neuronal subcompartments to result in a localized functional outcome. In this review, we focus on the various aspects of these local translation compartments such as size, biochemical and organelle composition, structural boundaries, and temporal dynamics. We also discuss the apparent absence of definitive components of translation in these local compartments and the emerging state‐of‐the‐art tools that could help dissecting these conundrums in greater detail in the future.