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B L Taylor

Publications and source records attributed to B L Taylor.

At least 37 records · Page 2Linked to original sources
PubMed1997

Magneto-aerotaxis in marine coccoid bacteria.

Magnetotactic cocci swim persistently along local magnetic field lines in a preferred direction that corresponds to downward migration along geomagnetic field lines. Recently, high cell concentrations of magnetotactic cocci have been found in the water columns of chemically stratified, marine and brackish habitats, and not always in the sediments, as would be expected for persistent, downward-migrating bacteria. Here we report that cells of a pure culture of a marine magnetotactic coccus, designated strain MC-1, formed microaerophilic bands in capillary tubes and used aerotaxis to migrate to a preferred oxygen concentration in an oxygen gradient. Cells were able to swim in either direction along the local magnetic field and used magnetotaxis in conjunction with aerotaxis, i.e., magnetically assisted aerotaxis, or magneto-aerotaxis, to more efficiently migrate to and maintain position at their preferred oxygen concentration. Cells of strain MC-1 had a novel, aerotactic sensory mechanism that appeared to function as a two-way switch, rather than the temporal sensory mechanism used by other bacteria, including Magnetospirillum megnetotacticum, in aerotaxis. The cells also exhibited a response to short-wavelength light (< or = 500 nm), which caused them to swim persistently parallel to the magnetic field during illumination.

Cell Movement↗
PubMed1997

How do bacteria avoid high oxygen concentrations?

Bacteria, such as Escherichia coli and Azospirillum brasilense, avoid microenvironments with elevated oxygen concentrations, not by sensing reactive oxygen derivatives, but by sensing a metabolic down-shift that results from elevated oxygen levels. A novel protein, Aer, and the chemotaxis serine receptor, Tsr, have recently been identified as transducers for aerotaxis which monitor internal energy levels in the bacteria.

Bacterial Physiological Phenomena↗
PubMed1997

Prediction of outcome from intensive care: a prospective cohort study comparing Acute Physiology and Chronic Health Evaluation II and III prognostic systems in a United Kingdom intensive care unit.

OBJECTIVE: To evaluate the ability of two prognostic systems to predict hospital mortality in adult intensive care patients. DESIGN: Prospective cohort study. SETTING: A mixed medical and surgical intensive care unit (ICU) in the United Kingdom. PATIENTS: A total of 1,144 patients consecutively admitted to the study. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Acute Physiology and Chronic Health Evaluation (APACHE) II and III prognostic systems were applied to assess probabilities of hospital mortality, which were compared with the actual outcome. The overall goodness-of-fit of both models was assessed. Hospital death rates were higher than those predicted by each system. Risk estimates showed a strong positive correlation between both systems (nonsurvivors r2 = 0.756, p < .0001; survivors r2 = 0.787, p < .0001). Calibration of APACHE II (chi 2 = 98.6, Lemeshow-Hosmer) was superior to that of APACHE III (chi 2 = 129.8, Lemeshow-Hosmer). The total correct classification rate of APACHE III was greater for all decision criteria applied; the best overall total correct classification rate was 80.6% for APACHE III and 77.9% for APACHE II (both for a decision criterion of 40%). The areas under the receiver operating characteristic curves were 0.806 and 0.847 for APACHE II and III, respectively, confirming the better discrimination of APACHE III. When patients were classified by diagnostic categories, risk predictions did not fit uniformly across the spectrum of disease groups. For both models, mortality ratios were highest for trauma patients and lowest for the group with respiratory disease. APACHE II predictions for patients with gastrointestinal disease were significantly better. Risk estimates for surgical admissions were superior with APACHE II (MR = 1.27) compared with APACHE III (MR = 1.56), but were similar for medical patients (1.22 vs. 1.28 for APACHE II and III, respectively). Bias induced by factors reflecting the clinical practice in an individual ICU (e.g., admission criteria, treatment before admission) may have considerable impact on risk estimates. The identification of such factors appears to be a prerequisite for the meaningful interpretation of observed and predicted death rates on the individual ICU level. CONCLUSIONS: Both predictive models demonstrated a similar degree of overall goodness-of-fit. APACHE II showed better calibration, but discrimination was better with APACHE III. Hospital mortality was higher than predicted by both models, but was underestimated to a greater degree by APACHE III. Risk estimates by both models showed considerable variation across the disease spectrum of ICU patients. Risk predictions for surgical patients and patients with gastrointestinal disease were better with APACHE II. Factors reflecting the clinical practice of an individual ICU are not accounted for by APACHE II and III. Overall, the performance of APACHE III was not superior to that of its predecessor for a cohort of United Kingdom ICU patients; for certain diagnostic categories, APACHE III performed worse than APACHE II despite an improved system of disease classification.

APACHE↗
PubMed1997

Glycerol elicits energy taxis of Escherichia coli and Salmonella typhimurium.

Escherichia coli and Salmonella typhimurium show positive chemotaxis to glycerol, a chemical previously reported to be a repellent for E. coli. The threshold of the attractant response in both species was 10(-6) M glycerol. Glycerol chemotaxis was energy dependent and coincident with an increase in membrane potential. Metabolism of glycerol was required for chemotaxis, and when lactate was present to maintain energy production in the absence of glycerol, the increases in membrane potential and chemotactic response upon addition of glycerol were abolished. Methylation of a chemotaxis receptor was not required for positive glycerol chemotaxis in E. coli or S. typhimurium but is involved in the negative chemotaxis of E. coli to high concentrations of glycerol. We propose that positive chemotaxis to glycerol in E. coli and S. typhimurium is an example of energy taxis mediated via a signal transduction pathway that responds to changes in the cellular energy level.

Bacterial Proteins↗
PubMed1997

Oxygen-dependent growth of the obligate anaerobe Desulfovibrio vulgaris Hildenborough.

Desulfovibrio vulgaris Hildenborough, a sulfate-reducing bacterium classified as an obligate anaerobe, swam to a preferred oxygen concentration of 0.02 to 0.04% (0.24 to 0.48 microM), a level which also supported growth. Oxygen concentrations of 0.08% and higher arrested growth. We propose that in zones of transition from an oxic to an anoxic environment, D. vulgaris protects anoxic microenvironments from intrusion of oxygen.

Aerobiosis↗
PubMed1996

Behavioral responses of Escherichia coli to changes in redox potential.

Escherichia coli bacteria sensed the redox state in their surroundings and they swam to a niche that had a preferred reduction potential. In a spatial redox gradient of benzoquinone/benzoquinol, E. coli cells migrated to form a sharply defined band. Bacteria swimming out of either face of the band tumbled and returned to the preferred conditions at the site of the band. This behavioral response was named redox taxis. Redox molecules, such as substituted quinones, that elicited redox taxis, interact with the bacterial electron transport system, thereby altering electron transport and the proton motive force. The magnitude of the behavioral response was dependent on the reduction potential of the chemoeffector. The Tsr, Tar, Trg, Tap, and CheR proteins, which have a role in chemotaxis, were not essential for redox taxis. A cheB mutant had inverted responses in redox taxis, as previously demonstrated in aerotaxis. A model is proposed in which a redox effector molecule perturbs the electron transport system, and an unknown sensor in the membrane detects changes in the proton motive force or the redox status of the electron transport system, and transduces this information into a signal that regulates phosphorylation of the CheA protein. A similar mechanism has been proposed for aerotaxis. Redox taxis may play an important role in the distribution of bacterial species in natural environments.

Bacterial Proteins↗
PubMed1996

Interactive effects of insulin with dihydrotestosterone on adrenergic tone in isolated rat tail arterial rings.

Reversal of sex-related differences in incidence of vascular diseases in Type II diabetics suggests that high circulating insulin may reverse normal differences in vascular actions of sex steroids. We have found that a high concentration of insulin can reverse small inhibitory actions of low estradiol on adrenergic tone in isolated arterial rings. Thus, we measured effects of high insulin on actions of dihydrotestosterone on adrenergic tone and specificity of these effects with respect to time of exposure to the steroid and its concentration. In the first of two studies, tail arterial rings from 16 male rats were incubated for 2 h with either dihydrotestosterone (0.0012 mumol/ L), insulin (0.5 mU/mL), dihydrotestosterone plus insulin, or vehicles. Rings were then contracted with norepinephrine administered cumulatively from 10(-9) to 10(-4) mol/L. Contractile responses to norepinephrine from 10(-7) to 10(-4) mol/L were increased by dihydrotestosterone in the absence (P < .05) but not in the presence of insulin. Also, norepinephrine's EC50 was reduced by dihydrotestosterone in the absence (P < .05) but not in the presence of insulin. In a second study (with rings from 12 more rats), the same low level of dihydrotestosterone failed to affect norepinephrine contractions acutely (that is, within 6 min), whereas much higher levels (12 and 120 mumol/L) rapidly inhibited the same contractions, independent of 2-h preincubation with insulin. Thus, prolonged exposure to a low physiological level of dihydrotestosterone enhances adrenergic tone, whereas acute exposure to high levels inhibits it. In addition, a high level of insulin specifically blunts the delayed enhancing effect of the low dihydrotestosterone. These results suggest possible mechanisms underlying sex-related differences in arterial vascular tone and the potential impact of hyperinsulinemia on such differences.

Animals↗
PubMed1996

Oxygen taxis and proton motive force in Azospirillum brasilense.

The microaerophilic nitrogen-fixing bacterium Azospirillum brasilense formed a sharply defined band in a spatial gradient of oxygen. As a result of aerotaxis, the bacteria were attracted to a specific low concentration of oxygen (3 to 5 microM). Bacteria swimming away from the aerotactic band were repelled by the higher or lower concentration of oxygen that they encountered and returned to the band. This behavior was confirmed by using temporal gradients of oxygen. The cellular energy level in A. brasilense, monitored by measuring the proton motive force, was maximal at 3 to 5 microM oxygen. The proton motive force was lower at oxygen concentrations that were higher or lower than the preferred oxygen concentration. Bacteria swimming toward the aerotactic band would experience an increase in the proton motive force, and bacteria swimming away from the band would experience a decrease in the proton motive force. It is proposed that the change in the proton motive force is the signal that regulates positive and negative aerotaxis. The preferred oxygen concentration for aerotaxis was similar to the preferred oxygen concentration for nitrogen fixation. Aerotaxis is an important adaptive behavioral response that can guide these free-living diazotrophs to the optimal niche for nitrogen fixation in the rhizosphere.

Azospirillum brasilense↗
PubMed1995

Investigation of transphosphorylation between chemotaxis proteins and the phosphoenolpyruvate:sugar phosphotransferase system.

Transphosphorylation between the chemotaxis proteins and phosphoenolpyruvate:sugar phosphotransferase system (PTS) from Escherichia coli was investigated by incubating the CheA, CheW and CheY proteins of the chemotaxis cascade, and Enzyme I, HPr and Enzyme IImtl of the PTS with [gamma-32P]ATP or [32P]phosphoenolpyruvate in the presence and absence of cell extract. In the absence of cell extract, ATP phosphorylated CheA, but in the presence of cell extract, Enzyme I was also phosphorylated. Phosphoenolpyruvate phosphorylated only PTS components. The transphosphorylation of Enzyme I by ATP did not require chemotaxis proteins, and likely occurred through acetate kinase. Regardless of phosphorylation state, the HPr protein did not inhibit the rate of ATP-dependent phosphorylation of the CheA or the CheY protein. It is concluded that chemotaxis to PTS substrates is not mediated by transphosphorylation between the PTS and chemotaxis systems.

Bacterial Proteins↗
PubMed1995

Behavior of Rhizobium meliloti in oxygen gradients.

Rhizobium meliloti cells responded to an abrupt change in oxygen concentration by changing the cell speed (chemokinesis), but they did not alter the frequency at which swimming cells stopped briefly (aerotaxis). Changes in cell speed upon stimulation with oxygen coincided with changes in membrane potential. The cells did not form an aerotactic band in a spatial gradient of oxygen as do the cells of other bacterial species. The fixL and fixJ genes which encode a heme-containing protein kinase that senses oxygen and a response regulator, respectively, were not involved in the behavior of R. meliloti in oxygen gradients.

Bacterial Proteins↗
PubMed1995

Continuous ascitic recirculation in severe ovarian hyperstimulation syndrome.

Massive ascites, hydrothorax, acute renal failure and thromboembolism are clinical manifestations of severe ovarian hyperstimulation syndrome (OHSS) which may complicate the induction of ovulation with exogenous gonadotrophins. We report a case of severe OHSS with ascites formation in excess of five litres per day. Massive ascites and bilateral pleural effusions resulted in respiratory failure. Continuous ascitic recirculation (AR) was commenced after repeated paracentesis and i.v. fluid therapy failed to improve the patient's condition. The procedure was undertaken for a total of 15 days and rapidly resulted in marked improvement of impaired respiratory function. Febrile episodes occurred on 3 occasions, but we did not observe coagulation disturbances or adverse haemodynamic effects. Continuous AR is a safe and effective treatment of complicated severe OHSS.

Adult↗
PubMed1995

Upper limb compartment syndromes: a complication of malignant hyperthermia in a patient with ill-defined myopathy.

We report a case of compartment syndrome complicating malignant hyperthermia (MH) in a 12-yr-old girl with a history of myopathy and multiple skeletal deformities; she underwent bilateral Achilles tendon surgery. Marked oedema of both forearms became evident in the immediate postoperative period and resolved after conservative treatment. Compartment syndrome is a rare complication of MH. Early recognition and therapy may prevent the onset of muscle ischaemia and distal neurovascular deficit. The need for urgent surgery and repeated anaesthesia in the early phase of recovery from an acute episode of MH may thus be reduced.

Abnormalities, Multiple↗