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Biomedical subjects

B L Taylor

Publications and source records attributed to B L Taylor.

At least 55 records · Page 3Linked to original sources
PubMed1995

Aerotaxis in Halobacterium salinarium is methylation-dependent.

The behavioural response to a gradient of oxygen (aerotaxis) has been characterized in the archaeon, Halobacterium salinarium. When the gas surrounding a drop of H. salinarium strain S9-P culture was changed abruptly from 10% (v/v) O2 to 100% N2, the bacteria transiently increased the frequency of reversing before they adapted and resumed random swimming. When the gas was returned to 10% O2 the bacteria responded by swimming smoothly for approximately 45 s. Aerotaxis was strongest when respiration in H. salinarium was highest and when bacteriorhodopsin and halorhodopsin were not contributing to the proton motive force. Starvation for methionine of the auxotrophic H. salinarium essentially abolished the step-down aerotactic response. Methanol production from demethylation of methyl-accepting chemotaxis proteins was transiently increased in H. salinarium S9-P by a step down or step up in oxygen concentration, as observed in methylation-dependent chemotaxis in H. salinarium. The taxis-negative and methyltransferase-deficient mutant, H. salinarium strain Pho72 did not exhibit changes in methanol release in response to aerotaxis or chemotaxis stimuli. This is the first report of an aerotactic response that is dependent on methylation of methyl-accepting chemotaxis proteins. Aerotaxis in Escherichia coli and Salmonella typhimurium is independent of transducer methylation.

Bacterial Proteins↗
PubMed1995

Role of methylation in aerotaxis in Bacillus subtilis.

Taxis to oxygen (aerotaxis) in Bacillus subtilis was characterized in a capillary assay and in a temporal assay in which the concentration of oxygen in a flow chamber was changed abruptly. A strong aerophilic response was present, but there was no aerophobic response to high concentrations of oxygen. Adaptation to a step increase in oxygen concentration was impaired when B. subtilis cells were depleted of methionine to prevent methylation of the methyl-accepting chemotaxis proteins. There was a transient increase in methanol release when wild-type B. subtilis, but not a cheR mutant that was deficient in methyltransferase activity, was stimulated by a step increase or a step decrease in oxygen concentration. The methanol released was quantitatively correlated with demethylation of methyl-accepting chemotaxis proteins. This indicated that methylation is involved in aerotaxis in B. subtilis in contrast to aerotaxis in Escherichia coli and Salmonella typhimurium, which is methylation independent.

Aerobiosis↗
PubMed1995

Amino acid efflux in response to chemotactic and osmotic signals in Bacillus subtilis.

We observed a large efflux of nonvolatile radioactivity from Bacillus subtilis in response to the addition of 31 mM butyrate or the withdrawal of 0.1 M aspartate in a flow assay. The major nonvolatile components effluxed were methionine, proline, histidine, and lysine. In studies of the release of volatile radioactivity in chemotaxis by B. subtilis cells that had been labeled with [3H]methionine, the breakdown of methionine to methanethiol can contribute substantially to the volatile radioactivity in fractions following addition of 0.1 M aspartate. However, methanol was confirmed to be released after aspartate addition and, in lesser quantities, after aspartate withdrawal. Methanol and methanethiol were positively identified by derivitization with 3,5-dinitro-benzoylchloride. Amino acid efflux but not methanol release was observed in response to 0.1 M aspartate stimulation of a cheR mutant of B. subtilis that lacks the chemotaxis methylesterase. The amino acid efflux could be reproduced by withdrawal of 0.1 M NaCl, 0.2 M sucrose, or 0.2 M xylitol and is probably the result of changes in osmolarity. Chemotaxis to 10 mM alanine or 10 mM proline resulted in methanol release but not efflux of amino acids. In behavioral studies, B. subtilis tumbled for 16 to 18 s in response to a 200 mosM upshift and for 14 s after a 20 mosM downshift in osmolarity when the bacteria were in perfusion buffer (40 mosM). The pattern of methanol release was similar to that observed in chemotaxis. This is consistent with osmotaxis in B. subtilis away from an increase or decrease in the osmolarity of the incubation medium. The release of methanol suggests that osmotaxis is correlated with methylation of a methyl-accepting chemotaxis protein.

Amino Acids↗
PubMed1995

CheA, CheW, and CheY are required for chemotaxis to oxygen and sugars of the phosphotransferase system in Escherichia coli.

We carried out studies with Escherichia coli to determine the site at which the methylation-independent pathways for taxis to oxygen and to sugars of the phosphoenolpyruvate:sugar phosphotransferase transport system converge with the methylation-dependent chemotaxis pathways. Using genetic reconstitution of the pathways in a null strain, we determined that all pathways examined required the products of the genes cheA, cheW, and cheY. Thus, we conclude that both the methylation-independent and methylation-dependent pathways converge at CheA, the histidine kinase product of cheA.

Bacterial Proteins↗
PubMed1994

Continuous measurement of systemic vascular resistance.

We have successfully linked a standard patient monitor system (Hewlett Packard M1166A-A66) with the Baxter Edwards Critical-Care Swan Ganz Intellicath continuous cardiac output catheter and the Vigilance continuous cardiac output monitor system to produce continuous values of systemic vascular resistance. Six cases are presented in which marked changes in indexed systemic vascular resistance were observed as a result of clinical interventions. The continuous derivation of systemic vascular resistance has much potential as a diagnostic and research tool as well as allowing rapid accurate assessment of the response of patients to therapy.

Cardiac Output↗
PubMed1994

Continuous invasive cardiac output monitoring--the Baxter/Edwards Critical-Care Swan Ganz IntelliCath and Viligance system.

We evaluated the Baxter/Edwards Critical-Care Swan Ganz IntelliCath continuous cardiac output catheter and Vigilance continuous cardiac output monitor in critically ill adult intensive care patients, and compared cardiac output measurements obtained from this new system with those from a standard bolus thermodilution technique using cold normal saline. Nine Swan Ganz IntelliCath catheters were inserted into patients selected at random, following the decision that pulmonary artery catheter monitoring was required. A total of 100 comparisons were made in nine patients. We found the Swan Ganz IntelliCath catheter to be both easy to insert and position, and simple to use. There were no complications or technical difficulties. The mean cardiac output measured by the continuous system was 8.00 l/min (SD 1.66/min) compared to 8.02 1/min (SD 1.74 l/min) using bolus techniques. Continuous cardiac output values correlated well with bolus measurements (r = 0.87), there was excellent accuracy (bias of 0.02 l/min) and precision was acceptable (limits of agreement of -1.71 to 1.75 l/min). These larger than anticipated limits of agreement may not reflect any inaccuracy in the continuous measurement system, rather they may highlight the extent of well recognised potential errors inherent in the intermittent bolus technique. The availability of a system to measure cardiac output continuously provides a major improvement in intensive care monitoring. This system will permit the rapid and accurate assessment of the response of patients to therapy while providing increased diagnostic facilities and a new research tool.

Adult↗
PubMed1993

Comparison of methods for specific depletion of ATP in Salmonella typhimurium.

Three methods of ATP depletion in Salmonella typhimurium were compared. ATP concentrations were lowest after arsenate treatment. Arsenate or alpha-methylglucoside-plus-azide treatment nonspecifically lowered all nucleotide triphosphate levels. Histidine starvation in a hisF mutant was relatively specific for ATP depletion and therefore has potential in distinguishing ATP-dependent processes from processes dependent on other nucleotides.

Adenosine Triphosphate↗