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Biomedical subjects

M J Johnson

Publications and source records attributed to M J Johnson.

At least 109 records · Page 6Linked to original sources
PubMed1977

Electrical potential of gastroduodenal mucosa measured by endoscopy.

The gastroduodenal mucosa has a negative electrical potential with regard to the blood stream, as measured by a potentiometer connected to an intravenous and an intragastric electrode. The intragastric electrode can be positioned on various points of the gastroduodenal surface under direct vision through the forceps channel of the gastroduodenoscope. The values of potential differences were determined in various areas of the stomach and duodenum of normal humans and also over gastric ulcers, duodenal ulcers, gastritis and gastric erosions. A deflection of the potential difference value toward zero characterizes any disruption of the normal mucosa, even if only a few millimeters in diameter. Localized reproduce localized potential difference deflections. Atrophic lesions are represented by larger areas of abnormal potential difference levels. The direct multiple determinations of potential differences over mucosal areas in which lesions are suspected is a useful, simple tool for more objective gastroduodenoscopic diagnoses.

Adult↗
PubMed1972

Bacterial cell production from hexadecane at high temperatures.

On mineral medium with hexadecane as the sole carbon source, stable mixed bacterial enrichment cultures were obtained from soil inoculum at 25, 35, 45, 55, and 65 C. Cell yields (grams of dry cells per gram of hexadecane) were determined for each of the enrichment cultures grown at the temperature at which they were enriched, and also for the 55 and 65 C cultures grown at various temperatures. In all cases, cell yields decreased with increasing growth temperature. The highest yield obtained at 65 C was 0.26, and the lowest yield obtained at 25 or 35 C was 1.02. Slower growth was observed at higher temperatures.

Alkanes↗
PubMed1971

Production of bacterial cells from methane.

A mixed methane-oxidizing bacterial culture capable of stable and predictable growth in continuous culture was isolated. The culture consisted of two types of gram-negative nonsporulating rods resembling pseudomonads. The culture grew well at 45 C on an inorganic medium without asepsis. Specific metal requirements for Ca(2+), Cu(2+), MoO(4) (2-), Zn(2+), Mn(2+), Mg(2+), and Fe(3+) (or Fe(2+)) were shown. The cells grown in continuous culture contained 11.7 to 12.1% total nitrogen. From an animal nutrition standpoint, the distribution of amino acids was satisfactory. The continuous fermentation was operated over a range of steady-state dilution rates from 0.085 to 0.301 hr(-1). The maximum specific growth rate for the culture, mu(max), was 0.303 hr(-1) (doubling time 2.29 hr). The average yield for all fermentations analyzed was 0.616 g (dry weight of cells per g of methane used and 0.215 g (dry weight) of cells per g of oxygen used. The yields on both methane and oxygen were higher for the oxygen-limited than for the methane-limited fermentations. The maximum productivity attained in the fermentor was 2.39 g (dry weight) of cells per hr per liter at a dilution rate of 0.187 hr(-1) and a cell concentration of 12.8 g (dry weight) of cells per liter. The limit on maximum cell productivity was determined only by the mass transfer rate of oxygen in the fermentor. The simultaneous volumetric mass-transfer coefficients (k(L)a in hr(-1)) for oxygen and methane were determined. The results appear to indicate an oxygen to methane mass-transfer coefficient ratio of approximately 1.4.

Amino Acids↗
PubMed1971

Alkane oxidation by a particulate preparation from Candida.

The oxidation of decane by a cell-free particulate preparation from Candida intermedia was studied. Decane is oxidized to decanoate via decanol and decanaldehyde. Oxidation of decane to decanol requires molecular oxygen. Decanol is oxidized to decanaldehyde by a nicotinamide adenine dinucleotide-linked dehydrogenase differing greatly in specificity from ordinary yeast alcohol dehydrogenase. Decanaldehyde is oxidized to decanoate by a nicotinamide adenine dinucleotide-linked dehydrogenase that oxidizes long-chain aldehydes but not short-chain aldehydes. The enzymes that oxidize decane, decanol, and decanaldehyde are all induced when decane is present in the medium. These enzymes are apparently located in the cell membrane.

Acids↗
PubMed1971

Equilibrium constant for conversion of pyruvate to acetyl phosphate and formate.

Preparations of pyruvate formate-lyase were made from Escherichia coli cells. Net reversal of the "phosphoroclastic split" of pyruvate was readily demonstrated with these preparations. Incubation of acetyl phosphate with formate resulted in the accumulation of pyruvate in concentrations up to 0.5 mm. Catalytic amounts of coenzyme A were essential. Pyruvate was also readily formed from acetyl coenzyme A and formate. The equilibrium constant of the reaction (pyruvate(-) + HPO(4) (2-) --> acetyl phosphate(2-) + formate(-)) has been determined to be about 23 at 37 C.

Acylation↗
PubMed1970

Pathways of anaerobic acetate utilization in Escherichia coli and Aerobacter cloacae.

Acetate-1-(14)C was added to anaerobic glucose-fermenting cultures of Escherichia coli and Aerobacter cloacae. In the E. coli culture, lactate formation occurred late in the fermentation, when the rate of production of formate and acetate had decreased. The occurrence of acetate label in the lactate indicated formation of pyruvate from acetyl-coenzyme A (CoA) and formate. In the A. cloacae cultures, substantial amounts of acetate label were found in the 2,3-butanediol formed. Evidence is presented that the label could have entered the diol only by conversion of formate and acetyl-CoA into pyruvate. The observed levels of radioactivity in the diol indicated that during diol formation the reaction yielding formate and acetyl-CoA from pyruvate CoA was operating close to equilibrium. The shift in metabolism from formation of acetate, ethyl alcohol, and formate to the formation of butanediol or lactate appears to be due basically to an approach to equilibrium of the pyruvate-splitting reaction, whatever the induction mechanism by which the shift is implemented.

Acetates↗
PubMed1968

Yields of bacterial cells from hydrocarbons.

A strain of Nocardia and one of Pseudomonas, both isolated on pristane (2,6,10,14-tetramethylpentadecane), gave cell yields of approximately 100% on n-octadecane and pristane. Both organisms grew more rapidly on the n-octadecane than on the pristane. A mixed culture, isolated on 3-methylheptane, whose two components were identified as species of Pseudomonas and of Nocardia, gave approximately 100% cell yields and grew with generation times of about 5 hr on n-heptane, n-octane, and 2-methylheptane. The generation time on 3-methylheptane was 8.6 hr and the cell yield was only 79%. A strain of Pseudomonas isolated from naphthalene enrichments and one from phenanthrene enrichments both gave a cell yield of 50% on naphthalene. The phenanthrene isolate gave a cell yield of 40% on phenanthrene. A Nocardia species isolated on benzene gave a 79% cell yield on benzene. The generation times of the bacteria isolated on aromatic hydrocarbons were related to the solubility of the aromatic hydrocarbons on which they were grown; the more insoluble hydrocarbons gave slower growth.

Benzene↗
PubMed1967

Cell yields of bacteria grown on methane.

Several mixed cultures of methane-oxidizing bacteria have been isolated. Among them, culture HR (consisting of two gram-negative rods, one 0.5 x 1.0 mu, the other 0.8 x 2 to 3 mu) was found to be the fastest-growing and to give the highest yields. Optimal conditions for rapid growth and high cell yields from methane were found to be: 30 C, NH(4) as nitrogen source, and pH 6.5. Requirements for CO(2) and Cu were observed. Under these conditions, generation times of approximately 3 hr and cell yields from methane between 65 and 70% could be attained. Culture HR can utilize methane, methanol, ethyl alcohol, 1-propanol, n-butyl alcohol, and glucose, but not propane, for growth. Yeast and beef extracts are inhibitory. Carbon balances demonstrate that few if any products other than cells and CO(2) are produced from methane under the growth conditions used. Cell analyses for carbon, hydrogen, nitrogen, and amino acid content of culture HR were also made.

Journal Article↗
PubMed1967

Experimental evaluation of liquid film resistance in oxygen transport to microbial cells.

A membrane probe was used to monitor the dissolved oxygen concentrations in continuous cultures of Candida utilis and Micrococcus roseus growing at low dissolved oxygen concentrations and various agitation levels. For the yeast fermentations, increasing the agitation level within the range of 0.1 to 0.3 w per liter lowered steady-state dissolved oxygen concentrations in the fermentor. The steady-state dissolved oxygen concentration in the fermentor was not influenced by the agitation level within the range of 0.3 to 1.8 w per liter. With M. roseus, no effect of agitation on steady-state dissolved oxygen concentrations in the fermentor was observed within the range of 0.1 to 1.8 w per liter. It was concluded that, under the conditions used, a measurable transfer barrier from the liquid to the yeast cells existed at agitation levels below 0.3 w per liter and that this barrier did not exist at agitation levels above 0.3 w per liter. The transfer barrier from the liquid to the yeast surface could be represented by a stagnant film of liquid 0.6 x 10 cm thick surrounding the cell at an agitation level of 0.10 w per liter. This film represented an oxygen concentration drop of 1.3 x 10 M from the bulk of the medium to the cells under the experimental conditions.

Journal Article↗
PubMed1967

Aerobic microbial growth at low oxygen concentrations.

Sterilizable membrane probes were used to study the relation between oxygen concentration and respiration rate in Candida utilis growing on acetate. When the organism was grown in a continuous fermentor at various dissolved oxygen concentrations (0.23 x 10(-6) to 32 x 10(-6)m), with time allowed for full adaptation to each oxygen concentration, the relationship between oxygen concentration and growth rate simulated Michaelis-Menten behavior, giving an apparent K(m) for oxygen of 1.3 x 10(-6)m. When respiration rate was measured at various oxygen concentrations without allowing time for adaptation, it was found that the respiration rate was directly proportional to O(2) concentration at low O(2) concentrations, and independent of O(2) concentration at high O(2) concentrations. Transition from one type of behavior to the other was fairly abrupt. The respiration rate in the presence of excess oxygen depended on the O(2) concentration at which the cells were grown, but the rate at low O(2) concentrations did not. There was evidence that, at low oxygen concentrations, oxygen diffusion through the cell substance limits respiration rate, at least in part.

Adaptation, Biological↗
PubMed1967

Anaerobic growth yields of Aerobacter cloacae and Escherichia coli.

Aerobacter cloacae UW-C83 and Escherichia coli K-12 were grown under various anaerobic environments. Y(atp) values were calculated by determination of cell weights and analyses for fermentation products. These Y(atp) values are compared with others reported in the literature. Limitation of growth by factors other than adenosine triphosphate supply is discussed.

Acetates↗
PubMed1967

Energy supply and cell yield in aerobically growth microorganisms.

Cell yields of Pseudomonas fluorescens, Aerobacter cloacae UW-C83, Escherichia coli K-12, Candida utilis UW-3, and Saccharomyces carlsbergensis UW-110 grown aerobically on several carbon sources are reported. The Y(atp) concept is discussed in relation to the yields on oxygen and to assumed P to O ratios for bacteria and reported P to O ratios for yeast.

Acetates↗
PubMed1967

Penicillin acyltransferase in Penicillium chrysogenum.

Isotopic exchange of (35)S between penicillins and 6-amino-penicillanic acid (6-APA) was observed in cell-free extracts of Penicillium chrysogenum. Sulfhydryl-containing compounds were required for activity. Dithiothreitol, dithioerythritol, mercaptoethanol, and glutathione served as activators. The acyltransferase was purified threefold by adsorption on calcium phosphate gel at pH 6 and elution at pH 8. The partially purified enzyme showed maximal activity at pH 8. The enzyme was stable at 25 C for at least 30 min at pH 8. Dissociable inhibitors or activators, other than the sulfhydryl-containing compounds, could not be demonstrated in the enzyme preparation. An apparent Michaelis constant of 1.5 +/- 0.5 mm was determined for penicillin G at a 6-APA concentration of 5 mm. The enzyme did not appear to possess penicillin amidase activity. The exchange mechanism probably involves an acyl-enzyme intermediate. Penicillins V, G, K, X, and dihydro F showed isotopic exchange with (35)S-6-APA. Penicillin N, methylpenicillin, and phenyl-penicillin did not show exchange. The level of acyltransferase in P. chrysogenum 51-20F3 was measured at times during the fermentation. The level of activity increased threefold between 40 and 55 hr, remaining high until about 90 hr.

Acyltransferases↗