PubMed Health⌕ Search

Biomedical subjects

J B Russell

Publications and source records attributed to J B Russell.

At least 127 records · Page 7Linked to original sources
PubMed1990

Effect of ionophores and pH on growth of Streptococcus bovis in batch and continuous culture.

Batch cultures (pH 6.7) of Streptococcus bovis JB1 were severely inhibited by 1.25 and 5 microM lasalocid and monensin, respectively, even though large amounts of glucose remained in the medium. However, continuous cultures tolerated as much as 10 and 20 microM, respectively, and used virtually all of the glucose. Although continuous cultures grew with high concentrations of ionophore, the yield of bacterial protein decreased approximately 10-fold. When pH was decreased from 6.7 to 5.7, the potency of both ionophores increased, but lasalocid always caused a larger decrease in yield. The increased activity of lasalocid at pH 5.7 could largely be explained by an increased binding of the ionophore to the cell membrane. Because monensin did not show an increased binding at low pH, some other factor (e.g., ion turnover) must have been influencing its activity. There was a linear increase in lasalocid binding as the concentration increased, but monensin binding increased markedly at high concentrations. Based on the observations that (i) S. bovis cells bound significant amounts of ionophore (the ratio of ionophore to cell material was more important than the absolute concentration), (ii) batch cultures responded differently from continuous cultures, and (iii) pH can have a marked effect on ionophore activity, it appears that the term "minimum inhibitory concentration" may not provide an accurate assessment of microbial growth inhibition in vivo.

Culture Media↗
PubMed1990

Transport and deamination of amino acids by a gram-positive, monensin-sensitive ruminal bacterium.

Strain F, a recently isolated ruminal bacterium, grew rapidly with glutamate or glutamine as an energy source in the presence but not the absence of Na. Monensin, a Na+/H+ antiporter, completely inhibited bacterial growth and significantly reduced ammonia production (85%), but 3,3',4',5-tetrachlorosalicylanide (a protonophore) and valinomycin had little effect on growth or ammonia production. Dicyclohexylcarbodiimide, a H(+)-ATPase, inhibitor had no effect. The kinetics of glutamate and glutamine transport were biphasic, showing unusually high rates at high substrate concentrations. On the basis of low substrate concentrations (less than 100 microM), the Km values for glutamate and glutamine were 4 and 11 microM, respectively. Strain F had separate carriers for glutamate and glutamine which could be driven by a chemical gradient of Na. An artificial delta psi was unable to drive transport even when Na was present. The glutamate carrier had a single binding site for Na with a Km of 21 mM; the glutamine carrier appeared to have more than one binding site, and the Km was 2.8 mM. Neither carrier could use Li instead of Na. Histidine and serine were also rapidly transported by Na-dependent systems, but serine alone did not allow growth even when Na was present. Because exponentially growing cells at pH 6.9 had little delta psi (-3 mV) and a slightly reversed Z delta pH (+17 mV), it appeared that the membrane bioenergetics of strain F were solely dependent on Na circulation.

Amino Acids↗
PubMed1990

Cloning and sequencing of a Bacteroides ruminicola B(1)4 endoglucanase gene.

Bacteroides ruminicola B(1)4, a noncellulolytic rumen bacterium, produces an endoglucanase (carboxymethylcellulase [CMCase]) that is excreted into the culture supernatant. Cultures grown on glucose, fructose, maltose, mannose, and cellobiose had high specific activities of CMCase (greater than 3 mmol of reducing sugar per mg of protein per min), but its synthesis was repressed by sucrose. B. rumincola did not grow on either ball-milled or acid-swollen cellulose even though the CMCase could hydrolyze swollen cellulose. The CMCase gene was cloned into Escherichia coli, and its nucleotide sequence contained a single open reading frame coding for a protein of 40,481 daltons. The enzyme was overproduced in E. coli under the control of the tac promoter and purified to homogeneity. The N-terminal sequence, amino acid composition, and molecular weight of the purified enzyme were similar to the values predicted from the open reading frame of the DNA sequence. However, the CMCase present in B. ruminicola was found to have a monomer molecular weight of 88,000 by Western immunoblotting. This discrepancy appeared to have resulted from our having cloned only part of the CMCase gene into E. coli. The amino acid sequence of the CMCase showed homology to sequences of beta-glucanases from Ruminococcus albus and Clostridium thermocellum.

Amino Acid Sequence↗
PubMed1990

Strategies of nutrient transport by ruminal bacteria.

The survival of bacteria in natural environments like the rumen depends on the ability of the bacteria to scavenge nutrients. It is now evident that ruminal bacteria use a variety of transport mechanisms. Hydrophobic substances, such as ammonia and acetate, are permeable to the lipid bilayers of cell membranes and can be taken up by passive diffusion. Hydrophilic compounds (e.g., sugars, amino acids, peptides) do not easily pass through lipid bilayers and must be transported across cell membranes on carrier proteins. Facilitated diffusion can display saturable kinetics but does not result in accumulation of solute. Active transport can establish extremely high concentration gradients, and this work may be driven by the hydrolysis of chemical bonds (e.g., ATP) or ion gradients, which are coupled to solute symport. Many solute symports involve protons, but sodium systems also are common in ruminal bacteria. The phosphotransferase system chemically modifies sugars as they pass across the cell membrane, and several ruminal bacteria have this method of group translocation. Many feed additives have either a direct or indirect effect on rumen bacterial transport. For instance, ionophores can inhibit transport by destroying (sometimes even reversing) ion gradients, lowering intracellular pH, or causing excessive ATP hydrolysis.

Animal Feed↗
PubMed1989

Transvaginal ultrasonographic detection of primary ovarian pregnancy with laparoscopic removal: a case report.

The use of transvaginal ultrasound has greatly increased our visualization of pelvic organs and our diagnostic capabilities. By combining transvaginal ultrasound with laboratory and clinical information, ectopic pregnancies can be diagnosed and treated early in the gestational period. Early diagnosis allows laparoscopic treatment of ectopic pregnancies. This case report combined the use of transvaginal ultrasound with laparoscopic treatment of an ovarian pregnancy.

Adult↗
PubMed1989

The effect of naloxone and metoclopramide on the hypothalamic pituitary axis in oligomenorrheic and eumenorrheic swimmers.

Eight highly competitive swimmers were followed over a 9-month period during a vigorous training schedule. When compared, four oligomenorrheic (group I, greater than 60 days without menses) and four eumenorrheic (group II) swimmers were not significantly different for age, years of training, body fat, intensity of training, and baseline estradiol (E2) levels. Both groups were challenged during the peak of their training schedule with 10 mg of naloxone and 10 mg of metoclopramide. The naloxone infusion revealed a significant increase in baseline luteinizing hormone (LH) levels in the oligomenorrheic swimmers when compared with the eumenorrheic swimmers. During the metoclopramide infusion prolactin (PRL) increased in all subjects, with a slightly higher increase in PRL in the eumenorrheic swimmers. The study suggests the menstrual dysfunction observed in these strenuously training swimmers to be related to the abnormalities of endorphin physiology as revealed by the elevation in LH after a naloxone infusion.

Adolescent↗
PubMed1989

Sodium-dependent transport of branched-chain amino acids by a monensin-sensitive ruminal peptostreptococcus.

A recently isolated ruminal peptostreptococcus which produced large amounts of branched-chain volatile fatty acids grew rapidly with leucine as an energy source in the presence but not the absence of Na. Leucine transport could be driven by an artificial membrane potential (delta psi) only when Na was available, and a chemical gradient of Na+ (delta uNa+) also drove uptake. Because Na+ was taken up with leucine and a Z delta pH could not serve as a driving force (with or without Na), it appeared that leucine was transported in symport with Na+. The leucine carrier could use Li as well as Na and had a single binding site for Na+. The Km for Na was 5.2 mM, and the Km and Vmax for leucine were 77 microM and 328 nmol/mg of protein per min, respectively. Since valine and isoleucine competitively inhibited (Kis of 90 and 49 microM, respectively) leucine transport, it appeared that the peptostreptococcus used a common carrier for branched-chain amino acids. Valine or isoleucine was taken up rapidly, but little ammonia was produced if they were provided individually. The lack of ammonia could be explained by an accumulation of reducing equivalents. The ionophore, monensin, inhibited growth, but leucine was taken up and deaminated at a slow rate. Monensin caused a loss of K, an increase in Na, a slight increase in delta psi, and a decrease in intracellular pH. The inhibition of growth was consistent with a large decrease in ATP.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids, Branched-Chain↗
PubMed1989

Non-proton-motive-force-dependent sodium efflux from the ruminal bacterium Streptococcus bovis: bound versus free pools.

Growing cells of Streptococcus bovis JB1 had a sodium content of 1,125 nmol/mg of protein and, based on a ratio of cell volume to protein of 4.3 microliters/mg, the apparent intracellular sodium concentration was more than 240 mM. Much of this sodium could not be removed by water washing even if cells were boiled or treated with the pore-forming ionophore, gramicidin, but it could be exchanged for potassium. Stationary cultures had a 2.6-microliters volume per milligram of protein and a total sodium content of 410 mM. When stationary cultures were energized with glucose at pH 6 to 8, sodium (more than 200 mM) was expelled within 2 min, and it appeared that growing cells had a very small pool of free intracellular sodium. Sodium-proton antiport activity could not be demonstrated with a sodium pulse, and the protonophore SF6847, valinomycin, and the H+-ATPase inhibitor dicyclohexylcarbodiimide (DCCD) had little effect on sodium efflux, even though these inhibitors greatly reduced the proton-motive force. SF6847, valinomycin, and DCCD had little effect on intracellular ATP, but iodoacetate, an inhibitor of glycolysis, decreased ATP as well as sodium efflux. Stationary cells from sodium-deficient medium expelled little sodium after glucose addition and had 35% more ATP than stationary cells which were grown in sodium medium and expelled sodium. An artificial electrochemical gradient of sodium was able to drive ATP synthesis in stationary cells, and this ATP formation was not sensitive to DCCD. These results indicated that bacteria could have a significant pool of bound sodium and that sodium expulsion from S. bovis was directly coupled to ATP hydrolysis.

Adenosine Triphosphate↗
PubMed1989

More monensin-sensitive, ammonia-producing bacteria from the rumen.

Two monensin-sensitive bacteria which utilized carbohydrates poorly and grew rapidly on amino acids were isolated from the bovine rumen. The short rods (strain SR) fermented arginine, serine, lysine, glutamine, and threonine rapidly (greater than 158 nmol/mg of protein per h) and grew faster on casein digest containing short peptides than on free amino acids ().34 versus 0.29 h(-1)). Gelatin hydrolysate, an amino acid source containing an abundance of long peptides, was unable to support growth or ammonia production, but there was a large increase in ammonia production if strain SR was cocultured with peptidase-producing ruminal bacteria (Bacteroides ruminicola or Streptococcus bovis). Cocultures showed no synergism with short peptides. Strain SR washed out of continuous culture ().1 h(-1)) at pH 5.9. The irregularly shaped organisms (strain F) deaminated glutamine, histidine, glutamate, and serine rapidly (greater than 137 nmol/mg of protein per min) and grew faster on free amino acids than on short peptides ().43 versus 0.21 h(-1)). When strain F was provided with casein or gelatin hydrolysate and cocultured with peptidase-producing bacteria, there was a more than additive increase in ammonia production. Strain F grew in continuous culture (0.1 h(-1)) when the pH was as low as 5.3. The irregularly shaped cells and short rods were present at less than 10(9)/ml in vivo, but they ahd very high specific activities of ammonia production (greater than 310 nmol of ammonia/mg of protein per min) and could play an important role in ruminal amino acid fermentation.

Amino Acids↗
PubMed1989

Transport of amino acids in Lactobacillus casei by proton-motive-force-dependent and non-proton-motive-force-dependent mechanisms.

Lactobacillus casei 393 cells which were energized with glucose (pH 6.0) took up glutamine, asparagine, glutamate, aspartate, leucine, and phenylalanine. Little or no uptake of several essential amino acids (valine, isoleucine, arginine, cysteine, tyrosine, and tryptophan) was observed. Inhibition studies indicated that there were at least five amino acid carriers, for glutamine, asparagine, glutamate/aspartate, phenylalanine, or branched-chain amino acids. Transport activities had pH optima between 5.5 and 6.0, but all amino acid carriers showed significant activity even at pH 4.0. Leucine and phenylalanine transport decreased markedly when the pH was increased to 7.5. Inhibitors which decreased proton motive force (delta p) nearly eliminated leucine and phenylalanine uptake, and studies with de-energized cells and membrane vesicles showed that an artificial electrical potential (delta psi) of at least -100 mV was needed for rapid uptake. An artificial delta p was unable to drive glutamine, asparagine, or glutamate uptake, and transport of these amino acids was sensitive to a decline in intracellular pH. When intracellular pH was greater than 7.7, glutamine, asparagine, or glutamate was transported rapidly even though the proton motive force had been abolished by inhibitors.

Amino Acids↗
PubMed1989

Transport of glutamine by Streptococcus bovis and conversion of glutamine to pyroglutamic acid and ammonia.

Streptococcus bovis JB1 cells energized with glucose transported glutamine at a rate of 7 nmol/mg of protein per min at a pH of 5.0 to 7.5; sodium had little effect on the transport rate. Because valinomycin-treated cells loaded with K and diluted into Na (pH 6.5) to create an artificial delta psi took up little glutamine, it appeared that transport was driven by phosphate-bond energy rather than proton motive force. The kinetics of glutamine transport by glucose-energized cells were biphasic, and it appeared that facilitated diffusion was also involved, particularly at high glutamine concentrations. Glucose-depleted cultures took up glutamine and produced ammonia, but the rate of transport per unit of glutamine (V/S) by nonenergized cells was at least 1,000-fold less than the V/S by glucose-energized cells. Glutamine was converted to pyroglutamate and ammonia by a pathway that did not involve a glutaminase reaction or glutamate production. No ammonia production from pyroglutamate was detected. S. bovis was unable to take up glutamate, but intracellular glutamate concentrations were as high as 7 mM. Glutamate was produced from ammonia via a glutamate dehydrogenase reaction. Cells contained high concentrations of 2-oxoglutarate and NADPH that inhibited glutamate deamination and favored glutamate formation. Since the carbon skeleton of glutamine was lost as pyroglutamate, glutamate formation occurred at the expense of glucose. Arginine deamination is often used as a taxonomic tool in classifying streptococci, and it had generally been assumed that other amino acids could not be fermented. To our knowledge, this is the first report of glutamine conversion to pyroglutamate and ammonia in streptococci.

Ammonia↗
PubMed1989

Effects of monensin and pH on the production and utilization of pyro-glutamate, a novel product of ruminal glutamine deamination.

Pure cultures of monensin-sensitive ruminal bacteria were involved in both the production and utilization of pyro-glutamate (pyrrolidone carboxylic acid), a novel product of glutamine fermentation, but the effect of monensin on pyro-glutamate accumulation in mixed cultures had not been assessed. Mixed ruminal bacteria (n = 3) fermented glutamine (40 mM) at a rapid rate (63 nmol/[mg protein-min]) and there was a transient increase in pyro-glutamate (3 mM). Monensin (5 ppm) decreased the rate of glutamine fermentation 70% and greatly enhanced the conversion of glutamine to pyro-glutamate (50 vs 7%). Glutamate was fermented at nearly the same rate as glutamine, and monensin eliminated glutamate fermentation. Glutamate was never converted to pyro-glutamate. Trypticase, a pancreatic digest of casein, contained pyro-glutamate, and a significant fraction (30%) of its N was never converted to ammonia. Pyro-glutamate utilization was reduced by monensin and low pH (less than 6.0). Based on these in vitro observations, pyro-glutamate could be a significant end-product of glutamine degradation when animals are fed monensin.

Animals↗
PubMed1988

Effect of tricarballylic acid, a nonmetabolizable rumen fermentation product of trans-aconitic acid, on Mg, Ca and Zn utilization of rats.

trans-Aconitic acid has been implicated in magnesium deficiency of ruminants since the 1960s, but recent experiments indicated that much of it can be converted by rumen bacteria to tricarballylic acid (TCBA). Rats were used as experimental models in the studies described here because analogous experiments in ruminants would have been very expensive. When TCBA was fed to young male Sprague-Dawley rats as 2% of an AIN-76A diet with marginal (200 mg/kg) or adequate (500 mg/kg) Mg, virtually all of the dietary acid was recovered in the urine. Mg and Ca absorptions were unaffected by TCBA but urinary losses of Mg, Ca and Zn were higher than in pair-fed controls. TCBA was highly correlated (r = 0.93) with titratable acid excretion, and Mg, Ca and Zn retentions were reduced by 90, 35 and 56%, respectively. Rats fed 2% citric acid, a structurally similar but metabolizable acid, excreted more Zn than controls but did not excrete excess Mg or Ca. Since TCBA led to a depletion of Mg and other cations, it could be a contributing factor in the etiology of the Mg deficiency known as grass tetany in ruminants. Additional work in ruminants now seems warranted.

Administration, Oral↗
PubMed1988

Potential opportunities and problems for genetically altered rumen microorganisms.

Rumen microbiologists are beginning to use genetic engineering techniques, and researchers should carefully consider both the potentials and limitations of using this technology to manipulate the rumen microbial ecosystem. Despite encouraging rhetoric, it is difficult to identify specific examples where genetic engineering would enhance ruminal performance. Many practical problems (lactic acidosis, deamination, etc.) might be better served by genetic engineering approaches that delete rather than add genes. The difficulty with this approach is that a highly selective means of preventing wild types from recolonizing the rumen would be needed. The addition of specific genes is confounded by 1) the fact that the rumen microorganisms are already adapted to the rumen, 2) the diversity of species inhabiting the rumen and 3) the complexity of interactions among these species. Aspects such as increased rates of cellulose digestion and changes in amino acid composition of the microflora are particularly sensitive to these biological constraints. Genetic engineering has, however, the potential to alleviate new limitations that humans have imposed on the rumen (detoxification, resistance to low pH, the digestion of novel feed materials, etc). A particular strategy of moving acid-resistant cellulose genes into noncellulytic, but acid-resistant, rumen bacteria is described.

Animals↗
PubMed1988

Fermentation of peptides and amino acids by a monensin-sensitive ruminal Peptostreptococcus.

A monensin-sensitive ruminal peptostreptococcus was able to grow rapidly (growth rate of 0.5/h) on an enzymatic hydrolysate of casein, but less than 23% of the amino acid nitrogen was ever utilized. When an acid hydrolysate was substituted for the enzymatic digest, more than 31% of the nitrogen was converted to ammonia and cell protein. Coculture experiments and synergisms with peptide-degrading strains of Bacteroides ruminicola and Streptococcus bovis indicated that the peptostreptococcus was unable to transport certain peptides or hydrolyze them extracellularly. Leucine, serine, phenylalanine, threonine, and glutamine were deaminated at rates of 349, 258, 102, 95, and 91 nmol/mg of protein per min, respectively. Deamination rates for some other amino acids were increased when the amino acids were provided as pairs of oxidized and reduced amino acids (Stickland reactions), but these rates were still less than 80 nmol/mg of protein per min. In continuous culture (dilution rate of 0.1/h), bacterial dry matter and ammonia production decreased dramatically at a pH of less than 6.0. When dilution rates were increased from 0.08 to 0.32/h (pH 7.0), ammonia production increased while production of bacterial dry matter and protein decreased. These rather peculiar kinetics resulted in a slightly negative estimate of maintenance energy and could not be explained by a change in fermentation products. Approximately 80% of the cell dry matter was protein. When corrections were made for cell composition, the yield of ATP was higher than the theoretical maximum value. It is possible that mechanisms other than substrate-level phosphorylation contributed to the energetics of growth.

Amino Acids↗