Effects of weak acids and external pH on the intracellular pH ofZygosaccharomyces bailii, and its implications in weak-acid resistance

Yeast ◽  
1987 ◽  
Vol 3 (1) ◽  
pp. 23-32 ◽  
Author(s):  
Martin B. Cole ◽  
Michael H. J. Keenan
Keyword(s):  
Intracellular Ph ◽  
Acid Resistance ◽  
Weak Acid ◽  
Weak Acids ◽  
External Ph

scholarly journals Weak Acid Resistance A (WarA), a Novel Transcription Factor Required for Regulation of Weak-Acid Resistance and Spore-Spore Heterogeneity in Aspergillus niger

mSphere ◽  
2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Ivey A. Geoghegan ◽  
Malcolm Stratford ◽  
Mike Bromley ◽  
David B. Archer ◽  
Simon V. Avery
Keyword(s):  
Transcription Factor ◽  
Aspergillus Niger ◽  
Sorbic Acid ◽  
Acid Resistance ◽  
Resistance Mechanisms ◽  
Weak Acid ◽  
Benzoic Acids ◽  
Weak Acids ◽  
Food Preservatives ◽  
Content Type

ABSTRACT Propionic, sorbic, and benzoic acids are organic weak acids that are widely used as food preservatives, where they play a critical role in preventing microbial growth. In this study, we uncovered new mechanisms of weak-acid resistance in molds. By screening a library of 401 transcription factor deletion strains in Aspergillus fumigatus for sorbic acid hypersensitivity, a previously uncharacterized transcription factor was identified and named weak acid resistance A (WarA). The orthologous gene in the spoilage mold Aspergillus niger was identified and deleted. WarA was required for resistance to a range of weak acids, including sorbic, propionic, and benzoic acids. A transcriptomic analysis was performed to characterize genes regulated by WarA during sorbic acid treatment in A. niger. Several genes were significantly upregulated in the wild type compared with a ΔwarA mutant, including genes encoding putative weak-acid detoxification enzymes and transporter proteins. Among these was An14g03570, a putative ABC-type transporter which we found to be required for weak-acid resistance in A. niger. We also show that An14g03570 is a functional homologue of the Saccharomyces cerevisiae protein Pdr12p and we therefore name it PdrA. Last, resistance to sorbic acid was found to be highly heterogeneous within genetically uniform populations of ungerminated A. niger conidia, and we demonstrate that pdrA is a determinant of this heteroresistance. This study has identified novel mechanisms of weak-acid resistance in A. niger which could help inform and improve future food spoilage prevention strategies. IMPORTANCE Weak acids are widely used as food preservatives, as they are very effective at preventing the growth of most species of bacteria and fungi. However, some species of molds can survive and grow in the concentrations of weak acid employed in food and drink products, thereby causing spoilage with resultant risks for food security and health. Current knowledge of weak-acid resistance mechanisms in these fungi is limited, especially in comparison to that in yeasts. We characterized gene functions in the spoilage mold species Aspergillus niger which are important for survival and growth in the presence of weak-acid preservatives. Such identification of weak-acid resistance mechanisms in spoilage molds will help in the design of new strategies to reduce food spoilage in the future.

scholarly journals Weak Acid Resistance A (WarA), a novel transcription factor required for regulation of weak-acid resistance and spore-spore heterogeneity in Aspergillus niger

2019 ◽  
Author(s):  
Ivey A. Geoghegan ◽  
Malcolm Stratford ◽  
Mike Bromley ◽  
David B. Archer ◽  
Simon V. Avery
Keyword(s):  
Transcription Factor ◽  
Aspergillus Niger ◽  
Sorbic Acid ◽  
Acid Resistance ◽  
Resistance Mechanisms ◽  
Weak Acid ◽  
Benzoic Acids ◽  
Food Spoilage ◽  
Weak Acids ◽  
Food Preservatives

ABSTRACTPropionic, sorbic and benzoic acids are organic weak acids that are widely used as food preservatives, where they play a critical role in preventing microbial growth. In this study, we uncovered new mechanisms of weak acid resistance in moulds. By screening a library of 401 transcription-factor deletion strains in Aspergillus fumigatus for sorbic acid hypersensitivity, a previously uncharacterised transcription factor was identified, and named as WarA (Weak Acid Resistance A). The orthologous gene in the spoilage mould Aspergillus niger was identified and deleted. WarA was required for resistance to a range of weak acids, including sorbic, propionic and benzoic acids. A transcriptomic analysis was performed to characterise genes regulated by WarA during sorbic acid treatment in A. niger. Several genes were significantly upregulated in the wild type compared with a ΔwarA mutant, including genes encoding putative weak acid detoxification enzymes and transporter proteins. Among these was An14g03570, a putative ABC-type transporter which we found to be required for weak acid resistance in A. niger. We also show that An14g03570 is a functional homologue of the Saccharomyces cerevisiae protein Pdr12p, and therefore named as PdrA. Lastly, resistance to sorbic acid was found to be highly heterogeneous within genetically-uniform populations of ungerminated A. niger conidia, and we demonstrate that pdrA is a determinant of this heteroresistance. This study has identified novel mechanisms of weak acid resistance in A. niger which could help to inform and improve future food spoilage prevention strategies.IMPORTANCEWeak acids are widely used as food preservatives, as they are very effective at preventing growth of most species of bacteria and fungi. However, some species of moulds can survive and grow in the concentrations of weak acid employed in food and drink products, thereby causing spoilage with resultant risks for food security and health. Current knowledge of weak acid resistance mechanisms in these fungi is limited, especially in comparison to that in yeasts. We characterised gene functions in the spoilage mould species Aspergillus niger which are important for survival and growth in the presence of weak acid preservatives. Such identification of weak acid resistance mechanisms in spoilage moulds will help to design new strategies to reduce food spoilage in the future.

Is intracellular pH a coupling factor in nutrient-stimulated pancreatic islets?

1988 ◽  
Vol 1 (1) ◽  
pp. 33-38 ◽  
Author(s):  
L. Best ◽  
E. A. Bone ◽  
J. E. Meats ◽  
S. Tomlinson
Keyword(s):  
Insulin Secretion ◽  
Lipid Metabolism ◽  
Intracellular Ph ◽  
Cell Function ◽  
Islet Cells ◽  
Coupling Factor ◽  
Weak Acid ◽  
Calcium Handling ◽  
Weak Acids ◽  
Rapid Fall

ABSTRACT Intracellular pH (pHi) was monitored in dispersed pancreatic islet cells from rats using the fluorescent dye 2′7′bis-carboxyethyl-5′(6′)-carboxyfluorescein. The addition of a weak acid (acetate, propionate or formate) provoked a rapid fall in pHi, corresponding to approximately 0·2 units, followed by a slower return to the basal value. Amiloride also caused a rapid fall in pHi, but no recovery occurred in this case. Addition of NH4Cl induced a rise in pHi. Of the nutrients tested, only glyceraldehyde produced a fall in pHi, both glucose and α-ketoisocaproate causing a gradual and sustained rise in pHi. Insulin secretion and inositol lipid metabolism in response to nutrient stimuli were markedly inhibited by NH4Cl. The responses to non-nutrient stimuli were unaffected. Glucose-induced insulin secretion and inositol lipid metabolism were potentiated in the presence of amiloride. No such potentiation, however, was observed in the presence of weak acids. Amiloride and weak acids shared the ability to reduce the fractional outflow rate of 45Ca2+. It is concluded that pharmacological manipulations of pHi can influence certain aspects of islet cell function, such as calcium handling, though it seems unlikely that the stimulation of islets by nutrient secretagogues occurs as a result of changes in pHi.

scholarly journals Humic acids trigger the weak acids stress response in maize seedlings

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Daiane Carvalho Baía ◽  
Fábio L. Olivares ◽  
Daniel B. Zandonadi ◽  
Cleiton de Paula Soares ◽  
Riccardo Spaccini ◽  
...  
Keyword(s):  
Abiotic Stress ◽  
Stress Response ◽  
Intracellular Ph ◽  
Humic Acids ◽  
Abiotic Stress Tolerance ◽  
Molecular Response ◽  
Maize Seedlings ◽  
Weak Acids ◽  
Acetoxymethyl Ester ◽  
Chemical Priming

Abstract Background Plants primed by humic acids showed physiological and molecular response against different abiotic stresses without the presence of stressor agents (salinity, drought, heavy metal toxicity). It is plausible that humic acids themselves can act as chemical priming substances in plants. We hypothesized that humic acids can trigger the weak acids stress response in cell plants acidifying the cytosol and thus eliciting the transduction signalling response cascade. Methods The dose–response curves of maize seedlings roots with different concentrations of humic, acetic and salicylic acids determined the most active and inhibitory concentration. These data were further used to evaluate changes on intracellular pH using BCECF-AM probe (2,7-bis(2-carboxyethyl)-5(and 6)-carboxyfluorescein, acetoxymethyl ester) and differential transcription level of genes related to weak stress response in plants by qPCR real time. Results Humic acids like short chain organic acids decrease the intracellular pH showed by the increased fluorescence of BCECF probe. The drop in cytosolic pH promoted by humic acids was not transient. We observed a high level of protein kinases related to cell energy-sensing and transcription factors associated to transduction of stress signalling. Conclusion The humic acids can be considered as a chemical priming agent, since in the appropriate concentration they can induce the typical plant abiotic stress response of weak acids inducing plant acclimation and enhancing the abiotic stress tolerance.

Effects of intracellular pH on hypoxic vasoconstriction in rat lungs

1987 ◽  
Vol 63 (6) ◽  
pp. 2524-2531 ◽  
Author(s):  
B. Raffestin ◽  
I. F. McMurtry
Keyword(s):  
Intracellular Ph ◽  
Hypoxic Pulmonary Vasoconstriction ◽  
Weak Acid ◽  
Hypoxic Response ◽  
Weak Bases ◽  
Rat Lungs ◽  
Hypoxic Vasoconstriction ◽  
Ethanesulfonic Acid ◽  
Vasoactive Mediator ◽  
Isolated Rat

Isolated rat lungs perfused with physiological salt-Ficoll solutions were studied to test whether hypoxic pulmonary vasoconstriction was potentiated by increases in intracellular pH (pHi) and blunted by decreases in pHi. Whereas addition to perfusate of 5 nM phorbol myristate acetate (PMA), a stimulator of exchange of intracellular H+ for extracellular Na+, potentiated hypoxic vasoconstriction, 1 mM amiloride, an inhibitor of Na+-H+ exchange, blunted the hypoxic response. Hypoxic vasoconstriction was also potentiated by the weak bases NH4Cl (20 mM), methylamine (10 mM), and imidazole (5 mM) and was inhibited by the weak acid sodium acetate (40 mM). NH4Cl, imidazole, and acetate had the same effects on KCl-induced vasoconstriction and on the hypoxic response. Hypoxic vasoconstriction was greater in lungs perfused with N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid (HEPES)-buffered solution than in those perfused with CO2/HCO3--buffered solution. Similarly, lungs perfused with CO2/HCO3--buffered solution containing 1.8 mM Cl- (NaNO3 and KNO3 substituted for NaCl and KCl) had larger hypoxic and angiotensin II pressor responses than those perfused with 122.5 mM Cl-. Because PMA, NH4Cl, methylamine, imidazole, HEPES-buffered solutions, and low-Cl- solutions can cause increases in pHi and amiloride and acetate can cause decreases in pHi, these results suggest that intracellular alkalosis and acidosis, respectively, potentiate and blunt vasoconstrictor responses to hypoxia and other stimuli in isolated rat lungs. These effects could be related to pHi-dependent changes in either the sensitivity of the arterial smooth muscle contractile machinery to Ca2+ or the release of a vasoactive mediator or modulator by some other lung cell.

Intracellular pH transients in rat diaphragm muscle measured with DMO

1978 ◽  
Vol 235 (1) ◽  
pp. C49-C54 ◽  
Author(s):  
A. Roos ◽  
W. F. Boron
Keyword(s):  
Intracellular Ph ◽  
Weak Acid ◽  
Diaphragm Muscle ◽  
Disulfonic Acid ◽  
Free Solution ◽  
Rat Diaphragm ◽  
Control Value ◽  
Acid Load ◽  
Acid Extrusion ◽  
Acid Loading

Changes of the intracellular pH of rat diaphragm muscle were monitored at 30-min intervals with the weak acid DMO (5,5-dimethyl-2,4-oxazolidinedione). Transferring the muscle from a CO2-containing to a CO2-free solution caused intracellular pH (pHi) to rise by an average of 0.18 during the first 30 min and then to level off at a slightly lower value over the next 60-90 min. Transferring the muscle from a CO2-free to a CO2-containing solution caused pHi to fall by 0.18 during the first 30 min and then to recover by 0.05 over the next 90 min. Subsequent return to the CO2-free solution caused pHi to overshoot the control value by 0.10. Both the recovery and the overshoot can be accounted for by an acid-extruding pump. Intracellular acid loading with 118 mM DMO similarly caused pHi to fall initially, to recover slowly during the acid loading, and then to overshoot the control pHi on removal of the acid load. In the absence of HCO3-/CO2, acid extrusion was reduced by about a fifth. SITS (4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid) had no effect. The absence of either Na+ or Cl- from HCO3-/CO2- free solution reduced acid extrusion by about a half.

scholarly journals Lowering pH in blood platelets dissociates myosin phosphorylation from shape change and myosin association with the cytoskeleton.

1987 ◽  
Vol 105 (4) ◽  
pp. 1761-1769 ◽  
Author(s):  
V T Nachmias ◽  
K Yoshida ◽  
M C Glennon
Keyword(s):  
Phorbol Esters ◽  
Shape Change ◽  
Blood Platelets ◽  
Chloride Ion ◽  
Weak Acids ◽  
Kinase C ◽  
Internal Ph ◽  
Mlc Phosphorylation ◽  
Active Interaction ◽  
External Ph

Platelet shape change induced by ADP is relatively independent of external pH over the range 6-7. If the chloride ion in the buffer is replaced by weak acids, however, shape change is rapidly and reversibly inhibited as a function of lowered pH (92% at pH 6.0). This inhibition is correlated with lowered internal pH caused by the weak acids, as measured by the 5,5-dimethyloxazolidine 2,4-dione technique. Shape change was 50% inhibited at internal pH 6.4 when 50 mM NaCl was replaced by propionate (PR). When platelets were stimulated with ADP 10-20 s after addition of PR to a final pH of 6 (PR6), both myosin light chain (MLC) phosphorylation and myosin and actin association with the cytoskeleton were reduced in correlation with the inhibition of shape change. But when ADP was added 30 s after PR6, the MLC phosphorylation was essentially the same in PR or in chloride, although shape change and myosin and actin association with the cytoskeleton remained inhibited. This was shown to be due mainly to endogenous phosphorylation of MLC. On return to neutral pH, platelets in PR immediately changed shape and myosin and actin became associated with the cytoskeleton. Two-dimensional tryptic peptides of MLC showed two major spots after PR6 treatment, indicating that both the MLC kinase site and the protein kinase C sites were phosphorylated. The results show that increased internal pH is not required for shape change, although it may affect the rate. In PR6, as after phorbol esters, MLC phosphorylation can be uncoupled from shape change. The association of myosin and actin with the cytoskeleton is closely correlated with shape change, suggesting that shape change requires the active interaction of these contractile proteins.

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