Weak acids adaptation

Piper, P., Calderon, C.O., Hatzixanthis, K. and Mollapour, M. (2001) Weak acid adaptation the stress response that confers yeasts with resistance to organic acid food preservatives . 

De Nobel, H., Lawrie, L., Brul, S., et al. 2001. Parallel and comparative analysis of the proteome and transcriptome of weak-acid adapted Saccharomyces cer-evisiae reveals a crucial function for the small heat-shock protein Hsp26. Yeast 18 1413-1428. 

The general approach illustrated by Example 18.7 is widely used to determine equilibrium constants for solution reactions. The pH meter in particular can be used to determine acid or base equilibrium constants by measuring the pH of solutions containing known concentrations of weak acids or bases. Specific ion electrodes are readily adapted to the determination of solubility product constants. For example, a chloride ion electrode can be used to find [Cl-] in equilibrium with AgCl(s) and a known [Ag+]. From that information, Ksp of AgCl can be calculated. 

The waste gas, charged with odour-intensive substances (room waste air and process waste air) is purified in a two-stage counter-flow sembber (1). The sembbing fluid for the first stage is weakly acidic (A) and for the second stage, weakly alkaline (B). Both sembbing fluids contain activated sludge which is adapted to the medium concerned. 

Figure 4.11. Alkalimetric titration of an acid rainwater with a pH = 4.26, consisting of a mineral acidity of [H-Acy] = 50 /xeq iiter and a weak acidity of 90 /xeq liter ([NH/] = 85 /iM and acetic acid [HA] = 5 fiM). COj has been expelled with N2 prior to the titration. In the conventional titration curve, the pH jump is equivalent to the mineral acidity [H-Acy]. If only mineral acidity (no weak acids) were present, the titration curve would correspond to the drawn-out line (a). The Gran titration procedure permits one to distinguish between total acidity [Acyj] (end point 2) = 140 /ieq liter" and mineral acidity, [H-Acy] (end point e ) = 50 ieq liter". (Adapted from Sigg and Stumm, 1994.)...

Fernandes, A.R., Mira, N.P., Vargas, R.C., Canelhas, I., and Sa-Correia, I. 2005. Saccharomyces cerevisiae adaptation to weak acids involves the transcription factor Haalp and Haalp-regulated genes. Biochemical and Biophysical Research Communications 337 95-103. 

It is constantly found that microorganisms can often be induced to become resistant when exposed to sublethal concentrations of an antimicrobial or preservative. For example, S. cerevisiae can be induced to adapt to weak-acid stress by addition of 0.5-2.5 mM sorbate or benzoate. The... 

Findings from a study done on acid-adapted Salmonella to lactic acid rinses from artificially inoculated beef muscle slices showed that acid-adapted strains were not any more resistant to acid decontamination than parental strains (Dickson and Kunduru, 1995). In a study done by Steiner and Sauer (2003), the overexpression of the ATP-dependent heli-case RecG was found to increase resistance to weak organic acids in E. coli. This was achieved by reduction of the toxic effects of the organic acids, reduction of the effects of the synthetic uncouplers (CCCP and DNP), and a reduction of the ATPase and cytochrome c inhibitor azide as a result of a decrease in pH or available ATP. In LAB, resistance mechanisms to... 

It is proposed that anions are actively extruded from cells to account for lower intracellular concentration. In theory, if anions are extruded from the cell, they would reassociate when exposed to the lower external pH and freely diffuse back into the cell, resulting in a futile cycle without resistance development. However, adapted yeast cells can reduce the diffusion coefficient of preservatives across the plasma membrane, and the diffusion of weak acids into the cell is then reduced. This adaptive mechanism is based on the efflux of preservative anions by Pdrl2. Efflux of anions together with a reduction in the diffusion coefficient of the membrane will result in the maintenance of cell homeostasis, which will enable the organism to survive and grow (Holyoak et al., 1999). 

Holyoak, C.D., Stratford, M., McMullin, Z., Cole, M.B., Crimmins, K., Brown, A.J.P., and Coote, P. 1996. Activity of the plasma-membrane H+-ATPase and optimal glycolic flux are required for rapid adaptation and growth in the presence of the weak acid preservative sorbic acid. Applied and Environmental Microbiology 62 3158-3164. 

Stratford, M. and Lambert, R.J.W. 1999. Weak-acid preservatives Mechanisms of adaptation and resistance by yeasts. Food Australia 51 26-29. 

By using buffers with sufficient capacity (> 0.05 M) that minimize the dynamic pH-gradients. Occasionally the substrates or products themselves provide such properties so that only the optimal external pH-value has to be adapted. It should not be lower than the pK-value of the weak acid and not lower than the optimum pH of the enzyme [95,96]. 

Colorless powder when pure usually grayish-red. mp 253-255. Practically insol in water sol in alcohol, use As indicator in 0.1% or 0.04% soln in ale. pH 7,3 colorless to reddish 8,7 greenish to blue. Particularly adapted for weak acids in strong alcoholic soln,... 

Ionization of weak acids is described by an adaptation of a classical Henderson asselbalch equation. 

Figure 13.14. Competition between strongly inflammatory eicosanoids (shown in bold letters) derived from arachidonic acid and weakly inflammatory eicosanoids derived from eicosapentaenoic acid and docosahexaenoic acid. Adapted from Gurr (1999).

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