Buffering capacity and membrane H⁺conductance of lactic acid bacteria

Abstract

Buffering capacity and membrane conductance to H+ were measured in Enterococcus faecalis and Lactobacillus acidophilus by a pulse technique. The magnitude of these parameters varied between one species and another. Over the pH range studied, from pH 3.72 to 7.74, the acidophile Lactobacillus acidophilus showed higher values of buffering capacity and membrane H+ conductance than the neutrophile Enterococcus faecalis. These results support the idea that acidophiles have high cytoplasmic buffering capacity, which may allow them to resist changes in cytoplasmic pH.

Protonmotive force regulates the membrane conductance of Streptococcus bovis in a non-ohmic fashion

“…Reported values of ' passive ' proton conductance in Gram-positive species are less than 1 mmol H + (g protein) −" h −" (Maloney, 1979 ;Rius & Lore! n, 1998 ;Rius et al, 1994 ;Bender et al, 1986). However, S. bovis had an ATP hydrolysis rate of 39 mmol ATP (g protein) −" h −" , and based on a ratio of protons pumped\ATP of 4, the proton conductance of S. bovis was 156 mmol H + (g protein) −" h −" , a value…”

“…n, 1998 ;Rius et al, 1994 ;Bender et al, 1986). These discrepancies can be explained by the non-ohmic relationship between proton conductance and driving force.…”

“…Converting rates of pH change to rates of proton flux is dependent on an estimate of cellular buffering capacity, and while literature values for lactic acid bacteria average approximately 200 nmol H + (mg protein) −" per pH unit over an internal pH of 7 to 8, values vary from 50 to at least 350 nmol H + (mg protein) −" per pH unit (Maloney, 1979 ;Rius et al, 1994 ;Rius & Lore! n, 1998).…”

“…However, proton flux rates predicted by these calculations were 20-50-fold faster than values previously measured in bacteria (Maloney, 1979 ;Rius & Lore! n, 1998 ;Rius et al, 1994 ;Bender et al, 1986).…”

Effect of Starter Cultures on Lactobacillus Acidophilus Survival and Gene Expression in Yogurt

“…Some studies reported that the low pH is the most important factor affecting the viability of L. acidophilus (most common Lactobacillus species incorporated in commercial yogurts in the US) and Bifidobacterium species (Laroia and Martin, 1991;Shah and Ravula, 2000) post-fermentation. On the other hand, Ruis et al (1994) pointed that L. acidophilus has a high cytoplasmic buffering capacity (pH 3.72-7.74), which allows it to resist changes in intracellular pH and therefore gain stability under acidic conditions. However, this effect has not been documented universally for all strains.…”