Intracellular pH distribution as a cell health indicator in Saccharomyces cerevisiae

Abstract

Internal pH regulation is vital for many cell functions, including transport mechanisms and metabolic enzyme activity. More specifically, transport mechanisms are to a wide degree governed by internal pH distributions. We introduce the term standard deviation of the intracellular pH (s.d.( pH int )) to describe the internal pH distributions. The cellular pH distributional response to external stress such as heat has not previously been determined. In this study, the intracellular pH ( pH i ) and the s.d.( pH int ) of Saccharomyces cerevisiae cells exposed to supralethal temperatures were measured using fluorescence ratio imaging microscopy (FRIM). An exponential decline in pH i was observed after an initial small decline. For the first time, we report the use of FRIM for determining in vivo plasma membrane proton permeability coefficients in yeast. Furthermore, the exponential decay of pH i and the rupture of the cell plasma membrane, as measured by propidium iodide staining, at 708C were not simultaneous but were separated by a significant temporal difference. Finally, a nonlinear relationship between the pH i and s.d.( pH int ) was found; i.e. the s.d.( pH int ) was significantly more sensitive to supralethal temperatures than pH i . s.d.( pH int ) is therefore proposed as an early health/vitality indicator in S. cerevisiae cells exposed to heat stress.

Probiotic potential of Saccharomyces cerevisiae and Kluyveromyces marxianus isolated from West African spontaneously fermented cereal and milk products

“…boulardii 259, had an ability to increase TEER across the Caco-2 monolayers, suggesting their potential to strengthen the epithelial barrier integrity. Accordingly, TEER increases were previously reported in in vitro studies with clinical and food isolates of S. cerevisiae and K. marxianus (Klingberg et al, 2008;Pedersen et al, 2012;Smith et al, 2015 (Aabo, Glückstad, Siegumfeldt, & Arneborg, 2011;Halm, Hornbaek, Arneborg, Sefa-Dedeh, & Jespersen, 2004;Mortensen et al, 2006). Even though we observed a slightly higher percentage of PI-stained cells of K. marxianus KM1 and KM5 at the end of perfusion, compared with S. cerevisiae SM1 and SN1, the proportion of PI-stained cells never exceeded 25%.…”

Intracellular pH homeostasis in Candida glabrata in infection-associated conditions

“…Indeed, the effect of nutrient status was strongly pH ex -dependent in S. cerevisiae. Also, we observed low pH i at high temperatures, consistent with the results of previous studies (Aabo et al, 2011;Coote et al, 1994). The exact mechanism of this temperature-related acidification is not known but it has been suggested that increased temperature lowers pH i by changing membrane permeability and interruption of the activity of membrane transporters (Aabo et al, 2011).…”

Synthesis of Morphinan Alkaloids in Saccharomyces cerevisiae

“…While the existence of a thebaine synthase enzyme involved in the conversion of salutaridinol-7- O -acetate to thebaine can’t be excluded, an enzyme with this activity has not been isolated so far [ 21 , 27 ]. However, the intermediate salutaridinol-7- O -acetate can spontaneously rearrange to thebaine in solution at pH 8–9 and our results demonstrate that it does rearrange to thebaine in yeast cell feeding assays with a pH ranging from 7.5 to 9, which is likely equivalent to a maximum intracellular pH of ~7.5–8 [ 28 ]. Furthermore, although cellular metabolism is likely affected at an external pH above 8, enzymes involved in the synthesis of morphinan alkaloids appear to remain active, as demonstrated by thebaine production at pH>8 and viable plate counts showing no significant cell death after 16 hrs of incubation at pH 7.5, 8, 8.5 or 9 ( S3 Fig ).…”