Intracellular pH homeostasis in Candida glabrata in infection-associated conditions

Abstract

Candida glabrata is an opportunistic fungal pathogen which is a growing concern for immunocompromised patients. It is ranked as the second most common cause of candidiasis after Candida albicans. For pathogenic yeasts, intracellular pH (pH i ) has been implicated in proliferation, dimorphic switching and virulence. We expressed the pH-sensitive green fluorescent protein variant ratiometric pHluorin in the cytosol of C. glabrata to study pH i dynamics in living cells. We evaluated the response of pH i to the various growth and stress conditions encountered during interaction with the host and during antifungal treatment. C. glabrata maintained a pH i higher than that of Saccharomyces cerevisiae in all growth conditions. The pH i of S. cerevisiae cells appeared better controlled than the pH i in C. glabrata when the cells were exposed to food and fermentation-associated conditions. C. glabrata in turn maintained its pH i better when exposed to host-associated conditions.

The CgHaa1-Regulon Mediates Response and Tolerance to Acetic Acid Stress in the Human Pathogen Candida glabrata

“…Functional clustering of the upregulated genes revealed an enrichment (p < 0.01) of genes encoding enzymes involved in central carbon metabolism (particularly in glycolysis, the Krebs cycle, the pentose phosphate pathway, and the catabolism of glycogen and trehalose); amino acid metabolism; ion transport (in particular ammonium, iron, potassium, and calcium); and the response to oxidative or to low pH (Figure S3 and Table S1). This transcriptional response is consistent with described toxic effects of acetic acid stress in fungal cells, which include the depletion of ATP and amino acid pools, intracellular acidification, inhibition of nutrient uptake, protein denaturation, and reduction of the internal iron pool (Ullah et al 2013; Mira et al 2010a,b; Cottier et al 2015a; Hueso et al 2012). A significant number of genes related to cell wall function was also found to be upregulated in acetic acid-stressed C. glabrata cells, including genes involved in the synthesis of β-1,3 and β-1,6 glucans ( e.g.…”

“…The plasma membrane proton pump Pma1 has an essential role in the control of internal pH homeostasis in yeasts, including in C. glabrata (Ullah et al 2013; Bairwa and Kaur 2011), and was found in this work to be upregulated under acetic acid stress under the dependence of CgHAA1 (Table 2). Additionally, the acetic acid-induced expression of CgPMP2 , CgHSP30 , CAGL0F03707g, and CAGL0C02893g genes, all predicted to encode regulators of CgPma1 activity, also required CgHaa1 (Table 2 and Table 3).…”

“…Thus, there are likely represent specific functional features of the CgHaa1 network. This observation is interesting, considering that intracellular acidification, energy depletion, and cell wall damage are toxic effects triggered by acetic acid both in C. glabrata and S. cerevisiae cells (Ullah et al 2013). The mechanisms underlying the regulation of internal pH homeostasis, particularly under stress, are still poorly studied in C. glabrata .…”

“…Besides passive diffusion, acetic acid was also found to enter S. cerevisiae cells through the aquaglyceroporin Fps1 (Mollapour and Piper 2007). Prominent intracellular acidification was found to occur upon exposure of unadapted S. cerevisiae cells to an inhibitory concentration of acetic acid, this being counteracted by the activity of two proton pumps, the plasma membrane H + -ATPase Pma1 and the vacuolar ATPase, which catalyze the extrusion of the exceeding protons from the cytosol to the cell exterior or to the vacuole lumen, respectively (Ullah et al 2013; Mira et al 2010c; Carmelo et al 1997). C. glabrata cells challenged with inhibitory concentrations of acetic acid also experience a reduction in internal pH (pH i ); however, this drop is much more subtle than the one observed in S. cerevisiae (Ullah et al 2013).…”

The Effect of Fermented Lingonberry Juice onCandida glabrataIntracellular Protein Expression

“…In our study, there was no significant difference in intracellular protein expression at pH 3.5 compared to pH 7.6. Indeed, Ullah et al [12] have shown that C. glabrata is capable of maintaining more stable intracellular pH compared to S. cerevisiae when challenged with low extracellular pH. Interestingly, FLJ treatment did have a long-term effect on C. glabrata intracellular protein expression.…”