Cellular pH measurements in Emiliania huxleyi reveal pronounced membrane proton permeability

Abstract

Key words: acid-base metabolism, BCECF (2¢,7¢-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein), bicarbonate transport, dissolved inorganic carbon (DIC), DIDS (4,4¢-diisothiocyanatostilbene-2,2¢-disulfonic acid), Emiliania huxleyi, nigericin, pH homeostasis. Summary• To understand the influence of changing surface ocean pH and carbonate chemistry on the coccolithophore Emiliania huxleyi, it is necessary to characterize mechanisms involved in pH homeostasis and ion transport.• Here, we measured effects of changes in seawater carbonate chemistry on the fluorescence emission ratio of BCECF (2¢,7¢-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein) as a measure of intracellular pH (pH i ). Out of equilibrium solutions were used to differentiate between membrane permeation pathways for H + , CO 2 and HCO 3) .• Changes in fluorescence ratio were calibrated in single cells, resulting in a ratio change of 0.78 per pH i unit. pH i acutely followed the pH of seawater (pH e ) in a linear fashion between pH e values of 6.5 and 9 with a slope of 0.44 per pH e unit. pH i was nearly insensitive to changes in seawater CO 2 at constant pH e and HCO 3 ) . An increase in extracellular HCO 3 ) resulted in a slight intracellular acidification. In the presence of DIDS (4,4¢-diisothiocyanatostilbene-2,2¢-disulfonic acid), a broad-spectrum inhibitor of anion exchangers, E. huxleyi acidified irreversibly. DIDS slightly reduced the effect of pH e on pH i .• The data for the first time show the occurrence of a proton permeation pathway in E. huxleyi plasma membrane. pH i homeostasis involves a DIDS-sensitive mechanism.

Effects of CO2 and their modulation by light in the life‐cycle stages of the coccolithophore Emiliania huxleyi

“…2b). Decreased C i affinities in response to elevated P CO 2 have been reported for diploid E. huxleyi (strain PLYB92/11; Rost et al 2003), a number of diatoms (Trimborn et al 2008), and also cyanobacteria (Sü ltemeyer et al 1998). The latter study suggests posttranslational modification being responsible for decreased affinities under elevated P CO 2 .…”

“…Also, these processes might be responsive to [H + ] rather than C i concentrations (Taylor et al 2010;Lefebvre et al 2012). Suffrian et al (2011) have shown that external pH perturbations translate linearly into cytoplasmic pH changes. An impairment of transport processes (e.g., for DIC and Ca 2+ ) due to low internal pH might weaken the process of biomineralization.…”

Influence of changing carbonate chemistry on morphology and weight of coccoliths formed by <i>Emiliania huxleyi</i>

“…Possibly, malformations found in our study are also resulting from a malfunctioning of the cytoskeleton, in our case with the chemical driving force being H + . This explanation seems plausible since H + is known to easily enter into the cytosol of E. huxleyi (Suffrian et al, 2011). Here, a change in [H + ] could disturb the correct functioning of cytoskeleton elements or the enzymes associated with them so that the controlled expansion of the CV is handicapped (Langer et al, 2006).…”

Acidified seawater impacts sea urchin larvae pH regulatory systems relevant for calcification

“…Four to five control and treatment larvae were measured in an alternate mode and used for further analysis. Nigericin was used to calibrate pH i of living cells as previously described by Suffrian et al (68). PMCs of pluteus larvae were exposed to 10 μmol·L −1 nigericin in the presence of 150 mmol·L −1 K + at pH 5.5, 6.5, 7, 7.5, and 8.5.…”