Cytoplasmic pH Measurement and Homeostasis in Bacteria and Archaea

Ratiometric Imaging of pH Probes

“…In general, cytoplasmic pH in most organisms from bacteria (Martinez et al, 2012;Wilks & Slonczewski, 2007) to yeasts (Bagar, Altenbach, Read, & Bencina, 2009;Grynkiewicz et al, 1985) to mammalian cells (Fig. 23.1) is slightly basic (pH is $7.0-7.8), with the exception of some acidophilic or basophilic bacteria (Paradiso et al, 1984;Slonczewski, Fujisawa, Dopson, & Krulwich, 2009). In contrast, the pH of lysosomes is acidic.…”

Transcriptomic analysis reveals how a lack of potassium ions increases Sulfolobus acidocaldarius sensitivity to pH changes

“…Increased RNA transcripts were observed for the subunit D of archaeal succinate dehydrogenase (Saci_0979) in the absence of sodium, while RNA transcripts for the cytochrome b homologue (soxC) of the Sox-ABCD complex (Saci_2087) increased under full salt. Primary electron transport proton pumps associated with pH homeostasis [reviewed in Slonczewski et al (2009) Fig. 1.…”

“…This suggested that an adequate concentration of K + ions was imported from the cytosol to generate an inside positive potential, that these ions were not responsible for the internal positive membrane potential in acidophilic archaea, or that additional pH homeostatic mechanisms [e.g. membranes resistant to influx of H + (van de Vossenberg et al, 1998)] were sufficient to maintain a near neutral pH (Slonczewski et al, 2009).…”

“…The reversed, as compared to neutrophiles, inside positive membrane potential is proposed to constitute an important adaptive mechanism for life in highly acidic conditions by creating a electrochemical barrier to proton influx [reviewed in Slonczewski et al (2009)] and to counter hyperosmotic stress (Cao et al, 2011;Follmann et al, 2009;Reed et al, 1985). Several reports provide circumstantial evidence that the acidophile membrane potential is created by potassium, and to a lesser extent, sodium ions.…”

“…These include that cations (potassium ions are the most effective) are required for respiration-linked proton extrusion in Sulfolobus species (Sch€ afer, 1996); generation of a membrane potential in Acidithiobacillus thiooxidans requires the presence of cations, with potassium being the most efficient (Suzuki et al, 1999); and the presence of numerous putative cation transporters found in the genome of acidophiles (Chen et al, 2005;Fütterer et al, 2004;She et al, 2001;Tyson et al, 2004). However, the mechanism for membrane potential generation is poorly understood (Slonczewski et al, 2009).…”