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Alkaliphiles:‘basic’molecular problems of pH tolerance and bioenergetics
Author(s) -
Krulwich Terry Ann
Publication year - 1995
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1995.tb02253.x
Subject(s) - antiporters , biology , bioenergetics , electrochemical gradient , chemiosmosis , biophysics , oxidative phosphorylation , homeostasis , biochemistry , motility , microbiology and biotechnology , atp synthase , electrochemical potential , mitochondrion , antiporter , electrochemistry , chemistry , membrane , enzyme , electrode
Summary Alkaliphilic Bacillus species provide experimental opportunities for examination of physiological processes under conditions in which the stress of the extreme environment brings issues of general biological importance into special focus. The alkaliphile, like many other cells, uses Na + /H + antiporters in pH regulation, but its array of these porters, and other ion‐flux pathways that energize and support their activity, result in an extraordinary capacity for pH homeostasis; this process nonetheless becomes the factor that limits growth at the upper edge of the pH range. Above pH 9.5, aerobic alkaliphiles maintain a cytoplasmic pH that is two or more units below the external pH. This chemiosmotically adverse δpH is bypassed by use of an electrochemical gradient of Na + rather than of protons to energize solute uptake and motility. By contrast, ATP synthesis occurs via completely proton‐coupled oxidative phosphorylation that proceeds just as well, or better, at pH10 and above as it does in the same bacteria growing at lower pH, without the adverse pH gradient. Various mechanisms that might explain this conundrum are described, and the current state of the evidence supporting them is summarized.