Chloride transport pathways and their bioenergetic implications in the obligate acidophile Bacillus coagulans.
The protonophore-mediated collapse of the large delta pH that acidophiles maintain across their cytoplasmic membranes was augmented by the presence of Cl-, and Cl- influx into the cells occurred evidently in response to the protonophore-induced increase in the inside-positive membrane potential (+ delta psi). In respiring cells, the addition of Cl- but not SO4(2-) salts caused a rapid and precipitous decrease in the + delta psi. A Nernstian relationship between the imposed transmembrane K+ gradient and the valinomycin-induced K+ diffusion potentials was observed when everted membrane vesicles were loaded with K2SO4 or KH2PO4 but not when loaded with KCl or KNO3. Thus, electrogenic Cl- transport occurred in Bacillus coagulans. In addition, a nonelectrogenic temperature-sensitive Cl- transport mechanism, with the net Cl- efflux coefficient (PCl-) ranging from 1.5 x 10(-4) to 6.1 x 10(-6) cm/s, accounted for the massive Cl- efflux from Cl(-)-loaded cells. Thus, B. coagulans, despite its dependence on the + delta psi and therefore the need to exclude anions, apparently possesses specific mechanisms for Cl- permeation. Active cells of B. coagulans prevented Cl- accumulation from attaining an electrochemical equilibrium, maintaining a delta micro Cl- of ca. -63 mV. B. coagulans therefore also possesses an energy-dependent mechanism for Cl- exclusion from the cells.
McLaggan
D
D
Department of Microbiology and Immunology, Stanford University, California 94305.
Keyhan
M
M
Matin
A
A
D000838:Anions; D001407:Bacillus / Q000378:metabolism*; D001693:Biological Transport, Active; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D002712:Chlorides / Q000378:metabolism*; D004734:Energy Metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology; D014634:Valinomycin / Q000494:pharmacology
D000838:Anions; D002712:Chlorides; D014634:Valinomycin; D011188:Potassium