We undertook the experiments reported here to determine whether bacterial motility is also powered by the proton movements that constitute the primary energy currency of Mitchell's theory. Chemiosmotic energy coupling, as originally proposed by Mitchell (14), is involved in the function of a number of bacterial transport systems, in oxidative phosphorylation, and in pyridine nucleotide transhydrogenation (for reviews see refs. We conclude that the flagella are driven by a protonmotive force. Similarly, when starved cells are suspended in a potassium-free medium containing both valinomycin and an attractant, many cells initially run rather than twiddle. added to cells swimming in the presence of ,1ucose, twiddles are transiently suppressed, and the cells run or a time. Valinomycin-induced twiddling occurs in the absence of external alkali or alkaline earth cations and without significant net synthesis of ATP. They also twiddle, although less vigorously, when the external pH is lowered. Starved cells suspended in a potassium-free medium respond to the addition of valinomycin b a brief period of vigorous twiddling. These cells become motile when an electrical potential or a pH gradient is imposed across the membrane. They stop swimming when deprived of glucose. The cells move steadily along smooth paths (run), jump about briefly with little net displacement (twiddle), and then run in new directions. Porter, April 18,1977 ABSTRACT Streptococcus strain V4051 is motile in the presence of glucose. HAROLDt, AND CHRIS VAN DER DRIFT§ * Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309 * Division of Molecular and Cellular Biology, National Jewish Hospital, Denver, Colorado 80206 an&§ Laboratory of Microbiology, Faculty of Science, University of Nijmegen, Nijmegen, The Netherlands Communicated by Keith R. 30603064, July 1977 Microbiology A protonmotive force drives bacterial flagella (bacterial motility/ionophores/fluorescent dyes) MICHAEL D.
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