Importance of sodium to the bioenergetic properties of Methanococcus voltae

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Abstract
The marine methanogen Methanococcus voltae has distinct sodium requirements for active transport and for methanogenesis. These requirements were separated by demonstrating that each process has very different sodium optima, and that sodium increases the affinity of the isoleucine transport system at least 15-fold without altering the maximum velocity. The cytoplasmic pH became alkaline upon activating methane synthesis by sodium. Ionophores collapsed the transmembrane pH gradient, and inhibited methanogenesis and transport. Comparisons of pH responses indicate that growth is limited at alkaline pH by a factor(s) other than the rates of transport of leucine or isoleucine, or methanogenesis.