Energy transduction in the methanogen Methanococcus voltae is based on a sodium current

Abstract

We provide experimental support for the proposal that ATP production in Methanococcus voltae, a methanogenic member of the archaea, is based on an energetic system in which sodium ions, not protons, are the coupling ions. We show that when grown at a pH of 6.0, 7.1, or 8.2, M. voltae cells maintain a membrane potential of approximately -150 mV. The cells maintain a transmembrane pH gradient (pH,. -pHo.t) of -0.1, -0.2, and -0.2, respectively, values not favorable to the inward movement of protons. The cells maintain a transmembrane sodium concentration gradient (sodiumo.,/sodium1.) of 1.2, 3.4, and 11.6, respectively. While the protonophore 3,3',4',5-tetrachlorosalicylanilide inhibits ATP formation in cells grown at pH 6.5, neither ATP formation nor growth is inhibited in cells grown in medium at pH 8.2. We show that when grown at pH 8.2, cells synthesize ATP in the absence of a favorably oriented proton motive force. Whether grown at pH 6.5 or pH 8.2, M. voltae extrudes Na+ via a primary pump whose activity does not depend on a proton motive force. The addition of protons to the cells leads to a harmaline-sensitive efflux of Na+ and vice versa, indicating the presence of Na+/H+ antiporter activity and, thus, a second mechanism for the translocation of Na+ across the cell membrane. M. voltae contains a membrane component that is immunologically related to the H+-translocating ATP synthase of the archaeabacterium Sulfolobus acidocaldanius. Since we demonstrated that ATP production can be driven by an artificially imposed membrane potential only in the presence of sodium ions, we propose that ATP production in M. voltae is mediated by an Na+-translocating ATP synthase whose function is coupled to a sodium motive force that is generated through a primary Na* pump.Evidence has been obtained with whole cells of Methanosarcina barkeri and with whole cells, protoplasts, and crude membrane vesicles of methanogenic bacterium strain Gol that reduction of the heterodisulfide of CH3-S-CoM [2-(methylthio)ethanesulfonate-methylcoenzyme M] and 7-mercaptoheptanoylthreoninephosphate leads to the generation of a proton motive force (PMF) that is coupled to the synthesis of ATP via an H+-translocating ATP synthase (3,4,9,10,23,32). In contrast, results obtained in studies directed towards elucidating the energetics of ATP formation in Methanococcus voltae have shown that methane formation and ATP synthesis can occur in the presence of the protonophore SF6847 and have led to the conclusion that the maintenance of a PMF is not required for ATP synthesis in this marine methanogen (7). On the basis of these findings, a novel and intriguing scheme of substrate-level phosphorylation was considered possible (27).To study the mechanism of ATP formation in M. voltae, we decided to reexamine the possibility that ATP formation was mediated by a chemiosmotically based mechanism by considering a mechanism in which the coupling ion is not a proton. Since growth, amino acid transport, and ATP production in whole cells of M. voltae had been shown...

Cysteine Is Not the Sulfur Source for Iron-Sulfur Cluster and Methionine Biosynthesis in the Methanogenic Archaeon Methanococcus maripaludis

“…To examine the physiological significance of these reactions, the intracellular amount of cystathionine in wild-type cells grown without exogenous cystathionine was determined ( Table 3). Assuming that proteins account for 60% of the cell dry weight and cells contain 2.5 l of water per mg dry weight (31), the intracellular cystathionine concentration would be ϳ0.1 mM. In M. maripaludis cell extracts, cystathionine ␥-cleavage activity had an apparent K m (cystathionine) of 8.7 Ϯ 0.5 mM and V max of 7.8 Ϯ 0.3 nmol/min/mg protein (Table 4).…”

Na+‐driven ATP synthesis in Methanobacterium thermoautotrophicum and its differentiation from H+‐driven ATP synthesis by rhodamine 6G

“…In this context it should be mentioned that the requirement of a high concentration of Na' for induction of the Enterococcus hirae Na'-ATPase and for the Na'-motive oxidase of Escherichia coli was reported [22,23]. In different methanogenic bacteria the existence of a sodium cycle has been suggested [9,24,25]. Up to now it is not clear why methanogenic bacteria establish a primary sodium concentration gradient.…”

The presence of H+ and Na+‐translocating ATPases in Methanobacterium thermoautotrophicum and their possible function under alkaline conditions

“…(iii) In Methanobacterium thermoautotrophicum strain Marburg, the scheme on the involvement of Na +-and H÷-cycles in the coupling of exergonic and endergonic reactions during methane formation has been suggested [9]. The importance of sodium ions in the bioenergetics of Methanobacterium thermoautotrophicum strain AH has also been recognized [10,11,20]; (iv) the existence of the Na+/H ÷ antiporter has been confirmed in different methanogens [8,12,13,21]. All these data strongly support the idea that H ÷-and Na+-cycles, linked by the Na+/H + antiporter, coexist also in methanogens and that their mutual cooperation could be responsible for the adaptive energetic behaviour under different physiological conditions.…”

“…Abbreviations: TCS, tetrachlorosalicylanilide; A/~N,+, electrochemical potential difference of Na+; zlpH and ApNa, difference in concentrations of H ÷ and Na ÷, respectively and an F~F0-ATP synthase translocating Na + ions have been confirmed in addition to an A1A0-ATP synthase using H + as the coupling ion [7]; (ii) in Methanococeus voltae, the energy transduction based on a sodium ion current has been proven [8]. (iii) In Methanobacterium thermoautotrophicum strain Marburg, the scheme on the involvement of Na +-and H÷-cycles in the coupling of exergonic and endergonic reactions during methane formation has been suggested [9].…”