A study of the Na /H antiport in the archaeon Methanobacterium thermoautotrophicum strain ΔH

Abstract

SummaryThe ability of the cells of Mb. thermoautotrophicum strain AH to generate a proton gradient (driven by a concentration gradient of sodium ions) at pH 6.8 as well as at pH 8 was demonstrated. The electrogenic Na+/H + antiport responsible for this process was shown to be inhibited by EIPA and also by DCCD. Artificially increasing of intracellular concentration of Ca 2+ in these cells enhanced the Na+/IT antiport activity, while the lowering of external Ca 2+ by EGTA significantly decreased this activity. The apparent K m values for Na § about 14 and 3 mM at pH 6.8 and 8, respectively, and Vm~ about 214 (pH 6.8) and 155 (pH 8) AQ/min per mg of cell proteins, respectively, were calculated. It is concluded that the described processes are mediated by the Na+/IT antiporter which might be a clue to the adaptive bioenergetic behaviour of the cells ofMb. thermoautotrophicum strain AH under the different physiological conditions.

Methanogenesis is Ca2+dependent inMethanothermobacter thermautotrophicusstrain ΔH

“…The Na + /H + antiport activity was not inhibited either in the presence of 40 μM Co 2+ ions or 40 μM Ni 2+ (data not shown). These results specify that Ca 2+ transport does not play any role in Ca 2+ control of the Na + /H + antiport described earlier (Majerník et al , 1997). Furthermore, ATP synthesis driven by an electrogenic potassium efflux in the presence of either H + or Na + ions was not inhibited by 10 mM EGTA (Table 2).…”

“…Further studies revealed that methane formation from H 2 +CO 2 is coupled to the generation of two primary ion gradients, an electrochemical proton gradient and an electrochemical sodium ion gradient (Müller et al , 1988; Kaesler & Schönheit, 1989; Thauer, 1990). It seems that Na + /H + antiport has a key function in this complex bioenergetic machinery via conversion of one of the gradients to the other in M. thermautotrophicus (Müller et al , 1987; Kaesler & Schönheit, 1989; Majerník et al , 1997).…”

“…The existence of a sophisticated transport system for Ca 2+ utilizing both primary ion gradients in M. thermautotrophicus implies the importance of intracellular calcium concentration on further cellular, and especially bioenergetic processes in these cells. Recently, we have found that Ca 2+ ions control Na + /H + antiport activity in resting cells of M. thermautotrophicus (Majerník et al , 1997). Following this line of reasoning, our main interest was in studying the effect of calcium ions on essential energy conserving processes such as methane, ATP or membrane potential formation in these microorganisms.…”

Isolation and characterization of an uncoupler-resistant mutant ofMethanothermobacter thermautotrophicus

“…Anaerobic conditions were maintained by a continuous flow of N 2 gas. pH changes were measured using semi‐micro glass pH electrode by pH meter (ORION) equipped with a recorder [20]. For the study of ATPase activity, Triton X‐100 permeabilised cells were prepared as described in [21].…”

Identification of a pH regulated Na+/H+ antiporter of Methanococcus jannaschii

“…Although many prokaryotic Na + /H + antiporters have been cloned and studied in antiporter deficient E. coli mutants [9–11], very little is known about antiporters from the archaeal kingdom. The only evidence for Na + /H + antiporters in archaea comes from studies using either intact cells or vesicles [12–14], but none of the genes has been cloned and studied in a heterologous system, yet.…”