Ammonium/urea-dependent generation of a proton electrochemical potential and synthesis of ATP in Bacillus pasteurii

Abstract

The influence of ammonium and urea on the components of the proton electrochemical potential (⌬p) and de novo synthesis of ATP was studied with Bacillus pasteurii ATCC 11859. In washed cells grown at high urea concentrations, a ⌬p of ؊56 ؎ 29 mV, consisting of a membrane potential (⌬) of ؊228 ؎ 19 mV and of a transmembranic pH gradient (⌬pH) equivalent to 172 ؎ 38 mV, was measured. These cells contained only low amounts of potassium, and the addition of ammonium caused an immediate net decrease of both ⌬ and ⌬pH, resulting in a net increase of ⌬p of about 49 mV and de novo synthesis of ATP. Addition of urea and its subsequent hydrolysis to ammonium by the cytosolic urease also caused an increase of ⌬p and ATP synthesis; a net initial increase of ⌬, accompanied by a slower decrease of ⌬pH in this case, was observed. Cells grown at low concentrations of urea contained high amounts of potassium and maintained a ⌬p of ؊113 ؎ 26 mV, with a ⌬ of ؊228 ؎ 22 mV and a ⌬pH equivalent to 115 ؎ 20 mV. Addition of ammonium to such cells resulted in the net decrease of ⌬ and ⌬pH without a net increase in ⌬p or synthesis of ATP, whereas urea caused an increase of ⌬p and de novo synthesis of ATP, mainly because of a net increase of ⌬. The data reported in this work suggest that the ATP-generating system is coupled to urea hydrolysis via both an alkalinization of the cytoplasm by the ammonium generated in the urease reaction and a net increase of ⌬ that is probably due to an efflux of ammonium ions. Furthermore, the findings of this study show that potassium ions are involved in the regulation of the intracellular pH and that ammonium ions may functionally replace potassium to a certain extent in reducing the membrane potential and alkalinizing the cytoplasm.

Sodium-coupled energy transduction in the newly isolated thermoalkaliphilic strain LBS3

“…K ϩ /H ϩ antiporters have also been implicated in the regulation of the intracellular pH (29) in such organisms as the moderately halophilic and alkaliphilic methanogen Methanolobus taylorii GS-16 (22). In this respect, K ϩ ions play a role in pH homeostasis in Bacillus alcalophilus (14) and in the ureolytic bacterium Bacillus pasteurii (10). In the latter case, K ϩ ions can be replaced by ammonium ions under certain conditions (10).…”

“…In this respect, K ϩ ions play a role in pH homeostasis in Bacillus alcalophilus (14) and in the ureolytic bacterium Bacillus pasteurii (10). In the latter case, K ϩ ions can be replaced by ammonium ions under certain conditions (10). The low magnitude of the ⌬ H ϩ in alkaliphiles has led to the suggestion that these bacteria may use the electrochemical gradient of sodium ions (⌬ Na ϩ) for the generation of ATP.…”

Biological aspects of microbial-induced calcite precipitation

“…This result could be achieved by excreting urease out of the cells and into the culture medium, thus removing the cell membrane that functions as a barrier between the enzyme and its substrate. Since S. pasteurii do not exhibit an active uptake mechanism of urea, urea concentration should exceed 200 mM, well over the 25 mM of urea present in this experimental setting, so that the diffusion rate will not be the ratelimiting step in ureolysis (Jahns, 1996). The exact mechanism for the excretion of urease is not yet known to the authors; however, the following mechanisms may be postulated: (a) release of enzymes, namely urease, by S. pasteurii due to depletion of nutrients (van Paassen, 2009); (b) release of enzymes by S. pasteurii due to predation (lysis) by B. subtilis; and (c) a combination of the two.…”

Improving the strength of sandy soils via ureolytic CaCO<sub>3</sub> solidification by <i>Sporosarcina ureae</i>

“…Treated, drained samples were washed twice with 25 mL of dd H 2 O and dried in an oven for 48 h at 65 • C. Washing with dd H 2 O was done to remove salts other than CaCO 3 to prevent cementation of the sand due to salt precipitation in the drying process as has been found in the literature (Jia and Jian, 2016;Zeng et al, 2018). The shear strength tests were performed in a direct shear machine (Model: ELE-26-2112/02).…”