Formation of Proton Motive Force Under Low-Aeration Alkaline Conditions in Alkaliphilic Bacteria

Abstract

In Mitchell’s chemiosmotic theory, a proton (H+) motive force across the membrane (Δp), generated by the respiratory chain, drives F1Fo-ATPase for ATP production in various organisms. The bulk-base chemiosmotic theory cannot account for ATP production in alkaliphilic bacteria. However, alkaliphiles thrive in environments with a H+ concentrations that are one-thousandth (ca. pH 10) the concentration required by neutralophiles. This situation is similar to the production of electricity by hydroelectric turbines under conditions of very limited water. Alkaliphiles manage their metabolism via various strategies involving the cell wall structure, solute transport systems and molecular mechanisms on the outer surface membrane. Our experimental results indicate that efficient ATP production in alkaliphilic Bacillus spp. is attributable to a high membrane electrical potential (ΔΨ) generated for an attractive force for H+ on the outer surface membrane. In addition, the enhanced F1Fo-ATPase driving force per H+ is derived from the high ΔΨ. However, it is difficult to explain the reasons for high ΔΨ formation based on the respiratory rate. The Donnan effect (which is observed when charged particles that are unable to pass through a semipermeable membrane create an uneven electrical charge) likely contributes to the formation of the high ΔΨ because the intracellular negative ion capacities of alkaliphiles are much higher than those of neutralophiles. There are several variations in the adaptation to alkaline environments by bacteria. However, it could be difficult to utilize high ΔΨ in the low aeration condition due to the low activity of respiration. To explain the efficient ATP production occurring in H+-less and air-limited environments in alkaliphilic bacteria, we propose a cytochrome c-associated “H+ capacitor mechanism” as an alkaline adaptation strategy. As an outer surface protein, cytochrome c-550 from Bacillus clarkii possesses an extra Asn-rich segment between the region anchored to the membrane and the main body of the cytochrome c. This structure may contribute to the formation of the proton-binding network to transfer H+ at the outer surface membrane in obligate alkaliphiles. The H+ capacitor mechanism is further enhanced under low-aeration conditions in both alkaliphilic Bacillus spp. and the Gram-negative alkaliphile Pseudomonas alcaliphila.

Halotolerance mechanisms of the methanotroph Methylomicrobium alcaliphilum

“…M. alcaliphilum grows optimally at pH 9. Alkaliphilic organisms are typically characterized by highly negative membrane potentials (Matsuno et al, 2018; Ventosa, Nieto, & Oren, 1998), which allows them to drive ATP synthase against the proton concentration gradient (consistent with an intracellular pH lower than that of their environment, 7.5 in the case of Salinivibrio costicola (Ventosa et al, 1998). In this section we aim to elucidate the effects that an increased Na + gradient across the membrane can have on other key parameters governing the functioning of the respiratory chain (internal pH and membrane potential).…”

Amphipathic Peptide Antibiotics with Potent Activity against Multidrug-Resistant Pathogens

“…As the disruption of ΔΨ, the probe would be released into the extracellular milieu and result in increased fluorescence. Conversely, the disruption of ΔpH would be compensated by increasing ΔΨ, resulting in enhanced DiSC 3 (5) uptake into the cytoplasmic membrane and therefore decreased fluorescence [ 48 ]. Our results showed that exposure of cells into varying concentrations of WW307 resulted in an immediate increase in DiSC 3 (5) fluorescence in a dose-dependent manner ( Figure 8 A,B), suggesting that WW307 selectively dissipated the ΔΨ component of the PMF.…”

The Poly-Glutamate Motif of GmMATE4 Regulates Its Isoflavone Transport Activity

“…In addition, the attraction of proton by the production of polyglutamic acid on the cell surface has been reported in Bacillus pseudofirmus OF4 cells [35,36]. It was suggested that such attraction of protons to the cell surface was associated with the formation of proton motive force across the membrane [36]. It is possible that the polyglutamate motif of GmMATE4 plays a similar role in attracting protons to the vacuolar membrane surface.…”

“…Nevertheless, based on the above examples, it could be deduced that glutamate residues play an important role in promoting proton affinity. In addition, the attraction of proton by the production of polyglutamic acid on the cell surface has been reported in Bacillus pseudofirmus OF4 cells [35,36]. It was suggested that such attraction of protons to the cell surface was associated with the formation of proton motive force across the membrane [36].…”