The role of Escherichia coli FhlA transcriptional activator in generation of proton motive force and FO F1 -ATPase activity at pH 7.5

Glucose concentration is determinant for the functioning of hydrogenase 1 and hydrogenase 2 in regulating the proton and potassium fluxes in Escherichia coli at pH 7.5

This study examines how FOF1-ATPase, hydrogenases (Hyd-1 and Hyd-2), and potassium transport systems (TrkA) interact to maintain the proton motive force (pmf) in E. coli during fermentation of different glucose concentrations (2 g L-1 and 8 g L-1). Our findings indicate that mutants lacking the hyaA-hyaC genes exhibited a 30 % increase in total proton flux compared to the wild type when grown with 2 g L-1 glucose. This has been observed during assays where similar glucose levels were supplemented. Disruptions in proton pumping, particularly in hyaB and hyaC single mutants, led to increased potassium uptake. The hyaB mutant showed a threefold increase in the contribution of FOF1-ATPase to proton flux, suggesting a significant role for Hyd-1 in proton translocation. In the hybC mutant grown in 2 g L-1 glucose conditions, DCCD-sensitive fluxes decreased by 70 %, indicating critical role of Hyd-2 in proton transport and FOF1 function. When cells were grown with 8 g L-1 glucose, the 2H+/1K+ ratio was significantly disturbed in both wild type and mutants. Despite these perturbances, mutants with disruptions in Hyd-1 and Hyd-2 maintained constant FOF1 function, suggesting that this enzyme remains stable in glucose-rich environments. These results provide valuable insights into how Hyd-1 and Hyd-2 contribute to the regulation of ion transport, particularly proton translocation, in response to glucose concentration. Our study uncovered potential complementary mechanisms between Hyd-1 and Hyd-2 subunits, suggesting a complex interplay between these enzymes via metabolic cross talk with FOF1 in response to glucose concentrations to maintain pmf.

Proton conductance and regulation of proton/potassium fluxes in Escherichia coli FhlA-lacking cells during fermentation of mixed carbon sources

Escherichia coli uptake potassium ions with the coupling of proton efflux and energy utilization via proton FOF1-ATPase. In this study contribution of formate hydrogen lyase (FHL) complexes in the proton/potassium fluxes and the formation of proton conductance (CMH+) were investigated using fhlA mutant strain. The proton flux rate (JH+) decreased in fhlA by ∼ 25 % and ∼70 % during the utilization of glucose and glycerol, respectively, at 20 h suggesting H+ transport via or through FHL complexes. The decrease in JK+ in fhlA by ∼40 % proposed the interaction between FHL and Trk secondary transport system during mixed carbon fermentation. Moreover, the usage of N,N'-dicyclohexylcarbodiimide (DCCD) demonstrated the mediation of FOF1-ATPase in this interaction. CMH+ was 13.4 nmol min-1 mV-1 in WT at 20 h, which decreased by 20 % in fhlA. Taken together, FHL complexes have a significant contribution to the modulation of H+/K+ fluxes and the CMH + for efficient energy transduction and regulation of the proton motive force during mixed carbon sources fermentation.

Regulation of metabolism and proton motive force generation during mixed carbon fermentation by an Escherichia coli strain lacking the FOF1-ATPase

Proton FOF1-ATPase is the key enzyme in E. coli under fermentative conditions. In this study the role of E. coli proton ATPase in the μ and formation of metabolic pathways during the fermentation of mixture of glucose, glycerol and formate using the DK8 (lacking FOF1) mutant strain was investigated. It was shown that the contribution of FOF1-ATPase in the specific growth rate was ∼45 %. Formate was not taken up in the DK8 strain during the initial hours of the growth. The utilization rates of glucose and glycerol were unchanged in DK8, however, the production of succinate, lactate and ethanol was decreased causing a reduction of the redox state up to -450 mV. Moreover, the contribution of FOF1-ATPase in the interplay between H+ and H2 cycles was described depending on the bacterial growth phase and main utilizing substrate. Besides, the H2 production rate in the DK8 strain was decreased by ∼60 % at 20 h and was absent at 72 h. Δp was decreased from -157 ± 4.8 mV to -140 ± 4.2 mV at 20 h and from -195 ± 5.9 mV to -148 ± 4.4 mV at 72 h, compared to WT. Taken together it can be concluded that during fermentation of mixed carbon sources metabolic cross talk between FOF1-ATPase-TrkA-Hyd-Fdh-H is taking place for maintaining the cell energy balance via regulation proton motive force.

Evidence for bidirectional formic acid translocation in vivo via the Escherichia coli formate channel FocA

Pentameric FocA permeates either formate or formic acid bidirectionally across the cytoplasmic membrane of anaerobically growing Escherichia coli. Each protomer of FocA has its own hydrophobic pore, but it is unclear whether formate or neutral formic acid is translocated in vivo. Here, we measured total and dicyclohexylcarbodiimide (DCCD)-inhibited proton flux out of resting, fermentatively grown, stationary-phase E. coli cells in dependence on FocA. Using a wild-type strain synthesizing native FocA, it was shown that using glucose as a source of formate, DCCD-independent proton efflux was ∼2.5 mmol min-1, while a mutant lacking FocA showed only DCCD-inhibited, FOF1-ATPase-dependent proton-efflux. A strain synthesizing a chromosomally-encoded FocAH209N variant that functions exclusively to translocate formic acid out of the cell, showed a further 20 % increase in FocA-dependent proton efflux relative to the parental strain. Cells synthesizing a FocAT91A variant, which is unable to translocate formic acid out of the cell, showed only DCCD-inhibited proton efflux. When exogenous formate was added, formic acid uptake was shown to be both FocA- and proton motive force-dependent. By measuring rates of H2 production, potassium ion flux and ATPase activity, these data support a role for coupling between formate, proton and K+ ion translocation in maintaining pH and ion gradient homeostasis during fermentation. FocA thus plays a key role in maintaining this homeostatic balance in fermenting cells by bidirectionally translocating formic acid.

Propionic and valproic acids have an impact on bacteria viability, proton flux and ATPase activity

Short-chain fatty acids like propionic (PPA) and valproic acids (VP) can alter gut microbiota, which is suggested to play a role in development of autism spectrum disorders (ASD). In this study we investigated the role of various concentrations of PPA and VP in gut enteric gram-negative Escherichia coli K12 and gram-positive Enterococcus hirae ATCC 9790 bacteria growth properties, ATPase activity and proton flux. The specific growth rate (µ) was 0.24 h-1 and 0.82 h-1 in E. coli and E. hirae, respectively. Different concentrations of PPA reduced the value of µ similarly in both strains. PPA affects membrane permeability only in E. hirae. PPA decreased DCCD-sensitive ATPase activity in the presence of K+ ions by 20% in E. coli and 40% in E. hirae suggesting the importance of the FOF1-K+ transport system in the regulation of PPA-disrupted homeostasis. Moreover, the H+ flux during PPA consumption could be the protective mechanism for enteric bacteria. VP has a selective effect on the µ depending on bacteria. The overwhelming effect of VP was detected on the K+-promoted ATPase activity in E. hirae. Taken together it can be suggested that PPA and VP have a disruptive effect on E. coli and E. hirae growth, viability, bioenergetic and biochemical properties, which are connected with the alteration of FOF1-ATPase activity and H+ flux rate or direction.

Metabolic pathways and ΔpH regulation in Escherichia coli during the fermentation of glucose and glycerol in the presence of formate at pH 6.5: the role of FhlA transcriptional activator

Escherichia coli is able to ferment mixed carbon sources and produce various fermentation end-products. In this study, the function of FhlA protein in the specific growth rate (µ), metabolism, regulation of ΔpH and proton ATPase activity was investigated. Reduced µ in fhlA mutant of ∼25% was shown, suggesting the role of FhlA in the growth process. The utilization rate of glycerol is decreased in fhlA ∼ 2 fold, depending on the oxidation-reduction potential values. Bacteria regulate the activity of hydrogenase enzymes during growth depending on the external pH, which manifests as a lack of hydrogen gas generation during glycerol utilization at pH values below 5.9. It is suggested that cells maintain ΔpH during the fermentative growth via formate-lactate-succinate exchange. The decrement of the value of pHin, but not of pHex in mutant cells, is regulating ΔpH and consequently proton motive force generation.