Sodium ion transport decarboxylases and other aspects of sodium ion cycling in bacteria

Metagenomics Revealed a New Genus 'Candidatus Thiocaldithrix dubininis' gen. nov., sp. nov. and a New Species 'Candidatus Thiothrix putei' sp. nov. in the Family Thiotrichaceae, Some Members of Which Have Traits of Both Na+- and H+-Motive Energetics

Two metagenome-assembled genomes (MAGs), GKL-01 and GKL-02, related to the family Thiotrichaceae have been assembled from the metagenome of bacterial mat obtained from a sulfide-rich thermal spring in the North Caucasus. Based on average amino acid identity (AAI) values and genome-based phylogeny, MAG GKL-01 represented a new genus within the Thiotrichaceae family. The GC content of the GKL-01 DNA (44%) differed significantly from that of other known members of the genus Thiothrix (50.1-55.6%). We proposed to assign GKL-01 to a new species and genus 'Candidatus Thiocaldithrix dubininis' gen. nov., sp. nov. GKL-01. The phylogenetic analysis and estimated distances between MAG GKL-02 and the genomes of the previously described species of the genus Thiothrix allowed assigning GKL-02 to a new species with the proposed name 'Candidatus Thiothrix putei' sp. nov. GKL-02 within the genus Thiothrix. Genome data first revealed the presence of both Na+-ATPases and H+-ATPases in several Thiothrix species. According to genomic analysis, bacteria GKL-01 and GKL-02 are metabolically versatile facultative aerobes capable of growing either chemolithoautotrophically or chemolithoheterotrophically in the presence of hydrogen sulfide and/or thiosulfate or chemoorganoheterotrophically.

Conserved and lineage-specific hypothetical proteins may have played a central role in the rise and diversification of major archaeal groups

BACKGROUND

Archaea play fundamental roles in the environment, for example by methane production and consumption, ammonia oxidation, protein degradation, carbon compound turnover, and sulfur compound transformations. Recent genomic analyses have profoundly reshaped our understanding of the distribution and functionalities of Archaea and their roles in eukaryotic evolution.

RESULTS

Here, 1179 representative genomes were selected from 3197 archaeal genomes. The representative genomes clustered based on the content of 10,866 newly defined archaeal protein families (that will serve as a community resource) recapitulates archaeal phylogeny. We identified the co-occurring proteins that distinguish the major lineages. Those with metabolic roles were consistent with experimental data. However, two families specific to Asgard were determined to be new eukaryotic signature proteins. Overall, the blocks of lineage-specific families are dominated by proteins that lack functional predictions.

CONCLUSIONS

Given that these hypothetical proteins are near ubiquitous within major archaeal groups, we propose that they were important in the origin of most of the major archaeal lineages. Interestingly, although there were clearly phylum-specific co-occurring proteins, no such blocks of protein families were shared across superphyla, suggesting a burst-like origin of new lineages early in archaeal evolution.

An acquired acyltransferase promotes Klebsiella pneumoniae ST258 respiratory infection

Klebsiella pneumoniae ST258 is a human pathogen associated with poor outcomes worldwide. We identify a member of the acyltransferase superfamily 3 (atf3), enriched within the ST258 clade, that provides a major competitive advantage for the proliferation of these organisms in vivo. Comparison of a wild-type ST258 strain (KP35) and a Δatf3 isogenic mutant generated by CRISPR-Cas9 targeting reveals greater NADH:ubiquinone oxidoreductase transcription and ATP generation, fueled by increased glycolysis. The acquisition of atf3 induces changes in the bacterial acetylome, promoting lysine acetylation of multiple proteins involved in central metabolism, specifically Zwf (glucose-6 phosphate dehydrogenase). The atf3-mediated metabolic boost leads to greater consumption of glucose in the host airway and increased bacterial burden in the lung, independent of cytokine levels and immune cell recruitment. Acquisition of this acyltransferase enhances fitness of a K. pneumoniae ST258 isolate and may contribute to the success of this clonal complex as a healthcare-associated pathogen.

Microbial interaction between the succinate-utilizing bacterium Phascolarctobacterium faecium and the gut commensal Bacteroides thetaiotaomicron

A large variety of microbes are present in the human gut, some of which are considered to interact with each other. Most of these interactions involve bacterial metabolites. Phascolarctobacterium faecium hardly uses carbohydrates for growth and instead uses succinate as a substrate. This study investigated the growth behavior of the co‐culture of the succinate‐specific utilizer P. faecium and the succinogenic gut commensal Bacteroides thetaiotaomicron. Succinate production by B. thetaiotaomicron supported the growth of P. faecium and concomitant propionate production via the succinate pathway. The succinate produced was completely converted to propionate. This result was comparable with the monoculture of P. faecium in the medium supplemented with 1% (w/v) succinate. We analyzed the transcriptional response (RNA‐Seq) between the mono‐ and co‐culture of P. faecium and B. thetaiotaomicron. Comparison of the expression levels of genes of P. faecium between the mono‐ and co‐cultured conditions highlighted that the genes putatively involved in the transportation of succinate were notably expressed under the co‐cultured conditions. Differential expression analysis showed that the presence of P. faecium induced changes in the B. thetaiotaomicron transcriptional pattern, for example, expression changes in the genes for vitamin B₁₂ transporters and reduced expression of glutamate‐dependent acid resistance system‐related genes. Also, transcriptome analysis of P. faecium suggested that glutamate and succinate might be used as sources of succinyl‐CoA, an intermediate in the succinate pathway. This study revealed some survival strategies of asaccharolytic bacteria, such as Phascolarctobacterium spp., in the human gut.

Molecular Basis for Bacterial Growth on Citrate or Malonate

Environmental citrate or malonate is degraded by a variety of aerobic or anaerobic bacteria. For selected examples, the genes encoding the specific enzymes of the degradation pathway are described together with the encoded proteins and their catalytic mechanisms. Aerobic bacteria degrade citrate readily by the basic enzyme equipment of the cell if a specific transporter for citrate is available. Anaerobic degradation of citrate in Klebsiella pneumoniae requires the so-called substrate activation module to convert citrate into its thioester with the phosphoribosyl dephospho-CoA prosthetic group of citrate lyase. The citryl thioester is subsequently cleaved into oxaloacetate and the acetyl thioester, from which a new citryl thioester is formed as the turnover continues. The degradation of malonate likewise includes a substrate activation module with a phosphoribosyl dephospho-CoA prosthetic group. The machinery gets ready for turnover after forming the acetyl thioester with the prosthetic group. The acetyl residue is then exchanged by a malonyl residue, which is easily decarboxylated with the regeneration of the acetyl thioester. This equipment suffices for aerobic growth on malonate, since ATP is produced via the oxidation of acetate. Anaerobic growth on citrate or malonate, however, depends on additional enzymes of a so-called energy conservation module. This allows the conversion of decarboxylation energy into an electrochemical gradient of Na+ ions. In citrate-fermenting K. pneumoniae, the Na+ gradient is formed by the oxaloacetate decarboxylase and mainly used to drive the active transport of citrate into the cell. To use this energy source for this purpose is possible, since ATP is generated by substrate phosphorylation in the well-known sequence from pyruvate to acetate. In the malonate-fermenting bacterium Malonomonas rubra, however, no reactions for substrate level phosphorylation are available and the Na+ gradient formed in the malonate decarboxylation reaction must therefore be used as the driving force for ATP synthesis.

Vitamin B12 as a modulator of gut microbial ecology

The microbial mechanisms and key metabolites that shape the composition of the human gut microbiota are largely unknown, impeding efforts to manipulate dysbiotic microbial communities toward stability and health. Vitamins, which by definition are not synthesized in sufficient quantities by the host and can mediate fundamental biological processes in microbes, represent an attractive target for reshaping microbial communities. Here, we discuss how vitamin B12 (cobalamin) impacts diverse host-microbe symbioses. Although cobalamin is synthesized by some human gut microbes, it is a precious resource in the gut and is likely not provisioned to the host in significant quantities. However, this vitamin may make an unrecognized contribution in shaping the structure and function of human gut microbial communities.

Artificial citrate operon confers mineral phosphate solubilization ability to diverse fluorescent pseudomonads

Citric acid is a strong acid with good cation chelating ability and can be very efficient in solubilizing mineral phosphates. Only a few phosphate solubilizing bacteria and fungi are known to secrete citric acids. In this work, we incorporated artificial citrate operon containing NADH insensitive citrate synthase (gltA1) and citrate transporter (citC) genes into the genome of six-plant growth promoting P. fluorescens strains viz., PfO-1, Pf5, CHAO1, P109, ATCC13525 and Fp315 using MiniTn7 transposon gene delivery system. Comprehensive biochemical characterization of the genomic integrants and their comparison with plasmid transformants of the same operon in M9 minimal medium reveals the highest amount of ∼7.6±0.41 mM citric and 29.95±2.8 mM gluconic acid secretion along with ∼43.2±3.24 mM intracellular citrate without affecting the growth of these P. fluorescens strains. All genomic integrants showed enhanced citric and gluconic acid secretion on Tris-Cl rock phosphate (TRP) buffered medium, which was sufficient to release 200–1000 µM Pi in TRP medium. This study demonstrates that MPS ability could be achieved in natural fluorescent pseudomonads by incorporation of artificial citrate operon not only as plasmid but also by genomic integration.

Plasmolysis and cell shape depend on solute outer-membrane permeability during hyperosmotic shock in E. coli

The concentration of chemicals inside the bacterial cytoplasm generates an osmotic pressure, termed turgor, which inflates the cell and is necessary for cell growth and survival. In Escherichia coli, a sudden increase in external concentration causes a pressure drop across the cell envelope that drives changes in cell shape, such as plasmolysis, where the inner and outer membranes separate. Here, we use fluorescence imaging of single cells during hyperosmotic shock with a time resolution on the order of seconds to examine the response of cells to a range of different conditions. We show that shock using an outer-membrane impermeable solute results in total cell volume reduction with no plasmolysis, whereas a shock caused by outer-membrane permeable ions causes plasmolysis immediately upon shock. Slowly permeable solutes, such as sucrose, which cross the membrane in minutes, cause plasmolysis to occur gradually as the chemical potential equilibrates. In addition, we quantify the detailed morphological changes to cell shape during osmotic shock. Nonplasmolyzed cells shrink in length with an additional lateral size reduction as the magnitude of the shock increases. Quickly plasmolyzing cells shrink largely at the poles, whereas gradually plasmolyzing cells invaginate along the cell cylinder. Our results give a comprehensive picture of the initial response of E. coli to hyperosmotic shock and offer explanations for seemingly opposing results that have been reported previously.

Citrate Fermentation by Lactococcus and Leuconostoc spp

Citrate and lactose fermentation are subject to the same metabolic regulation. In both processes, pyruvate is the key intermediate. Lactococcus lactis subsp. lactis biovar diacetylactis homofermentatively converted pyruvate to lactate at high dilution (growth) rates, low pH, and high lactose concentrations. Mixed-acid fermentation with formate, ethanol, and acetate as products was observed under conditions of lactose limitation in continuous culture at pH values above 6.0. An acetoin/butanediol fermentation with alpha-acetolactate as an intermediate was found upon mild aeration in continuous culture and under conditions of excess pyruvate production from citrate. Leuconostoc spp. showed a limited metabolic flexibility. A typical heterofermentative conversion of lactose was observed under all conditions in both continuous and batch cultures. The pyruvate produced from either lactose or citrate was converted to d-lactate. Citrate utilization was pH dependent in both L. lactis and Leuconostoc spp., with maximum rates observed between pH 5.5 and 6.0. The maximum specific growth rate was slightly stimulated by citrate, in L. lactis and greatly stimulated by citrate in Leuconostoc spp., and the conversion of citrate resulted in increased growth yields on lactose for both L. lactis and Leuconostoc spp. This indicates that energy is conserved during the metabolism of citrate.

Dual Mechanisms of Tricarboxylate Transport and Catabolism by Acidaminococcus fermentans

Acidaminococcus fermentans utilized citrate or the citrate analog aconitate as an energy source for growth, and these tricarboxylates were used simultaneously. Citrate utilization and uptake showed biphasic kinetics. High-affinity citrate uptake had a K(t) of 40 muM, but the V(max) was only 25 nmol/mg of protein per min. Low-affinity citrate utilization had a 10-fold higher V(max), but the K(s) was greater than 1.0 mM. Aconitate was a competitive inhibitor (K(i) = 34muM) of high-affinity citrate uptake, but low-affinity aconitate utilization had a 10-fold-lower requirement for sodium than did low-affinity citrate utilization. On the basis of this large difference in sodium requirements, it appeared that A. fermentans probably has two systems of tricarboxylate uptake: (i) a citrate/aconitate carrier with a low affinity for sodium and (ii) an aconitate carrier with a high affinity for sodium. Citrate was catabolized by a pathway involving a biotin-requiring, avidin-sensitive, sodium-dependent, membrane-bound oxaloacetate decarboxylase. The cells also had aconitase, but this enzyme was unable to convert citrate to isocitrate. Since cell-free extracts converted either aconitate or glutamate to 2-oxoglutarate, it appeared that aconitate was being catabolized by the glutaconyl-CoA decarboxylase pathway. Exponentially growing cultures on citrate or citrate plus aconitate were inhibited by the sodium/proton antiporter, monensin. Because monensin had no effect on cultures growing with aconitate alone, it appeared that citrate metabolism was acting as an inducer of monensin sensitivity. A. fermentans cells always had a low proton motive force (<50 mV), and cells treated with the protonophore TCS (3,3',4',5-tetrachlorosalicylanide) grew even though the proton motive force was less than 20 mV. On the basis of these results, it appeared that A. fermentans was depending almost exclusively on a sodium motive force for its membrane energetics.

Role of Asp544 in subunit I for Na(+) pumping by Vitreoscilla cytochrome bo

The conserved Glu540 in subunit I of Escherichia coli cytochrome bo (a H(+) pump) is replaced by Asp544 in the Vitreoscilla enzyme (a Na(+) pump). Site-directed mutagenesis of the Vitreoscilla cytochrome bo operon changed this Asp to Glu, and both wild type and mutant cyo's were transformed into E. coli strain GV100, which lacks cytochrome bo. Compared to the wild type transformant the Asp544Glu transformant had decreased ability to pump Na(+) as well as decreased stimulation in respiratory activity in the presence of Na(+). Preliminary experiments indicated that this mutant also had increased ability to pump protons, suggesting that this single change may provide cation pumping specificity in this group of enzymes.

Catabolite repression of the citrate fermentation genes in Klebsiella pneumoniae: evidence for involvement of the cyclic AMP receptor protein

Klebsiella pneumoniae is able to grow anaerobically with citrate as a sole carbon and energy source by a fermentative pathway involving the Na(+)-dependent citrate carrier CitS, citrate lyase, and oxaloacetate decarboxylase. The corresponding genes are organized in the divergent citC and citS operons, whose expression is strictly dependent on the citrate-sensing CitA-CitB two-component system. Evidence is provided here that the citrate fermentation genes are subject to catabolite repression, since anaerobic cultivation with a mixture of citrate and glucose or citrate and gluconate resulted in diauxic growth. Glucose, gluconate, and also glycerol decreased the expression of a chromosomal citS-lacZ fusion by 60 to 75%, whereas a direct inhibition of the citrate fermentation enzymes was not observed. The purified cyclic AMP (cAMP) receptor protein (CRP) of K. pneumoniae bound to two sites in the citC-citS intergenic region, which were centered at position -41.5 upstream of the citC and citS transcriptional start sites. Binding was apparently stimulated by the response regulator CitB. These data indicate that catabolite repression of the citrate fermentation genes is exerted by CRP and that in the absence of repressing carbon sources the cAMP-CRP complex serves to enhance the basal, CitB-dependent transcription level.

Sodium ion-translocating decarboxylases

The review is concerned with three Na(+)-dependent biotin-containing decarboxylases, which catalyse the substitution of CO(2) by H(+) with retention of configuration (DeltaG degrees '=-30 kJ/mol): oxaloacetate decarboxylase from enterobacteria, methylmalonyl-CoA decarboxylase from Veillonella parvula and Propiogenium modestum, and glutaconyl-CoA decarboxylase from Acidaminococcus fermentans. The enzymes represent complexes of four functional domains or subunits, a carboxytransferase, a mobile alanine- and proline-rich biotin carrier, a 9-11 membrane-spanning helix-containing Na(+)-dependent carboxybiotin decarboxylase and a membrane anchor. In the first catalytic step the carboxyl group of the substrate is converted to a kinetically activated carboxylate in N-carboxybiotin. After swing-over to the decarboxylase, an electrochemical Na(+) gradient is generated; the free energy of the decarboxylation is used to translocate 1-2 Na(+) from the inside to the outside, whereas the proton comes from the outside. At high [Na(+)], however, the decarboxylases appear to catalyse a mere Na(+)/Na(+) exchange. This finding has implications for the life of P. modestum in sea water, which relies on the synthesis of ATP via Delta(mu)Na(+) generated by decarboxylation. In many sequenced genomes from Bacteria and Archaea homologues of the carboxybiotin decarboxylase from A. fermentans with up to 80% sequence identity have been detected.

Catalytic properties of Na(+)-translocating V-ATPase in Enterococcus hirae

V-ATPases make up a family of proton pumps distributed widely from bacteria to higher organisms. We found a variant of this family, a Na(+)-translocating ATPase, in a Gram-positive bacterium, Enterococcus hirae. The Na(+)-ATPase was encoded by nine ntp genes from F to D in an ntp operon (ntpFIKECGABDHJ): the ntpJ gene encoded a K(+) transporter independent of the Na(+)-ATPase. Expression of this operon, encoding two transport systems for Na(+) and K(+) ions, was regulated at the transcriptional level by intracellular Na(+) as the signal. Structural aspects and catalytic properties of purified Na(+)-ATPase closely resembled those of other V-type H(+)-ATPases. Interestingly, the E. hirae enzyme showed a very high affinity for Na(+) at catalytic reaction. This property enabled the measurement of ion binding to this ATPase for the first time in the study of V- and F-ATPases. Properties of Na(+) binding to V-ATPase were consistent with the model that V-ATPase proteolipids form a rotor ring consisting of hexamers, each having one cation binding site. We propose here a structure model of Na(+) binding sites of the enzyme.

Evidence for Na(+) influx via the NtpJ protein of the KtrII K(+) uptake system in Enterococcus hirae

The ntpJ gene, a cistron located at the tail end of the vacuolar-type Na(+)-ATPase (ntp) operon of Enterococcus hirae, encodes a transporter of the KtrII K(+) uptake system. We found that K(+) accumulation in the ntpJ-disrupted mutant JEM2 was markedly enhanced by addition of valinomycin at pH 10. Studies of the membrane potential (DeltaPsi; inside negative) by 3, 3'-dihexyloxacarbocyanine iodide fluorescence revealed that the DeltaPsi was hyperpolarized at pH 10 in JEM2; the DeltaPsi values of the parent strain ATCC 9790 and JEM2, estimated by determining the equilibrium distribution of K(+) or Rb(+) in the presence of valinomycin, were -118 and -160 mV, respectively. DeltaPsi generation at pH 10 was accomplished by an electrogenic Na(+) efflux via the Na(+)-ATPase, whose levels in the two strains were quite similar. Na(+) uptake driven by an artificially imposed DeltaPsi (inside negative) was missing in JEM2, suggesting that NtpJ mediates Na(+) movement in addition to K(+) movement. Finally, the growth of JEM2 arrested in K(+)-limited high-Na(+) medium at pH 10 was restored by addition of valinomycin. These results suggest that NtpJ mediates electrogenic transport of K(+) as well as Na(+), that it likely mediates K(+) and Na(+) cotransport, and that Na(+) movement via NtpJ is the major Na(+) reentry pathway at high pH values.

Sodium-dependent glutamate uptake by an alkaliphilic, thermophilic Bacillus strain, TA2.A1

A strain of Bacillus designated TA2.A1, isolated from a thermal spring in Te Aroha, New Zealand, grew optimally at pH 9.2 and 70 degrees C. Bacillus strain TA2.A1 utilized glutamate as a sole carbon and energy source for growth, and sodium chloride (>5 mM) was an obligate requirement for growth. Growth on glutamate was inhibited by monensin and amiloride, both inhibitors that collapse the sodium gradient (DeltapNa) across the cell membrane. N, N-Dicyclohexylcarbodiimide inhibited the growth of Bacillus strain TA2.A1, suggesting that an F1F0-ATPase (H type) was being used to generate cellular ATP needed for anabolic reactions. Vanadate, an inhibitor of V-type ATPases, did not affect the growth of Bacillus strain TA2.A1. Glutamate transport by Bacillus strain TA2.A1 could be driven by an artificial membrane potential (DeltaPsi), but only when sodium was present. In the absence of sodium, the rate of DeltaPsi-driven glutamate uptake was fourfold lower. No glutamate transport was observed in the presence of DeltapNa alone (i.e., no DeltaPsi). Glutamate uptake was specifically inhibited by monensin, and the Km for sodium was 5.6 mM. The Hill plot had a slope of approximately 1, suggesting that sodium binding was noncooperative and that the glutamate transporter had a single binding site for sodium. Glutamate transport was not affected by the protonophore carbonyl cyanide m-chlorophenylhydrazone, suggesting that the transmembrane pH gradient was not required for glutamate transport. The rate of glutamate transport increased with increasing glutamate concentration; the Km for glutamate was 2.90 microM, and the Vmax was 0.7 nmol. min-1 mg of protein. Glutamate transport was specifically inhibited by glutamate analogues.

Inorganic cation transport and energy transduction in Enterococcus hirae and other streptococci

Energy metabolism by bacteria is well understood from the chemiosmotic viewpoint. We know that bacteria extrude protons across the plasma membrane, establishing an electrochemical potential that provides the driving force for various kinds of physiological work. Among these are the uptake of sugars, amino acids, and other nutrients with the aid of secondary porters and the regulation of the cytoplasmic pH and of the cytoplasmic concentration of potassium and other ions. Bacteria live in diverse habitats and are often exposed to severe conditions. In some circumstances, a proton circulation cannot satisfy their requirements and must be supplemented with a complement of primary transport systems. This review is concerned with cation transport in the fermentative streptococci, particularly Enterococcus hirae. Streptococci lack respiratory chains, relying on glycolysis or arginine fermentation for the production of ATP. One of the major findings with E. hirae and other streptococci is that ATP plays a much more important role in transmembrane transport than it does in nonfermentative organisms, probably due to the inability of this organism to generate a large proton potential. The movements of cations in streptococci illustrate the interplay between a variety of primary and secondary modes of transport.

ATP synthase: a tentative structural model

Adenosine triphosphate (ATP) synthase produces ATP from ADP and inorganic phosphate at the expense of proton- or sodium-motive force across the respective coupling membrane in Archaea, Bacteria and Eucarya. Cation flow through the intrinsic membrane portion of this enzyme (Fo, subunits ab2c9-12) and substrate turnover in the headpiece (F1, subunits alpha3beta3 gammadeltaepsilon) are mechanically coupled by the rotation of subunit gamma in the center of the catalytic hexagon of subunits (alphabeta)3 in F1. ATP synthase is the smallest rotatory engine in nature. With respect to the headpiece alone, it probably operates with three steps. Partial structures of six out of its at least eight different subunits have been published and a 3-dimensional structure is available for the assembly (alphabeta)3gamma. In this article, we review the available structural data and build a tentative topological model of the holoenzyme. The rotor portion is proposed to consist of a wheel of at least nine copies of subunits c, epsilon and a portion of gamma as a spoke, and another portion of gamma as a crankshaft. The stator is made up from a, the transmembrane portion of b2, delta and the catalytic hexagon of (alphabeta)3. As an educated guess, the model may be of heuristic value for ongoing studies on this fascinating electrochemical-to-mechanical-to-chemical transducer.

Molecular basis for the coupling ion selectivity of F1F0 ATP synthases: probing the liganding groups for Na+ and Li+ in the c subunit of the ATP synthase from Propionigenium modestum

The conserved glutamate residue at position 65 of the Propionigenium modestum c subunit is directly involved in binding and translocation of Na+ across the membrane. The site-specific introduction of the cQ32I and cS66A substitutions in the putative vicinity to cE65 inhibited growth of the single-site mutants on succinate minimal agar, indicating that both amino acid residues are important for proper function of the oxidative phosphorylation system. This growth inhibition was abolished, however, if the cF84L/cL87V double mutation was additionally present in the P. modestum c subunit. The newly constructed Escherichia coli strain MPC848732I, harboring the cQ32I/cF84L/cL87V triple mutation, revealed a change in the coupling ion specificity from Na+ to H+. ATP hydrolysis by this enzyme was therefore not activated by NaCl, and ATP-driven H+ transport was not affected by this alkali salt. Both activities were influenced, however, by LiCl. These data demonstrate the loss of the Na+ binding site and retention of Li+ and H+ binding sites within this mutant ATPase. In the E. coli strain MPC848766A (cS66A/cF84L/cL87V), the specificity of the ATPase was further restricted to H+ as the exclusive coupling ion. Therefore, neither Na+ nor Li+ stimulated the ATPase activity, and no ATP-driven Li+ transport was observed. The ATPase of the E. coli mutant MPC32N (cQ32N) was activated by NaCl and LiCl. The mutant ATPase exhibited a 5-fold higher Km for NaCl but no change in the Km for LiCl in comparison to that of the parent strain. These results demonstrate that the binding of Na+ to the c subunit of P. modestum requires liganding groups provided by Q32, E65, and S66. For the coordination of Li+, two liganding partners, E65 and S66, are sufficient, and H+ translocation was mediated by E65 alone.

Energetics of syntrophic cooperation in methanogenic degradation

Fatty acids and alcohols are key intermediates in the methanogenic degradation of organic matter, e.g., in anaerobic sewage sludge digestors or freshwater lake sediments. They are produced by classical fermenting bacteria for disposal of electrons derived in simultaneous substrate oxidations. Methanogenic bacteria can degrade primarily only one-carbon compounds. Therefore, acetate, propionate, ethanol, and their higher homologs have to be fermented further to one-carbon compounds. These fermentations are called secondary or syntrophic fermentations. They are endergonic processes under standard conditions and depend on intimate coupling with methanogenesis. The energetic situation of the prokaryotes cooperating in these processes is problematic: the free energy available in the reactions for total conversion of substrate to methane attributes to each partner amounts of energy in the range of the minimum biochemically convertible energy, i.e., 20 to 25 kJ per mol per reaction. This amount corresponds to one-third of an ATP unit and is equivalent to the energy required for a monovalent ion to cross the charged cytoplasmic membrane. Recent studies have revealed that syntrophically fermenting bacteria synthesize ATP by substrate-level phosphorylation and reinvest part of the ATP-bound energy into reversed electron transport processes, to release the electrons at a redox level accessible by the partner bacteria and to balance their energy budget. These findings allow us to understand the energy economy of these bacteria on the basis of concepts derived from the bioenergetics of other microorganisms.

Exchange of glutamate and gamma-aminobutyrate in a Lactobacillus strain

Lactobacillus sp. strain E1 catalyzed the decarboxylation of glutamate (Glu), resulting in a nearly stoichiometric release of the products gamma-aminobutyrate (GABA) and CO2. This decarboxylation was associated with the net synthesis of ATP. ATP synthesis was inhibited almost completely by nigericin and about 70% by N,N'-dicyclohexylcarbodiimide (DCCD), without inhibition of the decarboxylation. These findings are consistent with the possibility that a proton motive force arises from the cytoplasmic proton consumption that accompanies glutamate decarboxylation and the electrogenic Glu/GABA antiporter and the possibility that this proton motive force is coupled with ATP synthesis by DCCD-sensitive ATPase.

Catalytic mechanism of F1-ATPase

The structure of the core catalytic unit of ATP synthase, alpha 3 beta 3 gamma, has been determined by X-ray crystallography, revealing a roughly symmetrical arrangement of alternating alpha and beta subunits around a central cavity in which helical portions of gamma are found. A low-resolution structural model of F0, based on electron spectroscopic imaging, locates subunit a and the two copies of subunit b outside of a subunit c oligomer. The structures of individual subunits epsilon and c (largely) have been solved by NMR spectroscopy, but the oligomeric structure of c is still unknown. The structures of subunits a and delta remain undefined, that of b has not yet been defined but biochemical evidence indicates a credible model. Subunits gamma, epsilon, b, and delta are at the interface between F1 and F0; gamma epsilon complex forms one element of the stalk, interacting with c at the base and alpha and beta at the top. The locations of b and delta are less clear. Elucidation of the structure F0, of the stalk, and of the entire F1F0 remains a challenging goal.

Cross-linking of engineered subunit delta to (alphabeta)3 in chloroplast F-ATPase

Ser --> Cys mutations were introduced into subunit delta of spinach chloroplast F0F1-ATPase (CF0CF1) by site-directed mutagenesis. The engineered delta subunits were overexpressed in Escherichia coli, purified, and reassembled with spinach chloroplast F1-ATPase (CF1) lacking the delta subunit (CF1(-delta)). By modification with eosin-5-maleimide, it was shown that residues 10, 57, 82, 160, and 166 were solvent-accessible in isolated CF1 and all but residue 166 also in membrane-bound CF0CF1. Modification of the engineered delta subunit with photolabile cross-linkers, binding of delta to CF1(-delta), and photolysis yielded the same SDS gel pattern of cross-link products in the presence or absence of ADP, phosphate, and ATP and both in soluble CF1 and in CF0CF1. By chemical hydrolysis of cross-linked CF1, it was shown that deltaS10C was cross-linked within the N-terminal 62 residues of subunit beta. deltaS57C, deltaS82C, and deltaS166C were cross-linked within the N-terminal 192 residues of subunit alpha. Cross-linking affected neither ATP hydrolysis by soluble CF1 nor its ability to reassemble with CF0 and to structurally reconstitute ATP synthesis. Functional reconstitution, however, seemed to be impaired.

Na(+)-translocating cytochrome bo terminal oxidase from Vitreoscilla: some parameters of its Na+ pumping and orientation in synthetic vesicles

Vitreoscilla cytochrome bo ubiquinol oxidase is similar in some properties to the Escherichia coli enzyme, but unlike the latter, the Vitreoscilla oxidase functions as a primary Na+ pump. When purified Vitreoscilla cytochrome bo is incorporated into liposomes made from Vitreoscilla phospholipids and energized with a quinol substrate, it translocates Na+, not H+, across the vesicle membrane. Since protonophores CCCP (carbonyl cyanide m-chlorophenylhydrazone) and DTHB (3,5-di-tert-butyl-4-hydroxybenzaldehyde) stimulated the Na+ pumping, it is unlikely that it is a secondary effect due to the presence of Na+/H+ antiporter activity in the preparations. The efficiency of the Na+ pumping was 3.93 Na+ pumped per O2 consumed when ascorbate/TMPD was used as the substrate. The cytochrome has a K(m) and Kcat for Na+ of 2.9 mM and 277 s-1, respectively. When ferricytochrome c was entrapped within liposomes prepared from Vitreoscilla phospholipids, it was reduced by Q1H2 (ubiquinol-1) but not by ascorbate/TMPD (N,N,N',N'-tetramethyl-1,4-phenylenediamine). Although Q1H2 was oxidized by cytochrome bo in solution at a rate approximately 14 times that of the latter substrate, the rate of accumulation of Na+ within cytochrome bo vesicles driven by the membrane impermeable ascorbate/TMPD was 1.23 times that of the membrane permeable ubiquinol. These data allowed a calculation that in these synthetic proteoliposomes the cytochrome bo molecules are only 51% directed inward; a value of 61% inward-directed was estimated by measuring the ascorbate/TMPD oxidase activity of the proteoliposomes before and after disrupting them with Triton X-100. A random orientation of the E. coli cytochrome bo oxidase in proteoliposomes has also been reported.

Sodium-dependent succinate decarboxylation by a new anaerobic bacterium belonging to the genus Peptostreptococcus

An anaerobic bacterium was isolated from a polluted sediment, with succinate and yeast extract as carbon and energy sources. The new strain was Gram-positive, the cells were coccal shaped, the mol% G+G content of the genomic DNA was 29, and the peptidoglycan was of the L-ornithine-D-glutamic acid type. Comparative sequence analysis of the 16S rRNA gene showed the new strain to belong to the genus Peptostreptococcus. Succinate, fumarate, pyruvate, 3-hydroxybutyrate and lysine supported growth. Succinate was degraded to propionate and presumably CO2, with a stoichiometric cell yield. Key enzymes of the methylmalonyl-CoA decarboxylase pathway were present. The methylmalonyl-CoA decarboxylase activity was avidin-sensitive and sodium dependent, and about 5 mM Na+ was required for maximal activity. Whole cells, however, required at least 50 mM sodium for maximal succinate decarboxylation activity and to support the maximum growth rate. Sodium-dependent energy conservation coupled to succinate decarboxylation is shown for the first time to occur in a bacterium belonging to the group of Gram-positive bacteria containing the peptostreptococci and their relatives.

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

Strain LBS3 is a novel anaerobic thermoalkaliphilic bacterium that grows optimally at pH 9.5 and 50 degrees C. Since a high concentration of Na+ ions is required for growth, we have analyzed the primary bioenergetic mechanism of energy transduction in this organism. For this purpose, a method was devised for the isolation of right-side-out membrane vesicles that are functional for the energy-dependent uptake of solutes. A strict requirement for Na+ was observed for the uptake of several amino acids, and in the case of L-leucine, it was concluded that amino acid uptake occurs in symport with Na+ ions. Further characterization of the leucine transport system revealed that its pH and temperature optima closely match the conditions that support the growth of strain LBS3. The ATPase activity associated with inside-out membrane vesicles was found to be stimulated by both Na+ and Li+ ions. These data suggest that the primary mechanism of energy transduction in the anaerobic thermoalkaliphilic strain LBS3 is dependent on sodium cycling. The implications of this finding for the mechanism of intracellular pH regulation are discussed.

The ntpJ gene in the Enterococcus hirae ntp operon encodes a component of KtrII potassium transport system functionally independent of vacuolar Na+-ATPase

The ntpJ gene, the tail end in the vacuolar type Na+-ATPase (ntp) operon of Enterococcus hirae, encodes a putative 49-kDa hydrophobic protein resembling K+ transporter protein in Saccharomyces cerevisiae (Takase, K., Kakinuma, S., Yamato, I., Konishi, K., Igarashi, K., and Kakinuma, Y. (1994) J. Biol. Chem. 269, 11037-11044). Northern blotting experiment revealed that the ntpJ gene was transcribed as a cistron in the ntp operon. We constructed an Enterococcus strain in which the ntpJ gene was disrupted by cassette mutagenesis with erythromycin resistance gene. The growth of this mutant was normal at low pH. However, the mutant did not grow at high pH in K+-limited medium (less than 1 mM), while the wild type strain grew well; the internal K+ concentration of this mutant was as low as 7% of that of the wild type strain, suggesting that the K+ accumulation at high pH was inactivated by disruption of the ntpJ gene. Potassium uptake activity via the KtrII system, which had been proposed as the proton potential-independent, Na+-ATPase-coupled system working at high pH (Kakinuma, Y., and Harold, F. M. (1985) J. Biol. Chem. 260, 2086-2091), was missing in this mutant strain. However, this mutant retained as high activities of Na+-ATPase and Na+ pumping as the wild type strain. From these results, we conclude that the NtpJ is a membraneous component of the KtrII K+ uptake system but not a functional subunit of vacuolar Na+-ATPase complex; the interplay between the KtrII system and the Na+-ATPase was discussed.

The acyl carrier protein of malonate decarboxylase of Malonomonas rubra contains 2'-(5"-phosphoribosyl)-3'-dephosphocoenzyme A as a prosthetic group

Malonate decarboxylase of Malonomonas rubra is composed of soluble and membrane-bound components and contains an acetyl residue that is essential for catalytic activity. Upon incubation with hydroxylamine, the acetyl residue is removed, forming an inactive thiol enzyme, which is reactivated by acetylation with ATP, acetate, and a specific ligase. After incubation of the thiol enzyme with iodoacetate in the presence of excess dithioerythritol, the prosthetic group thiol residue was carboxymethylated and reactivation by acetylation was impaired. Radioactive labeling with [1-14C] iodoacetate revealed the site of carboxymethyation on a distinct cytoplasmic protein with the apparent molecular mass of 14 000 Da. The same protein was specifically labeled by enzymic acetylation of the thiol enzyme with [1-14C]acetate and ATP. Malonate decarboxlyation by [14C]acetyl malonate decarboxlyation resulted in the release of the radioactive acetyl residue from the enzyme,indicating that this acetyl residue is exchanged for a malonyl residue during catalysis. The acyl carrier protein has been purified as its [14C]carboxymethylated derivative to apparent homogeneity. The prosthetic group of the acyl carrier protein was isolated after alkaline hydrolysis, and its chemical structure was identified by high-performance liquid chromatography (HPLC) with the corresponding compound from citrate lyase from Klebsiella pneumoniae as reference and by mass spectrometry. Malonate decarboxylase was found to carry the same prosthetic group as citrate lyase, i.e. 2'-(5"-phosphoribosyl)-3'-dephospho-CoA.

Cloning, expression and sequence analysis of the genes encoding the heterodimeric methylmalonyl-CoA mutase of Porphyromonas gingivalis W50

Two genes that encode methylmalonyl-CoA mutase (MCM) have been characterised in Porphyromonas gingivalis W50 (Pg). The genes, designated mcmA and mcmB are transcribed in an operon and encode the MCM small subunit (SS, 68,626 Da) and the MCM large subunit (LS, 78,703 Da), respectively. A recombinant Escherichia coli (Ec) clone harbouring the Pg mcmA and mcmB genes expressed MCM activity 280-times higher than that of the Ec control. The C terminus of the MCM LS has sequence homology to domains of a variety of enzymes that consume or produce methylmalonyl-CoA, suggesting that the MCM LS C-terminal domain is involved in substrate binding. The MCM LS C-terminal region also exhibits homology to other enzymes that have cobalamin-containing cofactors. It is likely, therefore, that the C terminus of the MCM LS is an important MCM domain involved in both substrate and cofactor binding.

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

Two ATPases with different apparent molecular masses of approx. 500 kDa and 400 kDa were identified in the EDTA extract of the cell membranes of Methanobacterium thermoautotrophicum. Western blotting with polyclonal antiserum reactive with beta-subunit of mitochondrial ATPase from rat liver and yeast was used for further analysis of these ATPases. A strong crossreactivity with a single protein band with an apparent molecular weight of about 53 kDa (similar to beta-subunit of F-type ATPase from other sources) was found in protein extracts of whole cells of Methanobacterium thermoautotrophicum strains delta H and Marburg, as well as of Methanospirillum hungatei. This indicates the presence of F-type ATPase in methanogens. ATP synthesis driven by membrane potential which was generated by artificially-imposed delta pH in the presence of protonophorous uncoupler and sodium ions was stimulated by bafilomycin A1, an inhibitor of V- and A-type ATPases, as well as by harmaline, an inhibitor of Na+/H+ antiporter. These results indicate that cells of Methanobacterium thermoautotrophicum strain delta H contain the F-type ATP synthase which is Na(+)-translocating in addition to V- or A-type ATP synthase which is H(+)-translocating.

Expression of the sodium ion pump methylmalonyl-coenzyme A-decarboxylase from Veillonella parvula and of mutated enzyme specimens in Escherichia coli

The structural genes of the sodium ion pump methylmalonyl-coenzyme A (CoA)-decarboxylase from Veillonella parvula have recently been cloned on three overlapping plasmids (pJH1, pJH20, and pJH40) and sequenced. To synthesize the complete decarboxylase in Escherichia coli, the genes were fused in the correct order (mmdADECB) on a single plasmid (pJH70). A DNA region upstream of mmdA apparently served as promoter in E. coli because expression of the mmd genes was not dependent on the correct orientation of the lac promoter present on the pBluescript KS(+)-derived expression plasmid. To allow controlled induction of the mmd genes, the upstream region was deleted and the mmd genes were cloned behind a T7 promoter. The derived plasmid, pT7mmd, was transformed into E. coli BL21(DE3) expressing T7 RNA polymerase under the control of the lac promoter. The synthesized proteins showed the typical properties of methylmalonyl-CoA-decarboxylase, i.e., the same migration behavior during sodium dodecyl sulfate-polyacrylamide gel electrophoresis, stimulation of the decarboxylation activity by sodium ions, and inhibition with avidin. In methylmalonyl-CoA-decarboxylase expressed in E. coli from pT7mmd, the gamma subunit was only partially biotinylated and the alpha subunit was present in substoichiometric amounts, resulting in a low catalytic activity. This activity could be considerably increased by coexpression of biotin ligase and by incubation with separately expressed alpha subunit. After these treatments methylmalonyl-CoA-decarboxylase with a specific activity of about 5 U/mg of protein was isolated by adsorption and elution from monomeric avidin-Sepharose. To analyze the function of the delta and epsilon subunits, the corresponding genes were deleted from plasmid pT7mmd. E. coli cells transformed with pJHdelta2, which lacks mmdE and the 3' -terminal part of mmdD, showed no methylmalonyl-CoA-decarboxylase activity. In addition, a contrast, catalytically active methylmalonyl-CoA-decarboxylase was expressed in E. coli from plasmid pJHdelta1, which contained a deletion of the mmdE gene only. The mutant enzyme could be isolated, reconstituted into proteolipsomes, and shown to function in the transport of Na+ ions coupled to methylmalonyl-CoA decarboxylation. The small epsilon subunit therefore has no catalytic function within the methylmalonyl-CoA-decarboxylase complex but appears to increase the stability of this complex.

Mechanisms of membrane toxicity of hydrocarbons

Microbial transformations of cyclic hydrocarbons have received much attention during the past three decades. Interest in the degradation of environmental pollutants as well as in applications of microorganisms in the catalysis of chemical reactions has stimulated research in this area. The metabolic pathways of various aromatics, cycloalkanes, and terpenes in different microorganisms have been elucidated, and the genetics of several of these routes have been clarified. The toxicity of these compounds to microorganisms is very important in the microbial degradation of hydrocarbons, but not many researchers have studied the mechanism of this toxic action. In this review, we present general ideas derived from the various reports mentioning toxic effects. Most importantly, lipophilic hydrocarbons accumulate in the membrane lipid bilayer, affecting the structural and functional properties of these membranes. As a result of accumulated hydrocarbon molecules, the membrane loses its integrity, and an increase in permeability to protons and ions has been observed in several instances. Consequently, dissipation of the proton motive force and impairment of intracellular pH homeostasis occur. In addition to the effects of lipophilic compounds on the lipid part of the membrane, proteins embedded in the membrane are affected. The effects on the membrane-embedded proteins probably result to a large extent from changes in the lipid environment; however, direct effects of lipophilic compounds on membrane proteins have also been observed. Finally, the effectiveness of changes in membrane lipid composition, modification of outer membrane lipopolysaccharide, altered cell wall constituents, and active excretion systems in reducing the membrane concentrations of lipophilic compounds is discussed. Also, the adaptations (e.g., increase in lipid ordering, change in lipid/protein ratio) that compensate for the changes in membrane structure are treated.

Mechanisms of membrane toxicity of hydrocarbons

Microbial transformations of cyclic hydrocarbons have received much attention during the past three decades. Interest in the degradation of environmental pollutants as well as in applications of microorganisms in the catalysis of chemical reactions has stimulated research in this area. The metabolic pathways of various aromatics, cycloalkanes, and terpenes in different microorganisms have been elucidated, and the genetics of several of these routes have been clarified. The toxicity of these compounds to microorganisms is very important in the microbial degradation of hydrocarbons, but not many researchers have studied the mechanism of this toxic action. In this review, we present general ideas derived from the various reports mentioning toxic effects. Most importantly, lipophilic hydrocarbons accumulate in the membrane lipid bilayer, affecting the structural and functional properties of these membranes. As a result of accumulated hydrocarbon molecules, the membrane loses its integrity, and an increase in permeability to protons and ions has been observed in several instances. Consequently, dissipation of the proton motive force and impairment of intracellular pH homeostasis occur. In addition to the effects of lipophilic compounds on the lipid part of the membrane, proteins embedded in the membrane are affected. The effects on the membrane-embedded proteins probably result to a large extent from changes in the lipid environment; however, direct effects of lipophilic compounds on membrane proteins have also been observed. Finally, the effectiveness of changes in membrane lipid composition, modification of outer membrane lipopolysaccharide, altered cell wall constituents, and active excretion systems in reducing the membrane concentrations of lipophilic compounds is discussed. Also, the adaptations (e.g., increase in lipid ordering, change in lipid/protein ratio) that compensate for the changes in membrane structure are treated.

Cellodextrin efflux by the cellulolytic ruminal bacterium Fibrobacter succinogenes and its potential role in the growth of nonadherent bacteria

When glucose or cellobiose was provided as an energy source for Fibrobacter succinogenes, there was a transient accumulation (as much as 0.4 mM hexose equivalent) of cellobiose or cellotriose, respectively, in the growth medium. Nongrowing cell suspensions converted cellobiose to cellotriose and longer-chain cellodextrins, and in this case the total cellodextrin concentration was as much as 20 mM (hexose equivalent). Because cell extracts of glucose- or cellobiose-grown cells cleaved cellobioise and cellotriose by phosphate-dependent reactions and glucose 1-phosphate was an end product, it appeared that cellodextrins were being produced by a reversible phosphorylase reaction. This conclusion was supported by the observation that the ratio of cellodextrins to cellodextrins with one greater hexose [n/(n + 1)] was approximately 4, a value similar to the equilibrium constant (Keq) of cellobiose phosphorylase (J. K. Alexander, J. Bacteriol. 81:903-910, 1961). When F. succinogenes was grown in a cellobiose-limited chemostat, cellobiose and cellotriose could both be detected, and the ratio of cellotriose to cellobiose was approximately 1 to 4. On the basis of these results, cellodextrin production is an equilibrium (mass action) function and not just an artifact of energy-rich cultural conditions. Cellodextrins could not be detected in low-dilution-rate, cellulose-limited continuous cultures, but these cultures had a large number of nonadherent cells. Because the nonadherent cells had a large reserve of polysaccharide and were observed at all stages of cell division, it appeared that they were utilizing cellodextrins as an energy source for growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemiosmotic concept of the membrane bioenergetics: what is already clear and what is still waiting for elucidation?

The present state of the chemiosmotic concept is reviewed. Special attention is paid to (i) further progress in studies on the Na(+)-coupled energetics and (ii) paradoxical bioenergetic effects when protonic or sodium potentials are utilized outside the coupling membrane (TonB-mediated uphill transports across the outer bacterial membrane). A hypothesis is put forward assuming that the same principle is employed in the bacterial flagellar motor.

F0F1-ATPase of Vibrio parahaemolyticus: purification using new detergents and characterization

Previous attempts to isolate a stable F0F1-ATPase complex (H(+)-translocating ATPase) from Vibrio parahaemolyticus have been unsuccessful. Using new non-ionic detergents (alkyl thiomaltosides), a stable F0F1 complex with a high specific activity (15-25 units/mg protein) was purified and characterized. The purified F0F1-ATPase consists of eight subunits (alpha, beta, gamma, delta, epsilon, a, b and c). The new detergents, in combination with sucrose (or glycerol), lipid, dithiothreitol and phenylmethylsulfonyl fluoride, effectively stabilized the F0F1 complex. The ATPase activity of the F0F1 complex was greatly increased by anions, such as SO4(2-) and SO3(2-). Sodium ion increased the activity by about 2-fold. Dicyclohexylcarbodiimide, Zn2+, 4-acetamido-4'-isothiocyanostilben-2,2'disulfonate and tetrachlorosalicylanilide inhibited F0F1-ATPase activity. Ethanol, which stimulated F1-ATPase activity, inhibited F0F1-ATPase activity. Methanol, Na3VO4 and bafilomycin A1 did not have any significant effect on F0F1-ATPase activity, although methanol, like ethanol, stimulated F1-ATPase activity.

Role of Na+ in transport of Hg2+ and induction of the Tn21 mer operon

The effects of sodium ions on the uptake of Hg2+ and induction of the Tn21 mer operon were studied by using Escherichia coli HMS174 harboring the reporter plasmids pRB28 and pOS14. Plasmid pRB28 carries merRT', and pOS14 carries merRTPC of the mer operon, both cloned upstream of a promoterless luciferase gene cassette in pUCD615. The bioluminescent response to 1 microM Hg2+ was significantly inhibited in E. coli HMS174(pRB28) in minimal medium supplemented with sodium ions at 10 to 140 mM. After initial acceleration, light emission declined at 50 nM Hg2+ in the presence of Na+. The mer-lux assay with resting cells carrying pRB28 and 203Hg2+ uptake experiments showed increased induction and enhanced mercury uptake, respectively, in media supplemented with sodium ions. The presence of Na+ facilitated maintenance of bioluminescence in resting HMS174(pRB28) cells induced with 50 nM Hg2+. External K+ stimulated bioluminescent response in HMS174(pRB28) and HMS174(pOS14) grown in sodium phosphate minimal medium devoid of potassium ions. Sodium ions appear to facilitate mercury transport. We propose that sodium-coupled transport of mercuric ions can be one of the mechanisms for mercury uptake by E. coli and that the Na+ gradient may energize the transport of Hg2+.

Anaerobic growth of Salmonella typhimurium on L(+)- and D(-)-tartrate involves an oxaloacetate decarboxylase Na+ pump

We show here that the Enterobacterium Salmonella typhimurium LT2 has the capacity to grow anaerobically on L(+)- or D(-)-tartrate as sole carbon and energy source. Growth on these substrates was Na(+)-dependent and involved the L(+)- or D(-)-tartrate-inducible expression of oxaloacetate decarboxylase. The induced decarboxylase was closely related to the oxaloacetate decarboxylase Na+ pump of Klebsiella pneumoniae as shown by the sensitivity towards avidin, the location in the cytoplasmic membrane, activation by Na+ ions, and Western blot analysis with antiserum raised against the K. pneumoniae oxaloacetate decarboxylase. Participation of an oxaloacetate decarboxylase Na+ pump in L(+)-tartrate degradation by S. typhimurium is in accord with results from DNA analyses. The deduced protein sequence of the open reading frame identified upstream of the recently sequenced oxaloacetate decarboxylase genes is clearly homologous with the beta-subunit of L-tartrate dehydratase from Escherichia coli. Southern blot analysis with S. typhimurium chromosomal DNA indicated the presence of probably more than one gene for oxaloacetate decarboxylase.

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

Rhodamine 6G (3 microM) effectively inhibited delta pH-driven ATP synthesis in Methanobacterium thermoautotrophicum while delta pNA-driven ATP synthesis was not affected by it. Rhodamine 6G inhibited Mg(2+)-stimulated ATPase activity of membrane vesicles prepared from these cells but the ATPase catalytic sector detached from the membrane was insensitive to this inhibitor. Methanogenesis-driven ATP synthesis at pH 6.8 of the cells grown in the presence of 50 mM NaCl was inhibited by rhodamine 6G both in the presence of 5 mM and 50 mM NaCl. On the other hand, the methanogenesis-driven ATP synthesis at pH 8.0 of cells grown in the presence of 50 mM NaCl was slightly inhibited by rhodamine 6G in the presence of 5 mM NaCl and was not inhibited at all in the presence of 50 mM NaCl. The growth experiments have shown that cells of Methanobacterium thermoautotrophicum can grow under alkaline conditions even in the presence of rhodamine 6G and of high NaCl concentration when the growth media were inoculated with the cells which had been grown in the presence of 50 mM NaCl. These results indicate that sodium-motive force-driven ATP synthase in Methanobacterium thermoautotrophicum operates effectively at alkaline conditions and it might be the sole ATP synthesizing system when the proton motive force-supported ATP synthesis is inhibited by rhodamine 6G.

The F- or V-type Na(+)-ATPase of the thermophilic bacterium Clostridium fervidus

Clostridium fervidus is a thermophilic, anaerobic bacterium which uses solely Na+ as a coupling ion for energy transduction. Important features of the primary Na+ pump (ATPase) that generates the sodium motive force are presented. The advantage of using a sodium rather than a proton motive force at high temperatures becomes apparent from the effect of temperature on H+ and Na+ permeation in liposomes.

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

Rhodamine 6G (3 microM) effectively inhibited delta pH-driven ATP synthesis in Methanobacterium thermoautotrophicum while delta pNa-driven ATP synthesis was not affected by it. Rhodamine 6G inhibited Mg(2+)-stimulated ATPase activity of membrane vesicles prepared from these cells but the ATPase catalytic sector detached from the membrane was insensitive to this inhibitor. Methanogenesis-driven ATP synthesis at pH 6.8 of cells grown in the presence of 50 mM NaCl was inhibited by rhodamine 6G both in the presence of 5 mM and 50 mM NaCl. On the other hand, the methanogenesis-driven ATP synthesis at pH 8.0 of cells grown in the presence of 50 mM NaCl was slightly inhibited by rhodamine 6G in the presence of 5 mM NaCl and was not inhibited at all in the presence of 50 mM NaCl. The growth experiments have shown that cells of Methanobacterium thermoautotrophicum can grow under alkaline conditions even in the presence of rhodamine 6G and of high NaCl concentration when the growth media were inoculated with the cells which had been grown in the presence of 50 mM NaCl. These results indicate that sodium-motive force-driven ATP synthase in Methanobacterium thermoautotrophicum operates effectively in alkaline conditions and it might be the sole ATP synthesizing system when the proton-motive force-supported ATP synthesis is inhibited by rhodamine 6G.

Bacterial sodium ion-coupled energetics

For many bacteria Na+ bioenergetics is important as a link between exergonic and endergonic reactions in the membrane. This article focusses on two primary Na+ pumps in bacteria, the Na(+)-translocating oxaloacetate decarboxylase of Klebsiella pneumoniae and the Na(+)-translocating F1Fo ATPase of Propionigenium modestum. Oxaloacetate decarboxylase is an essential enzyme of the citrate fermentation pathway and has the additional function to conserve the free energy of decarboxylation by conversion into a Na+ gradient. Oxaloacetate decarboxylase is composed of three different subunits and the related methylmalonyl-CoA decarboxylase consists of five different subunits. The genes encoding these enzymes have been cloned and sequenced. Remarkable are large areas of complete sequence identity in the integral membrane-bound beta-subunits including two conserved aspartates that may be important for Na+ translocation. The coupling ratio of the decarboxylase Na+ pumps depended on delta muNa+ and decreased from two to zero Na+ uptake per decarboxylation event as delta mu Na+ increased from zero to the steady state level. In P. modestum, delta mu Na+ is generated in the course of succinate fermentation to propionate and CO2. This delta mu Na+ is used by a unique Na(+)-translocating F1Fo ATPase for ATP synthesis. The enzyme is related to H(+)-translocating F1Fo ATPases. The Fo part is entirely responsible for the coupling of ion specificity. A hybrid ATPase formed by in vivo complementation of an Escherichia coli deletion mutant was completely functional as a Na(+)-ATP synthase conferring the E. coli strain the ability of Na(+)-dependent growth on succinate. The hybrid consisted of subunits a, c, b, delta and part of alpha from P. modestum and of the remaining subunits from E. coli. Studies on Na+ translocation through the Fo part of the P. modestum ATPase revealed typical transporter-like properties. Sodium ions specifically protected the ATPase from the modification of glutamate-65 in subunit c by dicyclohexylcarbodiimide in a pH-dependent manner indicating that the Na+ binding site is at this highly conserved acidic amino acid residue of subunit c within the middle of the membrane.

Growth and Energy Generation by Lactococcus lactis subsp. lactis biovar diacetylactis during Citrate Metabolism

Growth of Lactococcus lactis subsp. lactis biovar diacetylactis was observed on media with citrate as the only energy source. At pH 5.6, steady state was achieved in a chemostat on a citrate-containing medium in the absence of a carbohydrate. Under these conditions, pyruvate, acetate, and some acetoin and butanediol were the main fermentation products. This indicated that energy was conserved in L. lactis subsp. lactis biovar diacetylactis during citrate metabolism and presumably during the conversion of citrate into pyruvate. The presumed energy-conserving step, decarboxylation of oxaloacetate, was studied in detail. Oxaloacetate decarboxylase was purified to homogeneity and characterized. The enzyme has a native molecular mass of approximately 300 kDa and consists of three subunits of 52, 34, and 12 kDa. The enzyme is apparently not sodium dependent and does not contain a biotin moiety, and it seems to be different from the energy-generating oxaloacetate decarboxylase from Klebsiella pneumoniae. Energy-depleted L. lactis subsp. lactis biovar diacetylactis cells generated a membrane potential and a pH gradient immediately upon addition of citrate, whereas ATP formation was slow and limited. In contrast, lactose energization resulted in rapid ATP formation and gradual generation of a proton motive force. These data were confirmed during studies on amino acid uptake. α-Aminoisobutyrate uptake was rapid but glutamate uptake was slow in citrate-energized cells, whereas lactose-energized cells showed the reverse tendency. These data suggest that, in L. lactis subsp. lactis bv. diacetylactis, a proton motive force could be generated during citrate metabolism as a result of electrogenic citrate uptake or citrate/product exchange together with proton consumption by the intracellular oxaloacetate decarboxylase.