Transport of H+, K+, Na+ and Ca++ in Streptococcus

Transcriptome analysis of Enterococcus faecalis in response to alkaline stress

Enterococcus faecalis is the most commonly isolated species from endodontic failure root canals; its persistence in treated root canals has been attributed to its ability to resist high pH stress. The goal of this study was to characterize the E. faecalis transcriptome and to identify candidate genes for response and resistance to alkaline stress using Illumina HiSeq 2000 sequencing. We found that E. faecalis could survive and form biofilms in a pH 10 environment and that alkaline stress had a great impact on the transcription of many genes in the E. faecalis genome. The transcriptome sequencing results revealed that 613 genes were differentially expressed (DEGs) for E. faecalis grown in pH 10 medium; 211 genes were found to be differentially up-regulated and 402 genes differentially down-regulated. Many of the down-regulated genes found are involved in cell energy production and metabolism and carbohydrate and amino acid metabolism, and the up-regulated genes are mostly related to nucleotide transport and metabolism. The results presented here reveal that cultivation of E. faecalis in alkaline stress has a profound impact on its transcriptome. The observed regulation of genes and pathways revealed that E. faecalis reduced its carbohydrate and amino acid metabolism and increased nucleotide synthesis to adapt and grow in alkaline stress. A number of the regulated genes may be useful candidates for the development of new therapeutic approaches for the treatment of E. faecalis infections.

Excellent antimicrobial properties of silver-loaded mesoporous silica SBA-15

AIMS

To synthesize silver-loaded mesoporous silica SBA-15 (Ag/SBA-15) materials and examine their antimicrobial action and antimicrobial mechanism.

METHODS AND RESULTS

Ag/SBA-15 materials were prepared by means of incipient wetness impregnation, impregnation and direct hydrothermal synthesis methods. The antimicrobial activity of Ag/SBA-15 was investigated using Escherichia coli as an indicator bacterium, and the antimicrobial mechanism was explored. The properties and Ag(+) release behaviour of Ag/SBA-15 materials were compared. Experimental results showed that Ag/SBA-15 materials resulted in 7·5 log inactivation of E. coli for only 60 min, which exhibited very high antimicrobial activities at room temperature without using any light or electrical power input. The cell wall and cell membrane were destroyed in the antimicrobial process, leading to leakage of intracellular components. The formation of extracellular reactive oxygen species (ROS) involved in the bactericidal process was confirmed. Production of intracellular ROS was also discovered.

CONCLUSIONS

Ag/SBA-15 exhibited high antimicrobial activity against E. coli. This antimicrobial effect was a synergistic action between extracellular ROS and the toxicity of Ag(+) , which induced intracellular ROS production and subsequent cell death.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study revealed for the first time the antimicrobial activities and mechanisms of Ag/SBA-15 materials prepared with different methods.

Efficient disinfection of Escherichia coli in water by silver loaded alumina

The catalytic inactivation of Escherichia coli (E. coli) in water by silver loaded alumina as catalyst was investigated. Ag/Al(2)O(3) and AgCl/Al(2)O(3) catalysts exhibited high bactericidal activity at room temperature in water with no need for any light or electrical power input. Dissolved oxygen which can be catalyzed to reactive oxygen species (ROS) was found to be essential for the strong bactericidal activities of the catalysts. Decomposition of the cell wall leading to leakage of the intracellular component and the complete lysis of the whole cell were directly observed by transmission electron microscopy (TEM). The resultant change in cell permeability was confirmed by potassium ion leakage. The different morphological changes between E. coli cells treated with the catalysts and Ag(+) were also observed. The formation of ROS involved in the bactericidal process by AgCl/Al(2)O(3) was confirmed by addition of catalase and ()OH scavenger. Higher temperature and pH value were found to have positive effect on the bactericidal activity of AgCl/Al(2)O(3). All these results indicated that the bactericidal effect of the catalyst was a synergic action of ROS and Ag(+), not an additive one. A possible mechanism is proposed.

A 100 kDa vanadate and lanzoprazole-sensitive ATPase from Streptococcus mutans membrane

The cariogenic potential of Streptococcus mutans is due to the production of organic acids derived from energy metabolism, which implies the need of mechanisms for the organism to tolerate this acidic environment. The F(1)F(o)-ATPase is generally considered as the main enzyme responsible for cytoplasmic proton extrusion, but mutations that resulted in a 50% reduction in F(1)F(o)-ATPase activity in S. mutans still allowed the micro-organism to grow and extrude acid, keeping the intracellular pH one pH unit above the extracellular ambient. This finding suggests the existence of other enzymatic (or cellular) mechanisms that keep the cytosolic pH neutral during micro-organism growth. This paper describes a membrane protein in S. mutans, with a molecular weight of 100 kDa, which exhibits ATPase activity inhibited by classic inhibitors of P-type ATPases (orthovanadate) and H(+),K(+)-ATPase (lanzoprazole), has an optimum pH comparable to other H(+)-ATPases and undergoes phosphorylation during the catalytic reaction, like that of H(+)-ATPases described in yeast and plant plasma membrane. Together, these results strongly suggest that the enzyme we describe here is a P-type H(+)-ATPase or H(+),ion-ATPase that can act in association with F(1)F(o)-ATPase during the growth of the S. mutans.

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.

Calcium signaling in Streptococcus pneumoniae: implication of the kinetics of calcium transport

The kinetics and pharmacological characterization of a Na+/Ca2+ exchange system, essential for the growth of the extracellular pathogen Streptococcus pneumoniae in high-calcium media, demonstrated that calcium transport, in addition to its role in calcium homeostasis, is involved in the induction of autolysis and of competence for genetic transformation. These responses are expressed respectively in cultures entering the stationary phase and growing with exponential rates. Experimental virulence also appears to be modulated by the kinetics of calcium transport. Calcium transport in S. pneumoniae is electrogenic and shows sigmoidicity, indicating a cooperative mechanism with an inflexion point at 1 mM Ca2+. Mutant strains with Hill number values of 4 and 1, compared to 2 in the wild-type strain, were isolated. These changes were associated with altered regulation of competence and autolysis, and also with reduced experimental virulence. By contrast, they could not be related to a specific calcium requirement for growth. This indicates that the cooperativity of Ca2+ transport is not involved in vegetative growth, but rather regulates competence and autolysis. Competence and autolysis represent two growth-phase-dependent responses to an oligopeptide-activator exported to the medium, the competence-stimulating peptide. Addition of this activator to noncompetent cells, triggers net and transient 45Ca2+ influx. One effect of the activator might be to activate a calcium transporter by enhancing its cooperativity. In addition to an increase in intracellular calcium, a transient membrane depolarization induced by electrogenic calcium influx may be part of the signaling mechanism. The competence activator is a quorum-sensing molecule whose synthesis is autoregulated. This regulation might involve calcium-mediated signaling. As an extracellular pathogen, S. pneumoniae probably develops in niches with variable calcium concentration. Interestingly, virulence depends strongly upon the kinetics of Ca2+ transport. Regulation of calcium influx may represent a common mechanism of sensing the environment, if the Na+/Ca2+ exchanger is the target for external mediators including the competence activator.

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.

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.

Mode of photocatalytic bactericidal action of powdered semiconductor TiO2 on mutans streptococci

Powdered semiconductor TiO2 has a photocatalytic bactericidal capacity on some kinds of bacteria, but its mechanism still remains unclear. The mode of its photocatalytic bactericidal action on the mutans group of streptococci was investigated. Powdered TiO2 had a bactericidal capacity on all serotypes of mutans streptococci. Streptococcus sobrinus AHT was mainly used for these experiments. The most effective concentration of TiO2 was about 1 mg ml-1 and, at this concentration, 10(5) colony-forming units of S. sobrinus AHT per millilitre were completely killed within 1 min. In order to search for the mechanism of this effect, a high bacterial cell density (10(9) colony-forming units ml-1) was used in the following studies. "Rapid" leakage of potassium ions from the bacteria occurred parallel to the decrease in cell viability. Protein and RNA were "slowly" released from bacterial cells for a reaction time up to 120 min. The pH of the reaction mixture decreased continuously to 4.5 after 120 min. Co-aggregation of S. sobrinus AHT and powdered TiO2 occurred at high bacterial densities (above 10(8) colony-forming units ml-1). Aggregates gradually decomposed with light irradiation. Transmission electron microscopy of S. sobrinus AHT after photocatalytic action for 60-120 min indicated complete destruction of bacterial cells. From these results, bacterial death appears to be caused by a significant disorder in cell membranes and finally the cell walls were decomposed.

Primary structure of the alpha-subunit of vacuolar-type Na(+)-ATPase in Enterococcus hirae. Amplification of a 1000-bp fragment by polymerase chain reaction

A 1000-bp fragment of Enterococcus hirae genomic DNA was amplified by the polymerase chain reaction method, using the oligonucleotide primers designed from amino acid sequences of both amino-terminal and a tryptic fragment of the Na(+)-ATPase alpha-subunit in this organism. DNA sequencing of this product revealed that the amino acid sequence of Na(+)-ATPase alpha-subunit is highly homologous to the corresponding sequences of large (alpha) subunits of vacuolar (archaebacterial) type H(+)-ATPases, supporting our proposal [Kakinuma, Y. and Igarashi, K. (1990) FEBS Lett. 271, 97-101] that the Na(+)-ATPase of this organism belongs to the vacuolar-type ATPase.

Efficient electrotransformation of Enterococcus hirae with a new Enterococcus-Escherichia coli shuttle vector

In the present study, an Enterococcus-Escherichia coli shuttle vector, pC3, was constructed that allows efficient transformation by electroporation of Enterococcus hirae ATCC9790. 5 x 10(6) transformants per microgram of plasmid DNA were obtained, using a commercial capacitor discharge device with an improved circuitry and a home-made electrode assembly, delivering pulses of 24 kV/cm across the cell suspension. The transformants were stable without selective pressure and plasmid DNA reisolated from transformed cells displayed no alterations in restriction enzyme analysis. Chromosomal DNA from E coli or E hirae, carried by pC3, was stably maintained in E hirae, making cloning and genetic manipulation in this organism feasible.

Mutants of Streptococcus faecalis sensitive to alkaline pH lack Na(+)-ATPase

Alkali-sensitive mutants which grow at pH 7.5 but not at pH 9.5 in Na(+)-rich media were isolated from Streptococcus faecalis ATCC 9790. One of the mutants, designated Nak1, lacked activities of both Na(+)-stimulated ATPase and KtrII (active K+ uptake by sodium ATPase). These activities were restored in a spontaneous revertant designated Nak1R. Active sodium extrusion from Nak1 was observed at pH 7.0, which allows the cells to generate a proton potential, but not at pH 9.5, which reverses the proton potential, making it positive. Sodium extrusion at pH 7.0 was inhibited by addition of dicyclohexylcarbodiimide and protonophores. Even at pH 9.5, Nak1 did grow well in Na(+)-poor media. In Na(+)-rich media at pH 7.5, growth of Nak1 but not that of 9790 was severely inhibited by a protonophore. These results indicate that mutant Nak1 lacks sodium ATPase but contains a sodium/proton antiporter and that sodium ATPase is essential for the growth of this organism at high pH in Na(+)-rich conditions.

Sodium-translocating adenosine triphosphatase in Streptococcus faecalis

Sodium-translocating ATPase in the fermentative bacterium Streptococcus faecalis exchanges sodium for potassium ions. Sodium ions stimulate its activity, but K+ ions have no significant effect at present. Although the molecular nature of the sodium ATPase is not clear, the enzyme is distinct from other ion-motive ATPases (E1E2 type and F1F0 type) as judged by its resistance to vanadate as well as dicyclohexylcarbodiimde. The sodium ATPase is induced when cells are grown on media rich in sodium, particularly under conditions that limit the generation of a proton potential or block the constitutive sodium proton antiporter, indicating that an increase in the cytoplasmic sodium level serves as the signal. The enzyme is not induced in response to K+ deprivation. The sodium ATPase may have evolved to cope with a sodium-rich environment under conditions that limit the magnitude of the proton potential.

Study by NMR of the mode of action of monensin on Streptococcus faecalis de-energized and energized cells

Streptococcus faecalis was used as a bacterial model for studying the mode of action of monensin by NMR investigations. Experiments were carried out in two states, characterized by several complementary methods: (i) the resting (de-energized) cell which was considered as an inert biological membrane, on which cationic transport induced by the ionophore alone can be investigated; (ii) the active (energized) cell where the ionophore-sensitive response of the living organism, particularly the cation pumps and the glycolysis, is probed. Studies of resting cells were performed, with changing external ionic concentrations, in the presence of monensin, which is preferentially a sodium carrier. Internal and external Na+ and H+ were followed by corresponding 23Na and 31P (inorganic phosphate) NMR resonances, K+ fluxes were measured by atomic absorption. It was shown that the induced cationic movements were linked to the existing ionic gradients for K+ and Na+. 31P and 13C NMR spectra for the intermediary metabolites detected in active cells showed that glycolysis is dramatically modified in the presence of monensin.

Bioenergetics and solute transport in lactococci

During the last few years the studies about the physiology and bioenergetics of lactic acid bacteria during growth and starvation have evolved from a descriptive level to an analysis of the molecular events in the regulation of various processes. Considerable progress has been made in the understanding of the modes of metabolic energy generation, the mechanism of homeostasis of the internal pH, and the mechanism and regulatory processes of transport systems for sugars, amino acids, peptides, and ions. Detailed studies of these transport processes have been performed in cytoplasmic membrane vesicles of these organisms in which a foreign proton pump has been introduced to generate a high proton motive force.

Sodium/proton antiporter in Streptococcus faecalis

Streptococcus faecalis, like other bacteria, accumulates potassium ions and expels sodium ions. This paper is concerned with the pathway of sodium extrusion. Earlier studies (D.L. Heefner and F.M. Harold, Proc. Natl. Acad. Sci. USA 79:2798-2802, 1982) showed that sodium extrusion is effected by a primary, ATP-linked sodium pump. I report here that cells grown under conditions in which sodium ATPase is not induced can still expel sodium ions. This finding suggested the existence of an alternate pathway. Sodium extrusion by the alternate pathway requires the cells to generate a proton motive force. This conclusion rests on the following observations. (i) Sodium extrusion required glucose. (ii) Sodium extrusion was observed at neutral pH, which allows the cells to generate a proton motive force, but not at alkaline pH, which reduces the proton motive force to zero. (iii) Sodium extrusion was inhibited by the addition of dicyclohexylcarbodiimide and of proton-conducting ionophores. (iv) In response to an artificial pH gradient (with the exterior acid), energy-depleted cells exhibited a transient sodium extrusion which was unaffected by treatments that dissipated the membrane potential and which was blocked by proton conductors. I propose that streptococci have two independent systems for sodium extrusion: an inducible sodium ATPase and a constitutive sodium/proton antiporter.

Protonmotive force driven 6-deoxyglucose uptake by the oral pathogen, Streptococcus mutans Ingbritt

Streptococcus mutans Ingbritt was grown in glucose-excess continuous culture to repress the glucose phosphoenolpyruvate phosphotransferase system (PTS) and allow investigation of the alternative glucose process using the non-PTS substrate, (3H) 6-deoxyglucose. After correcting for non-specific adsorption to inactivated cells, the radiolabelled glucose analogue was found to be concentrated approximately 4.3-fold intracellularly by bacteria incubated in 100 mM Tris-citrate buffer, pH 7.0. Mercaptoethanol or KCl enhanced 6-deoxyglucose uptake, enabling it to be concentrated internally by at least 8-fold, but NaCl was inhibitory to its transport. Initial uptake was antagonised by glucose but not 2-deoxyglucose. Evidence that 6-deoxyglucose transport was driven by protonmotive force (delta p) was obtained by inhibiting its uptake with the protonophores, 2,4-dinitrophenol, carbonylcyanide m-chlorophenylhydrazine, gramicidin and nigericin, and the electrical potential difference (delta psi) dissipator, KSCN. The membrane ATPase inhibitor, N,N1-dicyclohexyl carbodiimide, also reduced 6-deoxyglucose uptake as did 100 mM lactate. In combination, these two inhibitors completely abolished 6-deoxyglucose transport. This suggests that the driving force for 6-deoxyglucose uptake is electrogenic, involving both the transmembrane pH gradient (delta pH) and delta psi. ATP hydrolysis, catalysed by the ATPase, and lactate excretion might be important contributors to delta pH.

Effects of K+ on the proton motive force of Bradyrhizobium sp. strain 32H1

In previous studies, respiring Bradyrhizobium sp. strain 32H1 cells grown under 0.2% O2, conditions that derepress N2 fixation, were found to have a low proton motive force of less than -121 mV, because of a low membrane potential (delta psi). In contrast, cells grown under 21% O2, which do not fix N2, had high proton motive force values of -175 mV or more, which are typical of respiring bacteria, because of high delta psi values. In the present study, we found that a delta psi of 0 mV in respiring cells requires growth in relatively high-[K+] media (8 mM), low O2 tension, and high internal [K+]. When low-[O2], high-[K+]-grown cells were partially depleted of K+, the delta psi was high. When cells were grown under 21% O2 or in media low in K+ (50 microM K+), the delta psi was again high. The transmembrane pH gradient was affected only slightly by varying the growth or assay conditions. In addition, low-[O2], high-[K+]-grown cells had a greater proton permeability than did high-[O2]-grown cells. To explain these findings, we postulate that cells grown under conditions that derepress N2 fixation contain an electrogenic K+/H+ antiporter that is responsible for the dissipation of the delta psi. The consequence of this alteration in K+ cycling is rerouting of proton circuits so that the putative antiporter becomes the major pathway for H+ influx, rather than the H+-ATP synthase.

What family of ATPases does the vacuolar H+-ATPase belong to?

Polyacrylamide gel electrophoresis (PAGE) of partially purified ATPase from vacuoles of Saccharomyces carlsbergensis under non-dissociating conditions revealed 3 bands with ATPase activity. Further PAGE in dissociating conditions showed the similarity in composition of these 3 ATPase preparations. They were assumed to contain the same vacuolar ATPase exhibiting, however, different electrophoretic mobility due to the formation of enzyme complexes with different proteins and phospholipids. The ATPase preparation with the highest electrophoretic mobility contained 6 subunits of 75, 62, 16, 14, 12 and 9 kDa. Inhibitors of vacuolar ATPase [14C]DCCD and [14C]NEM bound to a 9 kDa polypeptide, while [14C]DES associated with a polypeptide of 75 kDa. A partially purified preparation of the vacuolar ATPase was not phosphorylated by [gamma-32P]ATP under conditions when plasma membrane ATPase formed a phosphorylated intermediate. Our results show that vacuolar H+-ATPase consists of several polypeptides, does not form the phosphorylated intermediate, and evidently represents a new type of H+-ATPase of yeast.

The bioenergetics of methanogenesis

The reduction of CO2 or any other methanogenic substrate to methane serves the same function as the reduction of oxygen, nitrate or sulfate to more reduced products. These exergonic reactions are coupled to the production of usable energy generated through a charge separation and a protonmotive-force-driven ATPase. For the understanding of how methanogens derive energy from C-1 unit reduction one must study the biochemistry of the chemical reactions involved and how these are coupled to the production of a charge separation and subsequent electron transport phosphorylation. Data on methanogenesis by a variety of organisms indicates ubiquitous use of CH3-S-CoM as the final electron acceptor in the production of methane through the methyl CoM reductase and of 5-deazaflavin as a primary source of reducing equivalents. Three known enzymes serve as catalysts in the production of reduced 5-deazaflavin: hydrogenase, formate dehydrogenase and CO dehydrogenase. All three are potential candidates for proton pumps. In the organisms that must oxidize some of their substrate to obtain electrons for the reduction of another portion of the substrate to methane (e.g., those using formate, methanol or acetate), the latter two enzymes may operate in the oxidizing direction. CO2 is the most frequent substrate for methanogenesis but is the only substrate that obligately requires the presence of H2 and hydrogenase. Growth on methanol requires a B12-containing methanol-CoM methyl transferase and does not necessarily need any other methanogenic enzymes besides the methyl-CoM reductase system when hydrogenase is present. When bacteria grow on methanol alone it is not yet clear if they get their reducing equivalents from a reversal of methanogenic enzymes, thus oxidizing methyl groups to CO2. An alternative (since these and acetate-catabolizing methanogens possess cytochrome b) is electron transport and possible proton pumping via a cytochrome-containing electron transport chain. Several of the actual components of the methanogenic pathway from CO2 have been characterized. Methanofuran is apparently the first carbon-carrying cofactor in the pathway, forming carboxy-methanofuran. Formyl-FAF or formyl-methanopterin (YFC, a very rapidly labelled compound during 14C pulse labeling) has been implicated as an obligate intermediate in methanogenesis, since methanopterin or FAF is an essential component of the carbon dioxide reducing factor in dialyzed extract methanogenesis. FAF also carries the carbon at the methylene and methyl oxidation levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of a Streptococcus pneumoniae mutant with altered electric transmembrane potential

It is possible to select transmembrane potential (delta psi)-altered mutants in Streptococcus pneumoniae on the basis of their resistance to the antifolate methotrexate. Comparison of such a mutant strain ( amiA9 ) with its parent was used to evaluate the role of delta psi in the uptake of certain amino acids. The delta psi-dependent uptake of isoleucine, leucine, valine, and asparagine showed a reduced maximum velocity of uptake, and decrease in the transport constant of the energy-dependent, delta psi-independent uptake of lysine, methionine, and glutamine was observed. No reduction of the intracellular pool of ATP or of lactate excretion could be detected in the mutant strain. Moreover, studies on membrane preparations suggest that the phenotype expressed by the amiA mutation is not a consequence of alteration of its ATPase activity or susceptibility to N,N'-dicyclohexylcarbodiimide. Therefore, it is unlikely that the amiA mutation affects the H+ F1F0 ATPase which is involved in the establishment of the proton motive force in anaerobic bacteria. We propose that another function contributes to delta psi in S. pneumoniae. The amiA gene may be the structural gene of that function.

Sodium-dependent uptake of taurine in encapsulated Staphylococcus aureus strain M

A novel uptake system for the unusual sulfonated amino acid taurine was discovered in the prokaryote, encapsulated Staphylococcus aureus strain M. This strain has been shown previously to contain taurine in its capsular polysaccharide. Taurine uptake by whole cells incubated in buffer showed a saturable dependency upon Na+ and taurine uptake was itself a saturable process, stimulated by glucose, and markedly affected by temperature. No evidence was found for the inducibility of taurine uptake. In the presence of 10 mM NaCl Lineweaver-Burk plots revealed a Km of 42 microM and Vmax of 4.6 nmol/min per mg dry weight for taurine uptake at 37 degrees C. Increasing concentrations of Na+ decreased the Km of the system and appeared to increase the Vmax. Of various other cations tested only Li+ supported marked taurine uptake. Excess unlabelled taurine did not cause efflux of radioactivity taken up. Taurine was taken up into cold trichloroacetic acid-soluble material and did not chromatograph as taurine, indicating rapid metabolism during or closely following uptake. Taurine uptake appeared to occur via a highly specific system because amino acids representing the major known groups of amino acid transport systems in S. aureus did not inhibit taurine uptake, and uptake was only slightly diminished by the structurally closely related compounds hypotaurine and 3-amino-1-propane sulfonic acid. Sulfhydryl group reagents, electron transport inhibitors, an uncoupler and inhibitors of Na+-linked transport processes inhibited taurine uptake. A variety of other metabolic inhibitors had little effect on taurine uptake.

Evidence that glucose and sucrose uptake in oral streptococcal bacteria involves independent phosphotransferase and proton-motive force-mediated mechanisms

Sugar transport and glycolysis in Streptococcus sanguis NCTC 7865, Streptococcus mitis ATCC 903, Streptococcus salivarius NCTC 8606 and several strains of Streptococcus mutans were investigated by following the rate of acid production by washed bacteria at a constant pH of 7.0. The phosphoenolpyruvate-phosphotransferase system (PTS) was inhibited by low concentrations of chlorhexidine. When this PTS-inhibitory concentration of chlorhexidine was added to cells washed and re-suspended in KCl, glucose uptake and glycolysis continued at a greatly-reduced rate. Chlorhexidine abolished glucose and sucrose uptake and metabolism in bacteria washed and incubated in saline. The Na+-inhibition was reproduced in KCl-washed bacteria using the cyclic peptide ionophores, valinomycin and gramicidin, to dissipate K+ and H+ gradients across the cell membrane. Glucose metabolism by Strep. mutans B13 was more resistant to chlorhexidine than that of Strep. mutans NCTC 10449 or Strep. sanguis but was more sensitive to the ionophores. Valinomycin had a greater inhibitory effect on strain B13 than the other two. That ion gradients are important in the chlorhexidine-resistant glucose-uptake mechanism was confirmed using the classical uncoupling agents, carbonylcyanide-m-chlorophenylhydrazone, 2,4-dinitrophenol and KSCN. Glucose metabolism was inhibited in the presence of both the uncouplers and the PTS-inhibitory concentration of chlorhexidine and significant inhibition was also observed in the absence of the PTS inhibitor. Lactate or the ATPase inhibitor, dicyclohexyl carbodiimide (DCCD), had similar inhibitory effects on the non-PTS uptake system.(ABSTRACT TRUNCATED AT 250 WORDS)

Proton motive force and Na+/H+ antiport in a moderate halophile

The influence of pH on the proton motive force of Vibrio costicola was determined by measuring the distributions of triphenylmethylphosphonium cation (membrane potential, delta psi) and either dimethyloxazolidinedione or methylamine (osmotic component, delta pH). As the pH of the medium was adjusted from 5.7 to 9.0, the proton motive force steadily decreased from about 170 to 100 mV. This decline occurred, despite a large increase in the membrane potential to its maximum value at pH 9.0, because of the loss of the pH gradient (inside alkaline). The cytoplasm and medium were of equal pH at 7.5; membrane permeability properties were lost at the pH extremes of 5.0 and 9.5. Protonophores and monensin prevented the net efflux of protons normally found when an oxygen pulse was given to an anaerobic cell suspension. A Na+/H+ antiport activity was measured for both Na+ influx and efflux and was shown to be dissipated by protonophores and monensin. These results strongly favor the concept that respiratory energy is used for proton efflux and that the resulting proton motive force may be converted to a sodium motive force through Na+/H+ antiport (driven by delta psi). A role for antiport activity in pH regulation of the cytosol can also explain the broad pH range for optimal growth, extending to the alkaline extreme of pH 9.0.