Physiology of acidophilic and alkalophilic bacteria

Impact of temperature on the virulence of Streptococcus agalactiae in Indonesian aquaculture: A better vaccine design is required

Due to their poikilothermic nature, fish are very sensitive to changes in temperature. Due to climate change, the average global temperature has increased by 1.5°C in the last century, which may have caused an increase in farmed fish mortality recently. Predictions using the model estimate that a 1°C increase in temperature could cause 3%-4% and 4%-6% mortality due to infectious diseases in organisms living in warm and temperate waters, respectively. There is a need to determine whether there is a relationship between increasing environmental temperature and disease virulence. This review examines the influence and impact of increasing temperatures due to climate change on the physiology and pathogenicity of Streptococcus agalactiae, which causes streptococcosis in tilapia and causes significant economic losses. Changes in the pathogenicity of S. agalactiae, especially its virulence properties due to increasing temperature, require changes in the composition design of the fish vaccine formula to provide better protection through the production of protective antibodies.

Highly Stable Liposomes Based on Tetraether Lipids as a Promising and Versatile Drug Delivery System

Conventional liposomes often lack stability, limiting their applicability and usage apart from intravenous routes. Nevertheless, their advantages in drug encapsulation and physicochemical properties might be helpful in oral and pulmonary drug delivery. This study investigated the feasibility and stability of liposomes containing tetraether lipids (TEL) from Thermoplasma acidophilum. Liposomes composed of different molar ratios of TEL:Phospholipon 100H (Ph) were produced and exposed to various temperature and pH conditions. The effects on size, polydispersity index, and zeta potential were examined by dynamic and electrophoretic light scattering. Autoclaving, which was considered an additional process step after fabrication, could minimize contamination and prolong shelf life, and the stability after autoclaving was tested. Moreover, 5(6)-carboxyfluorescein leakage was measured after incubation in the presence of fetal calf serum (FCS) and lung surfactant (Alveofact). The incorporation of TEL into the liposomes significantly impacted the stability against low pH, higher temperatures, and even sterilization by autoclaving. The stability of liposomes containing TEL was confirmed by atomic force microscopy as images revealed similar sizes and morphology before and after incubation with FCS. It could be concluded that increasing the molar ratio in the TEL:Ph liposome formulations improved the structural stability against high temperature, low pH, sterilization via autoclaving, and the presence of FCS and lung surfactant.

Distribution, Characterization, and Diversity of the Endophytic Fungal Communities on Korean Seacoasts Showing Contrasting Geographic Conditions

This study analyzed the distribution of endophytic fungi in 3 coastal environments with different climatic, geographical, and geological characteristics: the volcanic islands of Dokdo, the East Sea, and the West Sea of Korea. The isolated fungal endophytes were characterized and analyzed with respect to the characteristics of their host environments. For this purpose, we selected common native coastal halophyte communities from three regions. Molecular identification of the fungal endophytes showed clear differences among the sampling sites and halophyte host species. Isolates were also characterized by growth at specific salinities or pH gradients, with reference to previous geographical, geological, and climate studies. Unlike the East Sea or West Sea isolates, some Dokdo Islands isolates showed endurable traits with growth in high salinity, and many showed growth under extremely alkaline conditions. A smaller proportion of West Sea coast isolates tolerate compared to the East Sea or Dokdo Islands isolates. These results suggest that these unique fungal biota developed through a close interaction between the host halophyte and their environment, even within the same halophyte species. Therefore, this study proposes the application of specific fungal resources for restoring sand dunes and salt-damaged agricultural lands and industrialization of halophytic plants.

Specific rhizobacterial resources: characterization and comparative analysis from contrasting coastal environments of Korea

This study analyzed the rhizobacterial distribution from two coasts, which show contrasting climates and geographical and geological characteristics, to secure specific microbial resources. Furthermore, rhizobacteria were characterized and the results were comparatively analyzed with reference to the characteristics of two coastal environments. For this purpose, three representative halophyte species communities native to the Dokdo Islands and the East Sea coast of Korea were selected. Partial identification of rhizobacteria showed a clear difference between each sampling site and halophyte. Furthermore, isolates were characterized by their growth properties under NaCl or pH gradients related with previous geographical, geological, and climatic studies of the Dokdo Islands and the East Sea coast. A high proportion of the East Sea isolates showed halotolerance, but a high proportion of Dokdo isolates shared halophilic traits. Meanwhile, a higher proportion of East Sea isolates grew at a wider range of pH values than those of the Dokdo Islands. The results of our study suggest that unique rhizobacterial resources developed under specific rhizospheric conditions derived from halophytes interacting with their specific environment, even within the same coastal halophytic species. Therefore, this study proposes the necessity of securing characterized and unique microbial resources to apply to specific environments for the purpose of recovering and restoring sand dunes or salt-damaged agricultural lands.

Cultivation-dependent assessment, diversity, and ecology of haloalkaliphilic bacteria in arid saline systems of southern Tunisia

Haloalkaliphiles are polyextremophiles adapted to grow at high salt concentrations and alkaline pH values. In this work, we isolated 122 haloalkaliphilic bacteria upon enrichments of 23 samples from 5 distinct saline systems of southern Tunisia, growing optimally in media with 10% salt and at pH 10. The collection was classified into 44 groups based on the amplification of the 16S-23S rRNA internal transcribed spacers (ITS-PCR). Phylogenetic analysis and sequencing of the 16S rRNA genes allowed the identification of 13 genera and 20 distinct species. Three gram-positive isolates showing between 95 and 96% of 16S rRNA sequence homology with Bacillus saliphilus could represent new species or genus. Beside the difference in bacterial diversity between the studied sites, several species ecological niches correlations were demonstrated such as Oceanobacillus in salt crust, Nesterenkonia in sand, and Salinicoccus in the rhizosphere of the desert plant Salicornia. The collection was further evaluated for the production of extracellular enzymes. Activity tests showed that gram-positive bacteria were mostly active, particularly for protease, lipase, DNase, and amylase production. Our overall results demonstrate the huge phenotypic and phylogenetic diversity of haloalkaliphiles in saline systems of southern Tunisia which represent a valuable source of new lineages and metabolites.

Variation in Quantitative Requirements for Na for Transport of Metabolizable Compounds by the Marine Bacteria Alteromonas haloplanktis 214 and Vibrio fischeri

The rates of uptake by Alteromonas haloplanktis of 19 metabolizable compounds and by V. fischeri of 16 of 17 metabolizable compounds were negligible in the absence of added alkali-metal cations but rapid in the presence of Na. Only d-glucose uptake by V. fischeri occurred at a reasonable rate in the absence of alkali-metal cations, although the rate was further increased by added Na, K, or Li. Quantitative requirements for Na for the uptake of 11 metabolites by A. haloplanktis and of 6 metabolites by V. fischeri and the characteristics of the Na response at constant osmotic pressure varied with each metabolite and were different from the Na effects on the energy sources used. Li stimulated transport of some metabolites in the presence of suboptimal Na concentrations and for a few replaced Na for transport but functioned less effectively. K had a small capacity to stimulate lysine transport. The rate of transport of most of the compounds increased to a maximum at 50 to 300 mM Na, depending on the metabolite, and then decreased as the Na concentration was further increased. For a few metabolites, the rate of transport continued to increase in a biphasic manner as the Na concentration was increased to 500 mM. Concentrations of choline chloride equimolar to inhibitory concentrations of NaCl were either not inhibitory or appreciably less inhibitory than those of NaCl. All metabolites examined accumulated inside the cells against a gradient of unchanged metabolite in the presence of Na, even though some were very rapidly metabolized. The transport of l-alanine, succinate, and d-galactose into A. haloplanktis and of l-alanine and succinate into V. fischeri was inhibited essentially completely by the uncoupler 3,5,3',4'-tetrachlorosalicylanilide. Glucose uptake by V. fischeri was inhibited partially by 3,5,3',4'-tetrachlorosalicylanilide and also by arsenate and iodoacetate.

Isolation and characterisation of bacteria from the haloalkaline Lake Elmenteita, Kenya

Culture-independent studies show that soda lake environments harbour diverse groups of bacteria and archaea. In this study different enrichment and isolation media were used in an attempt to isolate novel groups of bacteria from Lake Elmenteita. Different media were prepared using filter-sterilised water from the lake. The isolates recovered were purified on tryptic soy agar supplemented with 1% sodium carbonate and 4% sodium chloride. Phylogenetic analysis of 181 partial 16S rRNA gene sequences with excellent quality showed that the majority of the isolates were affiliated to the class Gammaproteobacteria and to the genus Bacillus. Isolates from the genus Halomonas and Bacillus constituted 37 and 31% of the total sequenced isolates, respectively. Other groups recovered were related to Marinospirillum, Idiomarina, Vibrio, Enterococcus, Alkalimonas, Alkalibacterium, Amphibacillus, Marinilactibacillus and the actinobacteria Nocardiopsis and Streptomyces. Fifty-one different genera were represented with 31 and 15 cultures scoring with their nearest neighbour similarities below 98 and 97%, respectively. Some novel taxa were identified which had not been isolated previously from the soda environment. The results show that the use of different media with varying compositions can help retrieve novel bacterial diversity from the soda lake environment.

Alkalitolerance: a biological function for a multidrug transporter in pH homeostasis

MdfA is an Escherichia coli multidrug-resistance transporter. Cells expressing MdfA from a multicopy plasmid exhibit multidrug resistance against a diverse group of toxic compounds. In this article, we show that, in addition to its role in multidrug resistance, MdfA confers extreme alkaline pH resistance and allows the growth of transformed cells under conditions that are close to those used normally by alkaliphiles (up to pH 10) by maintaining a physiological internal pH. MdfA-deleted E. coli cells are sensitive even to mild alkaline conditions, and the wild-type phenotype is restored fully by MdfA expressed from a plasmid. This activity of MdfA requires Na(+) or K(+). Fluorescence studies with inverted membrane vesicles demonstrate that MdfA catalyzes Na(+)- or K(+)-dependent proton transport, and experiments with reconstituted proteoliposomes confirm that MdfA is solely responsible for this phenomenon. Studies with multidrug resistance-defective MdfA mutants and competitive transport assays suggest that these activities of MdfA are related. Together, the results demonstrate that a single protein has an unprecedented capacity to turn E. coli from an obligatory neutrophile into an alkalitolerant bacterium, and they suggest a previously uncharacterized physiological role for MdfA in pH homeostasis.

Microbial alkaline proteases: from a bioindustrial viewpoint

Alkaline proteases are of considerable interest in view of their activity and stability at alkaline pH. This review describes the proteases that can resist extreme alkaline environments produced by a wide range of alkalophilic microorganisms. Different isolation methods are discussed which enable the screening and selection of promising organisms for industrial production. Further, strain improvement using mutagenesis and/or recombinant DNA technology can be applied to augment the efficiency of the producer strain to a commercial status. The various nutritional and environmental parameters affecting the production of alkaline proteases are delineated. The purification and properties of these proteases is discussed, and the use of alkaline proteases in diverse industrial applications is highlighted.

Resistance to freezing and frozen storage of Streptococcus thermophilus is related to membrane fatty acid composition

The resistance to freezing and frozen storage of Streptococcus thermophilus was related to the fatty acid composition of the cell membrane. The effects of four experimental factors were investigated on the fatty acid concentrations and on the recovery of acidification activity of S. thermophilus stored at -20 degrees C by using a complete experimental design: incorporating oleic acid in the culture medium, fermentation pH, addition of glycerol as cryoprotective agent and duration of storage. The acidification activity decreased during the freezing and the frozen storage of S. thermophilus. The storage time slightly enhanced the unsaturated fatty acid concentrations. The addition of glycerol did not modify the fatty acid composition but increased the resistance to frozen storage. The addition of oleic acid and the decrease of the fermentation pH enhanced the ratio unsaturated:saturated fatty acids and improved the recovery of the acidification activity. These results indicate that the resistance to frozen storage was closely related to the membrane fatty acid composition. We interpreted this as an adaptation of S. thermophilus to the addition of oleic acid and the unfavorable growth conditions that corresponded to a low fermentation pH.

Physiological response ofPectinatus frisingensis,a beer spoilage bacterium,to mild heat treatments

Genus Pectinatus is strictly anaerobic bacteria described as a new beer spoilage flora. The physiological response of Pectinatus frisingensis to increasing heat treatments has been studied. Cell death occurred at temperatures higher than 50°C and increased with time. During heat treatment at 50°C, a potassium efflux of more than 50% of the internal potassium was measured at pH 6.2 in starving bacteria, whereas a small transient potassium efflux was measured with a similar 50°C treatment in energized cell suspensions. At beer pH values (pH 4.0), potassium content of P. frisingensis cells was not changed by a moderate heat treatment. Internal pH values of cells were only slightly (0.1 pH unit) decreased upon heat treatments. In contrast, membrane potential value was lowered by a heat treatment at pH 6.2 in deenergized cells, while only a transient decrease of delta was measured with glucose in the medium. A moderate heat treatment at 50°C had no effect on the membrane potential value at pH 4.0, even after 1 h of treatment. In addition, compared with a high level of adenylate energy charge (AEC) measured in energized cell suspensions, an AEC of 0.7 was routinely measured in starving cell suspensions. Moderate heat treatments at pH 4.0 lowered the AEC of cells to 0.6. The physiological response of P. frisingensis to mild heat treatments demonstrated a significant ability of the cell to maintain internal homeostasis at pH conditions encountered in beer.Key words: Pectinatus, thermal death, beer spoilage, homeostasis.

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.

Buffering capacity and membrane H+ conductance of neutrophilic and alkalophilic gram-positive bacteria

Buffering capacity and membrane H+ conductance were examined in three gram-positive bacteria, Staphylococcus aureus, Bacillus subtilis, and Bacillus alcalophilus. An acid pulse technique was used to measure both parameters. The buffering capacity and membrane H+ conductance of B. alcalophilus are influenced by the pH of the medium and the culture conditions. Suspensions of B. alcalophilus cells from both H. A. medium and L-malate medium cultures grown at pH 10.5 exhibited higher values for these parameters than cells grown at pH 8.5. B. alcalophilus grown aerobically had a lower buffering capacity and a lower membrane conductance for protons than the neutrophilic bacteria S. aureus and B. subtilis. Fermenting cells exhibited significantly higher values for both variables than respiring cells.

Lateral diffusion of the total polar lipids from Thermoplasma acidophilum in multilamellar liposomes

31P NMR lineshapes of multilamellar liposomes composed mostly of a bilayer-spanning tetraether lipid are consistent with rapid axially symmetric motion about the bilayer normal. The residual chemical shift anisotropy of 36 ppm is comparable to that seen for diacylphosphatidylglycerol systems and suggests comparable headgroup motion. The lateral diffusion rates for Thermoplasma acidophilum total polar lipids in mutilamellar liposomes was measured by two dimensional exchange NMR as a function of temperature. At 55 degrees C, near the growth temperature, the rate of lateral diffusion, DL, is comparable to that of diester phospholipids in the Lalpha liquid crystalline phase, having a value of 2 x 10(-8) cm2/s. DL decreases with temperature reaching a value of 8-6 x 10(-9) cm2/s at 30 degrees C. The activation energy Ea for lateral diffusion is estimated to be 10 kcal/mol (approximately 42 kJ/mol). The lateral diffusion rates indicate that the tetraether liposomes have a membrane viscosity at 30 degrees C which is considerably higher than that of diester phospholipids in the liquid crystalline phase.

Acidostable and acidophilic proteins: the example of the alpha-amylase from Alicyclobacillus acidocaldarius

Acidophilic microorganisms grow optimally at pH values between 1-4. They have adapted to the acid condition by maintaining their cytoplasmic pH at a value close to neutrality. Hence, only those (macro)-molecules, which face the acid medium, have had to adapt to this extreme condition. Literature data show that several exoproteins from thermoacidophilic prokaryotes are characterized by a low charge density. It is proposed that this property contributes to the stability of these proteins both below and above the pKa-values of their glutamate and aspartate residues. As an example of an acidophilic protein, the alpha-amylase from the Gram-positive Alicyclobacillus acidocaldarius ATCC27009 was studied. The enzyme is thermoacidophilic, with optima of temperature and pH of 75 degrees C and pH 3, respectively. The nucleotide sequence of the cloned gene (8) indicates that the alpha-amylase belongs to a large family of starch-degrading enzymes with a characteristic catalytic (beta alpha)8-domain. Three essential and probably catalytic acidic residues have been conserved, suggesting that the acidophilic alpha-amylase degrades starch with essentially the same mechanism as do its neutrophilic relatives. Still, the acidophilic protein contains three exchanges in residues uniformally or almost uniformally conserved among all members of the enzyme family. In order to test whether these exchanges contribute to the acidic pH optimum, the alpha-amylase gene was expressed in Escherichia coli. Sonication of the enzyme-producing cells released alpha-amylase activity associated with a 140 kDa protein. The optima of temperature and pH for the protein produced in E. coli were similar to those of the native enzyme. Experiments are underway in which it is tested which residues contribute to the acid pH optimum of the alpha-amylase.

Picrophilus gen. nov., fam. nov.: a novel aerobic, heterotrophic, thermoacidophilic genus and family comprising archaea capable of growth around pH 0

Two species belonging to a novel genus of archaea, designated Picrophilus oshimae and Picrophilus torridus, have been isolated from two different solfataric locations in northern Japan. One habitat harboring both organisms was a dry, extremely acidic soil (pH < 0.5) that was heated by solfataric gases to about 55 degrees C. In the laboratory both species grew heterotrophically on yeast extract and poorly on tryptone under aerobic conditions at temperatures between 45 and 65 degrees C; they grew optimally at 60 degrees C. The pH optimum was 0.7, but growth occurred even around pH 0. Under optimal conditions, the generation time was about 6 h, yielding densities of up to 10(10) cells per ml. The cells were surrounded by a highly filigreed regular tetragonal S-layer, and the core lipids of the membrane were mainly bis-phytanyltetraethers. The 16S rRNA sequences of the two species were about 3% different. The complete 16S rRNA sequence of P. oshimae was 9.3% different from that of the closest relative, Thermoplasma acidophilum. The morphology and physiological properties of the two species characterize Picrophilus as a novel genus that is a member of a novel family within the order Thermoplasmales.

The internal pH of the forespore compartment of Bacillus megaterium decreases by about 1 pH unit during sporulation

Previous work has shown that the internal pH of dormant spores of Bacillus species is more than 1 pH U below that of growing cells but rises to that of growing cells in the first minutes of spore germination. In the present work the internal pH of the whole Bacillus megaterium sporangium was measured by the distribution of the weak base methylamine and was found to decrease by approximately 0.4 during sporulation. By using fluorescence ratio image analysis with a fluorescein derivative, 2',7'-bis(2-carboxyethyl)-5 (and -6)-carboxyfluorescein (BCECF), whose fluorescence is pH sensitive, the internal pH of the mother cell was found to remain constant during sporulation at a value of 8.1, similar to that in the vegetative cell. Whereas the internal pH of the forespore was initially approximately 8.1, this value fell to approximately 7.0 approximately 90 min before synthesis of dipicolinic acid and well before accumulation of the depot of 3-phosphoglyceric acid. The pH in the forespore compartment was brought to that of the mother cell by suspending sporulating cells in a pH 8 potassium phosphate buffer plus the ionophore nigericin to clamp the internal pH of the cells to that of the external medium. We suggest that at a minimum, acidification of the forespore may regulate the activity of phosphoglycerate mutase, which is the enzyme known to be regulated to allow 3-phosphoglyceric acid accumulation during sporulation.

Biology, ecology, and biotechnological applications of anaerobic bacteria adapted to environmental stresses in temperature, pH, salinity, or substrates

Anaerobic bacteria include diverse species that can grow at environmental extremes of temperature, pH, salinity, substrate toxicity, or available free energy. The first evolved archaebacterial and eubacterial species appear to have been anaerobes adapted to high temperatures. Thermoanaerobes and their stable enzymes have served as model systems for basic and applied studies of microbial cellulose and starch degradation, methanogenesis, ethanologenesis, acetogenesis, autotrophic CO2 fixation, saccharidases, hydrogenases, and alcohol dehydrogenases. Anaerobes, unlike aerobes, appear to have evolved more energy-conserving mechanisms for physiological adaptation to environmental stresses such as novel enzyme activities and stabilities and novel membrane lipid compositions and functions. Anaerobic syntrophs do not have similar aerobic bacterial counterparts. The metabolic end products of syntrophs are potent thermodynamic inhibitors of energy conservation mechanisms, and they require coordinated consumption by a second partner organism for species growth. Anaerobes adapted to environmental stresses and their enzymes have biotechnological applications in organic waste treatment systems and chemical and fuel production systems based on biomass-derived substrates or syngas. These kinds of anaerobes have only recently been examined by biologists, and considerably more study is required before they are fully appreciated by science and technology.

Studies of the Physiological and Genetic Basis of Acid Tolerance in Rhizobium leguminosarum biovar trifolii

Acid-tolerant Rhizobium leguminosarum biovar trifolii ANU1173 was able to grow on laboratory media at a pH as low as 4.5. Transposon Tn 5 mutagenesis was used to isolate mutants of strain ANU1173, which were unable to grow on media at a pH of less than 4.8. The acid-tolerant strain ANU1173 maintained a near-neutral intracellular pH when the external pH was as low as 4.5. In contrast, the acid-sensitive mutants AS25 and AS28 derived from ANU1173 had an acidic intracellular pH when the external pH was less than 5.5. The acid-sensitive R. leguminosarum biovar trifolii ANU794, which was comparatively more sensitive to low pH than mutants AS25 and AS28, showed a more acidic internal pH than the two mutants when the three strains were exposed to medium buffered at a pH of less than 5.5. The two acid-sensitive mutants had an increased membrane permeability to protons but did not change their proton extrusion activities. However, the acid-sensitive strain ANU794 exhibited both a higher membrane permeability to protons and a lower proton extrusion activity compared with the acid-tolerant strain ANU1173. DNA hybridization analysis showed that mutants AS25 and AS28 carried a single copy of Tn 5 located in 13.7-kb (AS25) and 10.0-kb (AS28) Eco RI DNA fragments. The wild-type DNA sequences spanning the mutation sites of mutants AS25 and AS28 were cloned from genomic DNA of strain ANU1173. Transfer of these wild-type DNA sequences into corresponding Tn 5 -induced acid-sensitive mutants, respectively, restored the mutants to their acid tolerance phenotypes. Mapping studies showed that the AS25 locus was mapped to a 5.6-kb Eco RI- Bam HI megaplasmid DNA fragment, whilst the AS28 locus was located in an 8.7-kb Bgl II chromosomal DNA fragment.

Influence of pH on bacterial gene expression

Bacteria respond to changes in internal and external pH by adjusting the activity and synthesis of proteins associated with many different processes, including proton translocation, amino acid degradation, adaptation to acidic or basic conditions and virulence. While, for many of these examples, the physiological and biological consequence of the pH-induced response is clear, the mechanism by which the transcription/translation machinery is signalled is not. These examples are discussed along with several others in which the function of the gene or protein remains a mystery.

Unusual pressure dependence of the lateral motion of pyrene-labeled phosphatidylcholine in bipolar lipid vesicles

The lateral mobility of a pyrene-labeled phosphatidylcholine probe in liposomes containing archaebacterial bipolar lipids has been studied isothermally as a function of pressure. The pressure-dependence of the probe mobility, R, is found to be slightly positive or zero in the temperature range of 17 - 48 degrees C. At temperatures > 48 degrees C, R becomes negative and decreases with temperature. The data indicate that lateral mobility only becomes appreciable at high temperatures. In addition, the R values obtained with other lipid membranes are much lower than that obtained with bipolar liposomes, implying that the membranes of archaebacterial liposomes are laterally immobile, as compared to other lipid membranes.

The ATPase of Bacillus alcalophilus. Reconstitution of energy-transducing functions

The purified ATPase of Bacillus alcalophilus (F1F0) was reconstituted into proteoliposomes by gradual removal of the detergent Triton X-100 with Amberlite XAD-2. The reconstitution was apparently highly asymmetric with nearly 100% of the F1 portion of the ATPase becoming oriented to the outside. Similar to results obtained with the soluble enzyme, the membrane-bound ATPase required Mg2+ and methanol for maximum activity. With Ca2+ or Mg2+ without methanol, 25% and 1%, respectively, of the maximum activity were observed. The ATPase was unable to pump Na+ ions but catalyzed the translocation of protons into the reconstituted proteoliposomes. Optimum proton translocation required the presence of Mg2+, not Ca2+, as divalent metal ion. The proton pump was inhibited by dicyclohexylcarbodiimide, venturicidin and NaN3. On incubation of the reconstituted ATPase with [14C]dicyclohexylcarbodiimide, subunit c of the enzyme complex became specifically labeled. The proteoliposomes catalyzed the Mg2(+)-dependent incorporation of [32P]phosphate into ATP by ATP/[32P]phosphate exchange. This exchange was little affected by monensin, but was completely abolished by the uncoupler carbonyl cyanide m-chlorophenylhydrazone. Protons and not Na+ are thus the coupling ions of the ATPase of B. alcalophilus.

Chloride transport pathways and their bioenergetic implications in the obligate acidophile Bacillus coagulans

The protonophore-mediated collapse of the large delta pH that acidophiles maintain across their cytoplasmic membranes was augmented by the presence of Cl-, and Cl- influx into the cells occurred evidently in response to the protonophore-induced increase in the inside-positive membrane potential (+ delta psi). In respiring cells, the addition of Cl- but not SO4(2-) salts caused a rapid and precipitous decrease in the + delta psi. A Nernstian relationship between the imposed transmembrane K+ gradient and the valinomycin-induced K+ diffusion potentials was observed when everted membrane vesicles were loaded with K2SO4 or KH2PO4 but not when loaded with KCl or KNO3. Thus, electrogenic Cl- transport occurred in Bacillus coagulans. In addition, a nonelectrogenic temperature-sensitive Cl- transport mechanism, with the net Cl- efflux coefficient (PCl-) ranging from 1.5 x 10(-4) to 6.1 x 10(-6) cm/s, accounted for the massive Cl- efflux from Cl(-)-loaded cells. Thus, B. coagulans, despite its dependence on the + delta psi and therefore the need to exclude anions, apparently possesses specific mechanisms for Cl- permeation. Active cells of B. coagulans prevented Cl- accumulation from attaining an electrochemical equilibrium, maintaining a delta micro Cl- of ca. -63 mV. B. coagulans therefore also possesses an energy-dependent mechanism for Cl- exclusion from the cells.

Electron spin resonance measurements of the effect of ionophores on the transmembrane pH gradient of an acidophilic bacterium

The delta pH in ionophore-treated cells of an acidophile has been determined by electron spin resonance spectroscopy. The values obtained were comparable to those obtained using the more conventional techniques involving radiolabeled probes. No binding of the spin-labeled probe was observed as determined by two independent control experiments and by the characteristics of the probe signal. These results led us to conclude that the delta pH measured in protonophore/ionophore-treated cells is a result of a Donnan potential, which may be a physical property of all intact bacterial cells at low pH values.

The evolution of ecological tolerance in prokaryotes

The ecological ranges of Archaeobacteria and Eubacteria are constrained by a requirement for liquid water and the physico-chemical stability limits of biomolecules, but within this broad envelope, prokaryotes have evolved adaptations that permit them to tolerate a remarkable spectrum of habitats. Laboratory experiments indicate that prokaryotes can adapt rapidly to novel environmental conditions, yet geological studies suggest early diversification and long-term stasis within the prokaryotic kingdoms. These apparently contradictory perspectives can be reconciled by understanding that, in general, rates and patterns of prokaryotic evolution reflect the developmental history of the Earth's surface environments. Our understanding of modern microbial ecology provides a lens through which our accumulating knowledge of physiology, molecular phylogeny and the Earth's history can be integrated and focussed on the phenomenon of prokaryotic evolution.

A deficiency in cyclic AMP results in pH-sensitive growth of Escherichia coli K-12

Mutants of Escherichia coli K-12 deficient in adenyl cyclase (cya) and catabolite activator protein (crp) have been shown to grow more slowly than their parent strains in glucose-minimal medium. Their growth rate decreased markedly with increasing pH between 6 and 7.8. We have shown that this pH sensitivity is a direct consequence of the cya mutation, because a mutation to pH resistance also restored ability to ferment a variety of sugars. The proton motive force-dependent uptake of proline and glutamate was also reduced and sensitive to pH in the cya mutant. The membrane-bound ATPase activity was normal. The rate of oxygen uptake by cells, although reduced, was pH insensitive. We suggest several explanations for this phenotype, including a possible defect in energy transduction.

Methanogenesis and ATP synthesis in methanogenic bacteria at low electrochemical proton potentials. An explanation for the apparent uncoupler insensitivity of ATP synthesis

The rate of methane formation from H2 and CO2, the intracellular ATP content and the electrochemical proton potential (delta mu H+) were determined in cell suspensions of Methanobacterium thermoautotrophicum, which were permeabilized for K+ with valinomycin (1.2 mumol/mg protein). In the absence of extracellular K+ the cells formed methane at a rate of 4 mumol min-1 (mg protein)-1, the intracellular ATP content was 20 nmol/mg protein and the delta mu H+ was 200 mV (inside negative). When K+ was added to the suspensions the measured delta mu H+ decreased to the value calculated from the [K+]in/[K+]out ratio. Using this method of delta mu H+ adjustment, it was found that lowering delta mu H+ from 200 mV ([K+]in/[K+]out = 1000) to 100 mV ([K+]in/[K+]out = 40) had no effect on the rate of methane formation and on the intracellular ATP content. At delta mu H+ values below 100 mV ([K+]in/[K+]out less than 40) both the rate of methanogenesis and the ATP content decreased. Methanogenesis completely ceased and the ATP content was 2 nmol/mg when delta mu H+ was adjusted to values lower 50 mV ([K+]in/[K+]out less than 7). The data show that methanogenesis from H2 and CO2 and ATP synthesis in M. thermoautotrophicum are possible at relatively low electrochemical proton potentials. Similar results were obtained with Methanosarcina barkeri. Protonophoric uncouplers like 3,5,3',4'-tetrachlorosalicylanilide (TCS) or 3,5-di-tert-butyl-4-hydroxy-benzylidenemalononitrile (SF 6847) were found not to dissipate delta mu H+ below 100 mV in M. thermoautotrophicum even when used at high concentrations (400 nmol/mg protein). This finding explains the observed uncoupler insensitivity of methanogenesis and ATP synthesis in this organism.

The bioenergetics of alkalophilic bacilli

A summary, cum speculation, of the major bioenergetic characteristics of alkalophilic bacilli is presented in Figure 5. Further progress will depend heavily on the purification and characterization of the relevant proteins that catalyze the ion fluxes and on the development of much more potent genetic approaches to the outstanding issues of this interesting group of bacteria.

A variable stoichiometry model for pH homeostasis in bacteria

The composition of the proton-motive force of a hypothetical bacterial cell of wide pH tolerance is analyzed according to a model whereby the electron transport chain and various proton-linked sodium and potassium ion transporting modes are responsible for the development of the membrane potential and the chemical potentials of the three cations. Simultaneous use of two or more modes employing the same metal cation, but at a different stoichiometric ratio with respect to protons, produces nonintegral stoichiometry; the modes could represent either different devices or different states of a single device. Cycling of the cation, driven by proton-motive force, results. The relative conductances of the various modes are postulated to be pH-dependent. The pattern of potentials that results is qualitatively in accord with current knowledge and may reflect the mechanism of pH homeostasis in bacteria. The membrane potential is outwardly directed (positive inside) at extremely acid pH, becoming inwardly directed as the pH increases; the pH gradient across the membrane is large and inwardly directed (alkaline inside) at acid pH, becoming smaller and eventually inverting at alkaline pH values; the transmembrane potassium gradient is outwardly directed (high concentration inside) at all pH values; the transmembrane sodium gradient is inwardly directed at all pH values, following the pH gradient from acid through neutral pH, but then diverging at alkaline pH.

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

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Induction of SOS functions by alkaline intracellular pH in Escherichia coli

Alkalinization of intracellular pH (pHi) causes an increase in UV resistance in wild-type and pH-sensitive mutant (DZ3) cells of Escherichia coli. Utilizing cells transformed with a plasmid (pA7) which bears the uvrA promoter fused to galK galactokinase structural gene, it was shown that alkaline pHi leads to an increase in the specific activity of galactokinase. This effect was not displayed in a mutant bearing a recA-insensitive lexA gene, nor in cells harboring a plasmid (pA8) in which the galK is fused to a lexA-insensitive uvrA promoter. Hence, the effects of pHi on cells functions may involve the lexA product of the SOS system.

Isolation and characterization of new facultatively alkalophilic strains of Bacillus species

Four facultatively alkalophilic isolates were purified from enrichment cultures initiated with lime-treated garden soil. Four isolates, OF1, OF3, OF4, and OF6, were obligately aerobic, spore-forming, gram-positive, motile rods which were capable of growth at both pH 7.5 and pH 10.5. Strains OF1 and OF6 grew best at the lower pH value; and whereas growth of these strains at pH 10.5 was completely dependent on added Na+, growth at pH 7.5 was only partially dependent on added Na+. Strains OF3 and OF4 grew better at pH 10.5 than at pH 7.5, with strain OF3 growing modestly over its entire pH range, while OF4 grew well. Growth of OF3 and OF4 was completely dependent on added Na+ at both pH 7.5 and pH 10.5. DNA-DNA hybridization studies indicated that OF1 and OF6 are closely related strains but are not related to the other isolates, Bacillus subtilis, or two previously studied obligately alkalophilic bacilli. OF3 was unrelated to any of the other organisms examined in the study, whereas OF4 showed complete homology with obligately alkalophilic Bacillus firmus RAB. All four isolates maintained a cytoplasmic pH that was considerably lower than the external pH when the latter was 10.5. Although substantial transmembrane electrical potentials were observed, the total electrochemical proton gradient (delta mu H+) was low at pH 10.5 in all the strains. By contrast, delta mu H+ was substantial at pH 7.5 and at that pH was composed entirely of an electrical potential. These results are in contrast to previous findings that obligately alkalophilic bacilli generate only small electrical potentials at near neutral pH. All the isolates exhibited substantial rates of respiration as measured by oxygen consumption. Neither respiration nor NADH oxidation by everted membrane vesicles was significantly stimulated by Na+. Analyses of reduced versus oxidized difference spectra of membranes from OF4 showed that the total membrane cytochrome content was considerably higher in cells grown at pH 10.5 than at pH 7.5, with the levels of c- and a-type cytochromes exhibiting the largest pH-dependent differences. Initial examination of membrane protein profiles on gel electrophoresis also indicated a number of changes in pattern in each isolate, depending on the growth pH.

Bioenergetics of alkalophilic bacteria

The central problem for organisms which grow optimally, and in some cases obligately, at pH values of 10 to 11, is the maintenance of a relatively acidified cytoplasm. A key component of the pH homeostatic mechanism is an electrogenic Na+/H+ antiporter which--by virtue of kinetic properties and/or its concentration in the membrane--catalyzes net proton uptake while the organisms extrude protons during respiration. The antiporter is also capable of maintaining a constant pHin during profound elevations in pHout as long as Na+ entry is facilitated by the presence of solutes which are taken up with Na+. Secondary to the problem of acidifying the interior is the adverse effect of the large pH gradient, acid in, on the total pmf of alkalophile cells. For the purposes of solute uptake and motility, the organisms appear to largely bypass the problem of a low pmf by utilizing a sodium motive force for energization. However, ATP synthesis appears not to resolve the energetics problem by using Na+ or by incorporating the proton-translocating ATPase into intracellular organelles. The current data suggest that effective proton pumping carried out by the alkalophile respiratory chain at high pH may deliver at least some portion of the protons to the proton-utilizing catalysts, i.e., the F1F0-ATPase and the Na+/H+ antiporter, by some localized pathway.

Mechanism of delta pH maintenance in active and inactive cells of an obligately acidophilic bacterium

The acidophilic bacterium PW2 possessed a delta pH of ca. 1.9 and a delta psi of 0 mV, corresponding to a proton motive force (delta p) of--114 mV. Protonophore-treated cells possessed little delta p but a delta pH of ca. 1.5, as measured by salicylic acid distribution or pH measurement of cell lysates. Starving PW2 cells continued to possess a delta pH of ca. 1.7, but exhibited converse changes in delta psi and delta p, with the former rising to +80 to +100 mV and the latter dropping essentially to 0; progressive loss of respiration, cellular ATP, and culture viability accompanied these changes. Thus, the protonophore-treated or starving PW2 cells attained an H+ electrochemical equilibrium. Net H+ influx resulting from declining respiration probably accounted for the increased delta psi in these cells; indeed, when respiration was progressively inhibited in active cells, there was increasing transient H+ influx and a proportional increase in delta psi. This transient H+ influx was sufficient to lethally acidify the cytoplasm, but for a buffering capacity of 85 nmol of H+/mg of protein per pH unit. Thus, the linkage of the transient H+ influx with the rise in the delta psi and the cytoplasmic buffering capacity play central roles in acidophilism, and it is conceivable that the same impermeant cellular macromolecule(s) accounts for both. If so, the delta psi would be a Donnan potential that in active cells is offset by energy-dependent H+ extrusion.

Influence of Oxygen and pH on Methanethiol Production from l -Methionine by Brevibacterium linens CNRZ 918

The effects of dissolved oxygen concentration and pH on the growth of Brevibacterium linens CNRZ 918 and its production of methanethiol from l -methionine were investigated. Optimal specific methanethiol production was obtained at 25% saturation of dissolved oxygen and at a pH between 8 and 9, whereas optimal cell growth occurred at 50% oxygen saturation and when the pH was maintained constantly at 7. Methanethiol production by nonproliferating bacteria required the presence of l -methionine (7 mM) in the culture medium. This was probably due to the induction of enzyme systems involved in the process. The intracellular concentration of l -methionine seemed to play a key role in this process. B. linens CNRZ 918 tolerated alkaline pHs with a maximal growth pH of approximately 9. Its orange pigmentation seemed to depend on the presence of l -methionine in the culture medium and on the concentration of dissolved oxygen.

Alkalophilic Bacillus firmus RAB generates variants which can grow at lower Na+ concentrations than the parental strain

Obligately alkalophilic Bacillus firmus RAB cannot grow well on media containing less than 5 mM Na+. However, variant strains can be isolated on plates containing 2 to 3 mM Na+. These variants are observed only rarely in cultures that are plated before being subjected to repeated transfers in liquid medium. Cultures which have been transferred several times produce variants at an apparent frequency of 2 X 10(-4). Most of these variants are unstable, generating parental types at the high frequency of 10%; however, stable variants can be isolated. These strains grow better than the parental strain at very high pH values in the presence of 5 mM Na+ and have enhanced activity of the Na+ -H+ antiporter that has been implicated in pH homeostasis. By contrast, Na+ -coupled solute uptake is indistinguishable from that of the parental strain, and no obvious changes in the respiratory chain components are apparent in reduced versus oxidized difference spectra. The membranes of the variants show a marked enhancement, on sodium dodecyl sulfate-polyacrylamide gradient electrophoresis, in one polypeptide band with a molecular weight in the range of 90,000. The findings are discussed from the point of view of genetic mechanisms that might confer adaptability to even more extreme environments than usual and in view of earlier models relating the Na+ -translocating activities of the alkalophiles.