Antibiotic susceptibility of Salmonella spp. at different pH values

We have examined the effects of acidic pH, in the range of those prevailing within phagosomes and lysosomes, on the growth and the susceptibility to different antibiotics of several strains of Salmonella spp. The minimal inhibitory concentration and the minimal bactericidal concentration of several beta-lactams were increased considerably during culture at pH 5.2. The extent of the increase was a function of: (1) the beta-lactam structure and, more particularly, the hydrophobicity of the side-chain of the molecule; and (2) the bacterial serotype. This phenotypic resistance at acid pH was not due to beta-lactamase activity or to a lower growth rate. In contrast, rifamycin SV was more active at acidic pH than at neutral pH and chloramphenicol, another highly hydrophobic drug, was equally efficacious at both pH values. Membrane lipopolysaccharide mutants, but not porin mutants, cultivated at an acidic pH were inhibited by lower concentrations of the beta-lactams. This suggests that the increased resistance to beta-lactams, and the increased susceptibility to rifamycin SV, at acidic pH, could have resulted from modified permeability of the outer membrane to antibiotics.     

Two threshold values of low pH block endocytosis at different stages.

The influence of low extracellular pH on endocytosis was studied in baby hamster kidney cells. When the extracellular medium was adjusted to pH 5.7, the intracellular pH decreased within 2 min to pH 6.2 and the endocytosis of horseradish peroxidase (HRP) in the fluid phase dropped to an undetectable level. With an external pH of 6.3, the internal pH dropped to pH 6.8 and HRP was internalized at a normal rate for 5 min but accumulation during longer incubation times did not occur. Morphologically, HRP was visualized in the lumen of a subpopulation of tubular and vesicular endosomes. These observations were confirmed by subcellular fractionation studies using free flow electrophoresis. Low extracellular pH also had an effect on the endocytosis of the membrane-spanning glycoprotein G of vesicular stomatitis virus which was implanted into the plasma membrane. The internalization of G-protein was quantitated by a surface fluoroimmunoassay. The endocytosis of G-protein was not affected when the external pH was dropped to 6.3, but was reduced at an external pH of 5.7. The intracellular ATP was not depleted and the reduction of endocytosis was reversible upon return to physiological pH. Clathrin coated pits were detected by electron microscopy at the plasma membrane of the low-pH-treated cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Microaerophilic metabolism of Pachysolen tannophilus at different pH values

Microaerophilic production of xylitol by Pachysolen tannophilus from detoxified hemicellulose hydrolyzate was optimal between pH values 6.0 to 7.5 when about 90% of xylose was utilized for xylitol production, the rest being fermented to ethanol. At pH values of 3.0 and 12.0, respiration became important, consuming up to 30% of available xylose. A graphic procedure suggests that histamine and cysteine are at the active site of xylose reductase in this yeast.     

Relationship between the flexibility and the motility of actin filaments: effects of pH

Both the sliding velocity of fluorescently labeled actin filament and its persistence length as an index of the bending flexibility of the filament were examined in the motility assay as varying the pH values of the solution for preparing actin filaments. When the pH value was varied from 5.0 to 9.0 in the solution in which actin filaments were formed from the constituent monomers, the motile performance of Mg²⁺ bound actin filaments (Mg-F-actin) was apparently suppressed compared to the case of Ca²⁺ bound ones (Ca-F-actin). The persistence length for Ca-F-actin gradually increased with the increase of the pH value while the similar length for Mg-F-actin remained rather independent of the value. The largest sliding velocity of the filament, on the other hand, obtained at the persistence length of roughly 6 μm for both cases of Mg-F-actin and Ca-F-actin.     

Comparative effectiveness of nisin and bacteriocin J46 at different pH values

E. HUOT, C. BARRENA-GONZALEZ AND H. PETITDEMANGE. 1996. A Comparative study of the inhibitory activity of nisin, the well-known lantibiotic produced by certain strains of Lactococcus lactis subsp. lactis , and of the bacteriocin produced by L. lactis subsp. cremoris J46, a strain previously isolated from fermented milk, was conducted. For both bacteriocins, the activity against L. lactis subsp. cremoris decreased with increasing pH. In addition, the bacteriocin preparations were more stable at 4 than at 20°C. The influence of the storage temperature was more crucial for nisin. Essentially the same activity was observed for bacteriocin J46 stored for 3 h at 4 or 20°C. More interesting was the observed stability of bacteriocin J46 at pH values between 5.8 and 6.8. For example, about 23% of nisin activity was lost at pH 6.4 whereas no loss of bacteriocin J46 activity was observed.     

Vesicular stomatitis virus-mediated cell fusion subsequent to virus adsorption at different pH values.

Vesicular stomatitis virus (VSV)-mediated cell fusion from without can be induced by transient exposure to low pH, subsequent to adsorption of VSV at neutral pH. To study the mechanism of VSV-induced cell fusion, we examined the effect of pH condition at virus adsorption on acid-inducible VSV-mediated cell fusion. Although the binding of VSV to BHK-21 cells was most efficient under acidic condition (pH 5.7-6.3), extensive cell fusion was not observed under this condition. A temporary exposure to low pH after binding at neutral pH also decreased fusion activity. However, return to neutral pH for 2 min just after the acid binding restored the fusion activity. These results indicate the requirement of neutral pH condition for VSV-mediated cell fusion prior to the acid stimulation which induces conformational change of the virus glycoprotein into a fusogenic form.     

The content of alpha-helix and beta-structure in proteins crystallized at different pH values

Using the data of X-ray diffraction analysis for 100 three-dimensional structures of 26 proteins uniformly distributed among three main classes of the alpha-helix-beta-structure classification and without potentially polyanion regions, 154 comparisons of the content of alpha-helix and beta-structure content were made for structures obtained at different pH values of the medium, being distributed in the whole among all these proteins in the range from 1.5 to 12.0. No significant influence of pH of the medium on the size and localization of alpha-helices and beta-strands was found. As a consequence, it is suggested for the protein structure in a crystal that the alpha-helical-beta-structural backbone of protein structures does not depend on pH of the medium, except when the whole protein or its part can become a polyion so that the electrostatic interactions would either hinder or favour the formation of regular structures, and the conformational properties of ionizable amino acids are independent of pH of the medium. It is unclear, whether these assumptions can be extended to the case of solution, because the data for the structures in solution have been obtained for one protein only. These results can be used in investigations of protein structure, in protein engineering, and in the creation of specialized data banks of protein structures.     

Aflatoxin is degraded at different temperatures and pH values by mycella of Aspergillus parasiticus

Summary Blended 9-day-old mycelia of Aspergillus parasiticus NRRL 2999 were tested for their ability to degrade aflatoxins B₁ and G₁ at 7,19,28,36, and 45°C. Rates for degradation of aflatoxin B₁ and G₁ were maximum at 28°C. Intermediate rates of aflatoxin degradation were observed at 19 and 36°C while little aflatoxin was degraded at 7 and 45°C. Five different pH values (2.0, 3.0, 4.0, 5.0, and 6.5) were also tested to determine the effect of pH on ability of blended 9-day-old mycelia of A. parasiticus NRRL 2999 to degrade aflatoxins. The ability of mycelia to degrade aflatoxin was pH-dependent. Of the pH values tested, greatest rates of aflatoxin B₁ and G₁ degradation occurred when pH was in the range of 5 to 6.5. Little aflatoxin was degraded at pH 4.0 and essentially no aflatoxin was degraded by mycelia at pH 2.0 or 3.0 although some aflatoxin was degraded by acid conditions only at pH values of 4 or less.     

Long-time molecular dynamics simulations of botulinum biotoxin type-A at different pH values and temperatures

Botulinum neurotoxins type A (BoNT/A) are highly potent toxins, but are also useful in the treatment of illnesses. We studied the properties of BoNT/A at various temperatures and pH values in order to understand its toxicity and structure variations. The pH values of the environment of BoNT/A are obtained by changing the protonation states of certain titratable residue groups. Our results show that certain parts of the protein are active at acidic pH environments or at high temperatures. The protein is more stable in neutral environments at normal human body temperature, whereas, at high temperature, the protein is more stable in acidic environments. Also, the three domains of the protein tend to have relative motion rather than within individual domains.     

Investigation of apomyoglobin stability depending on urea and temperature at two different pH values

Equilibrium unfolding of apomyoglobin by urea was investigated in the temperature range from 5 to 25 degrees C at two pH values. The thermodynamic parameters of the apomyoglobin native-unfolded state transition were determined. Conformational changes in the protein structure were monitored by tryptophan fluorescence and far UV circular dichroism. Apomyoglobin preserves its native conformation at pH 5.7 and 6.2 in the temperature range used. It was shown that the apomyoglobin stability and its unfolding cooperativity are substantially lower at 5 degrees C than at other temperatures. This fact should be taken in account at the investigation of apomyoglobin.     

Differential responses of two wetland graminoids to high ammonium at different pH values

Enhanced soil ammonium () concentrations in wetlands often lead to graminoid dominance, but species composition is highly variable. Although is readily taken up as a nutrient, several wetland species are known to be sensitive to high concentrations or even suffer toxicity, particularly at low soil pH. More knowledge about differential graminoid responses to high availability in relation to soil pH can help to better understand vegetation changes. The responses of two wetland graminoids, Juncus acutiflorus and Carex disticha, to high (2 mmol·l^?1) versus control (20 μmol·l^?1) concentrations were tested in a controlled hydroponic set up, at two pH values (4 and 6). A high concentration did not change total biomass for these species at either pH, but increased C allocation to shoots and increased P uptake, leading to K and Ca limitation, depending on pH treatment. More than 50% of N taken up by C. disticha was invested in N‐rich amino acids with decreasing C:N ratio, but only 10% for J. acutiflorus. Although both species appeared to be well adapted to high loadings in the short term, C. disticha showed higher classic detoxifying responses that are early warning indicators for decreased tolerance in the long term. In general, the efficient aboveground biomass allocation, P uptake and N detoxification explain the competitive strength of wetland graminoids at the expense of overall biodiversity at high loading. In addition, differential responses to enhanced affect interspecific competition among graminoids and lead to a shift in vegetation composition.     

Activity and adsorption of lipase from Nigella sativa seeds on Celite at different pH values

Lipase from Nigella sativa seeds was immobilized by adsorption on Celite 535 from phosphate buffer solutions varying pH values of 5.0–8.0 at 25?°C. Langmuir isotherms described the adsorption equilibria well for lipase adsorption at all pH range. The saturation capacity for adsorption of lipase increased from 14.5 to 24.3 mg g^?1 Celite as the adsorption pH was reduced from 8 to 5, but the adsorption equilibrium constant remained constant and was determined to be 1.92 × 10⁵ M^?1. The adsorbed enzymes showed different activity values depending on the pH of the adsorption medium. The immobilized enzymes prepared at pH 6 displayed the highest activity values.     

End product profiles of starch hydrolysis by bacterial alpha-amylases at different temperature and pH values

Summary The end product profile of starch hydrolysis by four bacterial alpha-amylases was found to be dependent on the source of the enzyme, and pH and temperature conditions of reaction.     

Influence of pH on phosphatidic acid multilayers. A rippled structure at high pH values.

The influence of pH on the structure of 1,2-(ditetradecyl)-phosphatidic acid was investigated by differential scanning calorimetry and freeze-fracture electron microscopy. At pH 13.5--14 (2.6 M K+), where phosphatidic acid has two negative charges, calorimetric scans show a small transition (pretransition) below the main phase transition temperature. Freeze-fracture studies of the same dispersions reveal regular band patterns (so-called ripples) in the plane of the bilayers, when the lipid is quenched from below the main phase transition temperature. This rippled structure is similar to the well-known rippled structure of phosphatidylcholines.