A microcalorimetric method for studying the biological effects of La(3+) on Escherichia coli

Effects of Surface Charges on the Bactericide Activity of CdTe/ZnS Quantum Dots: A Cell Membrane Disruption Perspective

The inhibitory effects of CdTe/ZnS quantum dots (QDs) modified with 3-mercaptopropionic acid (negatively charged) or cysteamine (positively charged) on the metabolic activity of Escherichia coli were investigated using biological microcalorimetry. Results show that the inhibitory ratio of positive QDs is higher than that of negative QDs. Transmission electron microscopy images indicate that QDs are prone to be adsorbed on the surface of E. coli. This condition disturbs the membrane structure and function of E. coli. Fluorescence anisotropy results demonstrate that positive QDs show a significant increase in the membrane fluidity of E. coli and dipalmitoylphosphatidylcholine (DPPC) model membrane. Furthermore, fluorescence anisotropy values of DPPC membrane in the gel phase decreased upon the addition of positive QDs. By contrast, anisotropy values in the liquid-crystalline phase are almost constant. The change in membrane fluidity is associated with the increased permeability of the membrane. Finally, the kinetics of dye leakage from liposomes demonstrate that the surface charge of QDs is crucial to the interaction between QDs and membrane.

Quantification of vital adherent Streptococcus sanguinis cells on protein-coated titanium after disinfectant treatment

The quantification of vital adherent bacteria is challenging, especially when efficacy of antimicrobial agents is to be evaluated. In this study three different methods were compared in order to quantify vital adherent Streptococcus sanguinis cells after exposure to disinfectants. An anaerobic flow chamber model accomplished initial adhesion of S. sanguinis on protein-coated titanium. Effects of chlorhexidine, Betadine®, Octenidol®, and ProntOral® were assessed by quantifying vital cells using Live/Dead BacLight™, conventional culturing and isothermal microcalorimetry (IMC). Results were analysed by Kruskal-Wallis one-way analysis of variance. Live/dead staining revealed highest vital cell counts (P < 0.05) and demonstrated dose-dependent effect for all disinfectants. Microcalorimetry showed time-delayed heat flow peaks that were proportioned to the remaining number of viable cells. Over 48 h there was no difference in total heat between treated and untreated samples (P > 0.05), indicating equivalent numbers of bacteria were created and disinfectants delayed growth but did not eliminate it. In conclusion, contrary to culturing, live/dead staining enables detection of cells that may be viable but non-cultivable. Microcalorimetry allows unique evaluation of relative disinfectant effects by quantifying differences in time delay of regrowth of remaining vital cells.

Use of microcalorimetry to determine the costs and benefits to Pseudomonas putida strain KT2440 of harboring cadmium efflux genes

A novel microcalorimetric approach was used to analyze the responses of a metal-tolerant soil bacterium (Pseudomonas putida strain KT2440) to metal resistance gene deletions in cadmium-amended media. As hypothesized, under cadmium stress, the wild-type strain benefited from the resistance genes by entering the exponential growth phase earlier than two knockout strains. In the absence of cadmium, strain KT1, carrying a deletion in the main component (czcA1) of a Cd/Zn chemiosmotic efflux transporter (CzcCBA1), grew more efficiently than the wild type and released ∼700 kJ (per mole of biomass carbon) less heat than the wild-type strain, showing the energetic cost of maintaining CzcCBA1 in the absence of cadmium. A second mutant strain (KT4) carrying a different gene deletion, ΔcadA2, which encodes the main Cd/Pb efflux transporter (a P-type ATPase), did not survive beyond moderate cadmium concentrations and exhibited a decreased growth yield in the absence of cadmium. Therefore, CadA2 plays an essential role in cadmium resistance and perhaps serves an additional function. The results of this study provide direct evidence that heavy metal cation efflux mechanisms facilitate shorter lag phases in the presence of metals and that the maintenance and expression of tolerance genes carry quantifiable energetic costs and benefits.

Environmental toxicity testing of contaminated soil based on microcalorimetry

Contaminated site assessment and monitoring requires efficient risk-management tools including innovative environmental toxicity tests. The first application of microcalorimetry for toxicity testing draw the attention to a possible new tool to increase sensitivity, to eliminate matrix effect and to study effect-mechanism. A Thermal Activity Monitor (TAM) microcalorimeter was used for measuring the heat production of various test organisms when getting in contact with sterile toxic soils. Well known bacterial (Azomonas agilis), animal (Folsomia candida) and plant test organisms (Sinapis alba) were tested for heat production. The heat response of selected testorganisms was measured in case of metal (Cu and Zn) and organic pollutant (Diesel oil, DBNPA and PCP) contaminated soils. In addition to the quantitative determination of the heat production, the mechanism of the toxic effect can be characterized from the shape of the power-time curve (slope of the curve, height and time of the maximum). In certain concentration ranges the higher the pollutant concentration of the soil the lower the maximum of the time-heat curve. At low pollutant concentrations an increased heat production was measured in case of A. agile and 20 and 200 mg Zn kg(-1) soil. The microcalorimetric testing was more sensitive in all cases than the traditional test methods. Our results showed that the microcalorimetric test method offers a new and sensitive option in environmental toxicology, both for research and routine testing.

Bacterial melanin interacts with double-stranded DNA with high affinity and may inhibit cell metabolism in vivo

Melanin has been found to interact with a number of molecules including metal ions, antibiotics and proteins. In this study, we showed how melanin from bacteria can interact with double-stranded DNA. Investigation using capillary electrophoresis, various spectroscopic techniques and circular dichroism found that melanin interacts with DNA by intercalating between the base pairs of DNA. And this was further supported by simulating different forms of melanin docking to oligonucleotides. Transmission electron microscopy of recombinant Escherichia coli producing melanin suggested the interaction in vivo. Furthermore, we showed how the cytoplasmic localization of melanin may provide a novel function in inhibiting cellular metabolism using microcalorimetry. The implications of the interaction in prokaryotes and eukaryotes were discussed.

Isothermal microcalorimetry to investigate non specific interactions in biophysical chemistry

Isothermal titration microcalorimetry (ITC) is mostly used to investigate the thermodynamics of “specific” host-guest interactions in biology as well as in supramolecular chemistry. The aim of this review is to demonstrate that ITC can also provide useful information about non-specific interactions, like electrostatic or hydrophobic interactions. More attention will be given in the use of ITC to investigate polyelectrolyte-polyelectrolyte (in particular DNA-polycation), polyelectrolyte-protein as well as protein-lipid interactions. We will emphasize that in most cases these “non specific” interactions, as their definition will indicate, are favoured or even driven by an increase in the entropy of the system. The origin of this entropy increase will be discussed for some particular systems. We will also show that in many cases entropy-enthalpy compensation phenomena occur.

Investigation of the toxic effect of cadmium on Candida humicola and Bacillus subtilis using a microcalorimetric method

In this study, the technique of microcalorimetry based on heat-output by aerobic bacterial respiration was explored to evaluate the toxic effect of cadmium on Candida humicola, Bacillus subtilis, singularly or in a mixture of both. Power-time curves of the growth metabolism of C. humicola and B. subtilis and the effect of Cd(2+) were studied using the TAM III (the third generation thermal activity monitor) multi-channel microcalorimetric system, isothermal mode, at 28 degrees C. The differences in shape of the power-time curves and the thermodynamic and kinetic characteristics of microorganisms growth were compared. The effect of cadmium added into microorganism would significantly reduce the life cycle and change the thermal effect of microbial metabolic process with different concentrations of Cd(2+). The experimental results revealed that at the same concentration, the sequence of inhibitory ratio (I) and maximum thermal power (P(max)) of the Cd(2+) was: mixed microorganisms>C. humicola>B. subtilis. The sequence of total thermal effect (Q(total)) and growth rate constant (k) is mixed microorganisms>B. subtilis>C. humicola. These results are important to further studies of the physiology and pharmacology of C. humicola and B. subtilis and may support the theory of restoring contaminated soil.

Characterization of the mechanism of the Staphylococcus aureus cell envelope by bacitracin and bacitracin-metal ions

Bacitracin is a metal-dependent dodecapeptide antipeptide produced by Bacillus species. Microcalorimetry was used to study the antimicrobial activity of bacitracin and bacitracin-metal ion complexation inhibited on Staphylococcus aureus at 37 degrees C. The affinity of metal ions binding to bacitracin was investigated by isothermal titration calorimetry and was as follows: Cu(II) >or= Ni(II) > Co(II) > Zn(II) >or= Mn(II). The metal ion binding affinity is not relative to the antimicrobial activity of bacitracin-metal complexation. Atomic force microscopic images revealed that the surface of S. aureus treated by bacitracin-Zn(II) was rather rough compared to that treated by bacitracin only. The central cell surface displayed small depressed grooves around the septal annulus at the onset of division. Bacitracin mainly inhibited the splitting system within the thick cross walls as seen by transmission electron microscopy (TEM). The inhibition mechanism of bacitracin may be relative to the assistance of Zn(II) coordination with the cell surface as seen by TEM. We can put forward that the activity of bacitracin only inhibited growth and division initially from the synthesis of the cell wall, especially the cell wall of the septal annulus. The divalent metal ions function to increase the adsorption of bacitracin onto the cell surface.

Microcalorimetric studies of the biological effects of Ho(III) on Halobacterium halobium R1

The biological effect of Ho3+ on Halobacterium halobium R1 growth was analyzed using the microcalorimetric method. Using the LKB-2277 Bioactivity Monitor with the ampoule method at 37 degrees C, the thermogenic curves of the growth of H. halobium R1 were obtained. Then, the maximum power (P (m)) and the growth rate constants (k) were determined, and the values of P (m) and k were linked to the concentration of Ho3+. In all, the addition of Ho3+ cause a decrease in the maximum heat production and growth rate constants. To confirm the results, the shapes of H. halobium R1 cell addition with Ho3+ using a transmission electron microscope (TEM) were observed. According to the thermogenic curves and TEM photos of H. halobium R1 under different conditions, it is clear that the metabolic mechanism of H. halobium R1 growth has been changed with the addition of Ho3+.

Microcalorimetric study on the effect of Ce3+ on Halobacterium halobium R1

A microcalorimeric technique was used to evaluate the influence of rare earths Ce3+ on Halobacterium halobium R1 growth. By means of TAM air Thermal Activity Monitor, the thermogenic curves of H. halobium R1 growth were obtained. To analyze the results, the growth rate constant k and IC50 were calculated, indicating that the values of k are linked to the concentration of Ce3+. The growth rate constant k of H. halobium R1 decreased gradually in the low concentration; thus, rare earths restrained the growth of H. halobium R1. On the contrary, as the concentration of Ce3+ became higher, the value of k for H. halobium R1 increased gradually, which showed Ce3+ stimulated the growth of H. halobium R1. When the concentration of rare earths became much higher, the value of k for H. halobium R1 also decreased, and the growth of H. halobium R1 was restrained totally in the end. By using transmission electron microscopy (TEM), it was observed that the transforming of H. halobium R1 in the different concentrations of Ce3+ confirmed the results derived from microcalorimetry. According to the thermogenic curves and TEM photos of H. halobium R1 under various conditions, it showed that there was some special effect about the interaction between rare earths and H. halobium R1 growth.

Microcalorimetric studies of the biological effect of holmium (III) on Halobacterium halobium R1 growth

The biological effect of Ho3+ on Halobacterium halobium R1 growth was analyzed by a microcalorimetric technique. By means of LKB-2277 Bioactivity Monitor, ampoule method at 37 degrees C, we obtained the thermogenic curves of H. halobium R1 growth. To analyze the results, the maximum power (Pm) and the growth rate constants (k) were determined, which show that values of Pm and k are linked to the concentration of Ho3+. In all, the addition of Ho3+ causes a decrease of the maximum heat production and growth rate constants. For comparison, we observed the shapes of H. halobium R1 cell by means of transmission electron microscope (TEM). According to the thermogenic curves and TEM photos of H. halobium R1 under different conditions, it is clear that metabolic mechanism of H. halobium R1 growth has been changed with the addition of Ho3+.

Adhesion ofStreptococcus sanguinis to glass surfaces measured by isothermal microcalorimetry (IMC)

Bacterial adhesion is the first step in the development of the oral biofilm, called dental plaque. Plaque is the cause of caries, periodontal diseases, and periimplantitis. Investigations of dental plaque, including bacterial adhesion, employ various in vivo and in vitro models using microscopic methods. Microcalorimetry offers another direct approach. The model organism Streptococcus sanguinis is one of the first colonizers adhering to the saliva-coated human tooth surfaces or dental materials within minutes after tooth cleaning. TAM III thermostats, equipped with microcalorimeters, were used for isothermal microcalorimetric (IMC) measurements of heat production as a function of time, expressed by power-time (p-t) curves. Continuous measurements of heat production of growing S. sanguinis cells showed their overall metabolic activity and were highly reproducible. For the adhesion experiments the bacteria were allowed to adhere to different amounts of glass beads. Growing S. sanguinis cells produced a characteristic p-t curve with a maximum of 500 microW at 4.5 h when reaching 10(9) cells ml(-1). The same number of stationary S. sanguinis cells, suspended in PBS produced only approximately 30 microW at 0.5 h due to adhesion. But the amount of heat increased with available glass surface area, indicating that a portion of the heat of adhesion was measured. Similar results were obtained with stationary S. sanguinis cells suspended in human saliva. This study shows that microcalorimetric evaluation of initial bacterial adhesion is indeed possible and may become a rapid, reproducible screening method to study adhesion of different bacteria to different dental materials or to modified surfaces.

Studies on the toxic effects of La(3+) to Tetrahymena thermophila by microcalorimetry

The toxic effects of La(3+) on Tetrahymena thermophila have been studied by microcalorimetry at 28 degrees C. The metabolic rate constant (r) and peak time were linked to the concentration of La(3+). The changes of metabolic rate constant indicated that low-concentration La(3+) (0-75 mg/L) had no significant effects on the metabolism of Tetrahymena cells but high-concentration La(3+) (100-175 mg/L) could inhibit their metabolism. From the results obtained by cell counting and fluorescence depolarization measurements, the inhibition of metabolism resulted from the decrease in cell number and the reduction in cell membrane fluidity. According to the results, it is clear that the metabolic mechanism of Tetrahymena cells has been changed with the addition of high-concentration La(3+). In addition, microcalorimetry of Tetrahymena could be a sensible, easy-to-use, and convenient method for monitoring the potential effects of rare earth elements on cells and the freshwater ecosystem.

Study on the toxic effect of lead(II) ion on Escherichia coli

The toxic effects of lead(II) have been studied in Escherichia coli cells. Using microcalorimetric analysis, it was shown that E. coli growth was inhibited in the presence of Pb2+ resulting from damage to the cell membrane and that Pb2+ takes part in the metabolism of cells. Treatment with lysozyme confirms damage to the cell's outer membrane. Similarities between the ionic radii and charge/radius ratio cause Pb(II) to replace Ca(II) at the binding sites of lipopolysacharides, leading to rupture of protecting areas on the cell's surface. Consequently, the protection and functionality of outer membrane is lost, thus becoming the basis for the biological effect of Pb2+ on E. coli.

Structural basis for the biological effects of Pr(III) ions: alteration of cell membrane permeability

The biological effects of rare-earth ions on the organism have been studied using Pr3+ as a probe ion and Escherichia coli cell as a target. Atomic force microscopy (AFM) observation of the surface of E. coli cells shows that the presence of Pr3+ substantially changes the structure of the outer membrane. By induced coupled plasma-mass spectrometry (ICP-MS), more Cu2+ was found in the cells grown in the presence of Pr3+, indicating changes of cell permeability. Using energy dispersive X-ray spectroscopy (EDX), Ca2+ is found on the outer surface of the original cell. It is proposed that Pr3+ can replace Ca2+ from the binding sites because of their close ionic radii and similar ligand speciality.

Calorimetric comparison of the interactions between salivary proteins and Streptococcus mutans with and without antigen I/II

Antigen I/II can be found on streptococcal cell surfaces and is involved in their interaction with salivary proteins. In this paper, we determine the adsorption enthalpies of salivary proteins to Streptococcus mutans LT11 and S. mutans IB03987 with and without antigen I/II, respectively, using isothermal titration calorimetry. In addition, protein adsorption to the cell surfaces was determined spectrophotometrically. S. mutans LT11 with antigen I/II, yielded a much higher, exothermic adsorption enthalpy at pH 6.8 (ranging from -2073 x 10(-9) to -31707 x 10(-9) microJ per bacterium) when mixed with saliva than did S. mutans IB03987 (-165 x 10(-9) to -1107 x 10(-9) microJ per bacterium) at all bacterial concentrations studied (5 x 10(9), 5 x 10(8), and 5 x 10(7) ml(-1)), largest effects per bacterium being observed for the lowest concentration. However, the enthalpy of salivary protein adsorption to S. mutans LT11 became smaller at pH 5.8. Adsorption isotherms for the S. mutans LT11 showed considerable protein adsorption at pH 6.8 (1.2 - 2.1 mg/m(2)), that decreased only slightly at pH 5.8 (1.1 - 1.6 mg/m(2)), with the largest amount adsorbed at the lowest bacterial concentration. This suggests that the protein(s) in the saliva with the strongest affinity for antigen I/II is (are) readily depleted from saliva. In conclusion, antigen I/II surface proteins on S. mutans play a determinant role in adsorption of salivary proteins through the creation of enthalpically favorable adsorption sites.

Effect of nisin on the growth ofStaphylococcus aureus determined by a microcalorimetric method

A novel microcalorimetric technique based on the bacterial heat output was applied to evaluate the biological effect of nisin on the growth of Staphylococcus aureus. The thermogenic curves of S. aureus in the presence of nisin were studied by an LKB-2277 Thermal Activity Monitor. The thermokinetic parameters, such as the growth rate constant (k), the generation times (G), the inhibitory ratio (I), and the half inhibitory concentration (IC50), for the growth of S. aureus at different nisin concentrations were determined. The relationship between the growth rate constant (k) and the concentration of nisin (c) is nearly linear, which can be modeled by the formula k = 0.03794 - 4.005 x 10(-4) x c, with a correlation coefficient of -0.9971. Based on this model, we obtained the critical inhibitory concentration of nisin on the growth of S. aureus at 94.73 IU/mL. We proposed that this microcalorimetric method could be a useful tool in monitoring the biological effect of nisin on microorganisms, and providing valuable information on the study of microorganism metabolisms.

Study on biological effect of La 3+ on Escherichia coli by atomic force microscopy

The biological effects of rare-earth metal ions on the organism have been studied using La3+ as a probe ion and Escherichia coli cell as a target organism. Atomic force microscopy (AFM) studies reveal that La3+ substantially changes the structure of the outer cell membrane responsible for the cell permeability. Significant damages of the outer cell membrane are observed using scanning electron microscopy (SEM) after the introduction of La3+. In result, the cell becomes easily attacked by lysozyme. Moreover, inductively coupled plasma-mass spectrometry (ICP-MS) measurements show considerable amount of Ca2+ and Mg2+ in the supernatant from the La3+ exposed cells. It is proposed that La3+ can replace Ca2+ from the binding sites because of their close ionic radii and similar ligand specificities. Lipopolysaccharide (LPS), which forms the outer membrane of Gram-negative bacteria, could not serve as the cellular envelope steadily after Ca2+ and Mg2+ released from their binding sites on the LPS patches.