Growth Thermograms Research Articles

Calorimetric analysis of the effect of streptomycin, tetracycline and chloramphenicol on the growth of Escherichia coli.

The effects of streptomycin, tetracycline and chloramphenicol on the growth of Escherichia coli were studied quantitatively in a conduction-type batch calorimeter at pH 6.2 and 37°C. Change in the growth thermograms with increasing drug concentrations in the medium were analyzed with a kinetic model of non-competitive inhibition.The number of drug molecules needed to inactivate a unit viable cell, m, was estimated to be 1.2 + 0.1, 0.7 ±0.1 and 1.3 ±0.1 for streptomycin, tetracycline and chloramphenicol, respectively. With the assumption that the drug binding sites are all identical, the microscopic dissociation constant per binding site, K, for the drugs was found to be 0.19, 0.43 and 0.94μmoldm-3 for streptomycin, tetracycline and chloramphenicol, respectively. With these m and K{ values, drug potency curves were drawn for the three drugs.

Calorimetric study of Escherichia coli growth on bouillon medium.

Heat evolution during the growth of Escherichia coli in a stationary culture on bouillon medium was continuously monitored with a conduction-type batch calorimeter at different pHs and temperatures. The growth thermograms were found to be reproducible within percent errors of ±2.1%, ±0.8% and ±1.5% for the peak time of a thermogram, the peak height and the total heat evolution, respectively. The mean heat evolution for the formation of a unit E. coli cell was ω=(1.69±0.08)×10-8 J cell-1 at pH 6.2 and 37°C. The mean heat evolution rate per unit cell during growth was q=3.6 pw cell-1, which was consistent with values calculated for other microbial cells. The growth rate constant calculated on kinetic analysis of the growth thermograms was μ = 0.532±0.068 hr-1 at pH 6.2 and 37°C. The pH dependence of the growth rate constant showed that the growth activity of E. coli cells on bouillon medium is maximum in the pH range of 5.5 to 6.5. From the temperature-dependent variations in the growth rate constant, the apparent activation energy of E. coli growth was found to be Ea = 65.3±7.1 kJ mol-1.

Computer simulation of growth thermograms observed for microbial cultures in a batch calorimeter.

Computer simulations were employed to reconstruct the growth thermograms that are observable for microbial cultures in batch calorimeters having a culture vessel in the calorimetric unit. Differential equations were derived to characterize the heat evolution process on the basis of Monod’s growth equation with some modification. Theoretical growth thermograms were compared with actually observed calorimetric recordings and it was shown that the heat effect due to the microbial cells can be well reproduced for both non-growing and growing cultures of bakers’ yeast. It is concluded that the method used here gives a reasonable characterization of the thermograms observed for microbial cultures in a batch calorimeter, indicating the possibility of determining the appropriate kinetic parameters from calorimeter recordings by a parameter-fitting method.

Computer analysis of kinetic data for microbial growth thermograms observed with a batch calorimeter.

Methods are investigated for evaluating the kinetic parameters in a modified Monod’s equation which give the best fit to the growth thermograms for bacterial cultures observed in batch calorimeters. Four mathematical methods were employed as parameter fitting techniques. The growth thermograms observed for soil microbes cultured with glucose as a limiting substrate were used as the objects of the analysis. For the calculation of the heat evolution rate, the Runge-Kutta method, which is commonly used for the numerical analysis, was employed. A comparison of the results obtained by the four methods in terms of closeness of fit to the actual thermograms showed that optimization by direct searching with the Simplex method is the most effective procedure for obtaining the best values of the parameters to reproduce the observed thermograms.

Calorimetric studies of microbial growth: Kinetic analysis of growth thermograms observed for bakery yeast at various temperatures.

Growth thermograms of bakery yeast grown on a liquid synthetic medium containing glucose as a limiting energy source were studied at various temperatures. Kinetic analysis of the thermograms was performed to obtain the apparent maximum growth rate constant and the substrate constant. By using the Arrhenius equation, the activation energy of growth was estimated to be EA = 56.3 ±5.1 kJmol−1. From the variation of the substrate constant over the temperature range studied, the enthalpy change of glucose uptake by the yeast cells was determined to be ΔH=-6.2±2.5kJmol-1. The corresponding Gibbs energy and entropy changes were ΔH=-16.4±0.2kJ mol-1 and ΔS=34.2±8.4J mol-1K-1 at 25°C, respectively.

Calorimetric Studies of Microbial Growth: Quantitative Relation between Growth Thermograms and Inoculum Size

Calorimetric Studies of Microbial Growth: Quantitative Relation between Growth Thermograms and Inoculum Size

Calorimetric studies of microbial growth: Quantitative relation between growth thermograms and inoculum size.

Heat evolution during growth of bakery yeast was studied in a heat-conduction calorimeter. Growth thermograms observed for yeast grown on liquid synthetic media with various inoculum sizes were compared. The quantitative relation between actual heat evolution and inoculum size was discussed in terms of the exponential growth function.

Microcalorimetric studies of the growth of sulfate-reducing bacteria: energetics of Desulfovibrio vulgaris growth.

The metabolism of Desulfovibrio vulgaris Hildenborough grown on medium containing lactate or pyruvate plus a high concentration of sulfate (36 mM) was studied. Molecular growth yields were 6.7 +/- 1.3 and 10.1 +/- 1.7 g/mol for lactate and pyruvate, respectively. Under conditions in which the energy source was the sole growth-limiting factor, we observed the formation of 0.5 mol of hydrogen per mol of lactate and 0.1 mol of hydrogen per mol of pyruvate. The determination of metabolic end products revealed that D. vulgaris produced, in addition to normal end products (acetic acid, carbon dioxide, hydrogen sulfide) and molecular hydrogen, 2 and 5% of ethanol per mol of lactate and pyruvate, respectively. Power-time curves of growth of D. vulgaris on lactate and pyruvate were obtained, by the microcalorimetric Tian-Calvet apparatus. The enthalpies (delta Hmet) associated with the oxidation of these substrates and calculated from growth thermograms were -36.36 +/- 5 and -70.22 +/- 3 kJ/mol of lactate and pyruvate, respectively. These experimental values were in agreement with the homologous values assessed from the theoretical equations of D. vulgaris metabolism of both lactate and pyruvate. The hydrogen production by this sulfate reducer constitutes an efficient regulatory system of electrons, from energy source through the pathway of sulfate reduction. This hydrogen value may thus facilitate interactions between this strain and other environmental microflora, especially metagenic bacteria.

Aerobic growth thermograms of Streptococcus lactis obtained with a complex medium containing glucose.

With different culturing methods both simple and complex thermograms were obtained with Streptococcus lactis grown aerobically in a complex medium containing growth-limiting concentrations of glucose. The thermogram profiles have been interpreted in relation to growth rate, glucose degradation, and molar growth yields calculated for different time intervals during growth.

Microcalorimetric study of the anaerobic growth of Escherichia coli: growth thermograms in a synthetic medium.

A microcalorimetric technique was used for studying the growth of Escherichia coli during anaerobiosis. The growth thermograms obtained are complex and the shape of curves is dependent on the hydrogen lyase activity of the cells. Fermentation balances are given for different culture conditions, and simple growth thermograms are obtained when the hydrogen lyase activity is inhibitied.

Microcalorimetric study of the anaerobic growth of Escherichia coli: measurements of the affinity of whole cells for various energy substrates.

Microcalorimetry has been used to determine the affinity of whole cells of Escherichia coli for glucose, galactose, fructose, and lactose. Anaerobic growth thermograms were analyzed, and the Km and Vmax values for these energy substrates were measured at pH 7.8. Results obtained with this technique using various organisms growing anaerobically on different sugars are compared. This comparison shows that in practically all cases the cellular rate of catabolic activity is a hyperbolic function of the energy substrate concentrations at low sugar concentrations. In some cases this technique also allows determination of kinetics at high sugar concentrations.