Microbial Growth Rate Constant Research Articles

Application of anaerobic digestion model No. 1 on thermophilic anaerobic digestion with microbial immobilization media for biogas production from sugarcane vinasse

Anaerobic Digestion Model no.1 (ADM1) for the "Mixed Reactor Compartment" of AQUASIM with modified kinetic parameters was proven to be effective in predicting the behavior of thermophilic anaerobic digestion of sugarcane vinasse in a continuous stirred tank reactor (CSTR) equipped with unwoven textile as the microbial immobilization media. The modified kinetic parameters implied higher microbial growth rate constants in the CSTR with microbial immobilization media than the CSTR without media. The 16 s rRNA assay confirmed the inferences on the physical interpretation of the kinetic parameters. Microbial immobilization media shifted the initially homogeneous microbial composition in the CSTR’s bulk liquid into methanogenic dominance in the biofilm attached to the media and acidogenic dominance in the liquid bulk after 90 days of operation. The remarkable finding of this study was that the segregated microorganisms indicated a beneficial micro-environment for both acidogenic and methanogenic populations to have favorable conditions for each of them. ADM1 well predicted the effect of this segregation with modified kinetic parameters and confirmed by the 16 s rRNA assay on the reactor’s liquid and biofilm samples.

Effect of nitrogen fertilization on maize yield responses to soil microbial activity and root length density in the North China Plain

A maize field experiment in the North China Plain was conducted to understand the effect of different N fertilizer rate on the yield of maize, using soil microbial activity and root length density (RLD) as performance parameters, due to their possibility to enhance productivity. The four N fertilizer rates were 0 (N0), 120 (N120), 210 (N210) and 300 (N300) kg N hm-2. The results indicated that nitrogen (N) fertilizer had a significant influence not only on yield (p<0.05), but also on root length density (p<0.05) and soil microbial activity (p<0.05). In addition, the soil microbial activity and RLD were significantly related with maize yield. RLD differences were generally evident within the 100 cm soil layer, whereas there was no difference in the deeper soil under different N treatments. The most RLD concentrated in 0-60cm soil layer under N0, N120 and in 0-90cm soil layer under N210, N300. The microbial growth rate constant (k) was greater in N210 than other treatments. Generally, N fertilizer application can stimulate root growth and microbial activity, meanwhile, they can interact with each other, heighten the availability of N fertilizer in soil, thus enhanced yield of maize. According to our study, 210 kg N hm-2 was the optimum N fertilizer rate to achieve maximum yield and sustain the soil productivity.

Synthesis and biothermokinetic study of a new Schiff base and its bismuth(III) complex on the growth metabolism of S. pombe and H. pylori cell lines

In this study, a new Schiff base ligand [2-{[4-amino-5-(3,4,5-trimethoxy-benzyl)-pyrimidin-2-ylimino]-methyl}-6-methoxy-phenol, C22H24N4O5] and its bismuth(III) complex [BiC22H22N4O5Cl] were synthesized using o-vanillin and trimethoprim in anhydrous solvents. Chemical analysis, elemental analysis, spectrum analysis and TG–DSC analysis were employed to characterize the compositions and structures of the two new compounds. In particular, the metabolic thermogenic curves of Schizosaccharomyces pombe (S. pombe) and Helicobacter pylori (H. pylori) cells treated by the two new compounds at different concentrations were monitored by an isothermal microcalorimeter at 32.00 and 37.00 °C, respectively. On the basis of the metabolic thermogenic curves, some important biothermokinetic parameters such as the microbial growth rate constant (k), inhibition ratio (I) and half inhibition concentration (IC50) were estimated. The experimental results indicated that both the Schiff base ligand and its bismuth(III) complex could inhibit the growth metabolism of S. pombe and H. pylori, but the inhibitory abilities of the two compounds were as follows: the Schiff base ligand > the complex for S. pombe and the Schiff base ligand < the complex for H. pylori, respectively. More importantly, the results also found that the Schiff base bismuth(III) complex exhibited bidirectional biological effect and hormesis effect on H. pylori cell line, i.e., the complex can stimulate the growth metabolism of H. pylori at low concentration, while inhibiting its growth at high concentration.

Hotspots of Nitrous Oxide Emission in Fertilized and Unfertilized Perennial Grasses

Core Ideas We studied hotspots of nitrous oxide emission from perennial grasses on wet soil. Hotspots occurred in a limited range of soil moisture and temperature conditions. Hotspots recurred more frequently at specific places over a three year period. Hotspots of nitrous oxide (N2O) emission are thought to contribute substantially to annual emissions from agricultural soils. We observed N2O fluxes from fertilized and unfertilized C3 and C4 perennial grasses on a wet silt loam soil in New York, United States during the growing season in 2013, 2014, and 2015 using static chambers. Analysis of N2O hotspots within the research plots revealed that hotspots contributed between 34.3 and 39.1% of the total emissions, and constituted between 0.8% and 5.0% of all flux observations. Hotspots were more frequent and of greater magnitude in the fertilized treatments, and occurred when soil temperature was greater than 9.1°C and soil moisture was between about 40% and 80% water filled pore space (WFPS). A single chamber location in the fertilized switchgrass treatment was consistently a hotspot for N2O emission, suggesting that hotspots maintain a stable spatial pattern over extended periods. The maximum magnitude of N2O hotspot emission exhibited a relationship to soil temperature that is similar to that of the microbial growth rate constant.

Synthesis and microcalorimetric determination of the bioactivities of a new Schiff base and its bismuth(III) complex derived from o-vanillin and 2,6-pyridinediamine

In this work, a new Schiff base [N,N′-bis(2-hydroxy-3-methoxyphenylmethylidene)-2,6-pyridinediamine, C21H19N3O4] and its bismuth(III) complex [Bi(C21H17N3O4)]Cl·2H2O were synthesized with o-vanillin and 2,6-pyridinediamine in ethanol and THF solvent, respectively. The compositions and structures of the two synthetic compounds were characterized by elemental analysis, chemical analysis, spectrum analysis (including MS, FT-IR, NMR, and UV–Vis), and thermogravimetric analysis. The thermogenic curves for the growth metabolism of Helicobacter pylori (H. pylori) and Schizosaccharomyces pombe (S. pombe) treated by different concentrations of the two synthetic compounds were determined by isothermal heat conduction microcalorimetry at 37.00 and 32.00 °C, respectively. Based on the thermogenic curves, some important thermokinetic parameters including the microbial growth rate constant (k), inhibition ratio (I), and half inhibition concentration (IC50) were calculated. The obtained results revealed that the Schiff base stimulated the growth of H. pylori, while the complex inhibited its growth. By contrast, both the Schiff base and the complex inhibited the growth of S. pombe, but the inhibitory effect of the complex was stronger than that of the Schiff base.

SHIMMER (1.0): a novel mathematical model for microbial and biogeochemical dynamics in glacier forefield ecosystems

Abstract. SHIMMER (Soil biogeocHemIcal Model for Microbial Ecosystem Response) is a new numerical modelling framework designed to simulate microbial dynamics and biogeochemical cycling during initial ecosystem development in glacier forefield soils. However, it is also transferable to other extreme ecosystem types (such as desert soils or the surface of glaciers). The rationale for model development arises from decades of empirical observations in glacier forefields, and enables a quantitative and process focussed approach. Here, we provide a detailed description of SHIMMER, test its performance in two case study forefields: the Damma Glacier (Switzerland) and the Athabasca Glacier (Canada) and analyse sensitivity to identify the most sensitive and unconstrained model parameters. Results show that the accumulation of microbial biomass is highly dependent on variation in microbial growth and death rate constants, Q10 values, the active fraction of microbial biomass and the reactivity of organic matter. The model correctly predicts the rapid accumulation of microbial biomass observed during the initial stages of succession in the forefields of both the case study systems. Primary production is responsible for the initial build-up of labile substrate that subsequently supports heterotrophic growth. However, allochthonous contributions of organic matter, and nitrogen fixation, are important in sustaining this productivity. The development and application of SHIMMER also highlights aspects of these systems that require further empirical research: quantifying nutrient budgets and biogeochemical rates, exploring seasonality and microbial growth and cell death. This will lead to increased understanding of how glacier forefields contribute to global biogeochemical cycling and climate under future ice retreat.

Effects of enhanced UV-B radiation on the diversity and activity of soil microorganism of alpine meadow ecosystem in Qinghai-Tibet Plateau.

The effects of enhanced UV-B radiation on abundance, community composition and the total microbial activity of soil bacteria in alpine meadow ecosystem of Qinghai-Tibet Plateau were investigated. Traditional counting and 16S rRNA gene sequencing were used to investigate the culturable bacteria and their composition in soil, meanwhile the total microbial activity was measured by microcalorimetry. The population of soil culturable bacteria was slightly reduced with the enhanced UV-B radiation in both of the two depths, 2.46 × 10(6) CFU/g in upper layer (0-10 cm), 1.44 × 10(6) CFU/g in under layer (10-20 cm), comparing with the control (2.94 × 10(6) CFU/g in upper layer, 1.65 × 10(6) CFU/g in under layer), although the difference was not statistically significant (P > 0.05). However, the bacteria diversity decreased obviously due to enhanced UV-B, the number of species for upper layer was decreased from 20 to 13, and from 16 to 13 for the lower layer. The distribution of species was also quite different between the two layers. Another obvious decrease induced by enhanced UV-B radiation was in the total soil microbial activities, which was represented by the microbial growth rate constant (k) in this study. The results indicated that the culturable bacteria community composition and the total activity of soil microbes have been considerably changed by the enhanced UV-B radiation.

Microcalorimetric study of the effects of long-term fertilization on soil microbial activity in a wheat field on the Loess Plateau.

The effects of the long-term inorganic (nitrogen, N; phosphate, P) and organic (manure, M; straw, S) fertilizers/managemenet individually and in combinations (N, NP, SNP, M, and MNP) on soil microbial activity were investigated in a wheat field on the Loess Plateau, China. Microcalorimetry was used to determine microbial activity under different treatments. Nearly 30 years of consecutive fertilization has altered the culturable population of soil bacteria and fungi, the highest ones were detected in the treatments of manure and MNP, followed by the NP and SNP treatments. The microbial growth rate constant (μ/h(-1)) was significantly greater in the MNP treatment than all the other treatments. The total heat exchange values (Q/J) were the highest in the MNP and NP treatments, which were significantly different from the N and M treatments. The peak height (P(t)/μW) were significantly higher in MNP and NP treatments than in the remaining treatments. The peak time values (t(p)/h) among the MNP, NP, SNP and M, N and CK treatments were significantly different. In general, comparing with control, soil microbial activity was much higher in MNP, NP and SNP treatments, all including the phosphate fertilizer. Our results showed that the application of inorganic fertilizer and organic manure have positive effects on multiple soil chemical parameters, soil microorganism abundance and activity, and hence crop yield.

Synthesis, thermochemical and thermokinetic studies on the mononuclear copper Valen Schiff base complex

A mononuclear salen-type complex [Cu( vanen )(H 2 O)] was synthesized from the ligand [H 2 vanen = N , N - ethylene-bis(3-methoxysalicylideneimine)] and Cu(OAc) 2 ·H 2 O. Based on Hess law, a reasonable thermochemical cycle was designed. According to the cycle, the standard molar enthalpies of dissolution of samples in the calorimetric solvent of DMF ( N , N -dimethylformamide) were determined, respectively. The standard molar enthalpy change of the coordination reaction (Δ r H m θ ) was calculated to be -(16.61 ± 0.54) kJ/mol. Combined with some relevant literature data, the standard molar enthalpy of formation (Δ f H m θ ) of the complex was obtained to be -(756.5 ± 2.4) kJ/mol. At the temperature of 32 ℃, the metabolic thermogenetic curves of S. pombe under the influence of the complex with different concentration were determined by using a TAM air isothermal calorimeter. The relationships of the concentration of the complex with the microbial growth rate constant ( k ) of S. pombe , inhibition ratio (I), the half inhibition concentration (IC 50 ), the maximum heat output power ( P max ) and the time it took ( t max ) were analyzed. The results indicated that the complex possessed the Hormesis effect, which promoted the growth of S. pombe at lower concentration, but inhibited the growth at higher concentration.

2-{[4-氨基-5-(3,4,5-三甲氧基-苄基)-嘧啶-2-亚胺基]-甲基}-6-甲氧基-苯酚与酵母细胞和牛血清白蛋白的相互作用

用等摩尔的邻香草醛（C 8 H 8 O 3 ）与甲氧苄胺嘧啶（C 14 H 18 N 4 O 3 ）反应，合成了一种新的化合物2-{[4-氨基-5-（3，4，5-三甲氧基-苄基）-嘧啶-2-亚胺基] -甲基}-6-甲氧基-苯酚（APYP）. 通过元素分析、核磁共振、摩尔电导、红外光谱和紫外光谱等手段对其进行了表征，其化学式为C 22 H 24 N 4 O 5 . 采用微量热法测定了APYP在301.15 K时对粟酒裂殖酵母细胞的生长代谢的产热曲线，计算得到了粟酒裂殖酵母细胞生长速率常数 k ，抑制率I 以及半抑制浓度IC 50 等热动力学参数. 实验结果表明，随着APYP浓度的增加，粟酒裂殖酵母细胞的生长代谢速率常数 k 减小，抑制率I增加，半抑制浓度IC 50 为123.2 mg/L（或2.96×10 -4 mol/L），即APYP对粟酒裂殖酵母细胞有抑制作用. 同时利用荧光光谱和紫外光谱等方法研究了APYP与牛血清白蛋白（BSA）在接近生理条件下的相互作用，探讨了荧光猝灭机理，计算了反应的结合常数、结合位点、结合距离及热力学参数，研究了APYP与BSA之间的能量转移情况；并通过同步荧光光谱考察了APYP对BSA二级结构的影响.

Microcalorimetric evaluation of soil microbiological properties under plant residues and dogmatic water gradients in Red soil

A study of 6 months duration was carried out to investigate the effect of water regimes and organic amendments on the soil microbial biomass and microbial population under Red soil collected from Hunan Providence, China. The soil microbial biomass and population were measured with traditional methods and results obtained by conventional methods, corroborated with microcalorimetry. The incorporation of rice (Oryza sativa L.) straw (RS) and green manure (GM), especially at high rates, enhanced the soil microbial activities. We observed that the use of GM exhibited more significant stimulating effects on microbial activities than RS. Similarly, water regimes, 25% (W1) and 200% (W2) of water holding capacity, also had significant effects on microbial activities. Comparing the effects of water levels, we noticed that W2 had a significant negative influence on soil microbial biomass and population. To compare the results of conventional methods and to check the sensitivity of microcalorimetry, the thermodynamic parameters, microbial growth rate constant (k), total heat evolution (Q), peak height (Pmax) and peak time (tmax) were calculated. Highest Pmax, k and Q were observed in GM treatments at water regime W1, while highest tmax values were recorded in CK (control) and RS treatments at W2. The microcalorimetric parameters, Pmax, k and Q were positively correlated, whereas tmax negatively linked with microbial biomass and population at p < 0.01. Our results suggest that microcalorimetry successfully verified the results obtained from customary methods and microcalorimetric parameters Pmax, tmax, Q and k proved that they are highly sensitive to microbial properties and could be used as indices of microbial community shifts and activities in soil ecosystems.

Microcalorimetry study on the microbial activity of permafrost on the Tibetan plateau of China

Microcalorimetric techniques had been used to study the influence of different physicochemical parameters on microbial growth in different permafrosts on the Tibetan plateau. The total heat evolution of the permafrost samples amended with glucose, QT, the values of microbial growth rate constant, k, and the heat output power, Pt, were calculated from the power–time (P–t) curves. It is observed that the same coverage vegetation show similar P–t curves, which strongly suggest that the permafrost microorganisms of the homology vegetation coverage have similar structures of community. Furthermore, the vegetation degradation turns out to have significant influence, that is, the better the status of vegetation is, the higher the values of k, CFU and QT are.

Synthesis and Bioactive Studies of Complex 8-Hydroxyquinolinato-Bis-(Salicylato) Yttrium (III)

This paper reports the synthesis of a new bioactive complex, 8-hydroxyquinolinato-bis-(salicylato) yttrium (III) (HSAY), whose composition and structure were characterized by elemental analysis, IR spectra, thermogravimetric analysis, and X-ray diffraction. The power-time curves of the compounds HSAY, C(7)H(6)O(3), C(9)H(7)NO, and YCl(3)·6H(2)O on the growth metabolism of Schizosaccharomyces pombe (S. pombe) were determined at 32.00°C, respectively. The corresponding thermokinetics parameters, which include the microbial growth rate constant (κ), inhibition ratio (I), and half inhibition concentration (IC(50)), were also derived. The results showed that the generation time was 168.2 min, and all the compounds HSAY, C(7)H(6)O(3), C(9)H(7)NO, and YCl(3)·6H(2)O possessed good bioactivities on the growth metabolism of S. pombe, with the values of IC(50) being 0.055, 3.57, 0.057, and 1.35 mmol L(-1), respectively. The inhibition ability of these compounds above on the growth of the S. pombe has been observed to decrease in the order HSAY>C(9)H(7)NO>YCl(3)·6H(2)O>C(7)H(6)O(3).

Synthesis of Thioproline Salicylic Acid Samarium Complex and Microcalorimetric Study on Effects of the Complex on the Growth Metabolism of S. pombe Cells

AbstractThe product from reaction of samarium chloride hexahydrate with salicylic acid and thioproline, [Sm(C7H5O3)2·(C4H6NO2S)]·2H2O (TSAS), was synthesized and characterized by IR, elemental analysis and thermogravimatric analysis. Particularly, the effect of the compounds TSAS, SmCl3·6H2O, C7H6O3 and C4H7NO2S on the growth and metabolism of S. pombe by a TAM Air isothermal calorimeter at 32°C is also reported. The thermokinetic parameters, which included the microbial growth rate constant (κ), inhibition ratio (I) and half inhibition concentration (IC50), were obtained. The results showed that all the compounds TSAS, SmCl3·6H2O, C7H6O3 and C4H7NO2S possessed the bi‐directional biological effect and Hormesis effect. These stimulate the growth of the S. pombe at lower concentration, but inhibit the growth at higher concentration. The half inhibition concentrations (IC50) of TSAS, SmCl3·6H2O, C4H7NO2S and C7H6O3 were found to be 0.732, 0.746, 0.746 and 1.43 mmol·L−1, respectively. The inhibition ability of these compounds on the growth of the S. pombe has been observed to decrease in the order TSAS&gt;SmCl3·6H2O=C4H7NO2S&gt;C7H6O3. Moreover, the effect of TSAS on the growth and cytokinesis of S. pombe was investigated by cytomorphology and FT IR spectroscopy technique. The results indicated that TSAS had a direct impact on apoptosis, and could also inhibit the cell growth by reducing cytokinesis and the binding locations of drug (TSAS) in S. pombe cells could be the proteins and nucleic acid.

Microcalorimetric assessment of microbial activity in long-term fertilization experimental soils of Southern China

Microcalorimetry, plate count and PCR-denaturing gradient gel electrophoresis (DGGE) were employed to investigate microbial diversity and activity in soils from the Red Soil Experimental Station of the Chinese Academy of Agricultural Sciences, Hunan Province, China, where a wheat-corn rotation with 12 fertilization treatments was established in 1990. Fertilization greatly increased microbial biomass carbon (C) and nitrogen (N) (C(mic) and N(mic)) as well as the activities of phosphatase, urease, invertase, protease, catalase and dehydrogenase. Manure alone (M) enhanced the number of denitrifying and aerobic bacteria by 54.4% and 20.5%, respectively, whereas fallow (H) increased the number of aerobic cellulose decomposing bacteria by 31.4%. Fallow and soils amended with mineral fertilizers plus pig manure or straw increased both the DGGE band patterns and the Shannon index compared with mineral fertilizers or the control. Mineral treatments with lower bacterial numbers enhanced the values of the peak time (t(max)) more than did organic treatments. The peak height (P(max)) was positively correlated (P<0.01), with soil enzymes, C(mic) and N(mic), and the number of microorganisms, whereas the peak time (t(max)) was negatively connected (P<0.01) with these parameters. The microbial growth rate constant (k) was linked to bacteria (P<0.01), actinomycetes (P<0.05) and catalase (P<0.05). The total heat evolution (Q) had no relationships with any soil microbial properties (except for catalase). We propose that P(max) and t(max) could be used as indices of soil microbial activity, while the values of k and Q are poor indicators.

The effect of solid-liquid effluents from anaerobic digesters on soilmicrobial activity

A calorimetric procedure is developed to study the effect on the soil of the effluents resulting for the anaerobic digestion of slaughtering houses residues. DSC was used to study the pyrolysis properties of the effluent and the soil while isothermal calorimetry is applied to study the microbial activity in the effluent and to assess on its effect on the microbial activity of the soil where the industrial digester will be situated. The calorimetric data were studied together with the chemical and biological properties of that residue. Results showed that effluent is constituted by low levels of carbon and high levels of nitrogen. The power–time curves of the effluent have the typical shape of microbial growth yielding microbial growth rate constants between 0.37 and 0.53 h –1 for about 4 and 11 h. The addition of the effluent to the soil decreases the heat of pyrolysis with time and stimulates the heat flow rate of the microbial metabolism.

Influence of agricultural practices on soil microbial activity measured by microcalorimetry

To investigate the influence of different agricultural practices and vegetations on soil microbial activity and diversity, soil samples from different habitats were studied with their microbial activities measured by the microcalorimetric technique. Seven soil samples were collected in Wuhan, China from different locations with primary and regeneration forest, nursery and crop land, and uncultivated land. The number of microorganisms in soils was measured by viable count, and some physicochemical parameters were determined. Power–time curves were recorded for soil samples supplemented with glucose and ammonium sulphate, and the total heat changes of the microbial growth reaction, Q total (Jg −1) and the microbial growth rate constant, k (min −1) were calculated from the curves. All power–time curves presented typical changes of microbial activity. The curves of soil samples could be divided into two groups differing in agricultural practices and vegetations. The same grouping could also be reached according to the values of peak time ( t max). The most soil samples showed a higher correlation between the values of k and the counted bacterial numbers. The Q total correlated well with vegetation abundance and probably with microbial diversity. In conclusion, microbial activity of the soil samples determined by microcalorimetry reflected differences in soil vegetation and agricultural management.

Treatment of settled piggery waste by a down-flow anaerobic fixed bed reactor

A study of the effect of organic volumetric loading rate (B V ) on the performance of a down-flow anaerobic fixed bed reactor (DFAFBR) treating settled piggery waste was carried out at a range of between 1.1 and 6.8 g COD dm -3 d -1 . The reactor operated at good removal efficiencies and stability under the operational conditions studied. Logarithmic empirical equations described adequately the removal efficiency for different parameters studied (COD, SCOD, BOD, TS, VS, TSS, VSS and phosphorous). Although process stability was affected by the increase of B V , process failure was not observed. A logarithmic relationship was found to describe the influence of B V on the TVFA/alkalinity ratio (p). A linear correlation was found between the effluent substrate concentration and the values of p and between p and the CO 2 /CH 4 ratio in the biogas. The effect of the hydraulic volumetric loading rate (H v ) on the flow pattern of the reactor was evaluated. Dispersion number (D n ) was in the range of 0.17-0.37 for the maximum and minimum values of H V studied, respectively. The ratio between the real and theoretical HRT increased as the H V decreased. These results demonstrate that axial dispersion increased as the H V and the Reynolds number decreased. Due to the hydraulic behaviour of the reactor, the kinetic model developed by Lawrence and McCarty was used for describing the experimental results obtained. Maximum specific substrate removal rate (K), specific organic loading rate constant (K L ), microbial decay coefficient (K d ), microbial yield coefficient (Y), maximum microbial growth rate (U M ) and saturation constant (K S ) were found to be: 3.1 (g COD g VSS -1 d -1 ), 3.0 (g COD g VSS -1 d -1 ), 0.062 (d -1 ), 0.15 (g VSS g COD removed -1 ), 0.39 (d -1 ) and 2.6 (g SCOD dm -3 ), respectively.

The influence of some physicochemical parameters on the microbial growth in soils

Microcalorimetric techniques have been used to study the influence of different physicochemical parameters on microbial growth in different soils in Galicia (NW Spain). The study was carried out using a 4 channels Thermal Activity Monitor (Thermometric, Sweden). Two types of soil, humic cambisol and umbric regosol, with different uses, vineyard, orchard, maize field, and scrubland, were investigated. Microbial activity in all the soils studied was stimulated by the addition of 1.25 mg of glucose g −1 soil. The power–time curves recorded from every experiment were analysed and from these analyses characteristic parameters such as peak time, peak height and microbial growth rate constants were determined. The influence of different environmental parameters, temperature (ambience and soil), moisture content (sample and residual), pH in water, and C/N ratio, were considered.

Interpretation of the Metabolic Enthalpy Change, ΔHmet, Calculated for Microbial Growth Reactions in Soils

The microcalorimetric method was used to calculate the metabolic enthalpy change per mol of glucose degraded by soil microorganisms, ΔH met. This parameter has been calculated by microcalorimetry for many organic, inorganic and biochemical reactions, but there is only some information about its quantification for microbial growth reactions in soils. Values of ΔH met were calculated for different soil samples collected in Galicia (Spain) and Campinas (Săo Paolo, Brazil). Exponential microbial growth was stimulated in all soil samples by the addition of glucose and power-time curves were recorded. Results showed changes in the values of ΔH met calculated for all the soil samples, suggesting a dependence of this value with the microbial growth rate constant, with the percentage of growth, with the initial number of microorganisms of soil samples, with the quantity of glucose added and with the strain of bacteria growing in soil. The interpretation of variations of ΔH met provides important qualitative and quantitative information. It reports data that allow to interpret from a qualitative point of view, the increase in biomass as a consequence of the degradation of the organic matter in soil, to understand changes in the percentages of soil organic matter and to know if the microbial population growing in differential soil samples is homogeneous. Therefore, to report that value would be very important in ecological studies, but beforehand, it is necessary to solve some problems that can appear in the experiments done to make the quantification .