Nieves Barros

The effect of soil moisture on soil microbial activity studied by microcalorimetry

Abstract Microcalorimetry has been used to study the effect of moisture on soil microbial activity. Different moisture regimes produce changes on heat flow rate-time curves recorded for soil samples, affecting also certain parameters, such as the total heat evolution Q tot , the microbial growth rate constant μ and growth yield Y , which are calculated by the microcalorimetric method. A positive correlation was found between the percentage humidity, the total heat evolution and the microbial growth rate constant. The values of these parameters decrease with the dryness of the soil. Field capacity moisture appears to be the optimum moisture level for soil microbial activity.

A kinetic analysis of the degradation of glucose by soil microorganisms studied by microcalorimetry

Abstract Microcalorimetry was used to study the microbial degradation of glucose in soil. Relationships between heat evolution and the viable cell counts permit the quantification of kinetic parameters for microbial growth in soil, such as Monods substrate constant, Ks = 1.62±0.08 mM, and the maximum microbial growth rate constant, μmax= 0.26±0.01 h−1.

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

AbstractThe microcalorimetric method was used to calculate the metabolic enthalpy change per mol of glucose degraded by soil microorganisms, ΔHmet. 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 ΔHmet 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 ΔHmet 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 ΔHmet 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 .

A combined mass and energy balance to provide bioindicators of soil microbiological quality.

In this work, a method is proposed to quantify the efficiency of carbon utilization by soil microbes. Microcalorimetry was used to compute the heat yield (Y(Q/X)) of six soil samples collected in the Amazon. A combined mass and energy balance is developed to quantify the enthalpy of the glucose oxidation reaction (Delta(r)H(s)) and the biomass yield (Y(X/S)) from the experimental values of Y(Q/X). Results were compared by graphical analysis to establish the kinetics of the glucose oxidation and the microbial growth reactions in terms of energy dissipation. The correlations found suggest that the measured values for Y(Q/X) and Delta(r)H(s) are biomass yield dependent. The main environmental factors affecting the kinetics of the glucose oxidation and the microbial growth reactions in soils are the initial microbial population and the percentage of nitrogen of the samples. The comparative study among the samples showed that the deforestation of the Primary forests in the Amazon to establish arable lands, affected the efficiency of the carbon utilization by soil microorganisms.

Comparative study of the microbial activity in different soils by the microcalorimetric method

Abstract Microcalorimetry was applied to the study of the microbial activity of four soils with different percentages of organic matter. The qualitative study of the heat flow rate-time curves, recorded from soil samples amended with glucose, showed remarkable differences in the soil microbial activity. In order to show results in a more quantitative way, the total heat evolution, Q tot , the total heat evolution of soil samples amended with glucose, Q tot(glc.) , and the values of peak time and microbial growth rate constant, μ, were calculated from the heat flow rate-time curves recorded from all samples. Values of peak time increased with decreased microbial density and a positive correlation between total heat evolution, Q tot , and percentage of organic matter, was found. Microcalorimetry appears as a suitable technique to carry out both qualitative and quantitative comparative studies of microbial activity in soils.

Microcalorimetric determination of the cell specific heat rate in soils: relationship with the soil microbial population and biophysic significance

Microcalorimetry was applied to study the basal respiration in several soils collected in Galicia (Northwest Spain) and in the Brazilian Amazon. The microbial activity was recorded microcalorimetrically as power–time lines during 24 h. The soil mass specific heat rate JQ/S and the cell specific heat rate JQ/N were calculated, and compared to the microbial population of the soil samples and to the number of microorganisms per organic carbon. Results showed an inverse hyperbolic relation between JQ/N and number of microorganisms of the samples, and between JQ/N and the number of microorganisms per organic carbon. The microcalorimetric indexes of microbial activity were affected by some other soil properties, as percent of carbon, nitrogen, and C/N ratio, as well as by the introduction of agriculture, which affected the microbial population. We believe that the cell specific heat rate can be considered as an index that indicates the efficiency of the energy utilization by soil microorganisms, similarly to the specific respiration activity. The reason of its negative correlation with the microbial density could be attributed to changes in the strategy of the energy utilization by microorganisms in soils.

Effect of storage of soil at 4°C on the microbial activity studied by microcalorimetry

The effect of the storage of soils on their microbial activity has been studied using a microcalorimetric method. Soil samples were kept in closed polyethene bags at 4°C during 3–6 months. Results show changes in the slope of the differentP−t curves recorded from the samples stored at 4°C. This fact strongly suggest the existence of changes of the microbial activity of soil as the heat evolution is a direct measurement of the cells metabolic activity. The value of the Peak-time (time in which the microcalorimetric signal reaches the maximum value) is related with the microbial density of soil samples. This parameter was affected by the time of storage increasing with time. The total heat evolutionQ(t), of the soil samples amended with glucose calculated from the area limited by the Power-Time curves, also decreases with the time of storage. The soil that had been stored for 6 months before experiments, showed the lowest valu ofQ(t).ZusammenfassungMittels einer mikrokalorimetrischen Methode wurde der Einfluß der Lagerung von Böden auf ihre mikrobielle Aktivität untersucht. Bodenproben wurden bei 4°C über 3 bis 6 Monate hinweg in verschlossenen Polyethylenbeuteln gelagert. Die Ergebnisse zeigen eine Änderung des Anstieges der verschiedenenP−t Kurven, die von den bei 4°C gelagerten Proben aufgenommen wurden. Diese Tatsache lä\t stark auf die Existenz von Veränderungen der mikrobiellen Aktivität des Bodens schlie\en, da die Entwicklung von Wärme eine unmittelbare Me\möglichkeit für die metabolitische Aktivität der Zellen darstellt. Der Wert der Peak-Zeit (bei der das mikrokalorimetrische Signal sein Maximum erreicht) wird mit der Mikrobendichte der Bodenproben verglichen. Dieser Parameter ist abhängig von der Lagerungsdauer und steigt mit zunehmender Dauer an. Die anhand des von denP−t Kurven begrenzten Fläche berechnete totale WärmeentwicklungQ(t) der mit Glukose ergänzten Bodenproben sinkt mit zunehmender Lagerungsdauer. Bodenproben, die vor den Versuchen 6 Monate lang gelagert wurden, wiesen die geringstenQ(t)-Werte auf.

Assessment of the impact of soil heating on soil cations using the degree-hours method .

Para la evaluacion de la severidad de un incendio, tanto la duracion de la exposicion del suelo a una determinada temperatura como los factores que determinan la capacidad de transmision termica en el suelo (humedad, textura, contenido en materia organica, etc.) son parametros importantes a tener en cuenta. El presente estudio tiene como objetivo la aplicacion de la metodologia de los grados-hora (DH) en la caracterizacion de los impactos termicos de los incendios forestales en el suelo. Los tratamientos termicos se realizaron en el laboratorio usando muestras de suelo recogidas en el campo sin alterar su estructura para estudiar su efecto en el complejo de cambio del suelo. Los resultados obtenidos muestran un claro efecto en la capacidad de intercambio cationico (CIC) en funcion de los grados-hora (DH) suministrados, observandose un proceso de disminucion continuo de caracter exponencial. Esta funcion podria explicar de forma mas evidente el proceso de reduccion de la CIC que los valores maximos de temperatura alcanzados. Analizando la suma de cationes extraibles y su relacion con el tratamiento termico se observa como esta se incrementa gradualmente con la temperatura o los DH con una tendencia a la estabilizacion. Los diferentes cationes extraidos muestran un incremento progresivo con la intensidad del calentamiento, que cuando se relacionan con los DH pueden ajustarse a una funcion del tipo y=a+bxc con un elevado grado de confianza. La utilizacion de los DH como medida del calor aportado al suelo puede ser un parametro adecuado para establecer relaciones con los cambios edaficos que se pueden desencadenar en el mismo, sobre todo en el caso en el que los procesos varien de forma continua en el tiempo.

Exploring the potential of microcalorimetry to study soil microbial metabolic diversity

Microcalorimetry and BIOLOG are common tools in the study of soil microbial metabolism. When used combined, they may reveal further details about soil microbial metabolic diversity than individually. Through this study, we demonstrated the advantages of such a combinatorial methodology by comparing soil samples from two locations in China, each with (OM samples) and without (control) organic fertilization. We used BIOLOG and microcalorimetry to study soil microbes’ ability to metabolize different C substrates. Microcalorimetric measurements helped us further reveal the differences in the microbial growth kinetics under different BIOLOG-identified C substrates. Results showed that soils differed in the preferred C substrates, as denoted by the thermodynamic parameters. Some C substrates stimulated the active microbial biomass, while some stimulated microbial growth rate. Most interestingly, certain C substrates (e.g., l-arginine for Shandong soil and glycogen for Henan soil) showed stimulating effects on both OM and control soils, which could be attributed to the pH value and P availability in soil. Hence, we believe microcalorimetry could be potentially used to explore the soil microbial metabolic diversity by combining BIOLOG measurement, especially in determining how microbes assimilate different nutrient sources.

A microcalorimetric study of the inhibitory effects of ethanol on the fermentation process of d-xylose by Pichia supitis

Abstract Pichia stipitis is one of few yeasts capable of an efficient fermentation of pentoses to ethanol. This is a promising way to obtain ethanol from hemicellulose. In order to optimize the fermentation conditions for this process it is important to know the ethanol tolerance of the yeast. Here we report a microcalorimetric study of the inhibitory effects of ethanol on P. stipitis.