The 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
.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
A strain ofRhodococcus equi SHB-121 forming 3-cyanopyridine hydratase was screened from nitrile-polluted soil. The optimum conditions for the formation
of 3-cyanopyridine hydratase by the strain SHB-121 have been studied. Under the optimum conditions, the specific activity
of the enzyme reached 5.32 U/mg of dry cell, 95 times higher than that cultured in screening medium. In addition, the activity
of coexistent amidase was very low.
3-Cyanopyridine hydratase was purified from methylacrylamide-induced cells ofRh. equi SHB-121 by procedures including ultrasonic oscillation, ammonium sulfate precipitation, and column chromatographies on DEAE-cellulose
DE52, hydroxyapatite, and Sephadex G-25. The overall purification was 31-fold. The molecular weight of the enzyme was about
30 kDA by SDS-PAGE. The pI value was 4.1. The transition temperature and pH were 7.0°C and 6.0, respectively, resulting from
the differential spectra.
The optimum pH and temperature for the enzyme reaction were 8.0 and 30°C. The enzyme activity was strongly inhibited by Ag+, Hg2+, Cu2+, and NH4+, whereas it was enhanced by Fe3+ slightly. The enzyme catalyzed the hydration of 3-cyanopyridine to nicotinamide, and itsKm value was 0.1 mol/L. Uncompetitive inhibitor sodium cyanide has a K, value of 5 mmol/L. 相似文献
A reverse-phase high-performance liquid chromatographic (RP-HPLC) method coupled with an ultraviolet detector was developed to determine triclosan which had migrated into foodstuffs from packaging materials. The method includes extraction with hexane, followed by evaporation to dryness and residue re-dissolution in ACN 90%. Chromatographic separation was performed with a Kromasil 100 C18 column (15 cm x 0.4 cm ID, 5 microm particle size) at 30 degrees C and using ACN and water as mobile phases. Regarding recoveries, good results (higher than 83% and lower than 112%) were obtained for the three representative food matrixes selected (orange juice, chicken breast meat, and Gouda cheese). 相似文献
The high microbial load of fresh and dry natural casings increases the risk of meat product contamination with pathogenic microorganisms, agents of foodborn diseases.
The aim of this work is to evaluate the killing effect of gamma radiation of the resident microbial population of pork and beef casings, to improve their hygiene and safety.
Portions of fresh pork (small intestines and colon) and dry beef casings were irradiated in a Cobalt 60 source with with absorbed doses of 1,2,5 and 10 kGy.
The D10 values of total aerobic microorganisms in the pork casings were 1.65 kGy for colon and 1.54 kGy for small intestine. The D10 value found in beef dry casings (small intestine) was 10.17 kGy. Radurization with 5 kGy was able to reduce, at least, 6 logs the coliform bacteria in pork casings. The killing effect over faecal Streptococci was 4 logs for pork fresh casings and 2 logs for beef dry casings. Gamma radiation with 5 kGy proved to be a convenient method to reduce substantially the microbial population of pork fresh casings. Otherwise, the microbial population of beef dry casings still resisted to 10 kGy. 相似文献