Kinetics of glucose uptake by soil microorganisms

The kinetics of glucose uptake by soil microorganisms was investigated. Soil amended with an inorganic nutrient solution containing C glucose at concentrations of 2.5, 5.0, 10.0 or 20.0 mmol 1 −1 was maintained at 4, 12 or 25°C for varying times. The soil was analyzed for glucose, soluble 14C, total organic 14C and evolved 14CO 2 to develop a carbon balance for the system and to define Michaelis-Menten kinetic parameters ( K m and V max) for glucose uptake at each temperature. Glucose uptake rates, as measured by the depletion of glucose or soluble 14C from solution, were similar in soils maintained at 12 or 25°C. Based on the depletion of soluble 14C, values for K m were 2.25 and 2.43 mmol I −1 at 12 and 25°C, respectively, while V max values were 0.25 and 1.61 h 14', respectively. Glucose depletion at 4°C was faster than at 12C, while soluble 14C was removed at a significantly slower rate, suggesting soluble-C intermediates were produced in the 4°C system. Based on Chromatographie techniques and GC-MS, a soluble 14C-compound accumulating in the 4°C system was identified as maltose. The conversion of glucose to maltose resulted in K m and V max values of 17.29 mmol I −1 and 0.12h −1, respectively, for soluble 14C depletion and 4.96mmol1 −1 and 0.43 h −, respectively, for glucose depletion at 4δC. These results demonstrate the need to differentiate uptake rates for the parent compound as well as for transitory intermediates excreted into the growth medium. Evolution of CO 2 was shown to be a poor indicator of the rapid disappearance of glucose in soils.