2.5. Determination of the amount of viable cells in co-cultures by inoculation onto dense nutrient media (Koch method)
A number of successively diluted suspensions of microbial co-cultures (degree of dilution, 10−6) were prepared to produce separate colonies. Suspensions were inoculated by the surface method from three last dilutions (4 parallel inoculations). Colonies were counted after 7 days of incubation.
2.6. Biosensor measurements
Electrochemical measurements were carried out using an Ekspert-001-4.0.1 pH meter–ionometer–BOD thermal oximeter (Ekonics-expert Ltd., Russia) coupled with a computer operated by EXP2PR specialized software (Ekonics-expert Ltd., Russia). The software enables registration and processing of biosensor signals. The maximal rate of oxygen concentration change at the addition of substrates (mg/dm3·s) was the measured parameter (biosensor response). Clark-type oxygen electrodes containing immobilized microbial cells were used as transducers. Measurements were done in a 5-cm3 cuvette. A sodium–potassium phosphate buffer solution (pH 6.8) was used; the total concentration of the salts, 20 mM. The solution was mixed by a magnetic mixer (200 rpm). A mixture of glucose and glutamic acid (GGA) at a mass ratio of 1:1, applied as the BOD5 determination standard in the Russian Federation and in international practice [2], was used as a model mixture. In accordance with the regulatory documents, a value of BOD5 equal to 205 mg/dm3 was taken to correspond to a solution containing 150 mg/dm3 glucose and 150 mg/dm3 glutamic acid (BOD5 = 0.68 × СGGA).
2.5. Determination of the amount of viable cells in co-cultures by inoculation onto dense nutrient media (Koch method)A number of successively diluted suspensions of microbial co-cultures (degree of dilution, 10−6) were prepared to produce separate colonies. Suspensions were inoculated by the surface method from three last dilutions (4 parallel inoculations). Colonies were counted after 7 days of incubation.2.6. Biosensor measurementsElectrochemical measurements were carried out using an Ekspert-001-4.0.1 pH meter–ionometer–BOD thermal oximeter (Ekonics-expert Ltd., Russia) coupled with a computer operated by EXP2PR specialized software (Ekonics-expert Ltd., Russia). The software enables registration and processing of biosensor signals. The maximal rate of oxygen concentration change at the addition of substrates (mg/dm3·s) was the measured parameter (biosensor response). Clark-type oxygen electrodes containing immobilized microbial cells were used as transducers. Measurements were done in a 5-cm3 cuvette. A sodium–potassium phosphate buffer solution (pH 6.8) was used; the total concentration of the salts, 20 mM. The solution was mixed by a magnetic mixer (200 rpm). A mixture of glucose and glutamic acid (GGA) at a mass ratio of 1:1, applied as the BOD5 determination standard in the Russian Federation and in international practice [2], was used as a model mixture. In accordance with the regulatory documents, a value of BOD5 equal to 205 mg/dm3 was taken to correspond to a solution containing 150 mg/dm3 glucose and 150 mg/dm3 glutamic acid (BOD5 = 0.68 × СGGA).
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