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Estimation of type and intensity of nitrogen compounds degradation by total dehydrogenase activity measurement

Significant efforts in solving problems associated with nitrogen pollution are directed towards the microorganisms of the nitrogen cycle. Among rhem, the special attention has been devoted to nitrifiers and denitrifiers. Nitrification may be defined as the oxidation of reduced nitrogen compounds. Microorganisms that perform nitrification can be either autotrophic nitrifiers, using CO2 as carbon source and obtaining energy from ammonia oxidation, or heterotrophic nitrifiers (not only bacteria but also some fungi) demanding for their nitrfying activity external, organic substrate as carbon source, and gaining no energy from the reaction. Denitrifiers, generally but not exclusivela bacteria, are resposible for returning of fixed nitrogen to the atmosphere by reducing nitrate to N2 (usually via nitrite, NO and N2O). Both, nitrifying and denitrifying actiities have been extensively studied almost exclusively on bacterial monocultures. The parameters found to affect mostly these processes are pH and oxygen saturation. Of special interest are the observations that some strains can simultaneously perform nitrification and denitrification activities, enabling complete removal of most abundant initial nitrogen compound, as well as the intermediate products. Our idea was that mixed microorganism population, consisting of four different bacterial and one yeast strain, might posses heterogeneous and more powerfull enzymatic potentials then monocultures, for performing both, nitrifying and denitrifying activities. This associated microbial population (AMP), which behaves as a heterotrophic denitrifyer, was tested according to its ability to eliminate nitrate, nitrite and ammonia from cultura medium. For better understanding of complex processes in such a mixed and constantly transforming microbial population, total dehydrogenase activity (TTC-method) has been measured at different experimental steps. The results obtained prove a strong AMP denitrifying potential, as well as simultaneous nitrifying activities in aerobic conditions. Total dehydrogenase activity varied extensively during experiment, reflecting intensity and direction of oxido-reductive chemical reactions, which may be the result of enzyme activity and/or quantity changes, the same as changes in the microbial composition. Although much additional work is necessary for a better understanding of the mechanism of AMP denitrifying capabilities, the results presented are encouraging in the view of water quality improvement.

nitrogen compounds; total dehydrogenase activity; associated microbial population

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