DEVELOPMENT OF STABLE DENITRIFYING CULTURES DURING REPEATED AEROBIC-ANAEROBIC TRANSIENT PERIODS

The influence of repeated alternating aerobic-anaerobic growth conditi ons on the development of stable denitrification activity was studied with continuous cultures of Paracoccus denitrificans and with activate d sludge. Denitrification activity was determined by measuring the for mation of intermediates and by analysis of mRNAs for the individual de ntrification enzymes. Primarily, the length of the anaerobic period in fluenced the synthesis of the denitrification enzymes of P. denitrific ans. When the anaerobic period was 24 h, the cultures reached stable d enitrification activity within the first anaerobic phase. Then, dinitr ogen was the only denitrification product released. In contrast, when the anaerobic periods were short (1.5 h), P. denitrificans was not abl e to completely synthesize a stable denitrifying enzyme system within the course of the experiment, and a semi-steady stale was reached. Nit rite accumulated in the medium as the predominant denitrification prod uct. The transient characteristics of the activated sludge during the repeated aerobic-anaerobic conditions were similar to those observed w ith P. denitrificans. This finding indicates that information on the i nduction process of denitrification in P. denitrificans can be used re asonably well to assess induction of denitrifying activity in more com plex systems. Finally, the usefulness of the application of mRNA probe s are discussed. (C) 1997 Elsevier Science Ltd.