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Using cell-free extracts of Nitrobacter agilis, we investigated the effects of CIPC and eptam on the oxidative phosphorylation coupled to nitrite oxidation as well as upon the reduced nicotinamide adenine dinucleotide (NADH2) oxidation to determine possible effects of the herbicides upon electron transport. Both CIPC and eptam exerted an uncoupling effect on the oxidative phosphorylation linked to nitrite oxidation. Although nitrite oxidation was inhibited, an intensely severe inhibition of phosphorylation caused a 50% reduction in the P/O ratio (μmoles of 32P esterified per μatom of oxygen consumed) at about 2.3 × 10−4 M CIPC and at 8 × 10−4 M eptam. Likewise, 2,4-dinitrophenol (DNP), a classical phosphorylation uncoupler, affected the oxidative phosphorylation in N. agilis. Although oxygen uptake was inhibited, a 45% reduction in the P/O ratio occurred at 2.5 × 10−4 M DNP because of a greater effect on phosphate esterification. Neither CIPC nor eptam affected reduced nicotinamide adenine dinucleotide (NADH2) oxidase activity.

Few quantitative studies of the biological oxidation of nitrite by Nitrobacter have been made, although this process is important in nature. Without it, the concentration of nitrite produced by the oxidation of ammonia would soon reach toxic levels in water or in the soil. The influence of temperature and substrate concentration on the rate of this reaction has never been quantitatively studied, although much contradictory information can be found in the literature. Precise results may have been difficult to obtain and it is perhaps for this reason that the otherwise exhaustive investigations of Meyerhof (1916) do not mention the effect of temperature. The present paper attempts to summarize the data obtained regarding the effects of these two factors and their interaction on the rate of nitrite oxidation.

IT was reported by Simpson1 that 2,4-dinitrophenol, at a concentration of 1 mM, strongly inhibits nitrite oxidation by Nitrobacter, although compounds such as ethyl nitrite and nitromethane appeared to have no inhibitory action. Other workers2 have, however, failed to obtain any inhibition with 2,4-dinitrophenol. We have therefore re-investigated the effect of this compound on nitrite oxidation.

Phosphate accumulating organisms (PAO) and glycogen accumulating organisms (GAO) play an important role in aerobic granular biofilm systems used for wastewater treatment. Both are slow growing organisms which can take up and store carbon under anaerobic conditions. The growth of PAO over GAO is preferred because of their capacity to remove phosphate. As some PAOs and GAOs can utilize nitrite or nitrate as electron acceptor in absence of oxygen, they act also as denitrifiers (i.e. DPAO/DGAO). The presence of active DPAOs in a treatment system is desirable because the same carbon source is used for dephosphatation and denitrification. The aim of this study was to investigate and to compare the denitrification potential of aerobic granular biofilms having already a good phosphate removal activity, and that were cultivated with either propionate or acetate as model contaminats. The results show that both biofilms had considerably higher specific uptake rates for nitrite than for nitrate (3.26 times for acetate and 4.79 times for propionate). These results agree with a study (Martin et al., 2006) which showed, that some DPAO have no nitrate reductase genes and can therefore only reduce nitrite but not nitrate. Therefore, DGAO were likely responsible for nitrate and DPAO together with DGAO for nitrite removal. This assumption is supported by the observation that the nitrite uptake rate decreased in the absence of phosphate, whereas the nitrate uptake rate was not influenced by phosphate presence or absence. Furthermore we observed a 27% higher specific nitrite uptake rate in the propionate reactor than in the acetate reactor. This supports the hypothesis that granules fed with propionate may favor the development of PAO with nitrite reducing capacity. We conclude that (i) to enhance the denitrification and create a link to the P-removal, nitrite oxidation to nitrate has to be inhibited, and that (ii) propionate leads to more robust DPAO populations than acetate. In addition to the biochemical results presented in this abstract, microbial community analysis of granules will be done to complete the results.

[No abstract available], ST09044005