No abstract

The quantitative importance of bacteria in urea production and turnover in a defaunated sediment from a Danish estuary was studied. After collecting the sediment, benthic infauna was removed by sieving, followed by anoxic pre-incubation for a week. Yeast extract was added to half of the samples. The urea concentration, urea production/turnover rates and the net ammonium production rate, were followed during a 338 h incubation. The urea concentration was highest in the enriched sediment, although urea production and turnover rates were the same in the enriched and control sediment, indicating that the urea concentration was controlled by the urea turnover rate constant, kttre a. Net ammonium production, urea concentrations and the urea turnover declined towards the end of the experiment. Comparison of the net ammonium production rate and the urea turnover rate in the enriched and control treatments, showed that urea hydrolysis accounted for up to 100% of the ammonium produced, from all sources. More than 98% of the urea which was hydrolyzed, originated from production during incubation. This suggests that urea was a major nitrogen excretion product from bacteria in this sediment, and that bacteria could also be an important source of urea in other marine sediments.

No abstract

The production of urea by Thiosphaera pantotropha was studied. Batch cultures were grown on acetate as energy source and with NO3− or O2 as terminal electron acceptor. Urea accumulated in the media during exponential growth in aerobic and anaerobic cultures of T. pantotropha. Urea production continued after the cells had entered the stationary growth phase. Bacterial ability to produce urea was supported by studies of cultures enriched for denitrifying, sulphate‐reducing and fermenting bacteria. The results implied that urea production was common among bacteria normally considered to be important in marine sediments.