SUMMARY: The generic distribution of nitrate-respiring bacteria in tidal mudflats of six Scottish east-coast river estuaries has been determined. The predominant bacteria involved were identified as spp., together with lower numbers of enterobacteria. Pseudomonads accounted for only a small proportion of the nitrate-respiring populations. Samples of sediment from all the estuaries produced nitrite and ammonia after 7 d incubation at 15 °C with added nitrate. Studies with the isolate V48 and strains of (NCMB 1903 and NCMB 2047) demonstrated that when these bacteria were grown anaerobically under conditions of glucose limitation, nitrite was the primary product of nitrate respiration, whereas ammonia was excreted into the medium when nitrogen was limiting. Nitrate reduction was accompanied by the synthesis of a particulate nitrate reductase and under N-limitation a nitrite reductase was also induced.


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