Evidence for a novel nitrate reductase in the dissimilatory iron-reducing bacterium Geobacter metallireducens

Nitrate induced the expression of a membrane-bound nitrate reductase in the strict anaerobe Geobacter metallireducens. A fraction from a DEAE cellulose column which showed nitrate reductase activity contained polypeptides of Mr, 18, 36 and 43 K and three c type cytochromes (Mr 28, 46 and 68 K). Western and Southern blot analysis revealed no homology between the nitrate reductase from G. metallireducens and the nitrate reductases from respiratory (Escherichia coli) and denitrifying bacteria (Pseudomonas stutzeri, Pseudomonas aeruginosa) which were shown to be related. These data, in addition to this organism's inability to use fumarate or formate, suggest that its nitrate reductase is novel.