| Abstract: | The gross morphology, fine structure, and per cent guanine plus cytosine (GC) composition of deoxyribonucleic acid of 27 strains of nitrifying bacteria were compared. Based on morphological differences, the ammonia-oxidizing bacteria were separated into four genera. Nitrosomonas species and Nitrosocystis species formed one homogenous group, and Nitrosolobus species and Nitrosospira species formed a second homogenous group in respect to their deoxyribonucleic acid GC compositions. Similarly, the nitrite-oxidizing bacteria were separated into three genera based on their morphology. The members of two of these nitrite-oxidizing genera, Nitrobacter and Nitrococcus, had similar GC compositions, but Nitrospina gracilis had a significantly lower GC composition than the members of the other two genera. |
