GENOMIC HETEROGENEITY OF THE GENUS NITROBACTER

The genomic diversity among 22 Nitrobacter strains was investigated by determining rRNA gene restriction patterns, DNA hybridization characteristics, and DNA base compositions. The guanine-plus-cytosine contents of the DNAs ranged from 58 to 61 mol%. As determined by DNA hybridization (S1 nuclease method), five DNA genomic groups were differentiated, and these groups formed three genomic species. Genomic species 1, which corresponded to Nitrobacter winogradskyi, was split into three subspecies. Subspecies 1a contained strain W (= ATCC 25391), the type strain of N. winogradskyi; subspecies 1b contained proposed reference strain 6R; and subspecies 1c contained a strain of "Nitrobacter agilis" (strain ATCC 14123). Genomic species 2, which has not been described previously and which contained proposed reference strain LL and four strains that were isolated from lake sediments, was distinct from N. winogradskyi and Nitrobacter hamburgensis. This species is not named in this paper since it could not be differentiated from N. winogradskyi and N. hamburgensis on the basis of phenotypic characteristics. Genomic species 3 corresponded to N. hamburgensis and was distantly related to the other genomic species.