Phylogenetic diversity within the genus Nitrosomonas

The phylogenetic relationships within the genus Nitrosomonas were examined in order to obtain a basis for the development of a taxonomically, as well as ecophysiologically related gene probe system suitable for in situ analysis of natural populations of ammonia-oxidizing bacteria. In addition to the 10 validly described species and three undefined species of the genus Nitrosomonas, Nitrosococcus mobilis was included in this study. On the basis of 16S rRNA gene sequence results and DNA-DNA hybridization data, six distinct lines of descent, containing closely related or single species, can be distinguished. One of these lineages allied N. europaea and N. eutropha, which are both common in eutrophic freshwater habitats and which are both halotolerant, together with the obligately halophilic N. halophila. FLU these three species are urease negative. A second lineage vr;as defined by the three marine species N. marina, N. aestuarii and Nitrosomonas sp, Nm 51, which are all obligately halophilic and urease positive. Two other distinct groups comprised oligotrophic Nitrosomonas species originating from terrestrial or freshwater environments. Members of one group were N. ureae and N. oligotropha, both being urease positive, and the other group contained the urease positive N. nitrosa together with the urease negative N. communis and Nitrosomonas spp. Nm 33 and Nm 41. The remaining two lineages were represented by single marine species, N. cryotolerans and Nitrosococcus mobilis, respectively. Based on currently available 16S rDNA sequences primer pairs useful fur specific PCR assisted detection of ecophysiologically defined groups of ammonia oxidizers were selected.