A. Aakra et al., Detailed phylogeny of ammonia-oxidizing bacteria determined by rDNA sequences and DNA homology values, INT J SY EV, 51, 2001, pp. 2021-2030
Citations number
38
Categorie Soggetti
Microbiology
Journal title
INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY
A comparison of the phylogeny of 38 isolates of chemolithoautotrophic ammon
ia-oxidizing bacteria (AOB) based on 16S rRNA gene sequences, 16S-23S rDNA
intergenic spacer region (ISR) sequences and species affiliations based on
DNA homology values was performed. The organisms studied all belong to the
beta -subclass of the Proteobacteria and included representatives of Nitros
omonas, Nitrosococcus and Nitrosospira. The similarity values of the 16S rD
NA sequences were high, particularly within the Nitrosospira genus, and bas
ed on these sequences it is difficult to determine the phylogenetic positio
n of some AOB. As an alternative and supplement to 16S rRNA gene sequencing
, the ISR was sequenced and analysed phylogenetically. Due to considerably
lower similarity values, the ISR-based phylogeny gives a better resolution
than the phylogeny based on the functional 16S rRNA gene. Since the ISR-bas
ed phylogeny of AOB is highly consistent with the 16S rDNA based phylogeny,
ISR sequencing appears as a suitable tool for resolving the detailed phylo
geny of AOB. The phylogenetic position of two isolates of the former genus
'Nitrosolobus' (now included in the Nitrosospira genus) is not clear. These
organisms are close relatives of the former Nitrosospira spp. and 'Nitroso
vibrio' spp. (now Nitrosospira), but based on their marginal positions in t
he phylogenetic trees, DNA-DNA hybridization data and phenotypic characteri
stics, it is suggested that 'Nitrosolobus' should be a separate genus. DNA
homology determination of 11 Nitrosospira isolates revealed two new species
of Nitrosospira. The phylogeny of AOB reflected in the trees based on the
rDNA sequences is consistent with the species affiliations of AOB by DNA ho
mology values. This observation will probably be important for the interpre
tation of results from studies of natural diversity of AOB.