FIG. 2.

Phylogenetic tree showing the position within members of the class β-Proteobacteria of partial 16S rDNA sequences recovered from Buttermere lake sediments by using primers designed to amplify sequences from the β-subgroup ammonia-oxidizing bacteria. Sequences from the strains named were obtained from the RDP (25). Sequence analysis was performed for 345 base positions. E. coli was used as an outgroup. Bootstrap values represent percentages from 100 resamplings of the data (14, 31). The scale bar indicates 0.1 substitutions per nucleotide base. Environmental clones are referred to with reference to the sample site from which they were recovered, with PV₃ indicating profundal sediment (September), PV₂ indicating profundal sediment (August), LV₁ indicating littoral sediment (July), and LV₃ indicating littoral sediment (September). cons, consensus.