OTU numbers in the V5 'Artificial Community' as a function of percent sequence difference - linear. Numbers of OTUs formed at cut-offs of increasing percent sequence difference after complete linkage clustering of the 'Artificial Community' V5 data set (Table 1). Distances were calculated following pair-wise alignment with the Needleman-Wunsch algorithm, results are shown for the filtered sequences after pyrosequencing and PCR noise removal by AmpliconNoise (magenta line), for single-linkage preclustering at 1% (purple) and SLP at 2% (cyan), for the DeNoiser algorithm (orange), and for the original one-stage PyroNoise algorithm (dark green line). In all cases chimeric sequences were removed. For comparison the number of OTUs obtained by clustering the known reference sequences are shown in black. The y-axis is scaled linearly.