OTU numbers in the V5 'Artificial Community' as a function of percent sequence difference - logarithmic. 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 following filtering (red line), pyrosequencing noise removal by the first PyroNoise stage of AmpliconNoise (green line), further removal of PCR point mutations by the second SeqNoise stage (blue line) and following removal of chimeric sequences (magenta line). For comparison the number of OTUs obtained by clustering the known reference sequences are shown in black. The y-axis is logarithmically scaled.