Phylogenetic tree of partial nox gene sequences from 81 cultured Brachyspira isolates. Representative strains of recognized species are included for reference. Numbers at the nodes indicate bootstrap values out of 100 iterations. Scale bar indicates number of substitutions per site. Production stage is indicated by colour (legend) and square markers indicate strongly beta-haemolytic isolates. Genbank accession numbers are indicated in parentheses for published sequences. Clusters of unclassified isolates (Clusters 1, 2 and 3) are indicated, and discussed in the text.