A mothur "list" file is tab-separated text.
Each (very long!) line has information for a set of
OTUs clustered at a given identity. The tab-separated fields are:
1. Clustering identity given as fractional difference, e.g. 0.03 is 97%.
2. Number of OTUs. 3, 4, 5... Labels for each OTU. Labels for a
given OTU are separated by commas.