3. The estimation of species and genetic diversity based on DNA metabarcoding data from the aquatic environments
3.1 On the basis of the global reference
After the filtering and demultiplexing procedure, the COI fragment had 2188718 reads, of which 513152 reads were unique (Table 2). The control detected 1308 reads (0.06% of the total). The clustering revealed approximately 3,000 OTUs. Most of them were not classified to any of the life domains. After the blasting procedure based on the global reference database, 326 OTUs belonging to Eukaryota (284) and Bacteria (42) were retained for subsequent work. After the reduction of the taxonomy, a total of 243431 (27.4%) reads remained in the table, with a minimum threshold of 5 reads per OTU (Table S1). The number of reads attributable to different OTUs was highly non-uniform. The average value was 477.3±159.3. The modal group, which was 5 reads, characterized more than 17% of all the OTUs in the different samples.
Table 2. Number of reads and OTUs that corresponded to each of the aquatic DNA samples based on the global reference library