See also
Quality control
for OTU sequences
Contamint species can be introduced into your samples at every stage in the experimental protocol from sample collection to sequencing (e.g., residue on the flow-cell).
Detecting contaminants is difficult / impossible except in control samples
e.g., distilled water, or a mock community. Control samples can be used to
detect contaminants introduced in the stages from library preparation to
sequencing. Note that cross-talk can also cause
unexpected sequences in a control sample.