Copy number of total 16S rRNA genes present in a dilution series of S. bongori culture. Total bacterial DNA present in serial ten-fold dilutions of a pure S. bongori culture was quantified using qPCR. While the copy number initially reduces in tandem with increased dilution, plateauing after four dilutions indicates consistent background levels of contaminating DNA. Error bars indicate standard deviation of triplicate reactions. The broken red line indicates the detection limit of 45 copies of 16S rRNA genes. The no template internal control for the qPCR reactions (shown in blue) was below the cycle threshold selected for interpreting the fluorescence values (that is, less than 0), indicating the contamination did not come from the qPCR reagents themselves.