Table 2.

Comparison of the relative abundance of dfrB gene variants (copies per 16 S rRNA gene copies) in WWTP effluents and river samples.

Gene variant	Wastewater samples	River samples	Higher in	adj. p value	Signif. code	Confirmed by split sampling in
dfrB1	3.7e−05	1.8e−06	Wastewater	1.9e−17	***	2/2 subsets
dfrB2	3.9e−06	1.2e−06	Wastewater	6.3e−04	***	2/2 subsets
dfrB3	6.6e−05	5.9e−06	Wastewater	1.5e−05	***	2/2 subsets
dfrB4	1.9e−05	4.7e−06	Wastewater	2.4e−07	***	2/2 subsets
dfrB5	1.6e−06	0e+00	Wastewater	0.0064	**	1/2 subsets
dfrB7	4.7e−06	0e+00	Wastewater	8.8e−06	***	2/2 subsets
dfrB9	0e+00	4.6e−05	River samples	3.5e−06	***	2/2 subsets
dfrB10	2.4e−06	2e−04	River samples	1.3e−17	***	2/2 subsets
dfrB13	0e+00	2.2e−05	River samples	0.0011	**	1/2 subsets
dfrB14	3.5e−06	1.7e−05	River samples	0.26	n.s.
dfrB15	7.8e−07	2.3e−06	River samples	1	n.s.
dfrB16	3.9e−07	1.2e−06	River samples	0.65	n.s.
dfrB17	0e+00	1.2e−06	River samples	0.44	n.s.
dfrB19	0e+00	3.5e−06	River samples	0.14	n.s.
dfrB20	0e+00	5.9e−07	River samples	0.57	n.s.
dfrB21	0e+00	5.9e−07	River samples	0.57	n.s.

Reported p values refer to a Wilcoxon rank sum test with the null hypothesis being that the relative abundances of dfrB gene variants are equal in both groups. Each variant was considered a distinct hypothesis and p values were adjusted accordingly (***: p < 0.001, **: p < 0.01, n.s.: not significant). The rightmost column indicates whether the significance of contrasts (adj. p value  <  0.05) could be verified on independent data subsets, each representing 50% of the bacterial DNA from wastewater and river samples, respectively.