| Summary: | The ability of WWTP outflow bacteria at colonizing rock surfaces and contributing to the formation of river epilithic biofilms was investigated. Bacterial community structures of biofilms (b-) developing on rocks exposed to treated wastewaters (TWW) of a hospital (HTWW) and a domestic (DTWW) clarifier, and to surface waters of the stream located at 10 m, 500 m, and 8 km from the WWTP outlet, were compared. Biofilm bacterial contents were analyzed by cultural approaches and a <i>tpm</i>-based DNA metabarcoding analytical scheme. Co-occurrence distribution pattern analyses between bacterial datasets and eighteen monitored pharmaceuticals were performed. Higher concentrations of iohexol, ranitidine, levofloxacin, and roxithromycin were observed in the b-HTWW while atenolol, diclofenac, propranolol, and trimethoprim were higher in the b-DTWW. MPN growth assays showed recurrent occurrences of <i>Pseudomonas aeruginosa</i> and <i>Aeromonas caviae</i> among these biofilms. An enrichment of multi-resistant <i>P. aeruginosa</i> cells was observed in the hospital sewer line. <i>P. aeruginosa</i> MPN values were negatively correlated to roxithromycin concentrations. The <i>tpm</i> DNA metabarcoding analyses confirmed these trends and allowed an additional tracking of more than 90 species from 24 genera. Among the recorded 3082 <i>tpm</i> ASV (amplicon sequence variants), 41% were allocated to the <i>Pseudomonas</i>. Significant differences through ANOSIM and DESeq2 statistical tests were observed between ASV recovered from b-HTWW, b-DTWW, and epilithic river biofilms. More than 500 ASV were found restricted to a single sewer line such as those allocated to <i>Aeromonas popoffii</i> and <i>Stenotrophomonas humi</i> being strictly found in the b-HTWW file. Several significant correlations between <i>tpm</i> ASV counts per species and pharmaceutical concentrations in biofilms were recorded such as those of <i>Lamprocystis purpurea</i> being positively correlated with trimethoprim concentrations. A <i>tpm</i> source tracking analysis showed the b-DTWW and b-HTWW <i>tpm</i> ASV to have contributed, respectively, at up to 35% and 2.5% of the epilithic river biofilm <i>tpm</i>-taxa recovered downstream from the WWTP outlet. Higher contributions of TWW taxa among epilithic biofilms were recorded closer to the WWTP outlet. These analyses demonstrated a coalescence of WWTP sewer communities with river freshwater taxa among epilithic biofilms developing downstream of a WWTP outlet.
|
|---|