Metabarcoding reveals that bacterial and fungal microbiomes are perturbed by micropollutants in a fjord system (Hakefjorden and Askerofjorden) at the Swedish west coast

Fjord systems are susceptible to anthropogenic pressures, including discharges from wastewater treatment plants (WWTPs), which introduce micropollutants into coastal waters. We investigated the impact of micropollutants on bacteria and fungi within a fjord system adjacent to a significant petrochemical industry hub on the Swedish west coast. We characterised microbial assemblages along a land-to-sea transect, encompassing freshwater streams receiving agricultural and urban runoff, as well as the direct effluent from a WWTP. Our findings revealed elevated concentrations and a diverse array of micropollutants in the WWTP effluent and the stream running through the urban/industrial zone, highlighting these areas as major sources of pollution to the fjord. Bacterial and fungal communities inhabiting the WWTP effluent and the receiving marine waters near the marine outflow exhibited distinct structural compositions, indicating a selective pressure exerted in part by the micropollutant load. While freshwater sites generally displayed higher overall microbial diversity compared to marine sites, the WWTP effluent showed reduced diversity in both bacterial and fungal communities, likely due to the impact of micropollutants. Interestingly, marine sites far from the WWTP discharges exhibited a recovery in bacterial diversity, suggesting a potential response or adaptation. In contrast, fungal diversity remained comparable to that observed in other marine locations. Multivariate analyses identified physicochemical parameters and nutrients, alongside with summed fungicides and antibiotic stress as key factors driving the community dissimilarities across the fjord. Significant disruptions in potential bacterial metabolism and fungal ecological functions were evident at the WWTP discharge point, underscoring the ecological consequences of wastewater pollution. HighlightsO_LIWWTP discharge is the primary source of complex micropollutants in the fjord. C_LIO_LIAntibiotics and fungicides significantly shape bacterial and fungal communities. C_LIO_LIWastewater impacts reduce microbial diversity and disrupt functional potential. C_LIO_LIMarine sites show microbial recovery and enrichment away from discharge points. C_LIO_LIeDNA and toxic unit modeling link chemical stress to microbiome restructuring. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=108 SRC="FIGDIR/small/711609v1_ufig1.gif" ALT="Figure 1"> View larger version (64K): org.highwire.dtl.DTLVardef@1751e5forg.highwire.dtl.DTLVardef@1d0d78org.highwire.dtl.DTLVardef@15f446aorg.highwire.dtl.DTLVardef@184bb0a_HPS_FORMAT_FIGEXP M_FIG C_FIG