Genome-resolved analyses of oligotrophic groundwater microbial communities along phenol pollution in a continuous-flow biodegradation model system

Groundwater pollution is one of the major environmental concerns. The entrance of pollutants into the oligotrophic groundwater ecosystems alters native microbial community structure and metabolism. This study investigated the application of innovative Small Bioreactor Chambers and CaO2 nanoparticles for phenol removal within continuous-flow sand-packed columns for 6 months. Scanning electron microscopy and confocal laser scanning microscopy analysis were conducted to indicate the impact of attached biofilm on sand surfaces in bioremediation columns. Then, the influence of each method on the microbial biodiversity of the column's groundwater was investigated by next-generation sequencing of the 16S rRNA gene. The results indicated that the simultaneous application of biostimulation and bioaugmentation completely eliminated phenol during the first 42 days. However, 80.2% of phenol remained in the natural bioremediation column at the end of the experiment. Microbial diversity was decreased by CaO2 injection while order-level groups known for phenol degradation such as Rhodobacterales and Xanthomonadales dominated in biostimulation columns. Genome-resolved comparative analyses of oligotrophic groundwater prokaryotic communities revealed that Burkholderiales, Micrococcales, and Cytophagales were the dominant members of the pristine groundwater. Six-month exposure of groundwater to phenol shifted the microbial population towards increasing the heterotrophic members of Desulfobacterales, Pseudomonadales, and Xanthomonadales with the degradation potential of phenol and other hydrocarbons.

Automated summary

This study investigated the removal of phenol using Small Bioreactor Chambers and CaO2 nanoparticles in continuous-flow sand-packed columns. The results showed that simultaneous biostimulation and bioaugmentation could completely eliminate phenol within 42 days, while natural bioremediation columns still had 80.2% remaining at the end of the experiment. CaO2 injection decreased microbial diversity, with order-level groups such as Rhodobacterales and Xanthomonadales dominating in biostimulation columns. Long-term exposure to phenol shifted the microbial population towards heterotrophic members with the potential for phenol and hydrocarbon degradation.