Metagenomic analysis of an ecological wastewater treatment plant's microbial communities and their potential to metabolize pharmaceuticals.

Pharmaceuticals and other micropollutants have been detected in drinking water, groundwater, surface water, and soil around the world. Even in locations where wastewater treatment is required, they can be found in drinking water wells, municipal water supplies, and agricultural soils. It is clear conventional wastewater treatment technologies are not meeting the challenge of the mounting pressures on global freshwater supplies. Cost-effective ecological wastewater treatment technologies have been developed in response. To determine whether the removal of micropollutants in ecological wastewater treatment plants (WWTPs) is promoted by the plant-microbe interactions, as has been reported for other recalcitrant xenobiotics, biofilm microbial communities growing on the surfaces of plant roots were profiled by whole metagenome sequencing and compared to the microbial communities residing in the wastewater. In this study, the concentrations of pharmaceuticals and personal care products (PPCPs) were quantified in each treatment tank of the ecological WWTP treating human wastewater at a highway rest stop and visitor center in Vermont. The concentrations of detected PPCPs were substantially greater than values reported for conventional WWTPs likely due to onsite recirculation of wastewater. The greatest reductions in PPCPs concentrations were observed in the anoxic treatment tank where Bacilli dominated the biofilm community. Benzoate degradation was the most abundant xenobiotic metabolic category identified throughout the system. Collectively, the microbial communities residing in the wastewater were taxonomically and metabolically more diverse than the immersed plant root biofilm. However, greater heterogeneity and higher relative abundances of xenobiotic metabolism genes was observed for the root biofilm.

Isolation and characterization of pyrene metabolizing microbial consortia from the plant rhizoplane.

Most research on the ecology of PAH degrading bacteria in the rhizosphere has focused on individual strains that grow on specific PAHs. Thus, there are fundamental questions as to importance of microbial consortia for PAH degradation in the plant rhizosphere. The study reported here characterized cultivable pyrene degrading rhizoplane microbial communities from two different plant species using a root printing technique on agar plates. Colonies were revealed by formation of clearing zones on medium containing a thin film of pyrene on the surface of a mineral nutrient agar. Prints of the rhizoplane colonies were obtained from roots of Melilotus officinalis (sweet yellow clover) and Andropogon gerardii (big bluestem) plants. Phylogenetic characterizations of selected pyrene degrading colonies were assessed by PCR-DGGE and DNA sequencing. Results showed that different populations of cultivable pyrene degraders were obtained from representative consortia that were examined. Many of the PAH degrading consortia consisted of mixtures of bacterial species that were unable to degrade pyrene by themselves. While this study focused on culturable PAH degraders, the results suggest that pyrene degradation in the rhizosphere commonly involves the activity of bacterial consortia in which various species of bacteria interact to achieve PAH degradation.

Pyrene effects on rhizoplane bacterial communities.

Certain plant species promote biodegradation of polycyclic aromatic hydrocarbons (PAHs), but few studies have examined the microbial populations that are associated with the rhizoplane of these plants. In this study, the bacterial composition of the rhizoplane were characterized for four plant species during in soils with different histories of exposure to PAH and in the presence or absence of a pyrene spike at 100 mg kg(-1) pyrene. Three of the plant species including Andropogon gerrardii, Panicum coloratum and Melilotus officinalis were known to stimulate PAH degradation. Wheat (Triticum aestivum) was used as a reference species. Results showed that after 90 days, approximately 45% of the pyrene spike disappeared from soil without plants. In contrast, cultivation of plants resulted in 95% disappearance of pyrene. There were no significant differences in the extent of pyrene disappearance for different plants. In all cases, 16S rRNA gene profiles of the rhizoplane were less complex in the pyrene-spiked soils, suggesting that richness and evenness of the predominant bacteria were reduced. Our results show that pyrene contamination results in significant shifts in the composition of rhizosphere bacterial communities that are still further influenced by the plant species and prior exposure history to PAH contamination.