Changes in bacterial diversity and catabolic gene abundance during the removal of dimethylphenol isomers in laboratory-scale constructed wetlands
Constructed wetlands (CWs) are well-established wastewater treatment technologies and applied for bioremediation of contaminated water. Despite the optimal performance of CWs, the understanding of the bacterial processes in the rhizosphere, where mainly microbial degradation processes take place, is still limited. In the present study, laboratory-scale CWs planted with Juncus effusus and running under controlled conditions were studied in order to evaluate removal efficiency of dimethylphenols (DMPs), also in comparison to an unplanted bed. Next to removal rates, the bacterial community structure, diversity, and distribution, their correlation with physiochemical parameters, and abundance of the phenol hydroxylase gene were determined. As a result, better removal performance of DMP isomers (3,4-, 3,5-, and 2,6-DMP added as singles compounds or in mixtures) and ammonium loads, together with a higher diversity index, bacterial number, and phenol hydroxylase gene abundance in Juncus effusus CW in comparison with the non-planted CW, indicates a clear rhizosphere effect in the experimental CWs. An enhancement in the DMP removal and the recovery of the phenol hydroxylase gene were found during the fed with the DMP mixture. In addition, the shift of bacterial community in CWs was found to be DMP isomer dependent. Positive correlations were found between the bacteria harboring the phenol hydroxylase gene and communities present with 3,4-DMP and 3,5-DMP isomers, but not with the community developed with 2,6-DMP. These results indicate that CWs are highly dynamic ecosystems with rapid changes in bacterial communities harboring functional catabolic genes.
KeywordsConstructed wetlands Xylenols Biodegradation Phenol hydroxylase Rhizosphere effect Bacterial community
We thank the Department of Environmental Microbiology-UFZ for the collaboration with the equipment for the community analysis. Special thanks to Uwe Kappelmeyer for his suggestions during the conception of the study, the critical reading with the improvements in the manuscript. We also thank Roisin Murtagh for the improvement of the English language. We would also like to thank Dr. Sabine Kleinsteuber and Dr. Athaydes Francisco Leite Junior for their support for script management for n-MDS analysis.
Mónica A. Vásquez Piñeros received sustaining grant for Doctoral studies from COLCIENCIAS Departamento de Ciencia, Tecnología e Innovación- República de Colombia
Compliance with ethical standards
Human and animal studies
This article does not contain any studies with human or animals performed by any of the authors.
Conflict of interest
The authors declare that they have no conflict of interest.
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