Submerged filter biofilm formation by nitrate-contaminated groundwater microbiota

Abstract

Denitrifying biofilms developed in a lab-scale submerged filter by autochthonous bacteria from nitrate-contaminated groundwater were studied. The system was supplied with groundwater (16 mg N-NO₃ ⁻/L), from which the oxygen had been eliminated and to which an excess of carbon source had been added. The reactor was incubated in a thermostated chamber at 5°C, 10°C, 20°C and 30°C. Colonization of the support was studied using surface scanning microscopy, and biofilm bacterial composition was studied by PCR/TGGE. Support material was colonized at all the temperatures assayed, although this parameter affected the growth of the biofilm, which developed most at temperatures over 20°C. The composition of bacterial communities varied according to the temperature. Community profiles of the biofilm formed at 5°C and 10°C clustered away from those of the biofilm formed at 20°C and 30°C. 16S rDNA sequences reveled that the biofilm was mainly composed of psychrotolerant species typically inhabiting freshwaters, and we obtained sequencing bands that were affiliated to denitrifying and non-denitrifying heterotrophic species. The extent of colonization was low when compared to previously inoculated systems, and the capacity for nitrate elimination was also low.

Keywords:

• Biofilm
• colonization
• submerged filter
• temperature
• PCR-TGGE

Acknowledgments

This study was supported by funds from the European Union and Spanish Ministry of Education and Science (FIT-310200-2004-3). The study was carried out at the Institute of Water Research and the Department of Civil Engineering, University of Granada. The article was translated from Spanish by Julian Bourne of the Faculty of Translation and Interpreting, University of Granada.