Drinking water biofilms on copper and stainless steel exhibit specific molecular responses towards different disinfection regimes at waterworks

Abstract

Biofilms growing on copper and stainless steel substrata in natural drinking water were investigated. A modular pilot-scale distribution facility was installed at four waterworks using different raw waters and disinfection regimes. Three-month-old biofilms were analysed using molecular biology and microscopy methods. High total cell numbers, low counts of actively respiring cells and low numbers of cultivable bacteria indicated the high abundance of viable but not cultivable bacteria in the biofilms. The expression of the recA SOS responsive gene was detected and underlined the presence of transcriptionally active bacteria within the biofilms. This effect was most evident after UV disinfection, UV oxidation and UV disinfection with increased turbidity at waterworks compared to chemically treated and non-disinfected systems. Furthermore, live/dead staining techniques and environmental scanning electron microscopy imaging revealed the presence of living and intact bacteria in biofilms on copper substrata. Cluster analyses of DGGE profiles demonstrated differences in the composition of biofilms on copper and steel materials.

Keywords:

• biofilms
• drinking water
• copper and steel
• gene expression
• VBNC

Acknowledgements

The authors thank the German BMBF (Federal Ministry of Education and Research) for funding the project. Further, thanks are extended to the four German municipal drinking water suppliers for financial and technical support. Dr Annika Rieder and Johannes Alexander are acknowledged for critical reading of the manuscript. This study was supported by the Karlsruhe Institute of Technology (KIT).