The role of cell to cell interactions and quorum sensing in formation of biofilms in drinking water bacteria

Microorganisms such as bacteria, fungi, viruses and protozoa in drinking water distribution systems readily colonize the pipe surfaces and form biofilms. The bacteria in drinking water distribution systems (DWDS) affect water quality and hydrodynamic parameters and can pose various public health risks. Previous studies showed that the resistance of bacteria to disinfection residual and other processes and interactions occurring within in the distribution system is due to multispecies interaction and biofilm formation. Therefore, it is important to understand the mechanisms involved in biofilm formation, interactions and aggregation by bacteria. The aim of this research was to understand the biological and biophysical interactions involved in multispecies biofilm formation and aggregation by drinking water bacterial isolates. As a first step in achieving this aim, nineteen bacteria were isolated from drinking water collected from a domestic water tap in Sheffield and identified by 16S rRNA gene sequencing. Four of the 19 isolates namely Shingobium sp., Xenophilus sp., Methylobacterium sp. and Rhodococcus sp., were used for further studies. The results of biological interactions such as intergeneric growth, aggregation and production of extracellular polymeric substances and quorum sensing (QS) molecules suggests that biofilm formation is governed by production of QS molecules by Methylobacterium and this may act as a synergistic bacterium in forming a multispecies biofilm. The results of biophysical interactions such as analysis of the cell surface composition, cell surface charge and hydrophobicity show that the surface charge of Methylobacterium was less negative charge and produced more biofilms. XDLVO modelling for Methylobacterium predicts adhesion at secondary minimum suggesting reversible adhesion but they may strongly influence secondary colonization by synergistic interaction. The overall results indicate that controlling the target bacterium such as Methylobacterium by interrupting the QS mechanism is perhaps an effective strategy to control multispecies biofilm formation in DWDS.