Characterisation of the physical composition and microbial community structure of biofilms within a model full-scale drinking water distribution system.

Katherine E Fish,Isabel Douterelo,Nicola H Green,Rebecca L Sharpe,Richard Collins,Joby B Boxall,A Mark Osborn,A Mark Ibekwe

doi:10.1371/journal.pone.0115824

Katherine E Fish, Isabel Douterelo + Show 6 more

Open Access

https://doi.org/10.1371/journal.pone.0115824

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Abstract

Within drinking water distribution systems (DWDS), microorganisms form multi-species biofilms on internal pipe surfaces. A matrix of extracellular polymeric substances (EPS) is produced by the attached community and provides structure and stability for the biofilm. If the EPS adhesive strength deteriorates or is overcome by external shear forces, biofilm is mobilised into the water potentially leading to degradation of water quality. However, little is known about the EPS within DWDS biofilms or how this is influenced by community composition or environmental parameters, because of the complications in obtaining biofilm samples and the difficulties in analysing EPS. Additionally, although biofilms may contain various microbial groups, research commonly focuses solely upon bacteria. This research applies an EPS analysis method based upon fluorescent confocal laser scanning microscopy (CLSM) in combination with digital image analysis (DIA), to concurrently characterize cells and EPS (carbohydrates and proteins) within drinking water biofilms from a full-scale DWDS experimental pipe loop facility with representative hydraulic conditions. Application of the EPS analysis method, alongside DNA fingerprinting of bacterial, archaeal and fungal communities, was demonstrated for biofilms sampled from different positions around the pipeline, after 28 days growth within the DWDS experimental facility. The volume of EPS was 4.9 times greater than that of the cells within biofilms, with carbohydrates present as the dominant component. Additionally, the greatest proportion of EPS was located above that of the cells. Fungi and archaea were established as important components of the biofilm community, although bacteria were more diverse. Moreover, biofilms from different positions were similar with respect to community structure and the quantity, composition and three-dimensional distribution of cells and EPS, indicating that active colonisation of the pipe wall is an important driver in material accumulation within the DWDS.

Highlights

Drinking water distribution systems (DWDS) are an essential infrastructure integral to the provision of a safe water supply
It is recognised that fluorophores applied to target cells will stain extracellular DNA as well as intracellular DNA, eDNA has been reported at very low concentrations in extracellular polymeric substances (EPS) and, if present, is likely to be in concentrations below the limit of detection of staining methods [16]
The novel, full-scale experimental system and analyses presented provide a detailed approach to characterize the structure of drinking water biofilms formed under real-world conditions

Summary

Introduction

Drinking water distribution systems (DWDS) are an essential infrastructure integral to the provision of a safe water supply. DWDS function as microbiological and physico-chemical reactors which interact with drinking water and, in turn, impact upon the quality of the water supplied to customers. Accumulation of microbiological, organic and inorganic material at the pipe wall (and its subsequent release) plays a key role in water quality degradation [1]. Microorganisms have been shown to attach to surfaces and form biofilms comprising cells embedded within a microbially-produced matrix of extracellular polymeric substances (EPS) [2]. Research specific to full-scale DWDS pipeline surfaces is limited, it is likely that biofilms are integral to the accumulation of material upon the inner pipe surfaces. The subsequent mobilisation of microbial cells, EPS and any associated particles, into drinking water will have aesthetic, chemical and biological implications upon water quality

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