This research focuses on pyrosequencing analysis of bacteria in an experimental drinking water distribution system. Bulk water and biofilms had markedly different bacterial community structures. Biofilms had higher species richness and diversity under highly varied flow regimes, and more compact biofilms were generated.
Microbial biofilms formed on the inner-pipe surfaces of drinking water distribution systems (DWDS) can alter drinking water quality, particularly if they are mechanically detached from the pipe wall to the bulk water, e.g. resulting from changes in hydraulic conditions.
Here researchers at the University of Sheffield in the UK present results from applying 454 pyrosequencing of the 16S ribosomal RNA (rRNA) gene, to investigate the influence of different hydrological regimes on bacterial community structure.
They also study the potential mobilisation of material from the pipe walls to the network using a full-scale, temperature-controlled experimental pipeline facility that is accurately representative of a live drinking water distribution system.
Analysis of pyrosequencing and water physico-chemical data shows that habitat type (water versus biofilm) and hydraulic conditions influence the bacterial community structure and composition in this experimental DWDS.
The bacterial community composition clearly differs between biofilms and bulk water samples. Gammaproteobacteria and Betaproteobacteria were the most abundant phyla in biofilms, while Alphaproteobacteria were predominant in bulk water samples.
This suggests that bacteria inhabiting biofilms – predominantly species belonging to the genera Pseudomonas, Zooglea, and Janthinobacterium – have an enhanced ability to express extracellular polymeric substances to adhere to surfaces, and to favour co-aggregation between cells, than those found in the bulk water.
The highest species richness and diversity were detected in 28 days-old biofilms, and this was accentuated for highly varied flow conditions.
Flushing altered the pipe-wall bacterial community structure, but did not completely remove bacteria from the pipe walls, particularly under highly varied flow conditions. This suggests that more compact biofilms were generated under these conditions.
This research brings new knowledge regarding the influence of different hydraulic regimes on the composition and structure of bacterial communities within drinking water distribution systems, and the implications that this might have for drinking water quality.
