Abstract
The structure of biofilms in drinking water systems is influenced by the interplay between biological and physical processes. Bacterial aggregates in bulk fluid are important in seeding biofilm formation on surfaces. In simple pure and co-cultures, certain bacteria, including Methylobacterium, are implicated in the formation of aggregates. However, it is unclear whether they help to form aggregates in complex mixed bacterial communities. Furthermore, different flow regimes could affect the formation and destination of aggregates. In this study, real drinking water mixed microbial communities were inoculated with the Methylobacterium strain DSM 18358. The propensity of Methylobacterium to promote aggregation was monitored under both stagnant and flow conditions. Under stagnant conditions, Methylobacterium enhanced bacterial aggregation even when it was inoculated in drinking water at 1% relative abundance. Laminar and turbulent flows were developed in a rotating annular reactor. Methylobacterium was found to promote a higher degree of aggregation in turbulent than laminar flow. Finally, fluorescence in situ hybridisation images revealed that Methylobacterium aggregates had distinct spatial structures under the different flow conditions. Overall, Methylobacterium was found to be a key strain in the formation of aggregates in bulk water and subsequently in the formation of biofilms on surfaces.
Highlights
The formation of biofilms on pipe walls is controlled by physical, biological, and chemical processes [1]
The interaction between hydrodynamics and biofilm growth and morphology has received significant attention. Both modelling [66,67] and experimental studies [57,68] have revealed the important roles that, for example, shear-stress-induced detachment of cells or increased oxygen transport to a biofilm in turbulent flow conditions play on the structure and growth of an established biofilm
This does give some inkling of ways of managing the flow of the water distribution system to control the sloughing of biofilm material into the bulk water that emerges at the tap
Summary
The formation of biofilms on pipe walls is controlled by physical, biological, and chemical processes [1]. One important biological process is bacterial aggregation, where microorganisms interact with each other, forming a cluster that is free-floating and can be attached to a substratum as part-of or a precursor-to a biofilm [2] This adhesion mechanism has been suggested to influence the formation of complex multi-species biofilms in several diverse habitats [3]. Species of Methylobacterium are found in a wide variety of environments, such as soil, dust, freshwater, lake sediments, leaf surfaces, air, root nodules, rice grains, and hospital environments [15] They exhibit resistance to chlorination in drinking water, which might explain their prevalence in domestic water-associated environments, such as drinking water distribution systems, shower curtains, and showerhead biofilms [16,17].
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