Secondary Flow as a Mechanism for the Formation of Biofilm Streamers

Abstract

In most environments, such as natural aquatic systems, bacteria are found predominantly in self-organized sessile communities known as biofilms. In the presence of a significant flow, mature multispecies biofilms often develop into long filamentous structures called streamers, which can greatly influence ecosystem processes by increasing transient storage and cycling of nutrients. However, the interplay between hydrodynamic stresses and streamer formation is still unclear. Here, we show that suspended thread-like biofilms steadily develop in zigzag microchannels with different radii of curvature. Numerical simulations of a low-Reynolds-number flow around these corners indicate the presence of a secondary vortical motion whose intensity is related to the bending angle of the turn. We demonstrate that the formation of streamers is directly proportional to the intensity of the secondary flow around the corners. In addition, we show that a model of an elastic filament in a two-dimensional corner flow is able to explain how the streamers can cross fluid streamlines and connect corners located at the opposite sides of the channel.

Dynamics of Bacterial Aggregates in Microflows

“…γ is a measure of the biofilm cohesion estimated from the biofilm Young modulus. Reference [13] gives values in the range 70 − 140 Pa. To reduce the computational cost, we adjust it so that our biofilms involve a small number of tiles. Images in Reference [13] yield estimates for the adhesion time τ of 1 block of biomass per second.…”

Biomechanical Analysis of Infectious Biofilms

“…Non-linear streamers often form in rapid flow [89], whose visually-determined deformation fields can be fitted to those of simple elastic bodies to estimate static moduli [6,90]. More recently, microfluidic devices have been employed to provide better environmental control and ensure laminar flow [52,80,86,101], and fitting of visually-identified streamers [50] or partitioning walls [43] permits parameter estimation.…”

“…1, the relationship between the deformation and growth of immersed biofilms and the shear stresses generated by the surrounding fluid flow is complex and bidirectional. Biofilm morphology influences local flow patterns and hence the fluxes of dispersed phases such as nutrients, metabolites, and quorum sensing molecules [86,87,101], and flow can drive biofilm morphogenesis to rippled beds [42,89], streamers [80,89,90,101], and rolling clusters [79]. The relevance of such process to the formation, growth, and dispersal of both infectious and non-infectious biofilms demands quantitative modelling with a predictive capability, but this situation is far from being realised.…”

“…Streamers are elongated oscillating structures aligned with the flow direction that can form in turbulent conditions [89,90] or in rapid laminar flow in microfluidic devices [80,101], and can be visualised with optical or confocal microscopy and the profiles fitted to predictions for slender elastic filaments [6]. Note that fitting to elastic bodies only allows static quantities to be extracted, i.e.…”

Impact of tortuous flow on bacteria streamer development in microfluidic system during filtration

“…This difference in kinetics between these works could be partially attributed to the bacteria/channels size ratio differences. The mechanisms leading to streamer formation in such tortuous geometry has been discussed by Rusconi et al (2011). These authors highlighted the creation of EPS filaments and bacterial streamers between consecutive angles in the flow.…”