In a discovery that can have far-reaching implications for studying marine ecosystems and understanding how infections happen in medical devices, researchers have discovered that bacterial movement is slowed down in flowing water - enhancing the likelihood that the microbes will attach to surfaces.
The flow of liquid can have two significant effects on microbes. It quenches the ability of microbes to chase food and helps them find surfaces.“The phenomenon could lead to new approaches to tuning flow rates to prevent fouling of surfaces by microbes - potentially averting everything from bacteria getting a toehold on medical equipments to form biofilms,” explained Roman Stocker, an associate professor of civil and environmental engineering at Massachusetts Institute of Technology (MIT).The effect of flowing water on bacterial swimming was 'a complete surprise', he added.The team found that swimming bacteria cluster in the 'high shear zones' in a flow - the regions where the speed of the fluid changes most abruptly.
Such high shear zones occur in most types of flows and in many bacterial habitats.One prominent location is near the walls of tubes where the result is a strong enhancement of the bacteria's tendency to adhere to those walls and form biofilms.But this effect varies greatly depending on the speed of the flow, opening the possibility that the rate of biofilm formation can be tweaked by increasing or decreasing flow rates.“Our results might suggest additional design criteria for biomedical devices, which should operate outside this range of shear rates, when possible - either faster or slower,” added co-author Jeffrey Guasto, an assistant professor of mechanical engineering at Tufts University.Biofilms are found everywhere. They cause major problems in industrial settings such as by clogging pipes or reducing the efficiency of heat exchangers.Their adherence is also a major health issue. Bacteria concentrated in biofilms are up to 1,000 times more resistant to antibiotics than those suspended in liquid.The new findings, published in the journal Nature Physics, could also be important for studies of microbial marine ecosystems by affecting how bacteria move in search of nutrients when one accounts for the ubiquitous currents and turbulence.