THE FORMATION OF MICROBIAL STREAMERS AND THEIR HYDRODYNAMIC ROLES

Microbial streamers are productive, top-most roughness elements of surface-attached microbial communities that form under shallow, channelized turbulent flow. They are common features found in modern hotspring environments. Being very productive systems, they also represent an often missed link in the microbial carbon cycle. However, it is unclear how they form and if their presence affects the flows in any significant way. We developed flume experiments employing Particle Image/Tracking Velocimetry (PIV/PTV) to gain quantitative insights into the behaviors of flows around embedded objects. The use of 3D fabricated shapes, sheet laser, tracer particles and high speed cameras allowed visualization of flows and quantitative measurements. Results show that fluid shear is highest on the upper lee and stoss sides of our viscoelastic objects (made from xanthan gum, mimicking the physical properties of microbial EPS). Shear-induced deformation then drives the elongation of the top, forming what appears to be a streamer along the direction of the flow. In addition, our results also indicate that multiple streamers may naturally evolve depending on how the boundary layers were disturbed. Multiple streamers act to buffer turbulence while lifting up the boundary layers, reducing the shear below. This research helps explain unique microbial structures in Earth’s surface environments. The understanding of these fundamental processes guides the characterization of microbial life in the fossil records, as well as possibly on other planets where microbial life is unavoidably affected by flow.