Bacteria Exhibit Enhanced Upstream Swimming in Complex Fluids

Recent research has revealed significant advancements in understanding how bacteria swim upstream in complex fluid environments. The paper titled "Giant enhancement of bacterial upstream swimming in macromolecular flows" by Ding Cao, Ran Tao, Albane Théry, Song Liu, Arnold J. T. M. Mathijssen, and Yilin Wu explores the behavior of flagellated bacteria in macromolecular fluids, which are common in both natural and clinical settings.

The study combines high-resolution microscopy and numerical simulations to analyze how these bacteria respond to shear flows of various macromolecular fluids. The researchers found that, unlike in Newtonian fluids, bacteria can swim upstream against flow rates of up to approximately 65 s^-1. This rate is significantly higher than what is typically observed in Newtonian fluids, indicating a remarkable adaptation to their environment.

Key findings highlight that the enhanced upstream swimming is influenced by two main properties of the complex fluids: viscoelasticity and shear-thinning viscosity. The study suggests that increasing viscosity with a Newtonian polymer can hinder upstream swimming. The researchers attribute this phenomenon to a "weathervane effect," where the presence of a viscoelastic lift force and shear-thinning induced torque helps align the bacteria against the flow.

These findings have implications for understanding bacterial transport and surface colonization in environments rich in macromolecular substances. Additionally, the insights gained may inform the design of artificial microswimmers for biomedical applications, particularly in physiological conditions where similar fluid dynamics are present.

For further details, the paper can be accessed at arXiv:2408.13694.