Algae remains a focal point of scientific inquiry with its wide-ranging environmental, health, and energy applications. Among model organisms, the unicellular green alga Chlamydomonas reinhardtii holds significance, particularly in light of its responsiveness to temperature alterations impacting swimming velocity. Notably, this study investigates the intriguing ability of live Chlamydomonas cells to modulate suspension viscosity compared to non-living particles.

Under shear flow conditions, a captivating phenomenon termed "heat thickening" is unveiled in live algae suspensions. Unlike conventional fluids, heightened temperatures uniquely enhance viscosity in these suspensions due to the interplay between cell-generated stresslets and shear flow. This study aims to characterize the influence of temperature on microalgal swimming speeds, flagella beating frequencies, and its role in viscosity modulation.

An experimental setup with precise temperature control and water circulation is employed to achieve this. Both 2D and 3D tracking methods measure motility and inform the findings. Results demonstrate that swimming velocity and beating frequency increase with temperature until 35 degrees Celsius, followed by a decline. This trend aligns with the observed live cell suspension viscosity measurements, indicating the impact of motility on suspension rheology.

Quantitative research has indicated the simultaneous influence of beating frequency and swimming velocity on suspension viscosity, underscoring the importance of investigating motility's role. This study suggests that the motility of live algae cells holds the potential for interpreting and modulating suspension rheology, warranting further exploration under various temperature conditions. Such insights contribute to understanding algae behavior and its applications across environmental and industrial contexts.