Motility Response to Hydrodynamic Stress During the Growth Cycle in Active Fluid Suspensions

Abstract

In this work, we focus on the motility behavior of two model microorganisms widely used in the study of active fluids: Chlamydomonas reinhardtii microalga and Synechocystis sp. cyanobacterium. Understanding the physiological responses of microorganisms under variable environmental conditions is essential for bioreactor engineering. Yet, most of the previous studies focused on the observation of cellular motility regardless of the growth process. Here, we measure the motility of Chlamydomonas reinhardtii and Synechocystis sp. during their growth when subjected to different intensities of hydrodynamic shear stress. The results demonstrate a significant difference in the motility response of the two species against the applied hydrodynamic shear stress. Mechanical agitation appears to affect the motility of Chlamydomonas reinhardtii microalgae by stimulating the growth process and increasing the magnitude of the cellular swimming velocity. This effect is described using an empirical model for the time variation of the motility. Synechocystis cells show a high endurance to the applied shear such that the global effect of agitation intensity on their motility is insignificant. However, it seems that the peak of the swimming velocity always occurs in the middle of exponential phase of growth.

Investigation of Synechocystis sp. CPCC 534 Motility during Different Stages of the Growth Period in Active Fluids

“…To the best of the authors' knowledge, most previous studies have emphasized the motility of various microorganisms for a short time period during the cell's exponential growth phase [19,22]. In this study, the motility of Synechocystis sp.…”

“…This was concluded to be a result of a reduction in the "running" phase of the motility pattern. In a recent study by Fadlallah et al [19], the motility behavior of active fluids (suspensions of Chlamydomonas reinhardtii and Synechocystis sp.) was studied under different intensities of hydrodynamic shear stress for 15 days.…”

“…On the other hand, Synechocystis did not exhibit any specific trend during the growth cycle and showed higher resistance to shear stress. This could be explained by the lack of flagella in Synechocystis and/or its small size in comparison to C. reinhardtii [19].…”

Rheological and Biophysical Properties of Living Fluids Under Shear: Active Suspensions ofSynechocystissp. CPCC 534

“…It is noted that time-reversal symmetry breaking and the flow field associated with self-propulsion can have an influence on the viscosity of suspensions of self-propelling particles. In this regard, two classes of self-propelled particles can be distinguished among the flagellar bacteria (microswimmers): "pushers", such as Escherichia coli bacterium, which propels itself using a helical flagellar bundle powered by rotary motors, and "pullers", such as C. reinhardtii alga, which swim by beating two flagella at the front of each cell [63].…”

Analysis of Unique Motility of the Unicellular Green Alga Chlamydomonas reinhardtii at Low Temperatures down to −8 °C

“…In contrast, physical approaches such as motility analysis, while extensively studied at ambient temperatures [ 40 , 41 , 42 ], have, to the best of our knowledge, only been conducted at temperatures as low as 15 °C [ 43 ]. This is thought to be due to the substantial stress placed on the cells at lower temperatures, making long-term physiological studies challenging.…”