What is it about?

Microorganisms inhabit the Earth in a vast variety of environments. Some of these microorganisms respond to outside stimuli and move in selected directions. These responses are called taxis. Taxis responding to gravity, light, and chemicals are respectively called gravitaxis, phototaxis, and chemotaxis. In suspension, when a certain quantity of microorganisms accumulates near a free surface due to taxis, cells of the microorganisms fall, and thus bioconvection is generated because the cells are denser than water. A high-concentration region of bacteria in bioconvection is called a plume. Bioconvection is a three-dimensional phenomenon, and multiple plumes will exist in a chamber. Under such circumstances, the plumes interfere with each other, and the accompanying change in the wavelength of the bioconvection pattern affects the transport characteristics. From the above viewpoints, we simulate three-dimensional bioconvection generated by oxygen-reactive chemotactic bacteria and then clarify the bioconvection patterns, interference between plumes, the wavelengths of each pattern, and the transport characteristics of cells and oxygen when multiple plumes arise.

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Why is it important?

Microorganisms have been used for environmental cleanup in various fields. In addition, bioconvection can be applied to driving micromechanical systems, mixing chemicals, detecting toxicity, and controlling microorganisms in biochips, as well as other applications. Furthermore, the production of biofuels by microorganisms has attracted attention from the viewpoint of being clean and environmentally friendly. Therefore, for the efficient utilization of microorganisms in various fields, it is important to determine the behavior of microorganisms and the mass transfer characteristics in bioconvection generated by microorganisms with taxis. In this study, we conducted a three-dimensional numerical simulation on bioconvection generated by oxygen-reactive chemotactic bacteria. The bioconvection patterns, interference between plumes, the wavelength of the bioconvection pattern, and transport characteristics of cells and oxygen were clarified when multiple plumes occurred in the suspension.


We have studied bioconvection to clarify the transport characteristics in bioconvection and utilize microorganisms for engineering. Conventionally, research based on experiments and theory has been conducted. The previous numerical analyses have not captured the phenomenon of three-dimensional bioconvection because a stability analysis was performed or the fundamental equations were solved by similarity transformation. Therefore, in this study, we performed a three-dimensional numerical analysis considering nonlinearity. We hope that the results of this research will be valuable for engineering applications of microorganisms.

Professor Hideki Yanaoka
Iwate Daigaku

Read the Original

This page is a summary of: Pattern wavelengths and transport characteristics in three-dimensional bioconvection generated by chemotactic bacteria, Journal of Fluid Mechanics, November 2022, Cambridge University Press,
DOI: 10.1017/jfm.2022.898.
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