Abstract
Micro-organisms play a vital role in many biological, medical and engineering phenomena. Some recent research efforts have demonstrated the importance of biomechanics in understanding certain aspects of micro-organism behaviours such as locomotion and collective motions of cells. In particular, spatio-temporal coherent structures found in a bacterial suspension have been the focus of many research studies over the last few years. Recent studies have shown that macroscopic properties of a suspension, such as rheology and diffusion, are strongly affected by meso-scale flow structures generated by swimming microbes. Since the meso-scale flow structures are strongly affected by the interactions between microbes, a bottom-up strategy, i.e. from a cellular level to a continuum suspension level, represents the natural approach to the study of a suspension of swimming microbes. In this paper, we first provide a summary of existing biomechanical research on interactions between a pair of swimming micro-organisms, as a two-body interaction is the simplest many-body interaction. We show that interactions between two nearby swimming micro-organisms are described well by existing mathematical models. Then, collective motions formed by a group of swimming micro-organisms are discussed. We show that some collective motions of micro-organisms, such as coherent structures of bacterial suspensions, are satisfactorily explained by fluid dynamics. Lastly, we discuss how macroscopic suspension properties are changed by the microscopic characteristics of the cell suspension. The fundamental knowledge we present will be useful in obtaining a better understanding of the behaviour of micro-organisms.
Highlights
Micro-organisms can be categorized into three major groups: bacteria, archaea and eukaryotes (Ingraham & Ingraham 2004)
Recent research has shown that collective motions can be formed passively because of hydrodynamic forces (Ishikawa & Pedley 2008), and that biomechanics and biophysics play an important part in the behaviour of micro-organisms
The detailed roles of biological reactions are still unclear, these findings suggest that hydrodynamics play an important part in pairwise interactions of swimming micro-organisms
Summary
Micro-organisms can be categorized into three major groups: bacteria, archaea and eukaryotes (Ingraham & Ingraham 2004). Since it is estimated that there are approximately 5 Â 1030 bacterial cells on Earth, micro-organisms constitute the majority of terrestrial life in terms of both numbers and biomass (Madigan et al 2003). Recent research has shown that collective motions can be formed passively because of hydrodynamic forces (Ishikawa & Pedley 2008), and that biomechanics and biophysics play an important part in the behaviour of micro-organisms. We review recent studies on the suspension biomechanics of swimming microbes. Recent research has revealed that the suspension properties are considerably influenced by the collective motions of micro-organisms.
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