生物

The natural environments of microorganisms are generally composed of two or more phases. Microbial cells themselves are so small that the even distribution of molecules or ions is not fixed owing to thermal fluctuation. A large amount of microorganisms live at air-water, air-solid or water-solid interfaces. It was shown how a variety of microorganisms come to stay on the surfase of river bed stones. Soil is the most important habitat which accommodates a great variety of bacteria, fungi and protozoa. Multiphase microstructure of soil aggregate is considered to be essential to support the lives of these organisms.

Microorganisms play a vital role in many biological and medical phenomena. Transport phenomena in a suspension of microorganisms are extremely important, because they dominate the growth and distribution of cells. In terms of fluid mechanics, however, mathematical modeling of a suspension of swimming microorganisms is still under way. In this article, I explain recent developments in modeling a suspension of microorganisms. Macroscopic properties of a suspension are strongly affected by the mesoscale flow structures, and the mesoscale flow structures are affected by the interactions between microorganisms. Thus, 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 microorganisms.