WHAT SIZE SHOULD A BACTERIUM BE - A QUESTION OF SCALE

There are living prokaryotes (Bacteria and Archaea) that have cell siz es that range from 0.02-400 mu m(3). Over this tremendous range, vario us abilities to cope with the environment are needed. This review atte mpts to formulate some of the problems and some of the solutions. The smallest size for a free-living organism is suggested to be largely se t by the catalytic efficiency of enzymes and protein synthetic machine ry. Because of fluctuations in the environment, cells must maintain ma chinery to cope with various catastrophes; these mechanisms increase t he minimum size of the cell. On the other hand, the largest cell is re asonably assumed to be limited by the ability of diffusion to bring nu trients to the appropriate part of the cell and to dispose of waste pr oducts. To explore the limitation imposed by diffusion, analysis is de veloped of diffusion processes through stirred and unstirred media, di ffusion through media that contains obstacles, and the effect of size and shape.