Aerotaxis

Aerotaxis (from Greek aēr - air and taxis - order, arrangement), a chemotactic (see Chemotaxis) movement caused by oxygen in motile organisms. A. manifests either as an attractive effect of oxygen (positive A.) or as a repelling effect (negative A.), depending on the oxygen concentration and the organisms' needs. In motile bacteria, A. can be observed under a microscope in a water drop covered with a cover glass. Aerobes gather in a dense ring at the edge of the cover glass, while anaerobes are in the center of the drop where the oxygen concentration is lowest; bacteria requiring reduced oxygen concentration are at a certain distance from the periphery. The distribution patterns of bacteria characterizing their relationship to oxygen were called 'respiratory figures of bacteria' by Beijerinck (see Bacteria). Engelmann utilized bacterial aerotaxis in his 'biological method' for observing the assimilation of CO₂ by green plant cells. By placing a thread of green algae in a water drop with motile aerobic bacteria and illuminating it with a microspectroscope, he observed the accumulation of moving bacteria primarily at the sections of the thread illuminated by red and violet rays, where CO₂ assimilation and O₂ release occur most intensely. L. Kurganov,

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a -. ;:; a т- Aerotaxis of bacteria: 1-a diatom alga developing oxygen in the light and surrounded by spirilla; 2-a diatom alga, half illuminated (in part a), half shaded (in part b): bacteria have gathered in the illuminated half where oxygen is released; 3-an alga surrounded by bacteria: o-in the dark, o-in the light; bacteria have divided into two groups--aerophilic ones located near the alga, and aerophobic ones located on the periphery.