• (n.) The positive or negative stimulus exerted by oxygen on aerobic and anaerobic bacteria.
An organisms movement toward or away from oxygen as a reaction to its presence. The term is most often used when discussing aerobes (oxygen-using) versus anaerobes (which don't use oxygen). ... (09 Oct 1997) ... 
A taxis in response to oxygen (air).
A'ër·o·tax`is noun [ New Latin See Aëro- ; Taxis .] (Bacteriology) The positive or negative stimulus exerted by oxygen on aërobic and anaërobic bacteria. -- 
aerotaxis, aerotactic 1. A movement of an organism in response to the presence of molecular oxygen. 2. The directed movement of a motile organism towards (positive) or away from (negative) an air-liquid interface, or a concentration gradient of dissolved oxygen.