Response of Microrganisms to Gradients

Department of Biology

University of West Florida

Pensacola, FL

These photos supplement the article "Response of microorganisms to gradients", pp 151-156 in: Druger, M. & Anderson, O.R., eds., "Explore the World Using Protozoa". National Science Teachers Association & Society of Protozoologists, 1996)
Comments are welcomed. Please contact Richard A. Snyder:

Last updated: 3 July 1997

This is the basic setup, with agar based medium in the bottom and sample water over top, with cotton or synthetic wool plug to allow a cross gradient of oxygen and nutrients.


This close up shows a layer of microorganisms at the Redox transition zone (a), and a cloud of anaerobic bacteria just above the agar (b).






The layer at the redox transistion from the previous image is actually two layers: a bacterial layer (a) and a ciliate protist layer (b). Apparently the bacteria are able to tolerate slightly lower oxygen concentrations than the protists.


Methylene Blue at 2 mg/ml final concentration, is colorless at an Eo of +11 mV., pH 7.0, 30 degrees C (Jacob, 1970. Redox Potential in Norris & Ribbons, "Methods in Microbiology", AP press NY 2:92-123.) indicates the Redox transtion zone relative to the microbial layers.




Using sulfur bacteria medium in the agar and ambient (room) light, colorful anaerobic sulfur bacteria can develop.