The Identification of Gas Vacuoles and Their Abundance in the Hypolimnetic Bacteria of Arco Lake, Minnesota

Bright refractile granules in bacterial cells are identified as gas vacuoles if they disappear on application of a few atmospheres pressure. This paper describes a simple method for observing individual cells under the light microscope before and after application of pressure and the use of this method in making a comprehensive survey of gas-vacuolate organisms in a sample. In water samples from the hypolimnion of a stratified lake (Arco Lake) in Northern Minnesota, gas vacuoles were found in nearly 30 different bacteria, representing possibly 60% or more of those present. The pressure sensitivity of gas vacuoles in these organisms is illustrated by micrograph pairs. Gas vacuoles, which are otherwise uncommon in bacteria, are evidently of great selective value in the hypolimnia of stratified lakes, perhaps by regulating cell buoyancy.