Performance of roller agitators for cultivation of microorganisms.

Rapidly growing aerobic organisms can deplete oxygen in the nutrient medium even when culture vessels are open to the air. Agitation is beneficial under these conditions because it tends to expose more liquid to the air, and because the mixing tends to make conditions more homogeneous throughout the volume of the medium. Rotary and reciprocating shakers are capable of high rates of aeration when used with baffled Erlenmeyer and Fernbach flasks. However, the standard reciprocating or rotary shakers are not adapted to aerating test tube cultures. Aeration by rolling has been used previously for tightly stoppered cultures of animal cells (White, 1954). A typical application of the roller tube method makes use of standard 16by 150-mm test tubes. These are charged with a small quantity of liquid nutrient, then placed in a drum revolved about its longitudinal axis. The axis of revolution is inclined slightly from the horizontal so that the liquid which covers the lower side of the tube wets it about halfway or two thirds of the distance to the stopper. The drum turns from six to as high as 3000 revolutions per hr, depending on whether it is desired that the cells grow on the surface of the glass or in suspension in the liquid medium (Paul, 1959). In a somewhat different way Monod (1950) has used the principle of rolling to supply aeration in a continuous flow device called the "Bactogen." A significant difference between the Bactogen and the roller tube system is that in the Bactogen the culture vessel revolves about its own axis at approximately 400 rpm, a speed much higher than that of the roller drum. In both devices aeration is accomplished through the mechanical action which spreads the liquid over the inner surface of the culture vessel. The fact that rapid growth of animal cells occurs in roller tubes does not indicate that this device is capable of very high rate of oxygen transfer, since total cell mass and growth rate remain low in contrast with aerobic cultures of molds, yeasts, or bacteria. However, the simplicity of the rolling principle of aeration encouraged me to attempt it with test tube and flask cultures of aerobic organisms, and to make the quantitative tests which are described below. My particular need was for a method of measuring the growth of yeasts turbidometrically in 13-mm special test tubes designed for the Klett-Summerson Colorimeter.1 A high rate of aeration