Growth of psychrophilic microorganisms at subzero temperatures

Abstract

In an attempt to find a suitable medium for determining the ability of psychrophilic bacteria and yeasts to grow at subzero temperatures, six antifreeze compounds were added individually and in combination to Trypticase soy broth and agar. The media were tested for their ability to support good growth of psychrophilic bacteria at 20 °C and to resist freezing at subzero temperatures. In general, media which supported good growth at 20 °C froze at −7 °C, whereas media which did not freeze at −7 °C did not support good growth at 20 °C. In supercooled liquid media, however, three species of Bacillus grew at −2 °C, one at −4.5 °C, and five at −5 to −7 °C. Generation times were approximately 4 days at −2 °C, 7 days at −4.5 °C, and 9 to 11 days at −5 to −7 °C. On supercooled growth-supporting agar media, two Gram-positive cocci, one Gram-negative rod, and four species of yeast grew at −2 °C. The latter also grew at −4.5 °C. Three species of Bacillus grew at −7 °C, and two at −10 °C.