The ability of CO 2 to inhibit respiration and growth of representative strains of seven species of meat spoilage bacteria was examined. Enterobacter and Microbacterium thermosphactum were unaffected by CO 2 . Both respiration and growth of the other species were inhibited. With four of the species (fluorescent and nonfluorescent Pseudomonas, Alteromonas putrefaciens , and Yersinia enterocolitica ), the inhibition pattern in a complex medium was similar, and inhibition was incomplete and reached a maximum level at comparatively low concentrations of CO 2 . With Acinetobacter , inhibition continued to increase with increasing CO 2 concentration. The degree of inhibition with a constant concentration of CO 2 in solution increased with decreasing temperature for all CO 2 -susceptible species except the nonfluorescent Pseudomonas. Anaerobic growth of CO 2 -susceptible facultative anaerobes was unaffected by CO 2 .

In minimal medium at 30 degrees C, growth of Pseudomonas fluorescens was stimulated when the pressure (p) of CO2 in solution was 100 mm of Hg, but at higher concentrations the growth rate declined linearly with increasing pCO2. All concentrations of CO2 were inhibitory for growth in complex medium, and at 30 degrees C the maximum degree of inhibition was attained when pCO2 was 250 mm of Hg. The degree of inhibition at a constant pCO2 in solution increased with decreasing temperature. The degree of inhibition was directly proportional to temperature for growth in complex medium, but not in minimal medium. The inhibition of cell respiration by CO2 was the same whether cells had been grown in air or in the presence of CO2, indicating that adaptive enzyme synthesis does not occur in response to CO2.

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