EFFECT OF CARBON DIOXIDE ON BACTERIA 



119 



ture. Whatever inhibition has been ob- 

 served by earlier workers and by Novy 

 and Soule under certain conditions was, 

 according to them, entirely due to desicca- 

 tion. This conclusion was challenged, 

 however, by Rockwell and Highberger 

 (1916), who confirm Wherry's former 

 findings that M. tuberculosis cannot develop 

 without carbon dioxide and that the 

 inhibitive effect is not due to desiccation. 

 It was shown that with as much as 40 

 per cent dehydration (by sulphuric acid) 

 growth was as good as in the control 

 tube. 



In the realm of autotrophic bacteria, 

 Waksman and Starkey (192.1-2.3) and 

 Starkey (19x5) have shown that the 

 sulphur oxidizing bacillus, Thiobacillus 

 thiooxidans, requires and utilizes carbon 

 dioxide in a manner similar to the nitrify- 

 ing organisms. 



Masur (192.6) reported that he was able 

 to cultivate a strain of tubercle bacillus 

 for sixteen generations in a medium 

 containing no carbon except the carbon 

 dioxide of the air. An experiment was 

 also described which indicates that this 

 organism will not develop in the absence 

 of free carbonic acid gas. The investi- 

 gator concludes that "under certain condi- 

 tions the tubercle bacillus can utilize 

 directly the carbon dioxide of the atmos- 

 phere." 



Kulp (19x6) based his method of 

 determining the viability of L. acidophilus 

 on the principle recently announced by 

 Valley and Rettger (vide infra) that carbon 

 dioxide is necessary for bacterial develop- 

 ment. Carbonic acid gas, ten per cent by 

 volume, is supplied to the agar plates in a 

 special closed container. Considerably 

 higher viability counts are obtained in 

 this manner than by the customary open 

 method. Furthermore, the colonies are 

 also larger and, as a rule, more charac- 

 teristic. 



INHIBITION OF BACTERIAL GROWTH IN 

 ABSENCE OF CARBON DIOXIDE 



Valley and Rettger (192.5, 1916, 19x7) 

 studied a large number of bacterial species 

 and individual strains and their response 

 (1) to high concentrations of carbon 

 dioxide, and (2.) to complete carbon 

 dioxide removal from the environment. 

 From their studies it is evident that the 

 inhibiting effects observed with high 

 concentrations of carbon dioxide (30 to 

 100 per cent) are primarily, and in many 

 instances entirely, due to increased H-ion 

 concentration of the medium. Displace- 

 ment of oxygen from the environment by 

 the large amounts of CO2 gas is often a 

 factor also. They have found, on the 

 other hand, that bacterial growth is 

 inhibited by the complete removal of 

 carbon dioxide from the cultural environ- 

 ment. Under carbon dioxide-free, but 

 otherwise favorable conditions, many of 

 the organisms employed were actually 

 killed in 2.4 to 48 hours, presumably as the 

 result of complete inanition. A total of 

 109 different organisms were studied, the 

 selection comprising several important 

 representatives of the various bacterial 

 groups. These authors found that the 

 minimum C0 2 requirement for the various 

 groups or species varied within wide 

 limits. 



The findings of Valley and Rettger were 

 corroborated by Rockwell and Highberger 

 (19x7), who reported that Bact. coli, Pr. 

 vulgaris (B. proteus), Ps. pyocyanea and 

 Staph, albus were inhibited in their growth 

 by the removal of carbon dioxide from the 

 environment. The latter investigators 

 also showed that a strain of yeast (Saccha- 

 romyces) and a strain of mold (Mucor) 

 were likewise inhibited by the removal of 

 carbon dioxide. 



Rippel and Bortels (19x7) have shown 

 that Aspergillus niger spores germinate 

 very poorly when cultivated under C0 2 - 



