Search

A carbon dioxide requirement for growth of Streptococcus sanguis was readily demonstrated in a fermentor where the gas atmosphere could be controlled. Growth at a maximum rate occurred immediately in response to the appropriate CO(2) concentration; growth stopped when CO(2) was deleted. Washed inocula consisting of exponentially growing cells required a minimum of 2.4% CO(2), postexponential phase cells needed 1.2 to 1.8% CO(2) immediately and 2.4% CO(2) shortly thereafter, whereas stationary phase cells required three sequential increases in CO(2) from 0.3 to 1.8 to 2.4% within the first 90 min of growth. These CO(2) concentrations permitted each inoculum to initiate growth immediately at the same maximum rate. These results also showed that physiologically "old" cells had the same capacity for growth as "young" cells when the CO(2) concentrations were appropriate for the type of inoculum. Continued exponential growth of the culture at the same optimum rate required 2.4% CO(2). Lower concentrations of CO(2) were rate limiting and the resulting exponential rate was proportional to the CO(2) concentration. The "normal" lag period of S. sanguis appears to be an artifact induced by a CO(2) deficiency.