Carbon dioxide production by morphological variants of Streptococcus thermophilus CNRZ 368

The ability of 2 Streptococcus thermophilus morphological variants to produ ce carbon dioxide was examined by using a specific electrode. In the presen t study, we have demonstrated that CO2 production varied with the strain: t he opaque variant (strain D31) produced more CO2 than the diffuse one (stra in D12). We have also shown that the addition of 25 m M urea in TPPY broth at 42 degreesC, enhanced the production of CO2 of both strains. For the opa que strain grown without urea addition, the maximal production of CO2 was a pproximately 0.6 mM, whereas 12.0 mM of CO2 were produced in the presence o f exogenous urea. Our experiments revealed that the metabolic origin of CO2 was the cleavage of urea, and that the quantitative difference in CO2 prod uction between the variants was correlated with difference in their urease activity.