Carbon dioxide fixation by cells and cell-free extracts of Streptococcus thermophilus
1996
Louaileche, H. | Bracquart, P. | Guimont, C. | Linden, G.
Streptococcus thermophilus is a thermophilic lactic acid bacterium mainly used in the preparation of yogurt (in association with Lactobacillus delbrueckii subsp. bulgaricus), various fermented milks (Tamime & Robinson, 1988) and for the manufacture of different types of cheeses, particularly the 'cooked' cheeses (Auclair Accolas, 1983). In a previous study (Louaileche et al. 1993), we have shown that CO2 and sodium bicarbonate stimulate growth and exert a marked influence on the metabolic activities of Str. thermophilus. Several essential biosynthetic steps are known to incorporate CO2 or HCO3- into cell constituents such as amino acids and nucleotides. The mechanism by which CO2 is fixed in Str. thermophilus has not yet been elucidated. The present study describes fixation into cellular amino acids of 14C from NaH14CO3 by growing cells and cell-free extracts of Str. thermophilus, and the enzyme system responsible for fixation. In addition, a comparison was made of the bicarbonate uptake and carboxylase activity of two morphological variants.
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