Aspartate Biosynthesis Is Essential for the Growth of Streptococcus thermophilus in Milk, and Aspartate Availability Modulates the Level of Urease Activity

Stefania Arioli (1) , Christophe Monnet (2) , Simone Guglielmetti (3) , Carlo Parini (3) , Ivano de Noni (3) , Johannes Hogenboom (3) , Prakash Halami (4) , Diego Mora (3)

1 Department of Food Science and Microbiology
2 GMPA - Génie et Microbiologie des Procédés Alimentaires
3 Department of Food Science and Microbiology
4 Central Food Technological Research Institute

We investigated the carbon dioxide metabolism of Streptococcus thermophilus, evaluating the phenotype of a phosphoenolpyruvate carboxylase-negative mutant obtained by replacement of a functional ppc gene with a deleted and inactive version, ppc. The growth of the mutant was compared to that of the parent strain in a chemically defined medium and in milk, supplemented or not with L-aspartic acid, the final product of the metabolic pathway governed by phosphoenolpyruvate carboxylase. It was concluded that aspartate present in milk is not sufficient for the growth of S. thermophilus. As a consequence, phosphoenolpyruvate carboxylase activity was considered fundamental for the biosynthesis of L-aspartic acid in S. thermophilus metabolism. This enzymatic activity is therefore essential for growth of S. thermophilus in milk even if S. thermophilus was cultured in association with proteinase-positive Lactobacillus delbrueckii subsp. bulgaricus. It was furthermore observed that the supplementation of milk with aspartate significantly affected the level of urease activity. Further experiments, carried out with a pureI-gusA recombinant strain, revealed that expression of the urease operon was sensitive to the aspartate concentration in milk and to the cell availability of glutamate, glutamine, and ammonium ions.

Mots clés: CARBON DIOXIDE METABOLISM; PHOSPHOENOLPYRUVATE CARBOXYLASE; UREASE ACTIVITY; ASPARTATE; PPC GENE; MILK

Domaines: Ecologie, Environnement

Stefania Arioli, Christophe Monnet, Simone Guglielmetti, Carlo Parini, Ivano de Noni, et al.. Aspartate Biosynthesis Is Essential for the Growth of Streptococcus thermophilus in Milk, and Aspartate Availability Modulates the Level of Urease Activity. Applied and Environmental Microbiology, 2007, 73 (18), pp.5789-5796. ⟨10.1128/AEM.00533-07⟩. ⟨hal-01195413⟩