Article

Abstract

-Capnophiles are bacteria stimulated by bicarbonate and CO 2 , the two major forms of inorganic carbon (IC) in physiological neutral liquids. Capnophiles are often pathogenic heterotrophs found in IC-rich ecological niches such as human cavities. Like capnophiles, the growth of lactic acid bacteria (LAB) such as Lactobacillus plantarum and Enterococcus faecalis is stimulated by IC. CO 2 or HC are substrates in carbamoyl phosphate (CP) synthesis and other carboxylation reactions in amino acid and nucleotide biosynthesis. When media were supplemented with nucleotides and all the amino acids, potassium bicarbonate still stimulated L. plantarum growth. This suggests that IC may be involved in other aspects of L. plantarum physiology besides its implication as a substrate in carboxylation reactions. Carbonic anhydrase (CA) catalyses the hydration of CO 2 into bicarbonate. Since inorganic carbon stimulated L. plantarum growth, we searched for CA encoding genes in LAB genomes. CA can be classified into three classes according to their protein relatedness: α, β and γ . A class α CA was found in the L. plantarum, Leuconostoc mesenteroides, Streptococcus thermophilus, Oenococcus oeni, Enterococcus faecalis and Enterococcus faecium. These enterococci harboured a second CA encoding gene belonging to the γ class. No CA encoding gene was found in the Lactococcus lactis genome. These observations are discussed with regard to LAB evolution and ecological niches, which are often rich in IC.Lactic acid bacteria / Lactobacillus plantarum / carbon dioxide / bicarbonate / carbonic anhydrase Résumé -Effet du carbone inorganique sur le métabolisme des bactéries lactiques. Le carbone inorganique est trouvé principalement sous deux formes dans la plupart des milieux biologiques, le CO 2 (sous forme de gaz ou dissous) et le bicarbonate (HC ). Le carbone inorganique stimule ou inhibe la croissance d'un certain nombre d'organismes. Le terme de capnophiles désigne les bactéries dont la croissance est facilitée ou nécessite des concentrations de CO 2 plus élevées que celle de l'air. Ces bactéries à Gram négatif ou positif, chimio-organotrophes hétérotrophes, sont souvent trouvées dans la flore commensale ou pathogène de l'homme, et présentent un métabolisme aérobie strict ou anaérobie facultatif. Comme les capnophiles, les bactéries lactiques sont retrouvées dans divers environnements, souvent enrichis en carbone inorganique (tractus intestinal et vaginal, végétaux en décomposition ou fermentés). Le CO 2 stimule la croissance de certaines bactéries lactiques (Lactobacillus, Enterococcus faecalis) et de bactéries relativement proches phylogénétiquement (Streptococcus pneumoniae). Mais le rôle du carbone inorganique dans le métabolisme de ces bactéries a été très peu étudié. On considérait que l'effet du CO 2 chez ces hétérotrophes s'expliquait par son rôle de substrat dans les réactions de carboxylation. En analysant en détail l'effet du CO 2 et du bicarbonate (HC ) sur sa croissance, nous avons pu proposer que les réactions de carbo...

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