Article

Abstract

Capnophiles are bacteria stimulated by bicarbonate and CO2, 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. CO2 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 CO2 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