IBR   13079
INSTITUTO DE BIOLOGIA MOLECULAR Y CELULAR DE ROSARIO
Unidad Ejecutora - UE
artículos
Título:
Ca2+-citrate uptake and metabolism in Lactobacillus casei ATCC334.
Autor/es:
MORTERA, P.; PUDLIK, A.; MAGNI, CH.; ALARCON, S.; LOLKEMA, J.
Revista:
APPLIED AND ENVIRONMENTAL MICROBIOLOGY
Editorial:
AMER SOC MICROBIOLOGY
Referencias:
Lugar: Washington; Año: 2013 vol. 79 p. 4603 - 4612
ISSN:
0099-2240
Resumen:
The putative citrate metabolic pathway in LactobacilluscaseiATCC334 consists of the transporter CitH, a proton symporter of the citrate-divalent metal ion family of transporters CitMHS, citrate lyase, and the membrane-bound oxaloacetate decarboxylase complex OAD-ABDH. Resting cells of  LactobacilluscaseiATCC334 metabolized citrate in complex with Ca2+ and not as free citrate or the Mg2+-citrate complex thereby identifying Ca2+-citrate as the substrate of the transporter CitH. The pathway was induced in the presence of Ca2+ and citrate during growth and repressed by the presence of glucose and of galactose, most likely by a carbon catabolite repression mechanism. The end products of Ca2+-citrate metabolism by resting cellsof Lb.caseiwere pyruvate, acetate and acetoin demonstrating the activity of the membrane bound oxaloacetate decarboxylase complex OAD-ABDH. Following pyruvate, the pathway splits into two branches. One branch is the ?classical? citrate fermentation pathway producing acetoinby α-acetolactate synthase and α-acetolactate decarboxylase. The other branch yields acetate for which the route is still obscure. Ca2+-citrate metabolism in a modified MRS medium lacking a carbohydrate did not significantly affect the growth characteristics and generation of metabolic energy in the form of proton motive force was not observed in resting cells. In contrast, carbohydrate/Ca2+-citrate cometabolism resulted in higher biomass yield in batch culture. However, also with these cells, no generation of pmf was associated with Ca2+-citrate metabolism. It is concluded that citrate metabolism in Lb. casei is beneficial when it counteracts acidification by carbohydrate metabolism in later growth stages.