citrate metabolism in Lactobacillus casei

MORTERA, P.; PUDLIK, A.; LOLKEMA, J.; MAGNI, C.; ALARCON, S.

San Luis

Congreso; SAIB 2011; 2011

SAIB

Citrate metabolism has been extensively studied in the lactic acid bacterium (LAB) by our labs. The first step of the citrate fermentative pathway following the uptake from the medium by the precursor/product exchanger, is the conversion to oxaloacetate and acetate by the citrate lyase. Then, oxaloacetate is decarboxylated to pyruvate by a cytoplasmic oxaloacetate decarboxylase termed CitM. The pathway generates proton motive force by an indirect proton pumping mechanism. Lactobacillus casei ATCC334 is a probiotic microorganism used in the manufacture of different dairy fermented products. The genetic organization in the cit cluster in Lb casei differs from the organization found in others LABs. The steps in the pathway are the same but they are catalyzed by different enzymes. Uptake of citrate is catalyzed by a member of the Me2+-citrate transporter family and oxaloacetate is decarboxylated by a membrane bound complex (OAD) that in Gram-negative bacteria is a Na+ pump. The main objective of this work is to characterized citrate uptake and utilization in Lb casei.Resting cells of Lb casei require the presence of Ca2+-ions to metabolise citrate indicating that the citrate is taken up in complex with Ca2+. Similarly, Ca2+ was required for the generation of a pH gradient by the pathway. Expression of the pathway was studied under different growth conditions.