Citrate Catabolism and Production of Acetate and Succinate by L. helveticus ATCC

TORINO, MARÍA INÉS; TARANTO, MARÍA PÍA; FONT DE VALDEZ, GRACIELA

APPLIED MICROBIOLOGY AND BIOTECHNOLOGY

Springer

Lugar: Berlin Heidelberg; Año: 2005 vol. 69 p. 79 - 85

0175-7598

The citrate metabolism of Lactobacillus helveticus ATCC 15807 was studied under controlled-pH fermentations at 4.5 and 6.2. The microorganism was able to co-metabolize citrate and lactose (medium MBc) at both pH from the beginning of growth, which enhanced the lactose consumption and the lactic acid production compared to cultures without citrate. However, citrate displayed an opposing effect on cell growth according to the culture pH, i.e., inhibitory at pH 4.5 and stimulatory at pH 6.2. This dual effect was dependent on the balance between the ratio of dissociated to non-dissociated forms of the acetic acid produced and the extra ATP gained by the cells, both facts related to the citrate metabolism. The citrate catabolism determined a change in the fermentation pattern of Lb. helveticus ATCC 15807 from homolactic to a mixed-acid profile regardless the external pH. Within this new fermentation pattern acetate was the major product formed (13 to 20 mM) followed by succinate (2.4 to 3.7 mM) while acetoine, dyacetile or butanediol were not detected. The mixed-acid profile displayed by L. helveticus ATCC 15807 was linked to the NADH2 oxidase activity rather than to the Acetate Kinase enzyme.