Pleiotropic effects of lactate dehydrogenase inactivation in Lactobacillus casei.
In lactic acid bacteria, conversion of pyruvic to lactic acid through the activity of lactate dehydrogenase (Ldh) constitutes the final step of the homofermentative pathway. Lactobacillus casei has two characterized genes encoding Ldh activities. The ldhL gene codes for an L-Ldh, which specifically catalyzes the formation of L-lactate, whereas the hicD gene codes for a D-hydroxyisocaproate dehydrogenase (HicDH), which catalyzes the conversion of pyruvate into D-lactate. In L. casei cells fermenting glucose, a mixture of L-/D-lactate with a 97:3% ratio was formed. Inactivation of hicD led to undetectable D-lactate levels after glucose fermentation, while L-lactate levels remained constant. Inactivation of ldhL did not abolish the production of L-lactate, but the lactate final concentration decreased about 25% compared to the wild type, suggesting the presence of at least a second L-Ldh. Moreover, part of the pyruvate flux was rerouted and half of the lactate produced was in the D-isomer form. ldhL inactivation in L. casei showed additional interesting effects. First, the glycolytic flux from pyruvate to lactate was redirected and other fermentation products, including acetate, acetoin, pyruvate, ethanol, diacetyl, mannitol and CO(2), were produced. Second, a lack of carbon catabolite repression of lactose metabolism and N-acetyl-glucosaminidase activity was observed. This second effect could be partly avoided by growing the cells under aeration, since NADH oxidases could account for NAD+ regeneration.
Viana
Rosa
R
Biotechnology Department, Instituto de Agroquímica y Tecnología de Alimentos, IATA-CSIC, P.O. Box 73, 46100 Burjassot, Valencia, Spain.
Yebra
María Jesús
MJ
Galán
José Luis
JL
Monedero
Vicente
V
Pérez-Martínez
Gaspar
G
D000085:Acetates / Q000378:metabolism; D000093:Acetoin / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D003931:Diacetyl / Q000378:metabolism; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D005947:Glucose / Q000378:metabolism; D006596:Hexosaminidases / Q000378:metabolism; D007536:Isomerism; D007770:L-Lactate Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D019344:Lactic Acid / Q000032:analysis; D007780:Lacticaseibacillus casei / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D008353:Mannitol / Q000032:analysis; D016254:Mutagenesis, Insertional; D019289:Pyruvic Acid / Q000378:metabolism; D014169:Transformation, Bacterial
D000085:Acetates; D002245:Carbon Dioxide; D019344:Lactic Acid; D000431:Ethanol; D008353:Mannitol; D019289:Pyruvic Acid; D000093:Acetoin; D007770:L-Lactate Dehydrogenase; D006596:Hexosaminidases; D005947:Glucose; D003931:Diacetyl