Two different pathways for D -xylose metabolism and the effect of xylose concentration on the yield coefficient of L -lactate in mixed-acid fermentation by the lactic acid bacterium Lactococcus lactis IO-1

Abstract

In lactic acid bacteria, pentoses are metabolized via the phosphoketolase pathway, which catalyzes the cleavage of D-xylulose-5-phosphate to equimolar amounts of glyceraldehyde 3-phosphate and acetylphosphate. Hence the yield coefficient of lactate from pentose does not exceed 1.0 mol/mol, while that of Lactococcus lactis IO-1(JCM7638) at high D-xylose concentrations often exceeds the theoretical value. This suggests that, in addition to the phosphoketolase pathway, L. lactisIO-1 may possess another metabolic pathway that produces only lactic acid from xylose. In the present study, the metabolism of xylose in L. lactisIO-1 was deduced from the product formation and enzyme activities of L. lactisIO-1 in batch culture and continuous culture. During cultivation with xylose concentrations above ca. 50 g/l, the yield coefficient of L-lactate exceeded 1.0 mol/mol while those of acetate, formate and ethanol were very low. At xylose concentrations less than 5 g/l, acetate, formate and ethanol were produced with yield coefficients of about 1.0 mol/mol, while L-lactate was scarcely produced. In cells grown at high xylose concentrations, a marked decrease in the specific activities of phosphoketolase and pyruvate formate lyase (PFL), and an increase in those of transketolase and transaldolase were observed. These results indicate that in L. lactisIO-1 xylose may be catabolized by two different pathways, the phosphoketolase pathway yielding acetate, formate and ethanol, and the pentose phosphate (PP)/glycolytic pathway which converts xylose to L-lactate only. Furthermore, it was deduced that the change in the xylose concentration in the culture medium shifts xylulose 5-phosphate metabolism between the phosphoketolase pathway and the PP/glycolytic pathway in L. lactisIO-1, and pyruvate metabolism between cleavage to acetyl-CoA and formic acid by PFL and the reduction to L-lactate by lactate dehydrogenase.

Lactococcus lactis Metabolism and Gene Expression during Growth on Plant Tissues

“…lactis is generally considered to be a strictly homofermentative LAB species. However, this species also possesses the ptk gene coding for phosphoketolase, an enzyme required for heterofermentative metabolism and involved in the degradation of pentoses (54). Consistent with glucose depletion and transition to a heterofermentation (55), L. lactis KF147 ptk was induced in ATL.…”

Genome Sequence and Comparative Genome Analysis of Lactobacillus casei: Insights into Their Niche-Associated Evolution

“…Additionally, pentoses can be metabolized via transketolase (pentose phosphate cycle) and phosphoketolase pathways, leading to homolactic and heterolactic fermentation profiles (Tanaka et al 2002). The CDS for these intact pathways were found in ATCC 334.…”

Improvement of bacterial transformation efficiency using plasmid artificial modification

“…Next, we applied this method to another bacterium, L. lactis IO-1 (14), which is capable to utilizing xylose and produce lactic acid efficiently. This strain has the potential to utilize biomass for lactic acid production; however, the transformation efficiency was too low to produce using the gene knockout technique.…”