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首页> 外文期刊>Applied Microbiology and Biotechnology >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 10-1
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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 10-1

机译：D-木糖代谢的两种不同途径以及木糖浓度对乳酸菌乳球菌10-1混合酸发酵中L-乳酸产量系数的影响

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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. lactis IO-1 may possess another metabolic pathway that produces only lactic acid from xylose. In the present study, the metabolism of xylose in L. lactis IO-1 was deduced from the product formation and enzyme activities of L. lactis IO-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 ob-served. These results indicate that in L. lactis IO-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. lactis IO-1, and pyruvate metabolism between cleavage to acetyl-CoA and formic acid by PFL and the reduction to L-lactate by lactate dehydrogenase. [References: 44]
机译：在乳酸菌中，戊糖通过磷酸酮醇酶途径代谢，该途径催化D-木酮糖5-磷酸酶裂解为等摩尔量的3-磷酸甘油醛和乙酰磷酸酯。因此，戊糖中乳酸的产率系数不超过1.0mol / mol，而在高D-木糖浓度下乳酸乳球菌IO-1（JCM7638）的产率系数通常超过理论值。这表明，除了磷酸酮醇酶途径之外，乳酸乳球菌IO-1还可能具有另一种代谢途径，其仅从木糖产生乳酸。在本研究中，乳酸乳杆菌IO-1中木糖的代谢是由乳酸乳杆菌IO-1在分批培养和连续培养中的产物形成和酶活性推导的。在培养期间，木糖浓度高于约。 50 g / l，L-乳酸的产率系数超过1.0 mol / mol，而乙酸盐，甲酸和乙醇的产率非常低。在木糖浓度小于5 g / l时，产生乙酸盐，甲酸盐和乙醇，产率系数约为1.0 mol / mol，而几乎不产生L-乳酸盐。在高木糖浓度下生长的细胞中，观察到磷酸酮醇酶和丙酮酸甲酸裂解酶（PFL）的比活性显着下降，而转酮醇酶和反式醛缩酶的比活性显着增加。这些结果表明在乳酸乳球菌中，IO-1木糖可能通过两种不同的途径分解代谢，磷酸酮醇酶途径产生乙酸盐，甲酸盐和乙醇，以及戊糖磷酸酯（PP）/糖酵解途径仅将木糖转化为L-乳酸盐。此外，据推断，培养基中木糖浓度的变化使乳酸乳球菌IO-1中的磷酸酮醇酶途径和PP /糖酵解途径之间的木酮糖5-磷酸代谢发生了变化，并且在裂解为乙酰辅酶A和PFL还原成甲酸，乳酸脱氢酶还原成L-乳酸。 [参考：44]

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