Mn2+ and Mg2+ synergistically enhanced lactic acid production by Lactobacillus rhamnosus FTDC 8313 via affecting different stages of the hexose monophosphate pathway

Abstract

Aims: The study aimed to evaluate the effects of Mn2+ and Mg2+ on lactic acid production using response surface methodology and to further study their effects on interactions between the enzymes and substrates along the hexose monophosphate pathway using a molecular modelling approach. Methods and Results: A rotatable central composite design matrix for lactic acid production was generated with two independent factors namely, manganese sulfate and magnesium sulfate. The second-order regression model indicated that the quadratic model was significant (P < 0·05), suggesting that the model accurately represented the data in the experimental region. Three-dimensional response surface showed that lactic acid production was high along the region where the ratio of MnSO4 to MgSO4 was almost 1: 1, justifying the need for both Mg2+ and Mn2+ to be present simultaneously in stimulating the production of lactic acid. Molecular docking simulation was performed on a total of 13 essential enzymes involved in the hexose monophosphate pathway for the production of lactic acid with four different conditions namely in the presence of Mg2+, Mn2+, both Mg2+ and Mn2+ and in the absence of metal ions. Results showed that the presence of both Mg2+ and Mn2+ within the binding site improved the binding affinity for substrates in five enzymes namely, glucose-6-phosphate dehydrogenase, phosphogluconate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, phosphopyruvate hydratase and pyruvate kinase. Conclusions: Using response surface methodology and molecular modelling approach, we illustrated that Mg2+ and Mn2+ synergistically enhanced lactic acid production by Lactobacillus rhamnosus FTDC 8313 via affecting different stages of the hexose monophosphate pathway. Significance and Impacts of the Study: Mg2+ and Mn2+ synergistically improved lactic acid production of Lact. rhamnosus via improved binding affinity of the enzyme-substrate along the hexose monophosphate pathway, instead of purely affecting growth as previously understood. © 2013 The Society for Applied Microbiology.