Analysis Of Feasible Optimal Metabolic Pathways Of Klebsiella Pneumoniae Based On Improved Milp Model

In order to improve the metabolic properties of cells and achieve efficient production of specific target products,metabolic engineering mainly uses gene recombination technology to carry out purposeful transformation of cellular metabolic pathways.Flux balance analysis(FBA)is a commonly used theoretical analysis method for metabolic engineering.However,at present,only one set of optimal metabolic pathways can be obtained.How to obtain all feasible optimal metabolic pathways has attracted people's attention.The searching scope of the mixed integer linear programming(MILP)algorithm for finding all the optimal feasible solutions is too large,so this paper combines the variability analysis(FVA)to improve the MILP.The optimal feasible pathways analysis for carbon central metabolic network and genome metabolic network of glycerol to 1,3-propanediol(1,3-PD)from different sizes of Klebsiella pneumoniae was analyzed.It will provide theoretical guidance for genetically engineered strains.The main works of this paper were summarized as followed:Firstly,we combine with flux variability analysis to improve the MILP algorithm by getting the set of possible minimum values of reaction flux as constraints.The scope of variable search is narrowed and GAMS software is used to program and solve.According to the simplified metabolic network of Escherichia coli,all alternative optimal solutions of pyruvate kinase deficiency are obtained by using MILP and improved MILP algorithm respectively.And compared with the optimal feasible solution in the literature,it verifies the accuracy and feasibility of the algorithm.Secondly,according to the carbon center metabolic network of Klebsiella pneumoniae,the improved MILP model of K.pneumoniae under microaerobic andanaerobic conditions is established respectively.Further obtain the number of all optimal metabolic pathways under different oxygen consumption.ATP and key nodes are also analyzed for feasible metabolic pathways.Compared with the original MILP model,FVA improved MILP model can get more optimal solutions under different oxygen consumption.After the optimal pathway analysis is carried out under microaerobic,we find the metabolic pathway with the least consumption of ATP when the 1,3-PD yield is the same.And the reduction of equivalent conversion is the main way to consume ATP.With the increase of oxygen consumption,the choice of reaction pathways at the node of glycerol and dihytroxyacetone(DHA)will change.However,the optimal number of feasible metabolic pathways with the same 1,3-PD are less and the maximum yield of 1,3-PD is low under anaerobic conditions.And the pathway of sugar degradation is the main way to provide ATP for anaerobic metabolic network.Finally,according to the genome scale K.pneumoniae metabolic network,the genome scale metabolic network model is simplified according to the ladder transformation of the stoichiometric matrix and the FVA of the metabolic network.Then,we use MILP model and improved MILP model to get the optimal feasible pathways under different biomass and oxygen consumption.For the genome scale metabolic network,the improved MILP model obtains all the optimal solutions in less time.With the increase of biomass,the proportion of glycerol nodes entering into oxidation pathway increased.DHA and phosphoenol pyruvate(PEP)are more likely to consume ATP.And taking the minimum consumption of ATP as the sub-optimal goal,we get the optimal metabolic pathway of genome scale glycerol producing 1,3-PD maximum yield and performance.