The Relationship Between Glutamate Metabolism And Lipid Accumulation In Mortierella Alpina

The oleaginous filamentous fungus Mortierella alpina can produce arachidonic acid industrially,which makes it an ideal strain for sustainable production of polyunsaturated fatty acids.Nitrogen starvation significantly enhanced the lipid production of M.alpina,and intracellular carbon and nitrogen cycles centered on glutamate metabolism are tightly associated to lipid biosynthesis.This study was conducted to investigate intracellular"glutamate-lipid"metabolic mechanism in M.alpina and to promote lipid accumulation.Experiments were conducted to alter the growth pattern of M.alpina by supplementation with glutamate,and the changes in biomass,lipid production and metabolite abundance were determined.The results showed that glutamate supplementation changed the gene transcription and enzymatic activity levels of enzymes related to carbon and nitrogen metabolism in M.alpina,resulting in differences in metabolite abundance and lipid production.Furthermore,combined supplementation of amino acid significantly promoted lipid accumulation in M.alpina.The main contents are as follows:(1)The effects of glutamate supplementation on the lipid biosynthesis and metabolism of M.alpina were analyzed.Adding glutamate to the fermentation broth to a final concentration of 0.8 g/L at 72 h increased the fatty acid production of M.Alpina by 1.3 g/L(approximately10%of the dry weight).Analysis of metabolites in M.alpina showed that showed that glutamate metabolism significantly regulated the Tricarboxylic Acid cycle,glutamate dehydrogenation,glutamate decarboxylation,nitrogen metabolism and other pathways,resulting in changes in the content of metabolites including organic acids,amino acids,urea and nucleotides,and regulating many cellular behaviors such as signal conversion and transmission,respiration,and redox homeostasis in the intracellular environment.(2)The effect of glutamate metabolism on the gene transcription level and enzyme activity level of key enzymes of carbon and nitrogen metabolism in M.alpina was investigated.Glutamate supplemented in the medium was completely depleted in 96 h,which regulates gene transcription levels of enzymes related to carbon and nitrogen metabolism in M.alpina.Glutamate supplementation triggered a significant increase in glucose 6-phosphate dehydrogenase,NADP~+glutamate dehydrogenase and glutamate decarboxylase activities,which significantly enhanced the intracellular carbon and nitrogen metabolic fluxes of M.alpina.Moreover,Specific inhibition of glutamate decarboxylase activity negatively regulated M.alpina biomass and fatty acid production.(3)The relationship between intracellular amino acid abundance and lipid accumulation in M.alpina was investigated.Supplementation of glutamate caused differences in the abundance of intracellular glutamate and other amino acids(such as 4-aminobutanoate,arginine,and proline)in M.alpina at successive time points.Exogenous addition of sodium 4-propionate specifically inhibited the succinate-semialdehyde dehydrogenase activity,eliminating the elevated effect of glutamate metabolism on lipid production.Combined supplementation fermentation of glutamate and GABA increased fatty acid yield by 0.5 g/L(approximately 5%of dry weight)in M.alpina.Glutamate metabolism alters intracellular arginine abundance through regulation of argininosuccinate lyase activity in M.alpina,and combined supplementation fermentation of glutamate and GABA increased the fatty acid yield by nearly1.1 g/L(about 10%of dry weight).