Optimization Of Culture Conditions From Lactic Acid Fermentation And Omics Analysis Of Lactobacillus Pentosus

The composition of MRS medium used for lactic acid fermentation is very complex.There are four kinds of nitrogen sources whose cost is dominant in the cost of production.Now starch and refined sugar are still heavily used as carbon source in the fermentation of lactic acid,but these may compete with food supply chain needed by people and their prices are high.Cluture conditions of lactobacillus pentosus are optimized in this study to slove the above issues and reduce production cost.On the other hand,genome and transcriptome are sequenced to lay the foundation of further study.To reduce the type and consumption of nitrogen source,firstly the effects of different nitrogen sources on lactic acid fermentation were compared through signal factor experiment,and then the ratio of selected inorganic nitrogen sources and diammonium hydrogen citrate was optimized through response surface method to replace original components.The two better combinations after optimization were 17.71 g/L beef extract and 1.91 g/L ammonium hydrogen citrate,when these two compounds were used as nitrogen source,where 42.37 g/L lactic acid was produced.When corn steep liquor,yeast extract and ammonium hydrogen citrate were added at the concentration of 46.54,21.95 and 9.95 g/L,respectively,the maximum production of lactic acid could reach 41.06 g/L.When using different proportions of glucose and xylose as carbon sources for lactic acid fermentation,the production of acetic acid increased and the production of lactic acid dropped with the improvement of xylose proportion.As the ratio of glucose/xylose is 4:1,we got the highest lactic acid production 60.53 g/L.Effect of lignocellulosic hydrolysate on lactic acid fermentation was studied,the experimental results showed that hydrolysate can be used well by strain,and lactic acid production could reach 55.02 g/L.PH has signigicant effects on lactic acid fermentation,fermentation process was observed under different pH and lactic acid production of 67.16 g/L was the highest under pH6.4.Corresponding ORP less than-300 mV was the lowest as well.Because the strain used in this study was screened for the first time,its genome was resequenced.Using Lactobacillus plantarum WCFS which is the closest relative published on the site as a template,we found that many genes related to lactic acid metabolism are different from the template,and the coverage rate is low mainly bacause the genome integrated genes of exogenous phage,so the strain should be preservated carefully to avoid variation.Changed genes from genome mapping were involved in glycolytic pathway,TC A cycle,pentose phosphoketolase pathway and energy metabolism.Analyzing these genes could be beneficial to understa nd the metabolic pathways and mechanism of xylose and express or inhibit related genes to optimize the fermentation performance of the strain and lay the foundation for futher reconstruction.