Metabolic Analysis Of Intensified Interaction Between Vitamin C Producing Strains Based On Adaptive Evolution Strategy

Due to the complexity of the relationship between Ketogulonigenium vulgareand Bacillus cereus, Vitamin C productive strains, it brings many difficulties tosystemically optimize the fermentation process. To intensify the interaction as anentry point, this study of adaptive evolution method applied in the mixed cultureprovides a new example to improve the productivity of the target product, and a newway of thinking for further modification of vitamin C productive strains.The mixed culture attained steady state in the process of the150-day adaptiveevolution, characterized that2-KGA conversion rate, pH, the population of K. vulgareand B. cereus underwent dramatic fluctuations in the beginning50days and thenreached a relatively stable state. Evolution improved the adaptive capacity of themedium environment, the growth rate of K. vulgare and B. cereus, and the yield of2-KGA by K. vulgare evolved150days enhanced106.4%compared to ancestral K.vulgare. Cross-collocation of the evolved and ancestral species in an industrialfermentation medium dramatically increased the2-KGA conversion rate, and theyield of most efficient mixed culture reached93%compared to77%of ancestralstrains.Metabolism analysis found that evolved K. vulgare and B. cereus were differentfrom ancestral strains apparently, evolved strains cooperated more harmoniously andutilized the intracellular nutrients more efficiently, contributing to the synthesis of theobjective product2-KGA. Cell membrane permeability of B. cereus increased alongwith the evolution process, implying that B. cereus gradually adapted to the stress of2-KGA produced by K. vulgare. The cell membrane permeability of K. vulgare didnot change in the process of evolution. Phospholipid molecules of K. vulgare and B.cereus have changed significantly along with the evolution process, and the changerule consisted with the change of the growth of2-KGA production of both species,which manifested that the phospholipid composition and metabolic model cancharacterize changes of strain properties. In the process of adaptive evolution,phospholipid changes of B. cereus consistented with the changes of cell membranepermeability (e.g., the increase of LPE, PA, the change of chain length and degree of saturation, etc.), indicating that changes in exchange capacity of nutrients could be thekey factor in raising the yield of2-KGA.The swarm capacity of evolved B. cereus on K. vulgare significantly declined. Onthe amino acid metabolism, purine nucleotide metabolism, glycolysis pathway and theTCA cycle metabolism level, evolved K. vulgare and B. cereus showed higher abilityof cell-cell communication on the metabolic level. Evolved B. cereus displayed highercapacity of resistance to the harmful material produced by K. vulgare andcharacterized the deficiency of sporation. It further showed that relationships of K.vulgare and B. cereus significantly changed, from the relationship of mutualism andamensalism in different stages into the completely mutualism.