Sethoxydim-based Adaptive Evolution And Transcriptomic Analysis Of Chemical Modulators For Lipid Accumulation In Schizochytrium Sp.S31

As an ideal strain with rich DHA content,Schizochytrium sp.has a high growth rate and high content of lipid.However,in the process of long-term preservation and application,the degeneration of the strain may occur and thereby reduce the fermentation biomass.So,how to further improve the lipid content and thereby improve the intracellular DHA content are challenges to be faced.In this study,laboratory-based adaptive evolution was applied to increase the tolerance to the ACCase inhibitor sethoxydim in Schizochytrium sp.S31.Through an experimental evolution process of continuous 65 passages for 200 days,the sethoxydim tolerance in Schizochytrium sp.was increased from 200 ?mol/L to 500 ?mol/L.To further verify the domestication effect of evolved strain,fed-batch strategy was applied and 19.74% increase of biomass and 29.38% increase of DHA yield were observed.This study demonstrated that the application of the sethoxydim-tolerance increased the biomass accumulation and DHA production in Schizochytrium sp.S31.Seven chemical modulators from four groups were evaluated for their effects on lipid accumulation in Schizochytrium sp.S31.The results showed that naphthoxyacetic acid(BNOA),jasmonates(JA),2,4-dichlorophenoxyacetic acid(2,4-D)and butyl hydroxy anisd(BHA)increased lipid accumulation in Schizochytrium sp.S31 by 8.73%,10.57%,6.74% and 6.11%,respectively.High-throughput RNA sequencing technology was then employed to explore the mechanism for the lipid increase under BNOA or JA addition at the transcriptional level.The overall de novo assembly of the cDNA sequence data generated 22838 unigenes.The results revealed that when Schizochytrium sp.S31 was cultured with BNOA or JA at 24 h,94 and 143 genes were up-regulated;123 and 130 genes were down-regulated.Meanwhile,the glycolysis,pentose phosphate metabolism-associated genes were substantially up-regulated,which may result in increased overall acetyl-CoA content.Moreover,at 60 h,113 and 121 genes were up-regulated,including the expression of the fatty acid synthase(FAS)gene;101 and 145 genes were down-regulated in the BNOA and JA addition condition.These results may provide the theoretical basis for the effect of BNOA and JA to promote the lipid synthesis in Schizochytrium sp.S31.