期刊
MICROBIAL CELL FACTORIES
卷 18, 期 -, 页码 -出版社
BMC
DOI: 10.1186/s12934-019-1153-6
关键词
Lysine production; Escherichia coli; Adaptive laboratory evolution; GREACE; Fermentation broth
资金
- National Natural Science Foundation of China [31870081]
- Special Program of Talents Development for Excellent Youth Scholars in Tianjin [TJTZJH-QNBJRC-2-10]
- Youth Innovation Promotion Association of Chinese Academy of Sciences [2016164]
- Science and Technology Project of Tianjin [15PTCYSY00020, 14ZCZDSY00157]
BackgroundLate-stage fermentation broth contains high concentrations of target chemicals. Additionally, it contains various cellular metabolites which have leaked from lysed cells, which would exert multifactorial stress to industrial hyperproducers and perturb both cellular metabolism and product formation. Although adaptive laboratory evolution (ALE) has been wildly used to improve stress tolerance of microbial cell factories, single-factor stress condition (i.e. target product or sodium chloride at a high concentration) is currently provided. In order to enhance bacterial stress tolerance to actual industrial production conditions, ALE in late-stage fermentation broth is desired. Genome replication engineering assisted continuous evolution (GREACE) employs mutants of the proofreading element of DNA polymerase complex (DnaQ) to facilitate mutagenesis. Application of GREACE coupled-with selection under stress conditions is expected to accelerate the ALE process.ResultsIn this study, GREACE was first modified by expressing a DnaQ mutant KR5-2 using an arabinose inducible promoter on a temperature-sensitive plasmid, which resulted in timed mutagenesis introduction. Using this method, tolerance of a lysine hyperproducer E. coli MU-1 was improved by enriching mutants in a lysine endpoint fermentation broth. Afterwards, the KR5-2 expressing plasmid was cured to stabilize acquired genotypes. By subsequent fermentation evaluation, a mutant RS3 with significantly improved lysine production capacity was selected. The final titer, yield and total amount of lysine produced by RS3 in a 5-L batch fermentation reached 155.01.4g/L, 0.59 +/- 0.02g lysine/g glucose, and 605.6 +/- 23.5g, with improvements of 14.8%, 9.3%, and 16.7%, respectively. Further metabolomics and genomics analyses, coupled with molecular biology studies revealed that mutations SpeB(A302V), AtpB(S165N) and SecY(M145V) mainly contributed both to improved cell integrity under stress conditions and enhanced metabolic flux into lysine synthesis.Conclusions Our present study indicates that improving a lysine hyperproducer by GREACE-assisted ALE in its stressful living environment is efficient and effective. Accordingly, this is a promising method for improving other valuable chemical hyperproducers.
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