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Background  Genome reduction and metabolic engineering have emerged as intensive research hotspots for constructing the promising functional chassis and various microbial cell factories. Surfactin, a lipopeptide-type biosurfactant with broad spectrum antibiotic activity, has wide application prospects in anticancer therapy, biocontrol and bioremediation.  Bacillus amyloliquefaciens  LL3, previously isolated by our lab, contains an intact  srfA  operon in the genome for surfactin biosynthesis.    Results  In this study, a genome-reduced strain GR167 lacking ~ 4.18% of the  B. amyloliquefaciens  LL3 genome was constructed by deleting some unnecessary genomic regions. Compared with the strain NK-1 (LL3 derivative, Δ upp ΔpMC1), GR167 exhibited faster growth rate, higher transformation efficiency, increased intracellular reducing power level and higher heterologous protein expression capacity. Furthermore, the chassis strain GR167 was engineered for enhanced surfactin production. Firstly, the iturin and fengycin biosynthetic gene clusters were deleted from GR167 to generate GR167ID. Subsequently, two promoters PR  suc   and PR  tpxi   from LL3 were obtained by RNA-seq and promoter strength characterization, and then they were individually substituted for the native  srfA  promoter in GR167ID to generate GR167IDS and GR167IDT. The best mutant GR167IDS showed a 678-fold improvement in the transcriptional level of the  srfA  operon relative to GR167ID, and it produced 311.35 mg/L surfactin, with a 10.4-fold increase relative to GR167.    Conclusions  The genome-reduced strain GR167 was advantageous over the parental strain in several industrially relevant physiological traits assessed and it was highlighted as a chassis strain for further genetic modification. In future studies, further reduction of the LL3 genome can be expected to create high-performance chassis for synthetic biology applications.

Engineering of a genome-reduced strain Bacillus amyloliquefaciens for enhancing surfactin production