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

Abstract

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, ΔuppΔpMC1), 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 PRsuc and PRtpxi 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.

Bacterial genome reductions: Tools, applications, and challenges

“…As a proof of concept, GR167 was engineered to produce surfactin with two deletions and introduction of a stronger promoter in front of the native surfactant producing gene. These modifications, making strain GR167IDS, resulted in a 10.4-fold increase in surfactin compared to GR167 (Zhang et al, 2020). This highlights both the ease of manipulation of the reduced genome strain as well as the benefit of combining these reductions with other modifications to improve the expression of either native or foreign genes.…”

“…This strain showed significant improvements in heterologous gene expression with increased yields of cellulase (1.7-fold) and protease (2.5-fold) (Morimoto et al, 2008). In Bacillus amyloquefaciens, 4.18% of the genome was deleted, making strain GR167, improving transformation efficiency, growth rates, and heterologous gene expression (Zhang et al, 2020). These growth characteristics highlight this strain as a suitable chassis for further genetic modification and industrial applications.…”