Recombination of biosynthetic gene clusters including those of non-ribosomal peptide synthetases (NRPSs) is essential for understanding the mechanisms of biosynthesis. Due to relatively huge gene cluster sizes ranging from 10 to 150 kb, the prevalence of sequence repeats, and inability to clearly define optimal points for manipulation, functional characterization of recombinant NRPSs with maintained activity has been hindered. In this study, we introduce a simple yet rapid approach named "Seamed Express Assembly Method (SEAM)" coupled with Ordered Gene Assembly in Bacillus subtilis (OGAB) to reconstruct fully functional plipastatin NRPS. This approach is enabled by the introduction of restriction enzyme sites as seams at module borders. SEAM-OGAB is then first demonstrated by constructing the ppsABCDE NRPS (38.4 kb) to produce plipastatin, a cyclic decapeptide in B. subtilis. The introduced amino acid level seams do not hinder the NRPS function and enable successful production of plipastatin at a commensurable titer. It is challenging to modify the plipastatin NRPS gene cluster due to the presence of three long direct-repeat sequences; therefore, this study demonstrates that SEAM-OGAB can be readily applied towards the recombination of various NRPSs. Compared to previous NRPS gene assembly methods, the advantage of SEAM-OGAB is that it readily enables the shuffling of NRPS gene modules, and therefore, chimeric NRPSs can be rapidly constructed for the production of novel peptides. This chimeric assembly application of SEAM-OGAB is demonstrated by swapping plipastatin NRPS and surfactin NRPS modules to produce two novel lipopeptides in B. subtilis.
Keywords: Bacillus subtilis; NRPS; NRPS recombination; OGAB; SEAM; gene assembly; plipastatin.