Competence ofCorynebacterium glutamicumas a host for the production of type I polyketides

Type I polyketide synthases (PKSs) are large multi-domain proteins converting simple acyl-CoA thioesters such as acetyl-CoA and malonyl-CoA to a large diversity of biotechnologically interesting molecules. Such multi-step reaction cascades are of particular interest for applications in engineered microbial cell factories, as the introduction of a single protein with many enzymatic activities does not require balancing of several individual enzymatic activities. However, functional introduction of type I PKSs into heterologous hosts is very challenging as the large polypeptide chains often do not fold properly. In addition, PKS usually require post-translational activation by dedicated 4’-phosphopantetheinyl transferases (PPTases). Here, we introduce an engineeredCorynebacterium glutamicumstrain as a novel microbial cell factory for type I PKS-derived products. Suitability ofC. glutamicumfor polyketide synthesis could be demonstrated by the functional introduction of the 6-methylsalicylic acid synthase ChlB1 fromStreptomyces antibioticus. Challenges related to protein folding could be overcome by translation fusion of ChlB1Sato the C-terminus of the maltose-binding protein MalE fromEscherichia coli. Surprisingly, ChlB1Sawas also active in absence of a heterologous PPTase, which finally led to the discovery that the endogenous PPTase PptACgofC. glutamicumcan also activate ChlB1Sa. The best strain, engineered to provide increased levels of acetyl-CoA and malonyl-CoA, accumulated up to 41 mg/L (0.27 mM) 6-methylsalicylic acid within 48 h of cultivation. Further experiments showed that PptACgofC. glutamicumcan also activate nonribosomal peptide synthetases (NRPSs), renderingC. glutamicuma promising microbial cell factory for the production of several fine chemicals and medicinal drugs.