Engineering Corynebacterium glutamicum towards high yield vitamin A production

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In the human body, Vitamin A plays an essential role for growth and development, the maintenance of the immune system and good vision. It refers to a group of vitamers, most notably β-carotene, which can be converted into the bioactive form of the vitamin by organisms. Vitamin A deficiency (VAD) is a worldwide issue, especially in developing countries. The severe consequences of VAD (blindness, night blindness, death) are estimated to affect approximately one third of all children younger than five around the world. Industrial large-scale production is mainly (90%) realized by chemical synthesis, but the demand for naturally produced carotenoids is increasing. As microorganisms are capable of forming different carotenoids via the carotenogenesis, a microbial production process could represent a promising alternative for synthesizing vitamin A. In order to provide high amounts of β-carotene, it is essential to reduce production costs and achieve higher productivity. Microbial production hosts are naturally equipped with a complex metabolism, which is undesirable in the non-natural environment of a bioreactor, as it can negatively impact fermentation processes and lead to unsatisfactory yields. By systematic deletion of dispensable genes, microbial chassis-strains with reduced metabolic pathways can be generated, which still maintain the genetic stability and stress tolerance as the parental strain. These strains represent a promising basis for further engineering towards highly efficient production strains for industrial biotechnology. Only recently, the strain Corynebacterium glutamicum C1* was constructed by combinatorial deletions based on a library of reduced genomes. The C1* genome is reduced by 13.4% (412 deleted genes), but in the course of systematically reducing the genome some gene cluster deletions were found to be incompatible. For this reason, further chassis optimization requires alternative strategies. The proposed project focuses on the construction of a minimal genome of C. glutamicum by de novo synthesis of genomic regions containing essential genes. In parallel, β-carotene biosynthesis will be optimized in an already established production strain. Subsequently, this optimized synthesis pathway should be introduced into the C. glutamicum chassis strain, to first demonstrate the advantages of a minimal genome strain as synthesis organism and at the same time obtain an efficient production strain for the industrial production of vitamin A. Based on this β-carotene platform strain, further production strains for the synthesis of relevant carotenoids like lutein, zeaxanthin or astaxanthin can be developed.