Enzymatic transformations involved in the biosynthesis of microbial exo-polysaccharides based on the assembly of repeat units

Microbial exo-polysaccharides can serve as valuable biopolymers in medicine, food and the feed industry as well as in various technical applications as substitutes of petro-based polymers or with unusual performance. Due to their different natural functions, they have vastly diverse structures, which lead to a very different properties. This structural diversity is brought about by complex biosyntheses based on enzymes whose genes are mostly encoded in clusters within the genomes of the different microbial species. The organisation of the genes and the chemical structures of the corresponding polysaccharides are closely related. Here, we will mainly focus on the genetics and biosynthesis of some major bacterial hetero-polysaccharides that are based on repeat unit assembly and will present specific examples of enzymatic transformation steps. Finally, a short outlook will be given on how in vivo modifications based on enzymatic transformations could be used to engineer these polymers.