Can chitosans be produced biotechnologically?
In principle, there are two ways for a biotechnological chitosan production, namely in vitro and in vivo. In an in vitro bio-refinery process, chitosans may be produced enzymatically from chitin, using e.g. chitin de-N-acetylases. However, crystalline chitin is a very poor substrate for these enzymes so that only very minor deacetylations (probably on the surface of the crystals) occur. Thus, extensive pre-treatments are required to achieve substantial deacetylation, making this process not even easily feasible at the lab scale. Water-soluble chitosans with a high degree of acetylation, on the other hand, are good substrates for chitin deacetylases which can convert them to chitosans with a low degree of acetylation. Such chemo-enzymatically produced chitosans may be characterized by non-random patterns of acetylation, thus differing from conventional chitosans produced by chemical processes only. In an in vivo cell factory approach, genes for a chitin synthase and a chitin deacetylase would be co-expressed in a host system so that the genetically modified organism would produce chitosan. This has been achieved for the production of a limited set of chitosan oligomers, but not yet for chitosan polymers. Interestingly, this process is scalable and can thus yield commercially relevant amounts of specific monoclonal chito-oligosaccharides.