Chitosans are among the most promising and most versatile functional biopolymers, with superior material properties and biological functionalities. Chitosans can form gels, films, and fibers, nano-particles, nano-capsules, and nano-fibers, they have antimicrobial and plant strengthening, wound healing and drug delivering potential – but the best suited chitosan differs for each application, necessitating a detailed molecular understanding of structure/function relationships. The term chitosan really refers to a family of oligo- and polysaccharides differing in their degree of polymerisation (DP), degree of acetylation (DA), and pattern of acetylation (PA), and initial commercial chitosans were rather ill-defined mixtures with large batch-to-batch differences. Using series of well-defined chitosans with narrow ranges of DP and DA, and defined random PA, we showed that chitosans with low DA and intermediate DP exhibited the highest antimicrobial activities, independent of the bacteria or fungi studied, while chitosans with intermediate DA and high DP were best for plant strengthening, but the optimal chitosan differed between plant species and disease. These ‘second generation’ chitosans are now available on industrial scale and allow for the first time the development of reliable chitosan-based plant protectants with good efficacies. However, biomedical activities of these chitosans still tend to remain unreliable. We have argued that biological activities of chitosans will crucially be determined by their PA if the target tissue contains a sequence-specific chitosan hydrolase – such as human chitotriosidase. However, due to their chemical production processes from fully acetylated chitin or fully de-acetylated polyglucosamine, the PA of today’s chitosans is invariably random. We therefore aim to develop enzymatic ways to produce chitosans with controlled, non-random PA, and we have designed enzymatic/mass spectrometric fingerprinting tools for their analysis. In addition, we are developing biotechnological production ways for these ‘third generation’ bio-engineered chitosans using recombinant chitin and chitosan synthesizing and modifying enzymes in a cell factory approach. This research has received funding from the EU`s 5th, 6th, and 7th FP under grant agreements 00777, 013882, 222628, 613931, and EIB.10.042, as well as from the German Federal Ministry of Education and Research, BMBF, under grant agreements 03VWP0024, 0315935A and 0315543A.

Bioengineering of third generation chitosans

249th National Meeting (2015)

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