The cell factory approach toward biotechnological production of high-value chitosan oligomers and their derivatives: an update

Abstract

Chitin is one of the most abundant renewable resources, and chitosans, the partially deacetylated derivatives of chitin, are among the most promising functional biopolymers, with superior material properties and versatile biological functionalities. Elucidating molecular structure-function relationships and cellular modes of action of chitosans, however, it is challenging due to the micro-heterogeneity and structural complexity of polysaccharides. Lately, it has become apparent that many of the biological activities of chitosan polymers, such as in agricultural plant disease protection or in mediating scar-free wound healing, may be attributed to oligomeric break-down products generated by the action of chitosanolytic hydrolases present in the target tissues, such as human chitotriosidase. Consequently, the focus of current research is shifting toward chitosan oligomers so that the availability of well-defined chitosan oligosaccharides (COS) becomes a bottleneck. Well-known ways of producing COS use physical and/or chemical means for the partial depolymerization of chitosan polymers, typically leading to broad mixtures of COS varying in their degrees of polymerization (DP) and acetylation (DA), and with more or less random patterns of acetylation (PAs). Even after chromatographic separation according to DP and DA, such mixtures are of limited value to elucidate structure-function relationships and modes of action. More recently, enzymatic means using chitinases and/or chitosanases, and sometimes chitin deacetylases, have been proposed as these can be more tightly controlled and yield slightly better defined mixtures of COS. An alternative would be chemical synthesis of COS which in principle would allow for full structural control, but protocols for it are lengthy, costly, and not yet well developed, and yields are low. Synthetic biology now allows to develop today's in vitro bio-refinery approaches into in vivo cell factory approaches for the biotechnological production of defined COS using recombinant microbial strains expressing chitin oligomer synthases and chitin oligomer deacetylases. In this review, we will describe the state-of-the-art of this cell factory approach, as a basis for upcoming developments. We will briefly describe traditional chemical protocols and enzymatic production of COS as a background to the more detailed presentation of what has been achieved through in vivo biosynthesis. We will only briefly describe those as a background to the more detailed presentation of what has been achieved through in vivo biosynthesis. We will also touch on the production of COS derivatives that has been achieved in this way, as these oligomers open up another plethora of potential applications when used as building blocks for defined biomaterials.

A chitin deacetylase from the endophytic fungus Pestalotiopsis sp. efficiently inactivates the elicitor activity of chitin oligomers in rice cells

“…These are required for biotechnological investigations into structure-function relationships of partially acetylated chitosans, e.g. for agricultural, but also for biomedical and other applications313233.…”

Enzymatic Modification of Native Chitin and Conversion to Specialty Chemical Products

“…This yields mainly trimeric to monomeric glucosamines eventually, while statistical mixtures of higher DP product are obtained through the modulation of incubation time in the case of chitin [80]. Enzymatic degradation of partially acetylated chitosan polymers, however, tends to attain longer paCOS with mixed P A , D A , and DP and a higher likelihood of bioactivity [34,145]. (2) In vitro polymerisation of chito-oligomers using hydrolases with transglycosylating activity, resulting in high DP COS [146,147].…”

“…(2) In vitro polymerisation of chito-oligomers using hydrolases with transglycosylating activity, resulting in high DP COS [146,147]. (3) De-or re-N-acetylation of chitooligosaccharides, deploying chitin-or chitooligosaccharide-deacetylases to introduce specific P A and D A of choice [94,145], or (4) in-vitro synthesis of defined chito-oligomers with a heterologous system, expressing chitinsynthases and CDA from fungi [148].…”

Protein‐engineering of chitosanase from Bacillus sp. MN to alter its substrate specificity

“…Given their varying bioactivities, chitosan polymers, and partially acetylated chitosan oligomers (paCOS) have numerous potential applications in agriculture, cosmetics, biomedicine, and pharmaceutics (Aam et al, ; Bhatnagar & Sillanpää, ). However, as chitosan polymers are only soluble under slightly acidic conditions, much research has recently shifted towards focusing on more soluble paCOS (Das et al, ; Naqvi & Moerschbacher, ; Pillai, Paul, & Sharma, ). These paCOS are also of interest because they may actually be responsible for some of the biological activities reported for chitosan polymers, such as in plant protection and wound‐healing, since paCOS may originate in the target tissues when chitosan polymers are partially degraded by naturally occurring hydrolytic enzymes (El Gueddari, Schaaf, Kohlhoff, Gorzelanny, Moerschbacher, ).…”