Beyond single parameters: How structural combinations determine chitosans' antibacterial effects

Chitosans are versatile and promising functional biopolymers with diverse bioactivities that are strongly influenced by three characteristic structural parameters: the degree of polymerization (DP), the fraction of acetylation ( F A ), and the pattern of acetylation (PA). However, limited understanding of these structure-function relationships and of the underlying mechanisms compromises reproducibility and effective applications. To address this, we have produced a set of 16 different chitosans from a single parent chitosan (DP 1237, F A 0.01) yielding chitosans with defined DP and F A , and random (Bernoullian) PA. We analyzed the antimicrobial activity of selected chitosans against four phytopathogens, Pseudomonas syringae pv. tomato , Clavibacter michiganensis, Fusarium graminearum, and Ustilago maydis , observing strong antimicrobial activities for all chitosans. Detailed analysis including more chitosans against P. syringae revealed no consistent trend linking a low F A or a specific DP alone to enhanced antibacterial activity. Instead, the influence of F A on antibacterial efficacy was dependent on DP, and vice versa. There seems to be a complex interplay between DP and F A , and single-parameter interpretations seem insufficient. Further studies will have to show whether this conclusion can be generalized beyond P. syringae .