Efficiency of Chitosan Depolymerization by Microbial Chitinases and Chitosanases with Respect to the Antimicrobial Activity of Generated Chitooligomers

Specific features of the enzymatic degradation of chitosan with depolymerization degrees (DD) of 85 and 50% by microbial chitinases and chitosanases were studied in terms of the conversion degree, molecular-weight distribution (MWD), and antimicrobial activity of the generated reaction products. The enzyme complex produced by the strain B. thuringiensis B-387, which is characterized by high chitosanase production (>4.5 U mL –1 ), degraded the polymer to soluble, low molecular weight chitooligosaccharides (CHOs, M w ≤ 2 kDa), along with a minor yield (~5%) of alkali-precipitated oligochitosans (M w 2–16 kDa). The hydrolytic complexes produced by B. atrophaeus IB-33-1 and Cohnella sp. IB-P192, which mainly comprise chitinases (0.3–0.5 U mL –1 ), demonstrated the lowest rate and degree of chitosan (DD 85%) hydrolysis. The selection of an enzyme : substrate ratio in the range of 2–5 units/g (based on chitosanase) made it possible to reduce the hydrolysis depth of the initial polymer and to increase the yield of oligochitosans with a M w of ~15–17 kDa to 30% for chitosan (DD 85%) depolymerization by the enzyme complex from B. thuringiensis B-387. The decrease in the bactericidal and fungicidal effect of the oligomers that formed during the destruction of chitosan with varying deacetylation degrees (DD 85% and 50%) by enzyme complexes displaying high chitosanase activity was, as a rule, more distinct than that achieved with the use of chitinases. However, in some cases, there were both nonspecific and specific enhancements of the antimicrobial action of hydrolytic products in comparison with the initial polymer, which was determined by individual sensitivity of bacterial and micromycetes strains.