Antimicrobial Activity Of The Chitooligosaccharides Prepared By Enzymolysis

Low-molecular-weight chitosan(chitooligosaccharides)was reported to have antimicrobial ability,which has been drawn wide attention since then.This dissertation investigated the antimicrobial activity of chitooligosaccharides against several distinct strains of bacteria and fungi in different conditions.Chitooligosaccharides with different molecular weight were analyzed,which were prepared from chitosan by different enzymolysis manners.The purpose of this article is to seek for experimental evidence for possible application of chitooligosaccharides in agricultural and curatorial fields.Chitosanases were prepared from fermentation extracts of Penicillium sp.ZD-Z1,which is a bacteria strain screened out from the soil.After being fermented for 65-70 hours,the fermentation liquid was further managed by following steps:ultrafiltration,precipitation with 95%cold ethanol(3:1 V/V) and refrigerated concentrating spinning.At last,endo-chitosanase ChA and exo-chitosanase ChB were isolated by IEC.3%(W/V)chitosan solution was degraded by ChA or ChB respectively or together(mixed chitosanases),the products of which were filtered by ultrafiltration membrane with MWC 10kD, 5kD and 2kD successively.Chitooligosaccharides with different molecular weight was then achieved by spray-drying the ultrafiltrate.The mean molecular weight of the end chitooligosaccharide products were determined by HPLC plus acetylacetone.Antimicrobial activity of chitooligosaccharides were assayed against several widely-distributed bacteria and pohytopathogenic?(plant)fungi. Chitooligosaccharides prepared by endo-chitosanase showed higher antimicrobial activity than those prepared by mixed chitosanases,while those prepared by exo-chitosanase had nearly no antimicrobial activity,to some extent, which can promote the growth of some microorganism.To endo-chitosanase-treated products,among the three fungi tested,the growth of Colletotrichum lagenarium could be most efficiently inhibited,and the inhibitory activity against Clavibacter michiganensis was more efficient than that against Acidovorax avenae.In addition,we performed in vitro bacteriostatic assay of chitooligosaccharides,which have different molecular weight produced by endo-chitosanase enzymolysis,against H.pylori(Helicobacter pylori).The result turned out that all of the endo-chitosanase products(C3,C5,C6 and C7)could inhibit H.pylori growth compared to control.For the chitooligosaccharides with molecular weight between 1.5kD and 10kD,the antibacterial activity against H.pylori increased with the decreasing of molecular weight or with the increasing of concentration of chitooligosaccharides.In the PH range of 1.90—3.86,this H.pylori-resistant activity would increase along with the decreasing of pH value.