Chitosan, a polymer of glucosamine is industrially produced by chemical deacetylation of chitin from shellfish. Cell wall of zygomycetes is an alternative source for production of chitosan. In fungal cell wall, chitosan is produced by enzymatic deacetylation of chitin. The chitosan is a polycationic polymer, and therefore antimicrobial activity is one of the most important characteristics of this polymer. In this study we used a new method for chitosan extraction, which is via hot dilute sulfuric acid treatment. It is a new method for extraction of chitosan from cell wall material of fungi, developed by biotechnology research group at University of Bor?s in Sweden and this work was accomplished in collaboration with them. Sulfuric acid extraction method was used to determine chitosan yield in cell wall of three different strains: Rhizopus oryzae , Mucor indicuss , Rhizonucor pucillus obtained from culture collection of university of Goteborg , Sweden . The ability of fungi for production of chitosan was examined at different growth phases. The results indicated that within less than 24 h, the pH of the culture media of all fungi decreased from initial value 5.5 to less than 3. Without any control of the pH, maximum extractable chitosan from one Kg of dry biomass R. oryzae was about 52.4 g, M. indicus 36.5 g and R. pusillus 27.8 g, within 6 days. Phosphates and N-acetyl glucosamine were the other compounds measured in this study. Results showed that R. pusillus was the most active fungus for production of chitin and was able to produce 136.4 g chitin per kg dry biomass and its phosphate content was less than 10% of biomass for each three strains. Since R. oryzae had the highest chitosan yield, the effect of pH and salt concentration were also studied on the chitosan yield from cell wall of this microorganism. The results showed that at pH=6.5 chitosan and phosphate yields are 3.5 and 2.9 times higher than the same condition at pH=3.5, respectively. Furthermore, if the salt concentration was less than 10 g/l, with increasing the salt concentration chitosan yield from cell wall decreased, whereas chitosan yield increased if the salt concentration was above this value. Antimicrobial properties of fungal chitosan extracted form R. oryzae was studied against three typical human pathogenic microorganisms, Escherichia coli , Klebsiella pneumoniae and Staphylococcus aureus . The minimum bactericidal concentration (MBC) of the ....
