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International Journal of Microbiology
Volume 2009, Article ID 418595, 5 pages
Research Article

Inhibitory Effect of Gamma-Irradiated Chitosan on the Growth of Denitrifiers

1New Industry Creation Hatchery Center (NICHe), Tohoku University, Aoba 6-6-20, Aramaki, Aoba-ku, Sendai, Miyagi 980-8579, Japan
2Graduate School of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan

Received 6 August 2009; Revised 20 November 2009; Accepted 26 December 2009

Academic Editor: Thomas L. Kieft

Copyright © 2009 Javier Vilcáez and Tomohide Watanabe. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


In order to find an environmentally benign substitute to hazardous inhibitory agents, the inhibitory effect of 𝛾 -irradiated chitosans against a mixed culture of denitrifying bacteria was experimentally evaluated. Unlike other studies using pure aerobic cultures, the observed effect was not a complete inhibition but a transient inhibition reflected by prolonged lag phases and reduced growth rates. Raw chitosan under acid conditions (pH 6.3) exerted the strongest inhibition followed by the 100 kGy and 500 kGy irradiated chitosans, respectively. Therefore, because the molecular weight of chitosan decreases with the degree of 𝛾 -irradiation, the inhibitory properties of chitosan due to its high molecular weight were more relevant than the inhibitory properties gained due to the modification of the surface charge and/or chemical structure by 𝛾 -irradiation. High dosage of 𝛾 -irradiated appeared to increase the growth of mixed denitrifying bacteria in acid pH media. However, in neutral pH media, high dosage of 𝛾 -irradiation appeared to enhance the inhibitory effect of chitosan.