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

In order to find an environmentally benign substitute to hazardous inhibitory agents, the inhibitory effect of gamma-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 gamma-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 gamma-irradiation. High dosage of gamma-irradiated appeared to increase the growth of mixed denitrifying bacteria in acid pH media. However, in neutral pH media, high dosage of gamma-irradiation appeared to enhance the inhibitory effect of chitosan.