Multiple Heavy Metal Tolerant Ciliates, Oxytricha fallax and Paramecium caudatum, Isolated From Industrial Effluents and Their Potential Use in Wastewater Treatment

The multiple heavy metal resistant ciliates, Oxytricha fallax and Paramecium caudatum, isolated from industrial wastewater have been shown to be potential bioremediator of contaminated wastewater. The O. fallax showed tolerance against Zn2+ (17 mu g/ml), Hg2+ and Ni2+ (18 mu g/ml), and Cu2+ and Cd2+ (16 mu g/ml). P. caudatum was found to tolerate Ni2+, Cu2+, Hg2+, Zn2+, and Cd2+ at a concentration of 18, 15, 17, 15 and 14 mu g/ml, respectively. The metal ions slowed down the growth of the ciliates as compared to the culture grown without metal stress. The reduction in cell population of O. fallax was 70% for Cd2+, 59% for Hg2+, 28% for Zn2+, 71% for Cu2+ and 70% for Ni2+ after 8 days of metal stress. The decrease in cell population of P. caudatum was 56% for Cd2+, 44% for Hg2+, 34% for Zn2+, 80% for Cu2+ and 70% for Ni2+ after 8 days of metal stress. O. fallax decreased 91% of Zn2+, and 90% of Hg2+ from the medium after 96 hours of incubation in a culture medium containing 10 mu g/ml of the respective metal ions. Besides this, the ciliate could also remove 94% of Cu2+ and Cd2+ and 88% Ni2+- from the medium containing 5 mu g/ml of each metal after 96 hours, respectively. P. caudatum removed 95% of Zn2+ and 78% of Hg2+ from the medium containing 10 mu g/ml of the respective metal ions after 96 hours of incubation. The protozoan could also remove 94% of Cu2+, 82% of Cd2+ and 76% Ni2+ from the medium containing 5 mu g/ml of each metal after 96 hours, respectively. The ability of ciliates to take up multiple heavy metals from the medium could be exploited for metal detoxification and environmental clean-up operations.