Characterization of copper resistant ciliates: Potential candidates for consortia of organisms used in bioremediation of wastewater

Abstract

Metals are environmental pollutants of major concern due to their ecological, sanitary and even economic consequences. Both prokaryotes and eukaryotes inhabiting such environments carry cellular systems that maintain the metal homeostasis. The ciliate protists tolerate elevated concentrations of metals, which are accumulated, bound to metallothioneins (MTs) peculiar to these organisms. Copper is one of such contaminant found in the wastewater of local industries. The concentrations of copper which caused 50% reduction (LC₅₀) in the cell population of Tetrahymena sp RT1, and two Euplotes spp. RE-1 and RE-2, isolated from the industrial waste, were found to be 60, 48 and 49 ppm, respectively, compared to those of the cultures without copper in the media. RT-1 showed significantly high tolerance to copper ions and could uptake 52.66% of the copper ions from the medium. The axenic culture of RT-1 could uptake 61.2% of copper from the medium compared to 68.41 and 59.16% by the ATCC culture of Tetrahymena thermophila and T. pyriformis, respectively. RT-1 tolerated about 500 μM copper in the medium without affecting its movement. This ciliate showed promise as a member of the consortium used for bioremediation of copper contaminated wastewater.

Key words: Copper toxicity, metallothionein, growth curve of ciliates, metal uptake, bioremediation.