Comparative biodegradation of all chlorinated phenols by the microalga Scenedesmus obliquus — The biodegradation strategy of microalgae

Abstract

This work presents the comparative biodegradation of all chlorinated phenolic compounds by the green alga Scenedesmus obliquus and determines the microalgal bioenergetic strategy. The microalga manages its energy reserves rationally by investing them, either on growth or on the biodegradation of the toxic compound. The microalga seems to follow two distinct detoxification strategies. In the first one, when microalgae are surrounded by relatively low toxic phenolic compounds (phenol, monochlorophenols, 2,4-dichlorophenol and 2,6-dichlorophenol), they use all, or at least more of their energy reserves to increase the biomass production and not the biodegradation. In the second one, when surrounded by higher toxic chlorophenols (meta-substituted dichlorophenols, trichlorophenols, tetrachlorophenols and pentachlorophenol) the microalgae invest more, or all of their energy reserves directly in the biodegradation of the toxic compounds, while less or no energy is invested in biomass increase. The microalga biodegraded in five days approximately 9% of the lower toxic phenol and 90% of the higher toxic pentachlorophenol. Considering our ability to interfere with microalgae energy reserves, which define their stress tolerance in the toxic environment, and knowing the microalgal bioenergetic strategy, we could easily use microalgae to biodegrade toxic wastes in the frame of a rational biotechnological approach in the near future.