Impact of heavy metals in the microalga Chlorella sorokiniana and assessment of its potential use in cadmium bioremediation

The chlorophyte microalga Chlorella sorokiniana was tested for the bioremediation of heavy metals pollution. It was cultured with different concentrations of Cu2+, Cd2+, As (III) and As (V), showing a significant inhibition on its growth at concentrations of 500 mu M Cu2+, 250 mu M Cd2+, 750 mu M AsO33- and 5 mM AsO(4)(3-)or higher. Moreover, the consumption of ammonium was also studied, showing significant differences for concentrations higher than 1 mM of Cu2+ and As (III), and 5 mM of As (V). The determination of intracellular heavy metals concentration revealed that Chlorella sorokiniana is an outstanding Cd accumulator organism, able to accumulate 11,232 mg kg(-1) of Cd, and removing 65% of initial concentration of this heavy metal. Finally, antioxidant enzymes, such as catalase (CAT) and ascorbate peroxidase (APX), and enzymes involved in the production of glutamate and cysteine, such as glutamine syntethase (GS), glutamate dehydrogenase (GDH), O-acetylserine (thiol) lyase (OASTL) and NAD-isocitrate dehydrogenase (NAD-IDH) were studied both at gene expression and enzymatic activity levels. These enzymes exhibited different grades of upregulation, especially in response to Cd and As stress. However, GS expression was downregulated when Chlorella sorokiniana was cultured in the presence of these heavy metals.

Automated summary

The microalga Chlorella sorokiniana was tested for bioremediation of heavy metals pollution, showing significant inhibition on growth and ammonium consumption at high concentrations of Cu2+ and As (III). It exhibited outstanding Cd accumulation ability, with antioxidant enzymes and enzymes involved in glutamate synthesis showing different levels of upregulation in response to Cd and As stress, except for the downregulation of GS expression.