Abstract
The heavy metal pollution in soils and aquatic environments is a serious ecological problem. In the green-microalga Chlorella sorokiniana 211-8K (Chlorophyceae) exposed to ions of lead (Pb) and cadmium (Cd) we studied the metabolic responses to the toxicity of these two heavy metals. Our data indicate that both the pollutants alter the alga cell ultrastructure and its physiological characteristics (growth, photosynthesis, respiration, enzyme activities). The toxic effects of the two metals resulted time-dependent to the exposure. After 24 h of treatment with 250 μM Pb or Cd, photosynthesis was inhibited until to 77 and 86%, however respiration was strongly enhanced up to 300 and 350%, respectively. In the algal cells Pb or Cd exposure induced a reduction in the content of the total chlorophylls and a decrease of the soluble protein levels, significantly compromising the growth, particularly in cultures cadmium-treated. We report data on ultrastructural changes induced by the two heavy metals; they affected overall chloroplast ultrastructure of the alga. Most importantly, the O-acetyl-L-serine(thiol)lyase (OASTL) activity was appreciably increased after only 2 h of Cd exposure, indicating the existence of a link between the metal contamination and cysteine synthesis. Then, Chlorella sorokiniana cells seem to better tolerate high concentrations of Pb while appear to be more sensitive to Cd ions. These results provide some additional information that can lead to better understand consequences of heavy metal poisoning in microalgae.
Highlights
IntroductionSeveral of them are essential components of global ecosystems
Metals occur naturally, and several of them are essential components of global ecosystems
We suggest that the cytoplasm vesicles, and concentric multilamellar/multivesicular bodies were induced by heavy metal treatment and they might be involved in the transport of metal ions to vacuoles or vesicles and/or in the elaboration of massive newly formed or damaged material
Summary
Several of them are essential components of global ecosystems. The contamination by heavy metals has become a serious problem because they could enter into food chains. Microalgae, the primary producers at the base of the aquatic food chain, are the first target affected by heavy metal pollution. In microalgae trace concentrations of heavy metals are necessary as co-factor of enzymatic reactions, but high level of them could be extremely toxic (Travieso et al 1999). Lead (Pb) and cadmium (Cd), two non-essential and toxic heavy metals for many living organisms, accumulate in algae (Debelius et al 2009; Bajguz 2011). Algae possess extracellular and intracellular mechanisms to prevent metal toxicity (Scheidegger et al 2011). Microalgae provide important informations for predicting the environmental impact of heavy metal pollution (Akira et al 2005)
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