Purification and Characterization of Cadmium-Binding Protein from Unicelluar Alga Chlorella sorokinian

The interplay between microalgae and toxic metal(loid)s: mechanisms and implications in AMD phycoremediation coupled with Fe/Mn mineralization

Acid mine drainage (AMD) is low-pH with high concentration of sulfates and toxic metal(loid)s (e.g. As, Cd, Pb, Cu, Zn), thereby posing a global environmental problem. For decades, microalgae have been used to remediate metal(loid)s in AMD, as they have various adaptive mechanisms for tolerating extreme environmental stress. Their main phycoremediation mechanisms are biosorption, bioaccumulation, coupling with sulfate-reducing bacteria, alkalization, biotransformation, and Fe/Mn mineral formation. This review summarizes how microalgae cope with metal(loid) stress and their specific mechanisms of phycoremediation in AMD. Based on the universal physiological characteristics of microalgae and the properties of their secretions, several Fe/Mn mineralization mechanisms induced by photosynthesis, free radicals, microalgal-bacterial reciprocity, and algal organic matter are proposed. Notably, microalgae can also reduce Fe(III) and inhibit mineralization, which is environmentally unfavorable. Therefore, the comprehensive environmental effects of microalgal co-occurring and cyclical opposing processes must be carefully considered. Using chemical and biological perspectives, this review innovatively proposes several specific processes and mechanisms of Fe/Mn mineralization that are mediated by microalgae, providing a theoretical basis for the geochemistry of metal(loid)s and natural attenuation of pollutants in AMD.

Detox diets for toxin elimination and weight management: a critical review of the evidence

Detox diets are popular dieting strategies that claim to facilitate toxin elimination and weight loss, thereby promoting health and well-being. The present review examines whether detox diets are necessary, what they involve, whether they are effective and whether they present any dangers. Although the detox industry is booming, there is very little clinical evidence to support the use of these diets. A handful of clinical studies have shown that commercial detox diets enhance liver detoxification and eliminate persistent organic pollutants from the body, although these studies are hampered by flawed methodologies and small sample sizes. There is preliminary evidence to suggest that certain foods such as coriander, nori and olestra have detoxification properties, although the majority of these studies have been performed in animals. To the best of our knowledge, no randomised controlled trials have been conducted to assess the effectiveness of commercial detox diets in humans. This is an area that deserves attention so that consumers can be informed of the potential benefits and risks of detox programmes.

Growth-inhibitory and metal-binding proteins in Chlorella vulgaris exposed to cadmium or zinc

Phytochelatins, with the general structure of (gamma-Glu-Cys)n-Gly (n=2-11), are usually recognized as being strongly induced by metals in microalgae and play an important role in the detoxification of heavy metals in environment. However, there have been few studies on metallothionein (MT) synthesis in Chlorella vulgaris (C. vulgaris) exposed to heavy metals. The present study describes the growth inhibition of C. vulgaris exposed to different concentrations of cadmium and zinc, and the induction of metal-binding MT-like proteins in the cells. The amounts of metal-binding proteins, induced in the alga exposed to different concentrations of Cd and Zn, were analyzed with a size-exclusion HPLC coupled to ICP-MS. After being purified with a gel filtration column (Sephadex G-75, 3.5cmx80cm) and a desalting column (G-25, 1.5cmx30cm), the isoforms and sub-isoforms of Zn-binding protein were characterized by a reverse phase-HPLC coupled to electrospray ionization and a triple quadrupole mass spectrometer (HPLC-ESI-MS/MS). In addition, the ultraviolet spectra of purified Zn-binding proteins were analyzed in media with different pH values. The results showed that the significant inhibitory effects (at p<0.05) on the cell growth were observed when excessive metals such as 80micromoll(-1) of Cd, and 60 and 80micromoll(-1) of Zn were added. The Cd/Zn-binding proteins induced in C. vulgaris exposed to Cd and Zn were referred to as Cd/Zn-MT-like proteins in which the mean molecular mass of the apo-MT-like was 6152Da. The induced Cd/Zn-MT-like proteins might be involved in the detoxification of heavy metals, such as cadmium and zinc, by the alga.

Cadmium and heat response of the fungus Heliscus lugdunensis isolated from highly polluted and unpolluted areas

Induction of heat shock protein (Hsp) 70 and distinct metallothionein-like proteins (MTLPs) in response to Cd and heat treatment were studied in two strains of the aquatic hyphomycete Heliscus lugdunensis: Hl-H4, isolated from a heavy metal polluted site, and Hl-BB taken from an unpolluted area. Upon Cd-exposure, Hsp70 was actively synthesized in the strain Hl-H4, and to a much lower degree in the strain Hl-BB. The Hsp70-expression was time- and dose-dependent, reaching a maximum after 24 h incubation with 80 microM Cd. Upon heat-stress, a similar response was observed: a strong Hsp70-expression in Hl-H4, and only a marginal one in Hl-BB. The strains reacted to Cd-exposure by a specific, environmentally related induction of MTLPs, as shown by the highly sensitive bimane derivatisation method of SH-rich proteins. In Hl-H4, a strong expression of 11 kDa MTLP was registered, which followed strictly the induction pattern of Hsp70. This suggests interdependence of the induction mechanisms and roles of these stress proteins in metal resistance. On the contrary, in Hl-BB a weak expression of MTLP of about 20 kDa was observed, exhibiting completely different induction pattern. The results suggest that the specific induction of Hsp70 and/or distinct MTLPs in the range of 11 kDa in H. lugdunensis strain Hl-H4 are essential adaptive mechanisms to continuous heavy metal exposure.