The complexation with proteins in extracellular polymeric substances alleviates the toxicity of Cd (II) to Chlorella vulgaris. (August 2020)

• Record Type: Journal Article
• Authors: Xie, Qiting; Liu, Na; Lin, Daohui; Qu, Ruohua; Zhou, Qiongzhi; Ge, Fei
• Is Part Of: Environmental pollution. Volume 263(2020)Supplement Part A
• Publication Date: 2020-08
• Subjects: Complexation -- Extracellular Polymeric Substance -- Protein -- Heavy metal; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2020.114102
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: The complexation with extracellular polymeric substances (EPS) greatly reduces the toxicity of heavy metals towards organisms in the environment. However, the molecular mechanism of EPS−metal complexation remains unclear owing to the limitation of precise analysis for key fractions and functionalities in EPS that associate with metals. Herein, we explored the EPS−Cd (II) complexation by fluorescence excitation emission matrix coupled with parallel factor (EEM−PARAFAC), two-dimensional Fourier transform infrared correlation spectroscopy (2D-FTIR−COS) and X-ray photoelectron spectroscopy (XPS), attempting to explain the mechanisms of EPS in alleviating Cd (II) toxicity toward a green alga Chlorella vulgaris ( C. vulgaris ). When the algal EPS were removed, the cell internalizations of Cd (II), growth inhibition rate and chlorophyll autofluorescence increased, but the surface adsorption and esterase activities decreased, indicating that the sorption of Cd (II) by EPS was crucial in alleviating the algal toxicity. Moreover, the complexation with proteins in EPS controlled the sorption of Cd (II) to algal EPS, resulting in the chemical static quenching of the proteins fluorescence by 47.69 ± 2.37%. Additionally, the complexing capability of the main functionalities, COO − and C–OH in proteins with Cd (II) was stronger than that of C–O(H) and C–O–C in polysaccharides or C–OH in the humus-related substances. Oxygen atom in protein carboxyl C–O might be the key site of EPS−Cd (II) complexation, supported by the modified Ryan−Weber complexation model and the obvious shift of oxygen valence-electron signal. These findings provide deep insights into understanding the interaction of EPS with heavy metals in aquatic environment. Graphical abstract: Image 1 Highlights: The sorption by EPS was crucial in alleviating the toxicity of Cd (II) to algae. The complexation with proteins in EPS controlled the sorption of Cd (II) to EPS. The COO − and C–OH in proteins were the main functionalities complexing with Cd (II). Oxygen atom in protein carboxyl C–O might be the key site responsible for the EPS−Cd (II) complexation. Abstract : The complexation with proteins in EPS alleviates the Toxicity of Cd (II): Oxygen atom in protein carboxyl C–O might be the key complexation site.