Abstract
One of the main concerns in industrialized countries is represented by per- and poly-fluoroalkyl substances (PFAS), persistent contaminants hardly to be dealt with by conventional wastewater treatment processes. Phyco-remediation was proposed as a green alternative method to treat wastewater. Synechocystis sp. PCC6803 is a unicellular photosynthetic organism candidate for bioremediation approaches based on synthetic biology, as it is able to survive in a wide range of polluted waters. In this work, we assessed the possibility of applying Synechocystis in PFAS-enriched waters, which was never reported in the previous literature. Respirometry was applied to evaluate short-term toxicity of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), which did not affect growth up to 0.5 and 4 mg L−1, respectively. Continuous and batch systems were used to assess the long-term effects, and no toxicity was highlighted for both compounds at quite high concentration (1 mg L−1). A partial removal was observed for PFOS and PFOA, (88% and 37%, with removal rates of about 0.15 and 0.36 mg L−1 d−1, respectively). Measurements in fractionated biomass suggested a role for Synechocystis in the sequestration of PFAS: PFOS is mainly internalized in the cell, while PFOA is somehow transformed by still unknown pathways. A preliminary bioinformatic search gave hints on transporters and enzymes possibly involved in such sequestration/transformation processes, opening the route to metabolic engineering in the perspective application of this cyanobacterium as a new phyco-remediation tool, based on synthetic biology.
Highlights
Per- and poly-fluoroalkyl substances (PFAS) are man-made organic compounds sharing a hydrophilic head group and a hydrophobic alkyl chain of variable length partially or completely fluorinated [1]
In Veneto, a north-eastern region of Italy, PFAS are accounted for a contamination case-study, since they present at high concentrations both in surface and groundwater and in drinking water, with consequent human health impairment due to the significant exposure of the population living in this region [7,8]
Integrated, multidisciplinary research is, urgently required to develop new approaches for bioremediation, and this work aims at evaluating the potential of Synechocystis in remediation of wastewaters with a wide range of PFAS load
Summary
Per- and poly-fluoroalkyl substances (PFAS) are man-made organic compounds sharing a hydrophilic head group and a hydrophobic alkyl chain of variable length (from 4 to 16 C) partially (poly-fluorinated) or completely fluorinated (per-fluorinated) [1]. A number of useful characteristics, such as amphiphilic nature, ability to reduce liquids surface tension, high thermal stability, low chemical reactivity, absence of smell and color, high availability, and low cost [3,4], make PFAS ideal for several industrial applications and products, such as firefighting foams, non-stick materials for cookware, or stain high-temperature lubricants, among others [1,5]. All these chemical properties make them non-biodegradable, widespread, and persistent in the environment, subject to bioaccumulation and biomagnification in the environment [3]. In Veneto, a north-eastern region of Italy, PFAS are accounted for a contamination case-study, since they present at high concentrations both in surface and groundwater (up to μg L−1) and in drinking water, with consequent human health impairment due to the significant exposure of the population living in this region [7,8]
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