Glucose Synthesis in a Protein-Based Artificial Photosynthesis System

Bioaccumulation and toxicity of perfluorooctanoic acid and perfluorooctane sulfonate in marine algae Chlorella sp

The ocean is an important sink for perfluorinated alkyl acids (PFAAs), but the toxic mechanisms of PFAAs to marine organisms have not been clearly studied. In this study, the growth rate, photosynthetic activity, oxidative stress and bioaccumulation were investigated using marine algae Chlorella sp. after the exposure of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate acid (PFOS). The results showed that PFOA of <40 mg/L and PFOS of <20 mg/L stimulated algal reproduction, and high doses inhibited the algal growth. The absorbed PFOA and PFOS by algal cells damaged cell membrane and caused metabolic disorder. The photosynthesis activity was inhibited, which was revealed by the significantly reduced maximal quantum yield (Fv/Fm), relative electron transfer rate (rETR) and carbohydrate synthesis. However, the chlorophyll a content increased along with the up-regulation of its encoding genes (psbB and chlB), probably due to an overcompensation effect. The increase of ROS and antioxidant substances (SOD, CAT and GSH) indicated that PFOA and PFOS caused oxidative stress. The BCF of marine algae Chlorella sp. to PFOA and PFOS was calculated to be between 82 and 200, confirming the bioaccumulation of PFOA and PFOS in marine algae. In summary, PFOA and PFOS can accumulate in Chlorella sp. cells, disrupt photosynthesis, trigger oxidative stress and inhibit algal growth. PFOS shows higher toxicity and bioaccumulation than PFOA. The information is important to evaluate the environmental risks of PFAAs.

Installing a Green Engine To Drive an Enzyme Cascade: A Light-Powered In Vitro Biosystem for Poly(3-hydroxybutyrate) Synthesis

Many existing in vitro biosystems harness power from the chemical energy contained in substrates and co-substrates, and light or electric energy provided from abiotic parts, leading to a compromise in atom economy, incompatibility between biological and abiotic parts, and most importantly, incapability to spatiotemporally co-regenerate ATP and NADPH. In this study, we developed a light-powered in vitro biosystem for poly(3-hydroxybutyrate) (PHB) synthesis using natural thylakoid membranes (TMs) to regenerate ATP and NADPH for a five-enzyme cascade. Through effective coupling of cofactor regeneration and mass conversion, 20 mM PHB was yielded from 50 mM sodium acetate with a molar conversion efficiency of carbon of 80.0 % and a light-energy conversion efficiency of 3.04 %, which are much higher than the efficiencies of similar in vitro PHB synthesis biosystems. This suggests the promise of installing TMs as a green engine to drive more enzyme cascades.

Effect and mechanism of TiO2 nanoparticles on the photosynthesis of Chlorella pyrenoidosa

Titanium dioxide nanoparticles (n-TiO₂) have been used in numerous applications, which results in their release into aquatic ecosystems and impact algal populations. A possible toxic mechanism of n-TiO₂ on algae is via the disruption of the photosynthetic biochemical pathways, which yet remains to be demonstrated. In this study, Chlorella pyrenoidosa was exposed to different concentrations (0, 0.1, 1, 5, 10, and 20 mg/L) of a type of anatase n-TiO₂, and the physiological, biochemical, and molecular responses involved in photosynthesis were investigated. The 96 h half growth inhibition concentration (IC₅₀) of the n-TiO₂ to algae was determined to be 9.1 mg/L. A variety of cellular and sub-cellular damages were observed, especially the blurry lamellar structure of thylakoids, indicating the n-TiO₂ impaired the photosynthetic function of chloroplasts. Malondialdehyde (MDA) and glutathione disulfide (GSSG) significantly increased while the glutathione (GSH) content decreased. This implies the increased consumption of GSH by the increased intracellular oxidative stress upon n-TiO₂ was insufficient to eliminate the lipid peroxidation. The contents of photosynthetic pigments, including chlorophyll a (Chl a) and phycobiliproteins (PBPs) in the exposed algal cells increased along with the up-regulation of genes encoding Chl a and photosystem II (PS II), which could be explained by a compensatory effect to overcome the toxicity induced by the n-TiO₂. On the other hand, the photosynthetic activity was significantly inhibited, indicating the impairment on the photosynthesis via damaging the reaction center of PS II. In addition, lower productions of adenosine triphosphate (ATP) and glucose, together with the change of gene expressions suggested that the n-TiO₂ disrupted the material and energy metabolisms in the photosynthesis. These findings support a paradigm shift of the toxic mechanism of n-TiO₂ from physical and oxidative damages to metabolic disturbances, and emphasize the threat to the photosynthesis of algae in contaminated areas.