Boscalid is one of the most frequently detected pesticides in main coastal estuaries in California, with concentrations as high as 36 μg/L. However, ecotoxicology information about boscalid to aquatic organisms is scarce. To investigate toxic effects and mechanisms of boscalid on freshwater algae ( ), were exposed to a range of boscalid concentrations (0, 0.8, 1.6, 2.4 and 3.2 mg/L) for 96 h to study the changes in photosynthetic pigment contents, responses of the antioxidant enzyme system and alterations in endogenous substances. Results indicated that the growth of algae and the content of chlorophyll and carotenoids were significantly inhibited by 1.6 mg/L boscalid. Reactive oxygen species (ROS) and oxidative damage of could be induced by boscalid, in accordance with significant changes in ROS levels and a series of antioxidant enzyme activities. Moreover, the alterations in endogenous substances showed that boscalid could affect photosynthesis and energy metabolism of . These results demonstrated that boscalid could induce impacts on mainly through disturbing the photosynthesis, oxidative damage and energy metabolism. The present study provided a better understanding of the negative effects and mechanisms of bosaclid in microalgae. Boscalid may result in growth inhibition of through disturbing the photosynthesis, oxidative stress and energy metabolism.
An electric field (EF) generator device was fabricated and applied to the treatment of ISC33 at three distinct concentrations before cultivation. The EF of moderate intensity (2.7 kV cm ) has a hormetic effect on algal growth. The highest growth stimulation of 51% was observed after 50 min treatment of 0.4 g L algal suspension. The influence of EF on the system was then studied from both theoretical and experimental perspectives. The growth rate increased with treatment time up to a maximum because of improved membrane permeability, and then declined afterwards due to peroxide accumulation in the medium. The contents of chlorophylls, carotenoids, soluble carbohydrates, lipids, and proteins were also measured to understand possible changes on algal metabolism. The EF treatment of algal suspension has no observable effect on the cell metabolism while both algal growth and metabolism was significantly affected by the inoculum size.
Biofixation of CO by microalgae has been recognized as an attractive approach to CO mitigation. The main objective of this work was to maximize the rate of CO fixation ( ) by the green microalga P12 cultivated photoautotrophically in bubble column photobioreactors under different CO concentrations (ranging from 2% to 10%) and aeration rates (ranging from 0.1 to 0.7 vvm). Results showed that the maximum (2.22 g L d ) was obtained by using 6.5% CO and 0.5 vvm after 7 days of cultivation at 30 °C. Although final biomass concentration and maximum biomass productivity of microalgae were affected by the different cultivation conditions, no significant differences were obtained in the biochemical composition of microalgal cells for the evaluated levels of aeration and CO . The present study demonstrated that optimization of microalgal cultivation conditions can be considered a useful strategy for maximizing CO bio-mitigation by .
Cell walls of microalgae consist of a polysaccharide and glycoprotein matrix providing the cells with a formidable defense against its environment. We characterized enzymes that can digest the cell wall and weaken this defense for the purpose of protoplasting or lipid extraction. A growth inhibition screen demonstrated that chitinase, lysozyme, pectinase, sulfatase, β-glucuronidase, and laminarinase had the broadest effect across the various Chlorella strains tested and also inhibited Nannochloropsis and Nannochloris strains. Chlorella is typically most sensitive to chitinases and lysozymes, both enzymes that degrade polymers containing N-acetylglucosamine. Using a fluorescent DNA stain, we developed rapid methodology to quantify changes in permeability in response to enzyme digestion and found that treatment with lysozyme in conjunction with other enzymes has a drastic effect on cell permeability. Transmission electron microscopy of enzymatically treated Chlorella vulgaris indicates that lysozyme degrades the outer surface of the cell wall and removes hair-like fibers protruding from the surface, which differs from the activity of chitinase. This action on the outer surface of the cell causes visible protuberances on the cell surface and presumably leads to the increased settling rate when cells are treated with lysozyme. We demonstrate radical ultrastructural changes to the cell wall in response to treatment with various enzyme combinations which, in some cases, causes a greater than twofold increase in the thickness of the cell wall. The enzymes characterized in this study should prove useful in the engineering and extraction of oils from microalgae.
Biomass and lipid productivities of Chlorella vulgaris under different growth conditions were investigated. While autotrophic growth did provide higher cellular lipid content (38%), the lipid productivity was much lower compared with those from heterotrophic growth with acetate, glucose, or glycerol. Optimal cell growth (2 g l(-1)) and lipid productivity (54 mg l(-1) day(-1)) were attained using glucose at 1% (w/v) whereas higher concentrations were inhibitory. Growth of C. vulgaris on glycerol had a similar dose effects as those from glucose. Overall, C. vulgaris is mixotrophic.
The main goal of this present study is to investigate the feasibility of coupling algae production ) to an anaerobic digestion unit. An intermediate settling device was integrated in order to adapt the feed-flow concentration and the flow rate. Digestion of was studied under 16 and 28 days hydraulic retention times (HRT), with a corresponding organic loading rate of 1 g L . Increasing the HRT achieved 51% COD removal with a methane production measured at 240 mL . Performing different HRTs and dynamic monitoring during degradation highlighted differential hydrolysis of microalgae compartments. However, 50% of the biomass did not undergo anaerobic digestion, even under long retention times. This points out the interest for further studies on pre-treatment performances and more generally speaking on the need for intensifying microalgae biomass digestion.
To enhance the anaerobic digestion of , thermochemical pretreatments were conducted. All pretreatments markedly improved solubilisation of carbohydrates. Thermal treatments and thermal treatments combined with alkali resulted in 5-fold increase of soluble carbohydrates while thermal treatment with acid addition enhanced by 7-fold. On the other hand, proteins were only solubilized with thermo-alkaline conditions applied. Likewise, all the pretreatments tested improved methane production. Highest anaerobic digestion was accomplished by thermal treatment at 120 °C for 40 min without any chemical addition. As a matter of fact, hydrolysis constant rate was doubled under this condition. According to the energetic analysis, energy input was higher than the extra energy gain at the solid concentration employed. Nevertheless, higher biomass organic load pretreatment may be an option to achieve positive energetic balances.
In this study, the time-course of growth, chemical composition and gene expression were analyzed over four days of nitrogen starvation in var L3 cultures. This strain exhibited a two-stage response to nitrogen depletion. Early starvation led to a slight biomass increase, a marked reduction of nitrogen rich-molecules and a 4-fold increase in carbohydrate content. During this stage, genes involved in carbohydrate metabolism ( and ) and fatty acid synthesis ( , , and C) were little affected by nitrogen unavailability but the genes linked to carbon and nitrogen fixation ( S, , ) and triglyceride synthesis ( ) were significantly up-regulated. A more extended N-starvation period resulted in increased lipid content, whereas biomass and carbohydrates remained constant. In this late starvation stage, most of the analyzed genes were strongly down-regulated but the transcript level of the gene S remained unaffected and gene was up-regulated. The results suggest that photosynthetically fixed carbon is driven toward lipid synthesis when carbohydrate synthesis is stopped. ME enzyme seems to be the main source of NADPH for reserve lipid synthesis and it might also provide precursors for acetyl-CoA synthesis.
Freshwater microalga and marine microalga were used to investigate toxic effects induced by 50 nm silver nanoparticles (AgNPs). To induce AgNPs effect, we exposed and for 24 h to 0–10 mg/L. We showed that growth media had different effects in AgNPs agglomerates' formation. Cellular viability, reactive oxygen species (ROS) formation and lipids peroxidation were employed to assess the toxic effects of AgNPs. AgNPs were able to interact directly with the cells surface and large aggregates were observed. AgNPs have a negative effect on and , as manifested by a strong decrease in chlorophyll content, viable algal cells, increased ROS formation and lipids peroxidation. The variability in sensitivity of both algae towards AgNPs was observed. We conclude that AgNPs have a negative effect on aquatic algae and these alterations might have serious consequences on structure and function of aquatic plant communities. ► Two green algae were used to investigate silver nanoparticles' (AgNPs) effects. ► Growth media has an effect in aggregates' formation of AgNPs. ► Algae species vary in their response to AgNPs. ► AgNPs induced strong ROS induction and lipids peroxidation.
The economic feasibility of algal mass culture for biodiesel production is enhanced by the increase in biomass productivity and storage lipids. Effect of iron on growth and lipid accumulation in marine microalgae were investigated. In experiment I, supplementing the growth media with chelated FeCl in the late growth phase increased the final cell density but did not induce lipid accumulation in cells. In experiment II, cells in the late-exponential growth phase were collected by centrifugation and re-inoculated into new media supplemented with five levels of Fe concentration. Total lipid content in cultures supplemented with 1.2 × 10 mol L FeCl was up to 56.6% biomass by dry weight and was 3–7-fold that in other media supplemented with lower iron concentration. Moreover, a simple and rapid method determining the lipid accumulation in with spectrofluorimetry was developed.