Relative Electron Transfer Rate Research Articles

Alien emergent aquatic plants develop better ciprofloxacin tolerance and metabolic capacity than one native submerged species

Antibiotic pollution and biological invasion pose significant risks to freshwater biodiversity and ecosystem health. However, few studies have compared the ecological adaptability and ciprofloxacin (CIPR) degradation potential between alien and native macrophytes. We examined growth, physiological response, and CIPR accumulation, translocation and metabolic abilities of two alien plants (Eichhornia crassipes and Myriophyllum aquaticum) and one native submerged species (Vallisneria natans) exposed to CIPR at 0, 1 and 10 mg/L. We found that E. crassipes and M. aquaticum's growth were unaffected by CIPR while V. natans was significantly hindered under the 10 mg/L treatment. CIPR significantly decreased the maximal quantum yield of PSII, actual quantum yield of PSII and relative electron transfer rate in E. crassipes and V. natans but didn't impact these photosynthetic characteristics in M. aquaticum. All the plants can accumulate, translocate and metabolize CIPR. M. aquaticum and E. crassipes in the 10 mg/L treatment group showed greater CIPR accumulation potential than V. natans indicated by higher CIPR contents in their roots. The oxidative cleavage of the piperazine ring acts as a key pathway for these aquatic plants to metabolize CIPR and the metabolites mainly distributed in plant roots. M. aquaticum and E. crassipes showed a higher production of CIPR metabolites compared to V. natans, with M. aquaticum exhibiting the strongest CIPR metabolic ability, as indicated by the most extensive structural breakdown of CIPR and the largest number of potential metabolic pathways. Taken together, alien species outperformed the native species in ecological adaptability, CIPR accumulation and metabolic capacity. These findings may shed light on the successful invasion mechanisms of alien aquatic species under antibiotic pressure and highlight the potential ecological impacts of alien species, particularly M. aquaticum. Additionally, the interaction of antibiotic contamination and invasion might further challenge the native submerged macrophytes and pose greater risks to freshwater ecosystems.

Application of confocal microscopy and flow cytometry to identify physiological responses of Prorocentrum micans to the herbicide glyphosate

The physiological response of the dinoflagellate P. micans to the effect of the herbicide glyphosate at a concentration of 25–200 μg L−1 was evaluated. It has been shown that P. micans is able to grow due to the consumption of dissolved organic phosphorus formed as a result of the mineralization of glyphosate by bacteria. The addition of glyphosate to the medium inhibits the photosynthetic activity of cells; there is a pronounced inhibition of the relative electron transfer rate along the electron transport chain and the maximum quantum efficiency of the use of light energy. Morphological and ultrastructural changes in P. micans cells were evaluated at sublethal (150 μg L−1) and lethal (200 μg L−1) glyphosate concentrations. It has been shown that at a herbicide concentration of 150 μg L−1, the first signs of apoptosis appear in most P. micans cells: a decrease in lateral light scattering, cytoplasmic retraction, partial destruction of cytoplasmic organelles, a change in the morphology of nuclei, mitochondria, a change in the potential of mitochondrial membranes, and a decrease in the autofluorescence of chlorophyll in cells. At a glyphosate concentration of 200 μg L−1, P. micans showed signs of a late stage of apoptosis: violation of the integrity of intracellular organelles and chromatin organization, fragmentation of nuclei, condensation of cytoplasm, disorganization of chloroplasts in the cells, and the release of cell contents beyond the cell membrane. The effectiveness of using flow cytometry and laser scanning confocal microscopy methods for identifying signs and stages of cell apoptosis when exposed to glyphosate is discussed.

Light intensity influences the glycerolipid remodeling of Gracilariopsis lemaneiformis in response to short-term high temperature stress

Temperature and light are two pivotal environmental factors for the growth of marine photosynthetic organisms. While the responses of Gracilariopsis lemaneiformis to individual high temperature or light stress have been explored, our understanding of its combined stress responses remains limited. This study aimed to investigate the combined effects of short-term high temperature (33 °C, 8 h) and different light intensities, that is, low light (LL, 50 μmol photon m−2 s−1), medium light (ML, 150 μmol photon m−2 s−1), and high light (HL, 300 μmol photon m−2 s−1), on the physiological responses and lipid remodeling of G. lemaneiformis. Results demonstrated that short-term exposure to either high temperature or high light stress led to a reduction in maximum (Fv/Fm), effective photochemical efficiency (Fv'/Fm') and maximum relative electron transfer rate (rETRmax), and the combination of these stresses exerted a more pronounced inhibitory effect on photosystem II efficiency. Short-term exposure to heat stress led to an increase in superoxide dismutase (SOD) activity, as well as a rise in glutathione (GSH) and ascorbate (Asc) contents under LL, while the activities of antioxidant enzymes (SOD, peroxidase, and ascorbate peroxidase) and levels of non-enzymatic antioxidants (GSH and Asc) were reduced under ML and HL. Additionally, short-term heat stress induced the accumulations of phosphatidylcholine (PC), phosphatidylethanolamine, phosphatidylserine, phosphatidylglycerol, sulfoquinovosyldiacylglycerol, and triacylglycerol (TAG) under LL, while heat-induced lipid accumulation decreased under ML and HL. Furthermore, heat stress increased the accumulation of saturated or unsaturated PC species under LL. Specifically, there was an increase in the levels of saturated or monounsaturated acyl chain–containing PC species, whereas the levels of polyunsaturated acyl chain-containing PC species declined under ML and HL. Correspondingly, a significant increase in TAG species with polyunsaturated acyl chains was observed, particularly under LL conditions, suggesting a potential lipid turnover between PC and TAG. These results showed that the lipid metabolic plasticity of G. lemaneiformis enabled it to rapidly adapt to fluctuating environmental conditions, and the light environment regulated its heat stress response.

Allelopathic Inhibition and Mechanism of Quercetin on Microcystis aeruginosa.

The utilization of allelochemicals to inhibit algal overgrowth is a promising approach for controlling harmful algal blooms (HABs). Quercetin has been found to have an allelopathic effect on algae. However, its responsive mechanism needs to be better understood. In the present study, the inhibitory effects of different quercetin concentrations on M. aeruginosa were evaluated, and the inhibition mechanisms were explored. The results demonstrated that quercetin significantly inhibited M. aeruginosa growth, and the inhibitory effect was concentration-dependent. The inhibition rate of 40 mg L-1 quercetin on algal density reached 90.79% after 96 h treatment. The concentration of chlorophyll-a (chl-a) in treatment groups with quercetin concentrations of 10, 20, and 40 mg L-1 decreased by 59.74%, 74.77%, and 80.66% at 96 h, respectively. Furthermore, quercetin affects photosynthesis and damages the cell membrane, respiratory system, and enzyme system. All photosynthetic fluorescence parameters, including the maximum photochemical quantum yield (Fv/Fm), the actual photochemical quantum yield (YII), the maximum relative electron transfer rate (rETRmax), and light use efficiency (α), exhibited a downtrend after exposure. After treatment with 20 mg L-1 quercetin, the nucleic acid and protein content in the algal solution increased, and the respiration rate of algae decreased significantly. Additionally, superoxide dismutase (SOD) activities significantly increased as a response to oxidative stress. In comparison, the activities of ribulose 1,5-biphosphate carboxylase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) decreased significantly. These results revealed that quercetin could inhibit M. aeruginosa by affecting its photosynthesis, respiration, cell membrane, and enzymic system. These results are promising for controlling M. aeruginosa effectively.

Flocculation and lysis of Microcystis aeruginosa by Paebubacillus sp. A9 and inhibition of microcystin release

Algae such as Microcystis aeruginosa, which are involved in cyanobacterial harmful algal blooms (CyanoHABs), pose a serious threat to aquatic organisms and human health, and have become a severe environmental problem. In the search for efficient, eco-friendly and safe approaches to control CyanoHABs, we evaluated the algicidal potential of Paebubacillus sp. A9 (A9) cells, supernatants and cultures with flocculation properties against M. aeruginosa. The results showed that different fractions of A9 exhibited algicidal activity in a dose- and time-dependent manner. Initially, polysaccharides with a series of carboxyl groups released by A9 caused flocculation of M. aeruginosa cells, which was followed by the lysis of algal cells by the algicidal active compounds present in the A9 culture. The algicidal process activated the antioxidant system of M. aeruginosa, as evidenced by a dramatic increase in the activities of catalase (CAT) and superoxide dismutase (SOD) enzyme. Simultaneously, photosynthetic pigments (Chl a), photosynthetic efficiency (Fv/Fm) and maximum relative photosynthetic electron transfer rate (ETRmax) were significantly decreased, indicating the impairment of the photosynthetic system of M. aeruginosa by A9 culture. Notably, inoculation with 6% A9 culture reduced the microcystin-LR (MC-LR) concentration by 90.65% compared to the control. Further analysis of fluorescent dissolved organic contaminants, disinfection by-product precursors, and nitrogen and phosphorus nutrients in the algal culture, confirmed the environmentally safety of the A9-mediated algicidal process. Therefore, Paebubacillus sp. A9 be a potential candidate for controlling M. aeruginosa-induced CyanoHABs through its ”flocculation–lysis–degradation” mechanism, coupled with nutrient regulation.

Effects of suspended particles in the Jinjiang River Estuary on the physiological and biochemical characteristics of Microcystis flos-aquae.

The effects of different concentrations (100, 150, 200, 250mg/L) and different particle sizes (0-75μm, 75-120μm, 120-150μm, 150-500μm) on the soluble protein content, superoxide dismutase (SOD) and catalase (CAT) activity, malondialdehyde (MDA) content, chlorophyll a (Chla) content, and photosynthetic parameters of Microcystis flos-aquae were studied, and the mechanism of the effect of suspended particulate matter on the physiology and biochemistry of Microcystis flos-aquae was discussed. The results showed that the soluble protein content of Microcystis flos-aquae did not change noticeably after being stressed by suspended particles of different concentrations/diameters. The SOD activity of Microcystis flos-aquae first increased and then decreased with increasing suspended particulate matter concentrations. The SOD activity of Microcystis flos-aquae reached 28.03 U/mL when the concentration of suspended particulate matter was 100mg/L. The CAT activity of Microcystis flos-aquae increased with increasing concentrations of suspended particles and reached a maximum value of 12.45 U/mg prot in the 250mg/L concentration group, showing a certain dose effect. Small particles had a more significant effect on SOD, CAT, and MDA in Microcystis flos-aquae than large particles. The larger the concentration was and the smaller the particle size was, the stronger the attenuation of light and the lower the content of Chla. Both the maximum quantum yield of PSII (Fv/Fm) and the potential photosynthetic activity of PSII (Fv/F0) of Microcystis flos-aquae increased at first and then decreased under different concentrations/sizes of suspended particles. The relative electron transfer rate gradually returned to a normal level over time. There was no significant difference in the initial slope (α) value between the treatment group and the control group, and the maximum photo synthetic rate (ETRmax) and the semilight saturation (Ik) decreased.

Response of Juvenile Saccharina japonica to the Combined Stressors of Elevated pCO2 and Excess Copper.

Coastal macroalgae may be subjected to global and local environmental stressors, such as ocean acidification and heavy-metal pollution. We investigated the growth, photosynthetic characteristics, and biochemical compositions of juvenile sporophytes of Saccharina japonica cultivated at two pCO2 levels (400 and 1000 ppmv) and four copper concentrations (natural seawater, control; 0.2 μM, low level; 0.5 μM, medium level; and 1 μM, high level) to better understand how macroalgae respond to ongoing environmental changes. The results showed that the responses of juvenile S. japonica to copper concentrations depended on the pCO2 level. Under the 400 ppmv condition, medium and high copper concentrations significantly decreased the relative growth rate (RGR) and non-photochemical quenching (NPQ) but increased the relative electron transfer rate (rETR) and chlorophyll a (Chl a), chlorophyll c (Chl c), carotenoid (Car), and soluble carbohydrate contents. At 1000 ppmv, however, none of the parameters had significant differences between the different copper concentrations. Our data suggest that excess copper may inhibit the growth of juvenile sporophytes of S. japonica, but this negative effect could be alleviated by CO2-induced ocean acidification.

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.

Thermodynamic and Kinetic Investigation on Electrogeneration of Hydroxyl Radicals for Water Purification

The water oxidation reaction (WOR) is of fundamental importance for the development of promising technologies in the field of energy conversion and environmental remediation. Although effort has been devoted to uncovering the mechanism of the oxygen evolution reaction (OER) by four-electron WOR, little attention has been paid to an in-depth understanding of one-electron WOR for •OH formation, which is the key to the electrochemical advanced oxidation process (EAOP) for environmental applications. Currently, oxygen evolution potential (OEP) is generally regarded as an important thermodynamic descriptor responsible for •OH production, but the kinetic descriptor has been overlooked; thus, the trade-off between thermodynamic and kinetic factors remains unclear. In this study, the thermodynamic feasibility and kinetic activity of electrogeneration of •OH were regulated by doping three kinds of low-electronegativity elements (Ce, Al, and In) into the prototype PbO2 nonactive anode. We investigated these electrodes in terms of •OH production and electrochemical decontamination performance in the context of sulfamethoxazole (SMX) removal. The results showed that 0.8%Ce-PbO2 anode (OEP = 3.67 V vs Ag/AgCl) achieved the highest SMX removal performance (∼100%; kobs = 0.027 min–1) and the highest •OH production with a relatively high number of •OH = 2.7 × 107. In comparison, the highest OEP (5.98 V vs Ag/AgCl) for the 1.6%Ce-PbO2 anode exhibited the lowest SMX removal (∼59%; kobs = 0.008 min–1) and 1 order of magnitude lower •OH production (relative number of •OH = 1.5 × 106). This suggested that the electrogeneration of •OH was unlikely to be always positively correlated to the OEP of the anode. Both experimental results and theoretical calculations verified the importance of suitably high OEP and relative fast electron transfer rate toward WOR to generate H2O+ (oxidation intermediate of H2O) for the ideal anode of EAOP. This study not only demonstrates the trade-off existing between thermodynamic (OEP) and kinetic (charge/electron transfer) factors responsible for electrogeneration of •OH via WOR fundamentally but also suggests a possible strategy for developing a high-efficiency anode by doping low-electronegativity elements to optimize one-electron WOR for environmental applications.

Algicidal characteristics of novel algicidal compounds, cyclic lipopeptide surfactins from Bacillus tequilensis strain D8, in eliminating Heterosigma akashiwo blooms.

Heterosigma akashiwo blooms have caused severe damage to marine ecosystems, the aquaculture industry and human health worldwide. In this study, Bacillus tequilensis D8 isolated from an H. akashiwo bloom area was found to exert high algicidal activity via extracellular metabolite production. This activity remained stable after exposure to different temperatures and light intensities. Scanning electron microscopy observation and fluorescein diacetate staining indicated that the algicidal substances rapidly destroyed algal plasma membranes and decreased esterase activity. Significant decreases in the maximum photochemical quantum yield and relative electron transfer rate were observed, which indicated photosynthetic membrane destruction. Subsequently, the algicidal compounds were separated and purified by high-performance liquid chromatography and identified as three surfactin homologues by interpreting high-resolution electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy data. Among these, surfactin-C13 and surfactin-C14 exhibited strong algicidal activity against three HAB-causing species, namely, H. akashiwo, Skeletonema costatum, and Prorocentrum donghaiense, with 24 h-LC50 values of 1.2-5.31 μg/ml. Surfactin-C15 showed strong algicidal activity against S. costatum and weak algicidal activity against H. akashiwo but little activity against P. donghaiense. The present study illuminates the algicidal characteristics and mechanisms of action of surfactins on H. akashiwo and their potential applicability in controlling harmful algal blooms.

Postharvest application of 1-methylcyclopropene delays chloroplast degradation in Gynura bicolor DC under sugar scarcity conditions

• 1-MCP fumigation effectively delayed sugar scarcity. • 1-MCP fumigation delayed RuBisCo and chlorophyll degradation. • 1-MCP fumigation blocked the expression of GbATGs and GbSAG101 . • Sugar scarcity induced ROS burst in chloroplasts. • RuBisCo was preferentially degraded over chlorophyll. During postharvest transport and storage stage , Gynura bicolor DC ( G. bicolor ) is commonly handled in the darkness. However, long-term storage in the dark exacerbates postharvest sugar scarcity. 1-methylcyclopropene (1-MCP) was showing effective in inhibiting postharvest physiological metabolism of fruits and vegetables. The aim of this research was to uncover the mechanism underlying the effects of 1-MCP on the chloroplasts of G. bicolor under postharvest sugar scarcity conditions. The status of carbon sources, the enzymes and genes involved in chloroplast degradation were investigated. Furthermore, reactive oxygen species (ROS), chloroplast function, and chloroplast structure were also investigated to examine the physiological changes that occur in chloroplasts during storage. Degradations of starch, soluble sugar, and soluble protein were effectively retarded by 1-MCP. The increase of free amino acid content and decay rate were markedly inhibited by 1-MCP. 1-MCP not only inhibited the ROS burst, structural disintegration, and function (maximum photochemical efficiency Fv/Fm, effective quantum yield of PSII photochemistry QY, and relative electron transfer rate ETR) decreased in chloroplast, but also delayed the increased activities of chlorophyll degraded-related enzymes (chlorophyllase CHL, pheophytin pheophorbide hydrolase PPH and Mg-dechelatase), and proteinases (cysteine proteinase CP, serine proteinase SP and total proteinases TP), which retarding the ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo), and chlorophyll degradation. The upregulated expressions of GbCHL, GbPPH, Gb-proteinases, GbATGs , and GbSAG101 were markedly blocked by 1-MCP. Correlation analysis showed that ROS burst was associated with sugar scarcity, the upregulated expressions of GbATGs , and GbSAG101 were associated with sugar scarcity and ROS burst, chlorophyll degradation was associated with the RuBisCo level. In conclusion, 1-MCP effectively delayed chloroplast degradation in G. bicolor by retarding sugar scarcity, inhibiting ROS burst in chloroplast, blocking the upregulated expressions of genes involved chloroplast degradation, and delaying the activities increase in proteases and chlorophyll degraded-related enzymes.

Effects of nutrients on the utilization pattern of photosynthetic inorganic carbon of the tropical &amp;lt;italic&amp;gt;Thalassia hemprichii&amp;lt;/italic&amp;gt;

<p indent="0mm">Studies on the utilization strategy of photosynthetic inorganic carbon of seagrass can reveal its ecological adaptation mechanism. <italic>Thalassia hemprichii</italic>, a widely distributed seagrass species in the Indo-Pacific and Atlantic coastal seas, needs to evolve several utilization patterns of inorganic carbon to adapt different environments and meet its growth, development and reproduction. However, the effect of nutrient on the photosynthetic inorganic carbon utilization strategy in seagrass is still unknown and further research is urgently needed. Therefore, using oxygen electrode technology, chlorophyll fluorescence technology, and non-invasive micro-test technology, this study examined the similarity and difference in the utilization patterns of photosynthetic inorganic carbon of <italic>T</italic>.<italic> hemprichii </italic>from two typical tropical seagrass beds (Tanmen, Hainan Island, and Yongxing Island, Xisha), that were affected by varying degrees of human activity. Experiments showed that the photosynthetic oxygen release rate, maximum relative electron transfer rate, and half-saturated light intensity of <italic>T</italic>.<italic> hemprichii</italic> in Yongxing Island waters were 24.95%, 24.54%, and 28.73% higher than the corresponding in Tanmen, Hainan Island. This indicated that the growth status of <italic>T</italic>.<italic> hemprichii</italic> in the waters of Yongxing Island was better with higher photosynthetic efficiency. The addition of acetazolamide (AZ) and ethoxyzolamide (EZ) significantly reduced the photosynthetic oxygen release rate of <italic>T</italic>.<italic> hemprichii</italic>, with an insignificant difference in the inhibition between AZ and EZ. This indicated that it mainly absorbed HCO₃⁻ via extracellular carbonic anhydrase catalysis. Meanwhile, hydroxymethyl (Tris) inhibited the photosynthetic oxygen release of <italic>T</italic>.<italic> hemprichii</italic> in Tanmen by up to 100% and decreased the maximum relative electron transfer rate and the H⁺ inward flow rate, implying a synergistic H⁺/HCO₃⁻ transport mode. On the other hand, the rate of photosynthetic oxygen release and the maximum electron transfer rate of <italic>T</italic>.<italic> hemprichii</italic> in Xisha did not change significantly with the addition of AZ and EZ, while Tris buffer inhibited photosynthetic oxygen release by up to 100% and significantly reduced the maximum electron transfer rate. This suggested <italic>T</italic>.<italic> hemprichii </italic>in Xisha mainly relied on the H⁺/HCO₃⁻ synergistic transport. Therefore, <italic>T</italic>.<italic> hemprichii </italic>could uptake inorganic carbon in an environment with greater anthropogenic activity, larger nutrient load and lower light availability on Hainan Island by catalyzing HCO₃⁻ into CO₂ with extracellular carbonic anhydrase and the H⁺/HCO₃⁻ synergistic transport. In contrast, <italic>T</italic>.<italic> hemprichii</italic> in an environment with less anthropogenic activity, lower nutrient loading, and greater light availability, relied chiefly on H⁺/HCO₃⁻ synergistic transport. Facing a relatively unfavorable high-nutrient and low-light growth environment, <italic>T</italic>.<italic> hemprichii</italic> could increase the photosynthetic inorganic carbon utilization strategy (such as the activity of extracellular carbonic anhydrase) to improve its utilization ability of inorganic carbon to overcome stress and growth limitation. This suggested that <italic>T</italic>.<italic> hemprichii</italic> could adjust its inorganic carbon utilization patterns according to its geographical environment. With the continuous development of technology, it is urgent to study the utilization mechanism of inorganic carbon of seagrass by applying seagrass omics technology and stable isotope tracing to deepen the understanding of the carbon sink function of seagrass.

The inhibitory effects of simulated light sources on the activity of algae cannot be ignored in photocatalytic inhibition

Harmful algal blooms (HABs) destroy the balance of the aquatic ecosystem, causing huge economic losses and even further endangers human health. In addition to traditional methods of algae removal, photocatalytic inhibition of algae is drawing more and more interests with rich application scenarios and considerable potential. Simulated visible light sources are used to excite photocatalytic materials and optimize their performance. However, most of the light irradiation intensities used in the study exceeded 50 mW/cm2. And the effects of intense light irradiation conditions on algal growth have rarely been addressed in previous studies. So we focused on the effect of different intensity of light irradiation on the growth of algae. We explored the relationship between light irradiation intensity and algal inactivation rate, and investigated the changes in ROS levels in algal cells under different light irradiation and the resulting response of the antioxidant system. We have found that several major antioxidant enzyme activities, such as SOD and CAT, were significantly higher and lipid peroxidation products (MDA) were accumulating. Intense light irradiation had the most direct effect on the photosynthetic system of algal cells, with the photosynthetic rate and relative electron transfer rate decaying to almost 0 within 30 min, indicating that algal photosynthesis was inhibited in a fairly short period of time. We further observed the physiological and morphological changes of algal cells during this process using TEM and found that the progressive dissolution of the cell membrane system and the damage of organelles associated with photosynthesis play a major role in promoting cell death. We thus conclude that light irradiation has a significant effect on the physiological activity of algal cells and is a non-negligible factor in the study of photocatalytic removal of harmful algae. It will provide theoretical guidance for the future study of photocatalysis on algae inhibition.

Effects of Ginkgo biloba extract on growth, photosynthesis, and photosynthesis-related gene expression in Microcystis flos-aquae.

The inhibitory effect of plants on algae offers a new and promising alternative method for controlling harmful algal blooms. Previous studies showed that anti-algal effects might be obvious from extracts of fallen leaves from terrestrial plants, which had great potential for cyanobacterial control in field tests. To investigate the anti-algal activities and main algicidal mechanisms of Ginkgo biloba fallen leaves extracts (GBE) on Microcystis flos-aquae, the cell density, photosynthetic fluorescence, and gene expression under different concentrations of GBE treatments were tested. GBE (3.00 g L-1) showed a strong inhibitory effect against M. flos-aquae with an IC50 (96h) of 0.79 g L-1. All the inhibition rates of maximal quantum yield (Fv/Fm), effective quantum yield (Fq'/Fm'), and maximal relative electron transfer rate (rETRmax) were more than 70% at 96 h at 3.00 g L-1 and more than 90% at 6.00 g L-1. Further results of gene expression of the core proteins of PSII (psbD), limiting enzyme in carbon assimilation (rbcL), and phycobilisome degradation protein (nblA) were downregulated after exposure. These findings emphasized that photosynthetic damage is one of the main toxic mechanisms of GBE on M. flos-aquae. When exposed to 12.00 g L-1 GBE, no significant influence on the death rate of zebrafish or photosynthetic activity of the three submerged plants was found. Therefore, appropriate use of GBE could control the expansion of M. flos-aquae colonies without potential risks to the ecological safety of aquatic environments, which means that GBE could actually be used to regulate cyanobacterial blooms in natural waters.

Antagonistic and synergistic effects of warming and microplastics on microalgae: Case study of the red tide species Prorocentrum donghaiense

Bibliometric network analysis has revealed that the widespread distribution of microplastics (MPs) has detrimental effects on marine organisms; however, the combined effects of MPs and climate change (e.g., warming) is not well understood. In this study, Prorocentrum donghaiense, a typical red tide species in the East China Sea, was exposed to different MP concentrations (0, 1, 5, and 10 mg L−1) and temperatures (16, 22, and 28 °C) for 7 days to investigate the combined effects of MPs and simulated ocean warming by measuring different physiological parameters, such as cell growth, pigment contents (chlorophyll a and carotenoid), relative electron transfer rate (rETR), reactive oxygen species (ROS), superoxide dismutase (SOD), malondialdehyde (MDA), and adenosine triphosphate (ATP). The results demonstrated that MPs significantly decreased cell growth, pigment contents, and rETRmax, but increased the MDA, ROS, and SOD levels for all MP treatments at low temperature (16 °C). However, high temperatures (22 and 28 °C) increased the pigment contents and rETRmax, but decreased the SOD and MDA levels. Positive and negative effects of high temperatures (22 or 28 °C) were observed at low (1 and 5 mg L−1) and high MP (10 mg L−1) concentrations, respectively, indicating the antagonistic and synergistic effects of combined warming and MP pollution. These results imply that the effects of MPs on microalgae will likely not be substantial in future warming scenarios if MP concentrations are controlled at a certain level. These findings expand the current knowledge of microalgae in response to increasing MP pollution in future warming scenarios.

Algicidal Effects of a High-Efficiency Algicidal Bacterium Shewanella Y1 on the Toxic Bloom-Causing Dinoflagellate Alexandrium pacificum.

Alexandriumpacificum is a typical toxic bloom-forming dinoflagellate, causing serious damage to aquatic ecosystems and human health. Many bacteria have been isolated, having algicidal effects on harmful algal species, while few algicidal bacteria have been found to be able to lyse A. pacificum. Herein, an algicidal bacterium, Shewanella Y1, with algicidal activity to the toxic dinoflagellate A. pacificum, was isolated from Jiaozhou Bay, China, and the physiological responses to oxidative stress in A. pacificum were further investigated to elucidate the mechanism involved in Shewanella Y1. Y1 exhibited a significant algicidal effect (86.64 ± 5.04% at 24 h) and algicidal activity in an indirect manner. The significant declines of the maximal photosynthetic efficiency (Fv/Fm), initial slope of the light limited region (alpha), and maximum relative photosynthetic electron transfer rate (rETRmax) indicated that the Y1 filtrate inhibited photosynthetic activities of A. pacificum. Impaired photosynthesis induced the overproduction of reactive oxygen species (ROS) and caused strong oxidative damage in A. pacificum, ultimately inducing cell death. These findings provide a better understanding of the biological basis of complex algicidal bacterium-harmful algae interactions, providing a potential source of bacterial agent to control harmful algal blooms.

Photosynthetic Characteristics of Three Cohabitated Macroalgae in the Daya Bay, and Their Responses to Temperature Rises.

Biochemical compositions and photosynthetic characteristics of three naturally cohabitated macroalgae, Ulva fasciata, Sargassum hemiphyllum and Grateloupia livida, were comparably explored in the field conditions in Daya Bay, northern South China Sea, as well as their responses to temperature rise. Chlorophyll a (Chl a) and carotenoids contents of U. fasciata were 1.00 ± 0.15 and 0.57 ± 0.08 mg g−1 in fresh weight (FW), being about one- and two-fold higher than that of S. hemiphyllum and G. livida; and the carbohydrate content was 20.3 ± 0.07 mg g−1 FW, being about three- and one-fold higher, respectively. Throughout the day, the maximal photochemical quantum yield (FV/FM) of Photosystem II (PS II) of these three macroalgae species decreased from morning to noon, then increased to dusk and kept steady at nighttime. Consistently, the rapid light curve-derived light utilization efficiency (α) and maximum relative electron transfer rate (rETRmax) were lower at noon than that at morning- or night-time. The FV/FM of U. fasciata (varying from 0.78 to 0.32) was 38% higher than that of G. livida throughout the day, and that of S. hemiphyllum was intermediate. The superoxide dismutase (SOD) and catalase (CAT) activities in U. fasciata were lower than that in S. hemiphyllum and G. livida. Moreover, the rises in temperature species-specifically mediated the damage (k) caused by stressful high light and the corresponding repair (r) to photosynthetic apparatus, making the r/k ratio increase with the rising temperature in U. fasciata, unchanged in S. hemiphyllum but decreased in G. livida. Our results indicate that U. fasciata may compete with S. hemiphyllum or G. livida and dominate the macroalgae community under aggravatedly warming future in the Daya Bay.

Effects of electrolyte concentration and anion identity on photoelectrochemical degradation of phenol: Focusing on the change at the photoanode/solution interface

The effects of electrolytes on phenol degradation by typical photoelectrochemical cell (PEC) composed of TiO2-nanotube array (TNTA) and Pt were studied in terms of interfacial parameters; quantum efficiency, h+ generation rate, relative interfacial electron transfer rate, and equivalent resistances. Three different anions, Cl−, ClO4−, and SO42−, and 10−5 to 10−1 M of electrolyte concentrations have been covered. For all concentrations of interest, pseudo-1st-order kinetic constants for phenol degradation were 4.775 × 10−4–1.175 × 10−3, 3.974 × 10−4–8.893 × 10−3, and 3.902 × 10−4–8.810 × 10−4 min−1 for SO42−, Cl−, and ClO4−, respectively. The results of h+-generation rate, and relative electron transfer rate confirms that the rate of reactions at electrode/solution interface is in the order of SO42−, ClO4−, and Cl−; 0.038–3.552%, 0.023–2.900%, and 0.021–2.814% were obtained for the quantum efficiency of SO42−, ClO4−, and Cl−, respectively. The inconsistent trend between phenol degradation kinetic and quantum efficiency in terms of anion species shows that the phenol is mainly decomposed by the oxidant produced through the interfacial reactions, not by direct reaction between TiO2 and phenol. The difference in terms of anions would be attributed to the product of anions since the radicals other than hydroxyl radical would provide the retardation pathways to prolong the lifetime of radicals.

Depth optimization of inclined thin layer photobioreactor for efficient microalgae cultivation in high turbidity digestate

Turbidity is a problem with microalgal growth in anaerobic digestate (AD) due to increased light attenuation, consequently resulting in reduced biomass yields. In this study, Chlorella sp. MUR 268 was cultivated in semi-continuous mode using turbid, high NH3 concentrated (160 ± 10 mg L−1) AD of food waste, reaching biomass yield of 4.319 ± 0.18 g L−1 in a inclined thin layer photobioreactor occupying a surface area of 11 m2. Depth optimizations were performed by incrementally increasing the depth of the culture on the surface of the inclined thin layer photobioreactor through 0.005, 008, 0.011, 0.0145 and 0.02 m. The kinetics of electron flow around photosystem II of the microalgae in culture were used as descriptives for light utilization and limitations of the optimizations, via variables including relative electron transfer rate, rETR, and maximum quantum yield, Fv/Fm, and derived parameters including functional relative electron transfer rate (FrETR) and functional relative electron transfer rate ratio (FrETR-ratio). After optimizing the depth of the reactor, areal productivity was increased by approximately 105%, from 10 g m−2 d−1 to 21.134 ± 1.83 g m−2 d−1 (when depth increased from the 0.005 m to 0.011 m at an operational culture volume of 140 L). The most important parameters affecting growth rates and productivity were the mean irradiance inside the culture and the FrETR of photons for phytochemistry. Compared to previous study using digestate of similar turbidity, 9.5 times higher areal productivity was attained.

Effects of solar radiation on photosynthetic physiology of barren stalk differentiation in maize

Barren stalks and kernel abortion are the major obstacles that hinder maize production. After many years of inbreeding, our group produced a pair of barren stalk/non-barren stalk near-isogenic lines SN98A/SN98B. Under weak light stress, the barren stalk rate is up to 98 % in SN98A but zero in SN98B. Therefore, we consider that SN98A is a weak light-sensitive inbred line whereas SN98B is insensitive. In the present study, the near-isogenic lines SN98A/SN98B were used as test materials to conduct cytological and photosynthetic physiological analyses of the physiological mechanism associated with the differences in maize barren stalk induced by weak light stress. The results showed that weak light stress increased the accumulation of reactive oxygen species (ROS), decreased the function of chloroplasts, destroyed the normal rosette structure, inhibited photosynthetic electron transport, and enhanced lipid peroxidation. The actual photochemical quantum efficiency for PSI (Y(I)) and PSII (Y(II)), relative electron transfer rate for PSI (ETR(I)) and PSII (ETR(II)), and the P700 activities decreased significantly in the leaves of SN98A and SN98B under weak light stress, where the decreases were greater in SN98A than SN98B. After 10 days of shading treatment, the O2·– production rate, H2O2 contents, the yield of regulated energy dissipation (Y(NPQ)), the donor side restriction for PSI (Y(ND)) and the quantum efficiency of cyclic electron flow photochemistry were always higher in SN98A than SN98B, and the antioxidant enzyme activities were always lower in SN98A than those in SN98B. These results show that SN98B has a stronger ability to remove ROS at its source, and maintain the integrity of the structure and function of the photosynthetic system. This self-protection mechanism is an important physiological reason for its adaptation to weak light.