Growth-Phase Dependent Variation in Photosynthetic Activity and Cellular Protein Expression Profile in the Harmful Raphidophyte Chattonella antiqua

Rapid detection of Chattonella marina by PCR combined with dot lateral flow strip

In this study a novel technique referred to as PCR combined with dot lateral flow strip (PCDS) is proposed and its application to the detection of harmful microalgae was explored. For this purpose, using Chattonella marina as a test algal species, PCR targeting the D1-D2 region of large subunit ribosomal gene of this alga was performed with the tagged specific primers. The amplicons were then analyzed with the manually prepared dot lateral flow strip, and the strip could produce a test dot and a control dot that are naked-eye detectable, indicating the successful establishment of PCDS. The established PCDS assay does not require expensive instruments for the detection, and the results can be observed visually after adding 7.5 μL of PCR amplicons in combination with 92.5 μL of chromatography buffer to the sample pad of the strip for about 10 min. The PCR conditions were optimized to enhance the effectiveness of detection. The cross-reactivity test with 23 microalgae species, including Chattonella marina, showed good specificity of the PCDS. The detection limit of PCDS was 1.25 × 10^-2 ng µL^-1 for genomic DNA and 10¹ cells mL^-1 for crude cell extracts, which can meet the detection needs. In summary, the PCDS proposed in this study has low cost, clear, and intuitive detection results and good specificity and sensitivity, providing a novel detection method for C. marina.

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The online version contains supplementary material available at 10.1007/s10811-021-02667-x.

Recent Progress in the Study of Peroxiredoxin in the Harmful Algal Bloom Species Chattonella marina

Peroxiredoxin (Prx) is a relatively recently discovered antioxidant enzyme family that scavenges peroxides and is known to be present in organisms from biological taxa ranging from bacteria to multicellular eukaryotes, including photosynthetic organisms. Although there have been many studies of the Prx family in higher plants, green algae, and cyanobacteria, few studies have concerned raphidophytes and dinoflagellates, which are among the eukaryotic algae that cause harmful algal blooms (HABs). In our proteomic study using 2-D electrophoresis, we found a highly expressed 2-Cys peroxiredoxin (2-CysPrx) in the raphidophyte Chattonella marina var. antiqua, a species that induces mass mortality of aquacultured fish. The abundance of the C. marina 2-CysPrx enzyme was highest in the exponential growth phase, during which photosynthetic activity was high, and it then decreased by about a factor of two during the late stationary growth phase. This pattern suggested that 2-CysPrx is a key enzyme involved in the maintenance of high photosynthesis activity. In addition, the fact that the depression of photosynthesis by excessively high irradiance was more severe in the 2-CysPrx low-expression strain (wild type) than in the normal-expression strain (wild type) of C. marina suggested that 2-CysPrx played a critical role in protecting the cell from oxidative stress caused by exposure to excessively high irradiance. In the field of HAB research, estimates of growth potential have been desired to predict the population dynamics of HABs for mitigating damage to fisheries. Therefore, omics approaches have recently begun to be applied to elucidate the physiology of the growth of HAB species. In this review, we describe the progress we have made using a molecular physiological approach to identify the roles of 2-CysPrx and other antioxidant enzymes in mitigating environmental stress associated with strong light and high temperatures and resultant oxidative stress. We also describe results of a survey of expressed Prx genes and their growth-phase-dependent behavior in C. marina using RNA-seq analysis. Finally, we speculate about the function of these genes and the ecological significance of 2-CysPrx, such as its involvement in circadian rhythms and the toxicity of C. marina to fish.

Nutrient deficiency stimulates the production of superoxide in the noxious red-tide-forming raphidophyte Chattonella antiqua

The raphidophyte Chattonella antiqua is a single-celled alga that forms 'red tides' in coastal areas. C. antiqua produces superoxide anions (O₂^-), the excessive production of which has been associated with fish mortality. It is suggested that putative NADPH oxidase in the outer membrane oxidizes intracellular NADPH to produce O₂^- and secrete it externally. Earlier studies revealed that photosynthetic electron transport, a major producer of NADPH in photosynthetic organisms, is involved in the production of O₂^- in C. antiqua but the details of the O₂^- production mechanism have yet to be elucidated. Since nutrient deficiency adversely affects the formation of blooms of C. antiqua, in this study, we examined the effects of nutrient deficiency on O₂^- production in C. antiqua. When cells were grown under nitrogen (N)- or phosphorus (P)-deficient conditions, the production of O₂^- was stimulated. In particular, the extracellular levels of O₂^- under N- or P-deficient conditions were high during the dark period when photosynthetic activities in terms of actual quantum efficiency and photochemical quenching were low. The extracellular levels of O₂^- under the nutrient-deficient conditions were unaffected by the presence of 3-(3,4-dichlorophenyl)-1,1‑dimethylurea (DCMU), an inhibitor of photosynthetic electron transport, but decreased when the nutrients were present. Furthermore, the intracellular ratio of NADPH to NADP⁺ under N- or P-deficient conditions was higher than that under nutrient-replete conditions. These observations suggest that another metabolic pathway, independent of photosynthesis, provides NADPH for the production of O₂^- under nutrient deficiency.

Time-series responses in photosynthetic activity, 2-cysteine peroxiredoxin gene expression, and proteomics of Chattonella marina var. antiqua under different oxidative stress

Chattonella spp. are known to produce large amounts of reactive oxygen species (ROS); however, little is known about the mechanisms involved in mitigating the intracellular accumulation of ROS. In this study, a time-series of biological responses in C. marina var. antiqua under different oxidative stress conditions, induced by adding H₂O₂ at the initial concentrations of 100 and 500 µM, was investigated. Although the added exogenous H₂O₂ was rapidly consumed at 3 h post-exposure (hpe), intracellular ROS levels were enhanced in the 500 µM H₂O₂ group but decreased in the 100 µM H₂O₂ group. Accompanied by increased intracellular ROS levels, the photosynthetic activity of C. marina var. antiqua was considerably inhibited in the 500 µM H₂O₂ group, but not in the 100 µM H₂O₂ group. The F_v/F_m ratio and PI_ABS were negatively correlated with the intracellular ROS level, while the ABS/RC, TR₀/RC, and DI₀/RC were positively correlated with the intracellular ROS level. Expression of the gene encoding 2-cysteine peroxiredoxin (2-Cys Prx) was up-regulated in 100 µM H₂O₂ group at 6 hpe, but was down-regulated in 100 µM H₂O₂ group at 3 and 6 hpe. A negative relationship between the 2-Cys Prx transcript levels and intracellular ROS levels was detected. Results of the 2-DE proteomic analysis confirmed that the 500 µM H₂O₂ treatment down-regulated the expression of 2-Cys Prx and induced more damage to photosynthetic abilities of C. marina var. antiqua.

Extracellular secretion of superoxide is regulated by photosynthetic electron transport in the noxious red-tide-forming raphidophyte Chattonella antiqua

The raphidophyte Chattonella antiqua is a noxious red-tide-forming alga that harms fish culture and the aquatic environment. Chattonella antiqua produces and secretes superoxide anions (O₂^-), and excessive secretion of O₂^- into the water has been associated with fish mortality. It is known that strong light stimulates the production of O₂^- in Chattonella spp. but the mechanism of the light-induced production of O₂^- remains to be clarified. In the present study, we examined the effects of light on extracellular levels of O₂^- and photosynthesis in C. antiqua. Extracellular levels of O₂^- rose during growth under high-intensity light, and the level of O₂^- was correlated with the photosynthetic parameter qP, which reflects the rate of transport of electrons downstream of photosystem II. The production of O₂^- was inhibited in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of photosynthetic electron transport, suggesting that reducing power derived from electron transport might be required for the production of O₂^-. By contrast, the production of O₂^- was enhanced in the presence of glycolaldehyde, an inhibitor of the Calvin-Benson cycle, suggesting that the accumulation of NADPH might stimulate the production of O₂^-. Thus, it is likely that the production of O₂^- is regulated by photosynthesis in C. antiqua.

Thiobencarb herbicide reduces growth, photosynthetic activity, and amount of Rieske iron-sulfur protein in the diatom Thalassiosira pseudonana

We investigated the effects of the herbicide thiobencarb on the growth, photosynthetic activity, and expression profile of photosynthesis-related proteins in the marine diatom Thalassiosira pseudonana. Growth rate was suppressed by 50% at a thiobencarb concentration of 1.26 mg/L. Growth and photosystem II activity (Fv /Fm ratio) were drastically decreased at 5 mg/L, at which the expression levels of 13 proteins increased significantly and those of 11 proteins decreased significantly. Among these proteins, the level of the Rieske iron-sulfur protein was decreased to less than half of the control level. This protein is an essential component of the cytochrome b6 f complex in the photosynthetic electron transport chain. Although the mechanism by which thiobencarb decreased the Rieske iron-sulfur protein level is not clear, these results suggest that growth was inhibited by interruption of the photosynthetic electron transport chain by thiobencarb.