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

Diurnal-Rhythmic Relationships between Physiological Parameters and Photosynthesis- and Antioxidant-Enzyme Genes Expression in the Raphidophyte Chattonella marina Complex

Diurnal rhythms in physiological functions contribute to homeostasis in many organisms. Although relationships between molecular biology and diurnal rhythms have been well studied in model organisms like higher plants, those in harmful algal bloom species are poorly understood. Here we measured several physiological parameters and the expression patterns of photosynthesis-related and antioxidant-enzyme genes in the Chattonella marina complex to understand the biological meaning of diurnal rhythm. Under a light-dark cycle, Fv/Fm and expression of psbA, psbD, and 2-Cys prx showed significant increases in the light and decreases during the dark. These rhythms remained even under continuous dark conditions. DCMU suppressed the induction of psbA, psbD, and 2-Cys prx expression under both light regimes. Oxidative stress levels and H2O2 scavenging activities were relatively stable, and there was no significant correlation between H2O2 scavenging activities and antioxidant-enzyme gene expression. These results indicate that the Chattonella marina complex has developed mechanisms for efficient photosynthetic energy production in the light. Our results showed that this species has a diurnal rhythm and a biological clock. These phenomena are thought to contribute to the efficiency of physiological activities centered on photosynthesis and cell growth related to the diurnal vertical movement of this species.

Loss of 2-Cys-Prx affects cellular ultrastructure, disturbs redox poise and impairs photosynthesis in cyanobacteria

In a striking similarity to plant chloroplasts, the cyanobacterium Anabaena displays very low catalase activity, but expresses several peroxiredoxins (Prxs), including the typical 2-Cys-Prx (annotated as Alr4641), that detoxify H₂ O₂ . Due to the presence of multiple Prxs, the precise contribution of Alr4641 to the oxidative stress response of Anabaena is not well-defined. To unambiguously assess its in vivo function, the Alr4641 protein was knocked down using the CRISPRi approach in Anabaena PCC 7120. The knockdown strain (An-KD4641), which showed over 85% decrease in the content of Alr4641, was viable, but grew slower than the control strain (An-dCas9). An-KD4641 showed elevated levels of reactive oxygen species and the expression of several redox-responsive genes was analogous to that of An-dCas9 subjected to oxidative stress. The knockdown strain displayed reduced filament size, altered thylakoid ultrastructure, a marked drop in the ratio of phycocyanin to chlorophyll a and decreased photosynthetic parameters compared to An-dCas9. In comparison to the control strain, exposure to H₂ O₂ had a more severe effect on the photosynthetic parameters or survival of An-KD4641. Thus, in the absence of adequate catalase activity, 2-Cys-Prx appears to be the principal Prx responsible for maintaining redox homoeostasis in diverse photosynthetic systems ranging from chloroplasts to cyanobacteria.

Generation of Reactive Oxygen Species (ROS) by Harmful Algal Bloom (HAB)-Forming Phytoplankton and Their Potential Impact on Surrounding Living Organisms

Most marine phytoplankton with relatively high ROS generation rates are categorized as harmful algal bloom (HAB)-forming species, among which Chattonella genera is the highest ROS-producing phytoplankton. In this review, we examined marine microalgae with ROS-producing activities, with focus on Chattonella genera. Several studies suggest that Chattonella produces superoxide via the activities of an enzyme similar to NADPH oxidase located on glycocalyx, a cell surface structure, while hydrogen peroxide is generated inside the cell by different pathways. Additionally, hydroxyl radical has been detected in Chattonella cell suspension. By the physical stimulation, such as passing through between the gill lamellas of fish, the glycocalyx is easily discharged from the flagellate cells and attached on the gill surface, where ROS are continuously produced, which might cause gill tissue damage and fish death. Comparative studies using several strains of Chattonella showed that ROS production rate and ichthyotoxicity of Chattonella is well correlated. Furthermore, significant levels of ROS have been reported in other raphidophytes and dinoflagellates, such as Cochlodinium polykrikoides and Karenia mikimotoi. Chattonella is the most extensively studied phytoplankton in terms of ROS production and its biological functions. Therefore, this review examined the potential ecophysiological roles of extracellular ROS production by marine microalgae in aquatic environment.

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.

SUPPLEMENTARY INFORMATION

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

Superoxide Production by the Red Tide-Producing Chattonella marina Complex (Raphidophyceae) Correlates with Toxicity to Aquacultured Fishes

The marine raphidophyte Chattonella marina complex forms red tides, causing heavy mortalities of aquacultured fishes in temperate coastal waters worldwide. The mechanism for Chattonella fish mortality remains unresolved. Although several toxic chemicals have been proposed as responsible for fish mortality, the cause is still unclear. In this study, we performed toxicity bioassays with red sea bream and yellowtail. We also measured biological parameters potentially related to ichthyotoxicity, such as cell size, superoxide (O₂^•−) production, and compositions of fatty acids and sugars, in up to eight Chattonella strains to investigate possible correlations with toxicity. There were significant differences in moribundity rates of fish and in all biological parameters among strains. One strain displayed no ichthyotoxicity even at high cell densities. Strains were categorized into three groups based on cell length, but this classification did not significantly correlate with ichthyotoxicity. O₂^•− production differed by a factor of more than 13 between strains at the late exponential growth phase. O₂^•− production was significantly correlated with ichthyotoxicity. Differences in fatty acid and sugar contents were not related to ichthyotoxicity. Our study supports the hypothesis that superoxide can directly or indirectly play an important role in the Chattonella-related mortality of aquacultured fishes.