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    Suppression of red-tide and water-bloom by algaecidal bacteria: 1) the identification of algaecidal substances

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    Suppression of red tide and blue-green algae by algaecidal bacteria × SDGs

    •  SDGs6  

       Phytoplankton is an important organism that supports the aquatic ecosystem as a primary producer. However, depending on eutrophication and climatic conditions, they can proliferate abnormally, causing damage to fisheries and the environment. There are also many phytoplankton that produce toxins, and blue-green algae in lakes and marshes have become a problem for securing water for domestic use. We are developing environmentally friendly measures against blue-green algae and red tides with the help of algaecides that kill harmful algae. Through this kind of research, we hope to contribute to SDG (6 CLEAN WATER AND SANITATION).

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    Abstract


    • Red tide and blue-green algae, which are caused by excessive growth of phytoplankton, have a great impact on fisheries, coastal environment and aquatic life. Various physical and chemical methods, such as clay spraying, deep aeration, and filtration, have been used as countermeasures against red tide and blue-green algae. However, there is a need to develop better methods in terms of effectiveness, cost, and environmental impact.

      It has been reported that algicidal bacteria have the ability to kill microalgae that cause red tides and blue-green algae, suggesting that they may be involved in promoting the disappearance of red tides and blue-green algae and inhibiting their growth. In addition, algaecides are distributed in high density on the surface of seaweed and water plants, and it is possible that the decrease in water plants promotes the occurrence of red tide and blue-green algae. Therefore, environmentally harmonized measures are expected to suppress the occurrence of red tide and blue-green algae by artificially creating seaweed beds.

      Fig. Blue-green algae in Onuma, southern Hokkaido

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    Purpose of the research

    • The use of algaecides to control red tide and blue-green algae is expected to be an environmentally friendly method. In fact, many algaecidal bacteria have been reported, and algaecidal substances have been found in their culture media in some cases. However, there are still issues that need to be solved for their effective use.For example, the algaecidal mechanisms of many algaecides are still unknown, it is unclear whether the algaecides found are involved in algaecidal phenomena in the environment, and there is a possibility that unisolated (difficult-to-culture) algaecides exist.

      Therefore, in addition to conventional research on the identification of algaecides using natural product chemistry, we are conducting multifaceted analyses. For example, we are identifying biosynthetic genes through genome analysis of algaecides, examining the distribution of algaecides and causative algae in the environment through aquatic metagenome analysis, and detecting algaecides through metabolome analysis of environmental water. The goal of this project is to clarify algaecidal phenomena in the actual environment at the level of material science.


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    What bacteria kill algae?


    • Figs.
      (left) Environmental water and water plants
      (middle) Cultured bacteria
      (right) Algaecide test (liquid medium) and algaecide test (agar medium)

      Bacteria are isolated from environmental samples, and the bacteria that can be cultured are tested one by one for algaecide. Sometimes we use liquid medium, and sometimes we use agar medium. By using a variety of environmental samples and separation methods, we can obtain a variety of algaecides.


    • Figs.
      (left) Algaecides and genomic DNA
      (middle left) PCR amplified 16SrRNA region
      (middle right) Sequencing by sequencer
       (right) Find similar sequences in a database search

      The gene region (16S rRNA sequence) necessary for species identification is amplified from the bacteria that showed algaecidal activity by PCR. The amplified DNA is then sequenced by a sequencer. The obtained sequences are then searched in a database to find the most similar ones.


      So far, many algaecidal bacteria such as       Alteromonas spp. have been found in the ocean and Pseudomonas spp. in lakes. In both cases, many bacterial species seem to be relatively easy to culture. These cause algaecidal phenomena in the laboratory, but at this time, we still do not know if they really do so in the natural environment.

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    What kind of algaecide do they use?


    • Figs.
      (left)       Culture solution of algaecide bacteria
      (middle left) Purification of active substances by chromatography
      (middle right) Structure determination of active substances by spectral analysis
      (right) Identified algaecides

      The identification of algaecides is done by the same method as in conventional natural product chemistry. That is, we cultivate algaecides, extract the products, and purify them by various chromatographic methods using algaecidal activity as an indicator. Once purified, the structure is determined by various spectral analyses such as mass spectrometry and nuclear magnetic resonance.

      However, this is a culture medium, a specific environment that is completely different from the natural environment in that it is in a high nutrient state with no external enemies, and there are no microalgae to be killed. At this point, we still do not know if substances produced under such circumstances are involved in the actual algaecide phenomenon. In addition, spraying this substance like a pesticide is undesirable in terms of cost and environmental impact.

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    What kind of genes do they use?


    • Figs.
      (left) Algaecides and genomic DNA
      (middle) Full-length genome
      (right) Biosynthetic gene analysis using bioinformatics tools

      The first step in revealing the biosynthetic genes is to determine the genome of the algaecide bacteria. This requires next-generation sequencing, a high-specification instrument for DNA sequencing, but with current technology, determining bacterial genomes is not difficult (although it is expensive).

      Once the full-length genome is determined, we can use various bioinformatics tools to find gene clusters for biosynthesis of compounds. The figure above is the result of using the antiSMASH tool, which shows us the gene cluster composition and the structure of the expected product.

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    What are the impacts on other organisms?


    • Figs.
      (left) Microalgae that do not cause red tide or water blooms
      (middle left) Large algae and water plants
      (middle right) Small crustacean
      (right) Fish

    • Even if we can kill the algae that cause red tide and blue-green algae, it is not good if it has a huge impact on other aquatic organisms. We will also consider the effects of the identified algaecides on other organisms. Compared to Fish and other organisms that can swim to escape, we need to carefully examine the effects on plants and other photosynthetic organisms that cannot escape.

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    To be continued

    • By finding algae-killing bacteria and cultivating them in the laboratory, we were able to identify algaecidal substances and biosynthetic genes. Up to this point, we had made relatively smooth progress because we could use many research methods that had already been accumulated.

      However, are these substances really involved in algaecidal phenomena in the actual environment? Or are other non-culturable bacteria or substances that are not produced in the laboratory playing a major role? In order to make practical use of algaecidal bacteria to combat red tide and blue-green algae, we need to investigate the actual environment. From here on, we will be exploring the world by combining field research with compound and genetic research, which no one else in the world has yet achieved. Will this research be able to achieve its goal?

    • Does what happens in the lab really happen in the Onuma?

      Let's investigate the compounds and genes in Onuma using the information on bacteria and algaecides we've found so far!


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    Others

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    【 Related Courses 】

    Research Introduction Marine bioresources Chemistry  Red tides SDGs6