International Journal of Aquaculture, 2025, Vol.15, No.4, 165-174 http://www.aquapublisher.com/index.php/ija 166 2 Types and Biological Functions of Algae Toxins 2.1 Chemical structure and mechanism of common algae toxins There are many types of typical algae toxins, and there are obvious differences in their chemical structure and toxicological mechanism. For example, the microcystis toxins (MCs) produced by cyanobacteria are cyclic peptides, catalyzed by non-ribosomal peptide synthetase (NRPS) and polyketone synthetase (PKS). They are generally circulating peptides composed of 7 amino acids, which have a strong inhibitory effect on protein phosphatases 1 and 2A, resulting in increased risk of hepatocyte damage and liver cancer (Shishido et al., 2013). Neurotoxins include Anatoxin-a and paralytic shellfish toxin (PSP, mainly represented by Saxitoxin, STX), etc. They are mostly small-molecular alkaloids that cause neurotoxicity by blocking sodium channels or affecting the release of neurotransmitters. Amnesic shellfish toxins (polycarboxylic acids with glycol structure) produced by seaweed can overactivate glutamate receptors, leading to neuroexcitation toxicity (Maguire et al., 2018); Okada toxins and other diarrheal toxins (such as OA) are polyethers or fatty acid derivatives that cause diarrhea and cell damage by inhibiting protein phosphatase. 2.2 The ecological function of toxins in algae: defense and competition In addition to the occasional metabolites produced by algae, toxins often have important ecological significance. Existing research suggests that algatoxins may be used as a chemical defense substance for algae to inhibit competitive algae or to repel herbivorous organisms, thereby improving the competitiveness of toxin-producing populations. For example, some cyanobacteria secrete microcystis toxins or verbena toxins under nutritional deficiency or other stress conditions to affect the growth of coexisting populations; the production of anaphylactic toxins and paralytic shell toxins is also believed to reduce biological predation or competitors (Figure 1) (Teneva et al., 2023). In addition, toxins may also be related to stress tolerance in algae: studies have found that microcystis toxin plays a role in antioxidant stress and can help algae resist highlights or heavy metal stress; similarly, some dinoflagellate toxins are reported to be associated with population survival strategies under low temperature or low nutritional conditions. Algatoxins may play the role of signaling molecules, allelopathic substances or stress defense agents in the algae population ecology, so that toxin-producing algae have an advantage in resource competition and environmental stress. In addition, the accumulation of toxins through the food chain can weaken the growth and reproduction of algae predators or higher consumers, and also have an indirect effect on maintaining the stability of toxin-producing algae populations (Li, 2014). 2.3 Accumulation and transmission of toxins in the food chain The transmission characteristics of algatoxins in the food chain are an important manifestation of their ecological harm. Toxins produced by algae can be enriched biologically through feeding of benthic organisms such as zooplankton and shellfish, and are further transmitted to fish, birds and even humans along the food chain. Studies have shown that microcystis and other algatoxins are often detected in fish and shellfish. After being ingested, they can "amplify" the toxicity in the food chain. For example, after eating toxic shellfish, top predators or humans can experience symptoms of food poisoning (Kershaw et al., 2021). At the same time, atmospheric aerosols are also a way to spread toxins. Tide explosions and waves can spray toxins into the air, and it will also cause poisoning after being inhaled by the respiratory tract. Therefore, algatoxins not only threaten native plankton and benthic invertebrates, but also affect higher trophic levels through the feeding chain, becoming the focus of attention of the entire ecosystem and even public health. 3 Genes and Gene Clusters Related to Algae Toxin Synthesis 3.1 Discovery and identification methods of genes related to toxin synthesis With the development of molecular biology technology, toxin biosynthesis genes of toxin-producing algae are constantly being discovered. Traditional methods include designing primers using conserved sequences of known toxin synthase genes and detecting gene presence in unknown strains or environmental samples by PCR. For example, amplification of the microcystis toxin synthetase mcyE gene, the anaC gene of anaC gene and the paralytic castis toxin synthetase sxtA gene by conventional PCR can effectively detect and distinguish different types of toxin cyanobacteria (Ribeiro et al., 2020; Moraes et al., 2023). In recent years, high-throughput
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