International Journal of Aquaculture, 2025, Vol.15, No.4, 165-174 http://www.aquapublisher.com/index.php/ija 170 Figure 2 Light microscopy (LM) and confocal microscopy (CLSM) images of P. lima cells in P-limited conditions and a control. Representative confocal microscope images of P. lima cells showing oil bodies with green fluorescence are displayed (Adopted from Wan et al., 2023) 5.3 Microbial community and symbiosis/competitive relationship The interaction between algae and symbiotic or competitive microorganisms is also an important factor in affecting toxin production. Certain concomitant bacteria promote algae growth and toxin synthesis, such as indirectly affecting toxin levels by providing vitamins or breaking down nutrients. Conversely, inhibitory or competitive microbial communities may reduce the growth rate of toxin production by producing antagonistic substances or competing nutrients. In natural water bodies, pathogenic microorganisms or special bacteria can also degrade toxins and alleviate toxin accumulation (Zeng et al., 2020). Clusters of bacterial genes that have the ability to degrade microcystis toxins (such as mlrA-D) have been found to break the toxin into a nontoxic component. Therefore, water body microbial community structure, bacterial and algae symbiosis and microbial competition may all significantly regulate the production and decomposition process of algatoxins. 5.4 Case analysis: research on the relationship between nutrient salt and toxin level in freshwater lakes In many freshwater nutritious lakes (such as Taihu Lake in China, Dianchi Lake, etc.), research has found that nutrient load is highly correlated with microcystis toxin content. Specifically, the input of excess nitrogen and phosphorus nutrients promotes the outbreak of microcysticus, but long-term high nitrogen often makes phosphorus in water a limiting factor, and the concentration of cytotoxin tends to increase when phosphorus is relatively scarce. Monitoring data show that in these lakes, when the temperature rises in spring and summer accompanied by the peak of nitrogen and phosphorus input, the microcystis community proliferates rapidly and produces a large number of MCs; after the nutrients are consumed in autumn, the MCs released by the rupture of the algae maintain a high level of water toxicity (Schampera and Hellweger, 2024). Therefore, lake nutrition regulation strategies (such as reducing exogenous nitrogen and phosphorus load) are crucial to control algatoxin levels, and fine adjustments to nutrient structure will also affect the final toxin output (Lawson and Young, 2025). These research cases highlight the key role of nutrition management in ecological restoration and toxin prevention.
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