Water eutrophication has emerged as a pressing concern for massive algal blooms, and these harmful blooms can potentially generate harmful toxins, which can detrimentally impact the aquatic environment and human health. Consequently, it is imperative to identify a safe and efficient approach to combat algal blooms to safeguard the ecological safety of water. This study aimed to investigate the procedure for extracting total flavonoids from Z. bungeanum residue and assess its antioxidant properties. The most favorable parameters for extracting total flavonoids from Z. bungeanum residue were a liquid–solid ratio (LSR) of 20 mL/g, a solvent concentration of 60%, an extraction period of 55 min, and an ultrasonic temperature of 80 °C. Meanwhile, the photosynthetic inhibitory mechanism of Z. bungeanum residue extracts against M. aeruginosa was assessed with a particular focus on the concentration-dependent toxicity effect. Z. bungeanum residue extracts damaged the oxygen-evolving complex structure, influenced energy capture and distribution, and inhibited the electron transport of PSII in M. aeruginosa. Furthermore, the enhanced capacity for ROS detoxification enables treated cells to sustain their photosynthetic activity. The findings of this study hold considerable relevance for the ecological management community and offer potential avenues for the practical utilization of resources in controlling algal blooms.

With rapid growth and high lipid contents, microalgae have become promising environmentally friendly candidates for renewable biodiesel and health supplements in our era of global warming and energy depletion. Various pathways have been explored to enhance algal lipid production, especially gene editing. Previously, we found that the functional loss of PhoD-type alkaline phosphatase (AP), a phosphorus-stress indicator in phytoplankton, could lead to increased lipid contents in the model diatom Phaeodactylum tricornutum, but how the AP mutation may change lipid composition remains unexplored. This study addresses the gap in the research and investigates the effects of PhoD-type AP mutation on the lipid composition and metabolic regulation in P. tricornutum using transcriptomic and lipidomic analyses. We observed significantly modified lipid composition and elevated production of fatty acids, lysophosphatidylcholine, lysophosphatidylethanolamine, ceramide, phosphatidylinositol bisphosphate, and monogalactosylmonoacylglycerol after PhoD_45757 mutation. Meanwhile, genes involved in fatty acid biosynthesis were upregulated in mutant cells. Moreover, the mutant exhibited increased contents of ω-3 long-chain polyunsaturated fatty acid (LC-PUFA)-bound phospholipids, indicating that PhoD_45757 mutation could improve the potential bioavailability of PUFAs. Our findings indicate that AP mutation could influence cellular lipid synthesis and probably redirect carbon toward lipid production and further demonstrate that AP mutation is a promising approach for the development of high-value microalgal strains for biomedical and other applications.

Zanthoxylum bungeanum residue has attracted increasing attention owing to its antibacterial effect, which presents potential as novel antimicrobial agents for the management of algal blooms. In this study, the ability of Z. bungeanum residue extract to control algal blooms has been firstly verified. Then, the response surface methodology was employed to optimize flavonoids yield, the primary antimicrobial component in extract, and the underlying photosynthetic inhibition mechanisms of extract on Tetrodesmus obliquus was investigated. Results showed that the highest yield of total flavonoids was increased to 4.08% when the extraction conditions were a liquid-to-solid ratio of 10:1, ethanol concentration of 60%, extraction temperature of 80°C, and extraction time of 30 min. Meanwhile, treatment with Z. bungeanum residue extract at doses of 40.0 mg/L significantly decreased the Fv/Fm and PIabs values of T. obliquus by 24.36 and 88.87% at 50 h, respectively. The added extract induced damage at multiple levels of physiological and biochemical processes in algal cells, including reduced electron transport capability, disrupted energy transfer in photosystem II, disruption of OEC structure, and altered energy distribution in PSII reaction center. To our knowledge, this study was the first verification of Z. bungeanum residue’s algicidal potential, and these findings in our study contribute to a deeper understanding of the allelopathic mechanisms of Z. bungeanum residue extract and offer valuable insights for the management of algal blooms.