Zanthoxylum bungeanum leaves were regarded as a waste byproduct for a long period of time, yet their functional components presented potential as novel antimicrobial agents. However, their effectiveness in controlling algal blooms remains unexplored. In this study, the inhibition effect of Z. bungeanum leaf extracts on algal blooms was firstly demonstrated, and the flavonoid profiles of the leaf extract were identified using non-targeted metabolomics analysis. Then, response surface methodology was performed for extraction to further evaluate the feasibility of industrial application. Specifically, the effects of extracts on the cell density, photosynthetic efficiency, and antioxidant activity of Tetrodesmus obliquus was investigated. The results showed that the extraction yield of flavonoids from Z. bungeanum leaves reached 6.85% under the optimized conditions of an ultrasonic power of 600 W, an LSR of 20:1 mL/g, an ethanol concentration of 77.5%, an ultrasonic duration of 18 min, and an ultrasonic temperature of 80 °C, which significantly decreased the Fv/Fm and PIabs values by 54.60% and 98.22%, respectively, after exposure of T. obliquus to 40.0 mg/L Z. bungeanum leaf extract for 66 h. Meanwhile, treatment with Z. bungeanum leaf extract at a dose of 40.0 mg/L generated T-AOC values that were 4.0 times higher than the control without the addition of Z. bungeanum leaf extracts. These results suggest that Z. bungeanum leaf extracts could be used in the development of potentially effective biological algicides. Our study provides data to support the development of algicides and realizes the resource application of Z. bungeanum leaf waste, achieving a synergistic outcome of both economic and ecological benefits.

Dolichospermum sp. FACHB-82, a representative harmful bloom-forming cyanobacterium, has garnered widespread attention in freshwater ecosystems due to its high environmental adaptability and potential for rapid proliferation. Phenyllactic acid (PLA) is a structurally defined aromatic organic acid with known antimicrobial activity, but its inhibitory effects on FACHB-82 and their photosynthetic apparatus remain poorly understood. In this study, we investigated the concentration-dependent effects of PLA on biomass accumulation, photosynthetic pigment production and photosynthetic activity in FACHB-82. The findings revealed that PLA induced a concentration-dependent biphasic response on biomass accumulation and photosynthetic pigment synthesis of FACHB-82. Chlorophyll a fluorescence analyses revealed that high-concentration PLA exposure disrupted functions of PSII at multiple levels, including reduced PSII performance, enhanced Q_A⁻ accumulation, accelerated reaction center closure, decreased energetic connectivity, impaired donor side function, and restricted downstream electron transport. Although NPQ was significantly upregulated under high PLA stress, dark-recovery analysis demonstrated that the increased non-photochemical energy dissipation was accompanied by incomplete recovery of PSII photochemical efficiency. Our finding, for the first time, provides physiological insight into the anticyanobacterial activity of PLA for the control of FACHB-82 growth, thus offering a theoretical basis for the control of cyanobacterial blooms.

SPX domain-containing proteins (SPXc) are crucial for regulating phosphorus (P) homeostasis in plants. Recently, the SPX gene was identified in the diatom model Phaeodactylum tricornutum and shown to serve as a negative regulator of P acquisition. Whether SPXc occurs in dinoflagellates is unclear. Here, we report the presence and potential functions of genes encoding SPXc in dinoflagellates (dino-SPXc). Four classes of SPXc were identified in dinoflagellates, including the three known classes—the stand-alone SPX, SPX-EXS, and SPX-VTC—and SPX-other, with SPX and SPX-EXS being dominant. Using the TARA Oceans database, we investigated the taxonomic and geographic distributions of dino-SPXc and found variations in dino-SPXc expression among size classes of dinoflagellates. The harmful algal bloom-causative species Prorocentrum shikokuense possesses all four classes of SPXc proteins, showing a fluctuating expression pattern under different nutrient conditions and during different phases of the cell cycle and algal bloom. In addition, the SPXc genes in Symbiodiniaceae respond not only to P stress but also to thermal variations. These results are consistent with a role of dino-SPXc in maintaining P homeostasis in dinoflagellates and suggest the importance of SPX-related genes in enabling dinoflagellates to sustain population growth in nutrient-variable oceans, warranting further research.