Development of a Potentially New Algaecide for Controlling Harmful Cyanobacteria Blooms Which is Ecologically Safe and Selective

Unleashing the power of acetylacetone: Effective control of harmful cyanobacterial blooms with ecological safety

Harmful algal blooms resulting from eutrophication pose a severe threat to human health. Acetylacetone (AA) has emerged as a potential chemical for combatting cyanobacterial blooms, but its real-world application remains limited. In this study, we conducted a 42-day evaluation of AA's effectiveness in controlling blooms in river water, with a focus on the interplay between ecological community structure, organism functional traits, and water quality. At a concentration of 0.2 mM, AA effectively suppressed the growth of Cyanobacteria (88 %), Bacteroidia (49 %), and Alphaproteobacteria (52 %), while promoting the abundance of Gammaproteobacteria (5.0 times) and Actinobacteria (7.2 times) that are associated with the degradation of organic matter. Notably, after dosing of AA, the OD680 (0.07 ± 0.02) and turbidity (8.6 ± 2.1) remained at a satisfactory level. AA induced significant disruptions in two photosynthesis and two biosynthesis pathways (P < 0.05), while simultaneously enriching eight pathways of xenobiotics biodegradation and metabolism. This enrichment facilitated the reduction of organic pollutants and supported improved water quality. Importantly, AA treatment decreased the abundance of two macrolide-related antibiotic resistance genes (ARGs), ereA and vatE, while slightly increased the abundance of two aminoglycoside-related ARGs, aacA and strB. Overall, our findings establish AA as an efficient and durable algicide with favorable ecological safety. Moreover, this work contributes to the development of effective strategies for maintaining and restoring the health and resilience of aquatic ecosystems impacted by harmful algal blooms.

Plastoquinone synthesis inhibition by tetrabromo biphenyldiol as a widespread algicidal mechanism of marine bacteria

Algae and bacteria have complex and intimate interactions in the ocean. Besides mutualism, bacteria have evolved a variety of molecular-based anti-algal strategies. However, limited by the unknown mechanism of synthesis and action of these molecules, these strategies and their global prevalence remain unknown. Here we identify a novel strategy through which a marine representative of the Gammaproteobacteria produced 3,3',5,5'-tetrabromo-2,2'-biphenyldiol (4-BP), that kills or inhibits diverse phytoplankton by inhibiting plastoquinone synthesis and its effect cascades to many other key metabolic processes of the algae. Through comparative genomic analysis between the 4-BP-producing bacterium and its algicidally inactive mutant, combined with gene function verification, we identified the gene cluster responsible for 4-BP synthesis, which contains genes encoding chorismate lyase, flavin-dependent halogenase and cytochrome P450. We demonstrated that in near in situ simulated algal blooming seawater, even low concentrations of 4-BP can cause changes in overall phytoplankton community structure with a decline in dinoflagellates and diatoms. Further analyses of the gene sequences from the Tara Oceans expeditions and 2750 whole genome sequences confirmed the ubiquitous presence of 4-BP synthetic genes in diverse bacterial members in the global ocean, suggesting that it is a bacterial tool potentially widely used in global oceans to mediate bacteria-algae antagonistic relationships.

Design, Synthesis, and Bioassay for the Thiadiazole-Bridged Thioacetamide Compound as Cy-FBP/SBPase Inhibitors Based on Catalytic Mechanism Virtual Screening

Cyanobacterial fructose-1,6-/sedoheptulose-1,7-bisphosphatase (Cy-FBP/SBPase) was an important regulatory enzyme in cyanobacterial photosynthesis and was a potential target enzyme for screening to obtain novel inhibitors against cyanobacterial blooms. In this study, we developed a novel pharmacophore screening model based on the catalytic mechanism and substrate structure of Cy-FBP/SBPase and screened 26 S series compounds with different structures and pharmacophore characteristics from the Specs database by computer-assisted drug screening. These compounds exhibited moderate inhibitory activity against Cy-FBP/SBPase, with 9 compounds inhibiting >50% at 100 μM. Among them, compound S5 showed excellent inhibitory activity against both Cy-FBP/SBPase and Synechocystis sp. PCC6803 (IC50 = 6.7 ± 0.7 μM and EC50 = 7.7 ± 1.4 μM). The binding mode of compound S5 to Cy-FBP/SBPase was predicted using the molecular docking theory and validated by sentinel mutation and enzyme activity analysis. Physiochemical, gene transcription level, and metabolomic analyses showed that compound S5 significantly reduced the quantum yield of photosystem II and the maximum electron transfer rate, downregulated transcript levels of related genes encoding the Calvin cycle and photosystem, reduced the photosynthetic efficiency of cyanobacteria, thus inhibited metabolic pathways, such as the Calvin cycle and tricarboxylic acid cycle, and eventually achieved an efficient algicide. In addition, compound S5 had a high safety profile for human-derived cells and zebrafish. In summary, the novel pharmacophore screening model obtained from the current work provides an effective solution to the cyanobacterial bloom problem.

Design, synthesis and mechanism research of novel algicide based on bioactive fragments synthesis strategy

The frequency and intensity of harmful cyanobacterial blooms (HCBs) are increasing all over the world, their prevention and control have become a great challenge. In this paper, a series of 1,3,4-thiadiazole thioacetamides (T series) were designed and synthesized as potential algaecides. Among them, the compound T3 showed its best algacidal activity against Synechocystis sp. PCC 6803 (PCC 6803, EC₅₀ = 1.51 μM) and Microcystis aeruginosa FACHB 905 (FACHB905, EC₅₀ = 4.88 μM), which was more effective than the lead compound L1 (PCC6803, EC₅₀ = 7.7 μM; FACHB905, EC₅₀ = 8.8 μM) and the commercially available herbicide prometryn (PCC6803, EC₅₀ = 4.64 μM；FACHB905, EC₅₀ = 6.52 μM). Meanwhile, T3 showed a lower inhibitory activity (EC₅₀ = 12.76 μM) than prometryn (EC₅₀ = 7.98 μM) to Chlorella FACHB1227, indicating that T3 had selective inhibition to prokaryotic algae (PCC6803, FACHB905) and eukaryotic algae (FACHB1227). Furthermore, the algacidal and anti-algae activities of T3 were significantly better than those of prometryn, while the toxicity of zebrafish and human cells was less than prometryn. Electron microscope, physiological, biochemical and metabonomic analysis showed that T3 interfered with light absorption and light conversion during photosynthesis by significantly reducing chlorophyll content, thus inhibited metabolic pathways such as the Calvin cycle and TCA cycle, and eventually led to the cell rupture of cyanobacteria. These results afforded further development of effective and safe algaecides.