Necrosis of Microcystis aeruginosa causing tannin derivatives in Rhus chinensis stem.

BACKGROUND: Algal infestation in Korean lakes, rivers, and in agroecosystems is a catastrophic problem resulting in contaminated drinking and agricultural irrigation water. Developing allelochemical-based algicides has previously faced difficulties, including dosage requirements and chemical instability. Despite these challenges, these algicides have enormous potential for eco-friendly use. This study presents the efficient use of tannin derivatives as antialgal chemicals modeled on a tannin-rich stem extract of Rhus chinensis in a thermal processing application. RESULTS: Tannic acids are the key component of algal necrosis in R. chinensis stem extract, and although heat extraction from the stem increased the crude extraction yield 1.8-fold, the procedure induced the conversion of tannic acids to gallic acid, resulting in lower antialgal activity. Gallotannin showed stronger antialgal activity (The 50% lethal dosage (LD50 )= 44.6 mg L-1 ) than gallic acid (LD50  = 99.2 mg L-1 ), and the nonheated extract exhibited 3.7-fold lower LD50 (0.66 g L-1 ) than the heated extract (LD50  = 2.45 g L-1 ), resulting in 2.6-fold higher content of gallotannin. CONCLUSION: These results demonstrate that heat treatment of R. chinensis stems during the extraction process is not beneficial to algal control because of the acceleration of thermal tannin degradation, despite it showing higher crude extract yields. Therefore, it is suggested extraction processes minimizing the loss of tannic acids should be the preferred methods used to develop tannin-based natural algicides for controlling algal infestation. Tannic acids showed higher toxicity into necrosis of M. aeruginosa than gallic acid where heat-processed extraction of R. chinensis stems produces more gallic acid content resulting in thermal degradation of tannic complexes than the extraction of nonthermal treatment. © 2022 Society of Chemical Industry.

Ionic liquids vs. ethanol as extraction media of algicidal compounds from mango processing waste.

The race for environmentally-safe pesticides and biocides has been showing solutions ranging from pest-pathologic microorganisms to safer botanical extracts that can be incorporated in several formulations. Often linked to high biological activities, fruit residues can be recovered from food processing factories to obtain complex extracts enriched with several bioactive chemicals. Mango (Mangifera indica) fruits are processed into food products in high volumes across the globe and generate a consistent residue that contains, among others, the xanthonoid mangiferin and the flavonoid hyperoside. Both compounds have been linked to several pharmacological and pesticidal activities, although not yet studied for algicidal applications, a current concern specially for antifouling and harmful algae blooms control products. The challenge lies, however, not only on the degree of activity of the natural compounds, but also on the processes necessary to separate, isolate and formulate the bioactive compounds in order to obtain an effective final product. The solvent choice plays an important part regarding the selectivity of the separation and isolation of the main bioactive compounds from the solid waste matrix. Ethanolic mixtures in water have been consolidated recently as a promising extraction medium for flavonoids and xanthonoids, although hindered by solubility limitations. In this paper, aqueous solutions of ionic liquids (ILs) were tested, screened and optimized using Box-Behnken design and Response Surface Methodology to obtain mangiferin and hyperoside-enriched extracts. Results showed a greater concentration of mangiferin and hyperoside with 1-octyl-3-methylimidazolium chloride ([C8MIm] Cl), when compared to choline acetate and ethanolic extracts using optimized parameters. In terms of sufficiency, solvent selection between ILs and ethanolic extraction media was discussed considering economic and environmental factors. Ethanol/water mango waste extracts were then studied for their activity against Raphidocelis subcapitata microalgae, which showed a higher growth inhibition in comparison to standard solutions of mangiferin and hyperoside, either individually and in a 1:1 mixture. A EC50 value was found in relative low concentrations of mangiferin and hyperoside (0.015 mg L-1) detected in the extract, showcasing a promising approach to the direct use of residuary plant extracts in biocidal formulations.

Amentoflavone, a novel cyanobacterial killing agent from Selaginella tamariscina.

Harmful cyanobacterial bloom (HCB) by Microcystis aeruginosa is increasingly becoming a serious concern to the environment and human health alike. Currently, many physical, chemical, and biological controls are underway to eliminate HCB, but natural chemicals are rarely used. To find a control agent with low environmental toxicity and high potential for practical use, 60 plant extracts were screened. Only Selaginella tamariscina extract killed all four Microcystis aeruginosa strains, but not the other tested bacteria. Chloroform fraction of S. tamariscina extract (CSE) showed the highest killing activity. The effects of CSE on M. aeruginosa were monitored using differential interference contrast microscopy and flow-cytometry analysis, scanning electron microscopy, and transmission electron microscopy. The images showed that CSE-treated cells were abnormally altered, with damaged cell membranes, peptidoglycan layers, and cytoplasm. Quadrupole time-of-flight liquid chromatography-mass spectrometry was used to identify amentoflavone as a major active compound. Pure amentoflavone, even at low concentrations showed a powerful killing effect on M. aeruginosa, but not on other non-cyanobacteria. Overall, in this study, we have highlighted the potentials of S. tamariscina extracts and amentoflavone as selective HCB control agents.

CpMCA, a novel metacaspase gene from the harmful dinoflagellate Cochlodinium polykrikoides and its expression during cell death.

Metacaspases (MCAs) are cysteine proteases that share sequence homology with caspases, and may play roles in programmed cell death (PCD). In the present study, we identified a novel MCA gene (CpMCA) from the red tide dinoflagellate Cochlodinium polykrikoides, and examined its molecular characteristics and gene expression in response to algicide-induced cell death. CpMCA cDNA is 1164 bp in length, containing a dinoflagellate spliced leader sequence (dinoSL), an 879-bp open reading frame (ORF), which codes for a 293-aa protein, and a poly (A) tail. Multi-sequence comparison indicated that CpMCA belongs to type I MCA, but it has a different structure at the N-terminal. Phylogenetic analysis showed that C. polykrikoides may have acquired the MCA gene from bacteria by means of horizontal gene transfer (HGT). In addition, expressions of CpMCA significantly increased following exposure to the common algicides copper sulfate and oxidizing chlorine, which trigger cell death in dinoflagellates, suggesting that CpMCA may be involved in cell death.