Effect of algicidal compound Nω-acetylhistamine on physiological response and algal toxins in Heterosigma akashiwo

Algicidal mechanism and algicidal active metabolites of Alteromonas abrolhosensis against harmful dinoflagellates Karenia mikimotoi

Harmful algal blooms (HABs) are a global environmental concern, posing significant threats to marine ecosystems and human health. Algicidal bacteria offer a promising biological approach for mitigating HABs. Herein, the mechanism of an algicidal bacterium Alteromonas abrolhosensis JY-JZ1 against Karenia mikimotoi was investigated and algicidal metabolites from the strain JY-JZ1 were analyzed. The significant decrease in maximum quantum yield (Fv/Fm), relative electron transport rate (rETR), maximum relative electron transport rate (rETRmax) and apparent photosynthetic efficiency (α) indicated destruction of photosynthetic system. Biochemical analyses showed that the JY-JZ1 supernatant induced reactive oxygen species (ROS) overproduction and malondialdehyde (MDA) accumulation in K. mikimotoi. Contents of superoxide dismutase (SOD) and glutathione (GSH) increased responding to JY-JZ1 supernatant treatments. Optical microscope observation and propidium iodide (PI) staining confirmed the destruction of the cell membrane structure. Gene expression analysis showed that the extracellular metabolites of JY-JZ1 altered gene expression associated with photosynthesis, respiration, and cell wall integrity in K. mikimotoi. The metabolites of strain JY-JZ1 for 8 h and 24 h were harvested and analysed. Among the metabolites, 3-hydroxy-kynurenine, 10-undecenoic acid, 10-hydroxy-2-decenoic acid, 3-hydroxymandelic acid and catechol were first proved to exhibit algicidal activity against K. mikimotoi. This study provides the first report of these metabolites as novel algicidal substances. These results demonstrated that A. abrolhosensis JY-JZ1 exhibits significant potential for controlling HABs and offers multiple algicidal active compounds with promising application prospects.

Algicidal activity and mechanism of novel Bacillamide a derivative against red tide algae Skeletonema costatum and Prorocentrum minimum

Frequent red tide outbreaks pose a serious threat to biodiversity and the safety of aquatic ecosystems. Bacillamides showed algicidal activity against algae. However, the low natural concentrations and their structural complexity hinder development of these molecules. Inspired by the natrual algicide Bacillamide A, a series of thiourea derivatives were synthesized. Bacillamide A derivative (3B) showed excellent algicidal activity against S. costatum (EC50 = 0.52 μg/mL) and P. minimum (EC50 = 2.99 μg/mL), respectively. In addition, it has low toxicity to mammals and is less toxic than copper sulfate. 3B treatment resulted in loss of algal cell integrity. It also decreased the Chlorophyll a content and Fv/fm of algal cells, while increasing the levels of malondialdehyde content, superoxide dismutase, and reactive oxygen. 3B also induced expression of the photosynthetic genes, including psaB, psbB, as well as the antioxidant genes SOD2 and CAT. This study demonstrates that Bacillamide A derivatives could provide a safer alternative for red tide algal management.

Warfare under the waves: a review of bacteria-derived algaecidal natural products

Covering: 1960s to 2024Harmful algal blooms pose a major threat to aquatic ecosystems and can impact human health. The frequency and intensity of these blooms has increased over recent decades, driven primarily by climate change and an increase in nutrient runoff. Algal blooms often produce toxins that contaminate water sources, disrupt fisheries, and harm human health. These blooms may also result in oxygen-deprived environments leading to mass fish deaths that threaten the survival of other aquatic life. In freshwater and estuarine ecosystems, traditional chemical strategies to mitigate algal blooms include the use of herbicides, metal salts, or oxidants. Though effective, these agents are non-selective, toxic to other species, and cause loss of biodiversity. They can persist in ecosystems, contaminating the food web and providing an impetus for cost-effective, targeted algal-control methods that protect ecosystems. In marine ecosystems, harmful algal blooms are even more challenging to treat due to the lack of scalable solutions and the challenge of dispersal of algal control agents in open ocean settings. Natural products derived from algae-bacteria interactions have led to the evolution of diverse bacteria-derived algaecidal natural products, which are highly potent, species specific and have potential for combating harmful algal blooms. They provide valuable starting points for the development of eco-friendly algae control methods. This review provides a comprehensive overview of all bacterial algaecides and their activities, categorized into two major groups: (1) algaecides produced in ecologically significant associations between bacteria and algae, and (2) algaecides with potentially coincidental activity but without an ecological role in specific bacteria-algae interactions. This review contributes to a better understanding of the chemical ecology of parasitic algal-bacterial interactions, "the warfare under the waves", and highlights the potential applications of bacteria-derived algaecides to provide solutions to harmful algal blooms.

Bacteria associated with Karenia mikimotoi in modulating its ichthyotoxicity

Harmful algae are often associated with bacteria but whether their toxicity is affected by bacteria is unclear. This study elucidated roles of bacteria associated with Karenia mikimotoi (KMHK) in modulating its ichthyotoxicity. Results revealed KMHK ichthyotoxicity increased in the order of xenic (with algal-associated bacteria) < axenic (free from associated bacteria) < "re-xenic" cultures (with bacterial consortium re-inoculated back to axenic KMHK), indicating the modulation of ichthyotoxicity depended on bacterial composition and types. Ichthyotoxicity of "re-xenic" KMHK culture with white or yellow pigmented isolate was higher than the red one, and white isolate "re-xenic" culture also exhibited higher haemolytic effect than the red isolate and xenic culture. However, "re-xenic" NIES2411, a very toxic strain isolated from Japan, with white bacterial isolate had lower ichthyotoxicity than the respective xenic culture, while the non-toxic strain (CAWD133) from New Zealand was unaffected by associated bacteria, implying bacterial modulation of ichthyotoxicity was algal strain-specific.

Impact of algicidal fungus Aspergillus welwitschiae GF6 on harmful bloom-forming cyanobacterium Microcystis aeruginosa: Growth and physiological responses

Harmful cyanobacterial blooms (HCBs) have become a common issue in freshwater worldwide. Biological methods for controlling HCBs are relatively cost effective and environmentally friendly. The strain of ascomycete GF6 was isolated from a water sample collected from the estuarine zone of the eastern part of the Gulf of Finland. Based on cultural and morphological features and data of phylogenetic analysis, the strain was identified as Aspergillus welwitschiae GF6. The isolated GF6 strain has algicidal activity against both cyanobacteria and green algae. The highest sensitivity to the algicidal action of strain GF6 was found in cyanobacteria (98.5-100%). The algicidal effect on green algae did not exceed 63-70%. It was shown that GF6 strain exhibited an indirect attack mode by releasing metabolites that inhibit and/or degrade algal cells. In this study, significantly increased malondialdehyde content in Microcystis aeruginosa cells indicated that GF6 strain caused oxidative damage to the algal cell membrane. Enhanced production of phytosynthetic pigments, increase in lifetime chlorophyll a fluorescence and in the levels of antioxidants were noted in Microcystis aeruginosa cells. Besides this, GF6 strain could reduce the microcystins content in the medium under inhibiting the growth of M. aeruginosa. Apart from the growth inhibition and cell degradation of M. aeruginosa, GF6 strain is able to remove microcystin-LR (MC-LR). The content of MC-LR at an initial concentration of 0.51 μg/mL decreased by 61% after 72 h of A.welwitschiae GF6 strain cultivation. In the process of MC-LR biodestruction, transformation products were identified - the conjugate of microcystin with glutathione and the linearized form of MC-LR. The isolated strain with algicidal activity and the ability to degrade microcystin is of interest for further research in order to be able to use it for convergent technology to prevent the mass development of cyanobacteria and detoxification of cyanotoxins in water bodies.

Wheat domestication alters root metabolic functions to drive the assembly of endophytic bacteria

The domestication process progressively differentiated wild relatives from modern cultivars, thus impacting plant-associated microorganisms. Endophytic bacterial communities play vital roles in plant growth, development, and health, which contribute to the crop's sustainable development. However, how plant domestication impacts endophytic bacterial communities and relevant root exudates in wheat remains unclear. First, we have observed that the domestication process increased the root endophytic microbial community diversity of wheat while decreasing functional diversity. Second, domestication decreased the endophytic bacterial co-occurrence network stability, and it did significantly alter the abundances of core microorganisms or potential probiotics. Third, untargeted LC-MS metabolomics revealed that domestication significantly altered the metabolite profiles, and the abundances of various root exudates released were significantly correlated with keystone taxa including the Chryseobacterium, Massilia, and Lechevalieria. Moreover, we found that root exudates, especially L-tyrosine promote the growth of plant-beneficial bacteria, such as Chryseobacterium. Additionally, with L-tyrosine and Chryseobacterium colonized in the roots, the growth of wild wheat's roots was significantly promoted, while no notable effect could be found in the domesticated cultivars. Overall, this study suggested that wild wheat as a key germplasm material, and its native endophytic microbes may serve as a resource for engineering crop microbiomes to improve the morphological and physiological traits of crops in widely distributed poor soils.

Natural algicidal compounds: Strategies for controlling harmful algae and application

The expanding impact of algal blooms on marine areas poses a severe threat to the sustainable development of aquaculture, human health, and the ecological safety of coastal areas. To address this issue, the exploration of natural algicidal compounds with high efficiency, selectivity, and environmental friendliness has gained attention as potential substances for algae removal. However, the integration of related work still needs to be improved. Therefore, an in-depth study of algicidal strategies and applications of algicidal compounds for biodiversity has become crucial. Here, we aim to consolidate the current advancements in research on the sources and types of algicidal compounds. We also delve into various algicidal strategies, including the damage inflicted on algal structures, inhibition of photosynthesis, effects on oxidative damage, and impacts on gene expression. Additionally, we highlight practical applications of algicidal compounds, taking into account their specificities and limitations. This review contributes to the protection of marine biodiversity and the promotion of sustainable environmental development. Furthermore, we provide recommendations for future research on algicidal compounds to overcome existing barriers. By doing so, we hope to offer valuable references for researchers engaged in further studies on managing algal outbreaks.

Investigating the molecular mechanisms of Pseudalteromonas sp. LD-B1's algicidal effects on the harmful alga Heterosigma akashiwo

Heterosigma akashiwo is a harmful algal bloom species that causes significant detrimental effects on marine ecosystems worldwide. The algicidal bacterium Pseudalteromonas sp. LD-B1 has demonstrated potential effectiveness in mitigating these blooms. However, the molecular mechanisms underlying LD-B1's inhibitory effects on H. akashiwo remain poorly understood. In this study, we employed the comprehensive methodology, including morphological observation, assessment of photosynthetic efficiency (Fv/Fm), and transcriptomic analysis, to investigate the response of H. akashiwo to LD-B1. Exposure to LD-B1 resulted in a rapid decline of H. akashiwo's Fv/Fm ratio, with cells transitioning to a rounded shape within 2 hours, subsequently undergoing structural collapse and cytoplasmic leakage. Transcriptomic data revealed sustained downregulation of photosynthetic genes, indicating impaired functionality of the photosynthetic system. Additionally, genes related to the respiratory electron transfer chain and antioxidant defenses were consistently downregulated, suggesting prolonged oxidative stress beyond the cellular antioxidative capacity. Notably, upregulation of autophagy-related genes was observed, indicating autophagic responses in the algal cells. This study elucidates the molecular basis of LD-B1's algicidal effects on H. akashiwo, advancing our understanding of algicidal mechanisms and contributing to the development of effective strategies for controlling harmful algal blooms.

Discovery of two novel bioactive algicidal substances from Brevibacillus sp. via metabolomics profiling and back-validation

Identifying potent bacterial algicidal agents is essential for the development of effective, safe, and economically viable algaecides. Challenges in isolating and purifying these substances from complex secretions have impeded progress in this field. Metabolomics profiling, an efficient strategy for identifying metabolites, was pioneered in identifying bacterial algicidal substances in this study. Extracellular secretions from different generations of the algicidal bacterium Brevibacillus sp. were isolated for comprehensive analysis. Specifically, a higher algicidal efficacy was observed in the secretion from Generation 3 (G3) of Brevibacillus sp. compared to Generation 1 (G1). Subsequent metabolomics profiling comparing G3 and 1 revealed 83 significantly up-regulated metabolites, of which 9 were identified as potential algicidal candidates. Back-validation highlighted the potency of 4-acetamidobutanoic acid (4-ABC) and 8-hydroxyquinoline (8-HQL), which exhibited robust algicidal activity with 3d-EC50 values of 6.40 mg/L and 92.90 µg/L, respectively. These substances disrupted photosynthetic activity in M. aeruginosa by ceasing electron transfer in PSⅡ, like the impact exerted by Brevibacillus sp. secretion. These findings confirmed that 4-ABC and 8-HQL were the main algicidal components derived from Brevibacillus sp.. Thus, this study presents a streamlined strategy for identifying bacterial algicidal substances and unveils two novel and highly active algicidal substances. ENVIRONMENTAL IMPLICATION: Harmful cyanobacterial blooms (HCBs) pose significant environmental problems and health effects to humans and other organisms. The increasing frequency of HCBs has emerged as a pressing global concern. Bacterial-derived algicidal substances are expected to serve as effective, safe, and economically viable algaecides against HCBs. This study presents a streamlined strategy for identifying bacterial algicidal substances and unveils two novel substances (4-ABC and 8-HQL). These two substances demonstrate remarkable algicidal activity and disrupt the photosynthetic system in M. aeruginosa. They hold potential as prospective algaecides for addressing HCBs.

The novel application of violacein produced by a marine Duganella strain as a promising agent for controlling Heterosigma akashiwo bloom: Algicidal mechanism, fermentation optimization and agent formulation

Controlling harmful algal blooms with algicidal bacteria is thought to be an efficient and eco-friendly way but lack of comprehensive studies from theory to practice limited the field application. Here we presented a purple bacterial strain Duganella sp. A3 capable of killing several harmful algae, including Heterosigma akashiwo, a world-wide fish-killing microalga. A bioactivity-guided purification and identification approach revealed the major algicidal compound of A3 as the pigment violacein, which was never reported for its algicidal potential before. Violacein rapidly disrupted cell permeability, caused long-term oxidative stress, but mildly affected algal photosystem, which might explain its highly species-specific activity against unarmored H. akashiwo. To explore the application potential of violacein, a fermentation optimization approach combing single-factor and multi-factor experiments was conducted to increase the violacein yield, which finally reached 0.4199 g/L just using a simple medium formula beneficial for compound purification. Finally, taking advantages of the physical and chemical stabilities, we successfully developed the novel application of violacein as a sustained-releasing and easy-to-preserve algicidal agent using alginate-acacia-gum-chitosan encapsulation, which paved the path for its future application in controlling H. akashiwo bloom.

Broad spectrum and species specificity of plant allelochemicals 1,2-benzenediol and 3-indoleacrylic acid against marine and freshwater harmful algae

Allelochemicals derived from plants have shown great potential in mitigating harmful algal blooms (HABs), although different algal species can respond differently to these chemicals. Therefore, we first investigated the allelopathic effects of two newly identified plant-derived allelochemicals, 1,2-benzenediol (1,2-BD) and 3-indoleacrylic acid (3-IDC), on six algal species. Then we further evaluated the allelopathic responses of two bloom-forming species, Microcystis aeruginosa FACHB-905 and Heterosigma akashiwo to 1,2-BD. Results showed that 1,2-BD had a broader antialgal spectrum than 3-IDC. Allelopathic response analysis indicated that 1,2-BD consistently and stably inhibit the growth of M. aeruginosa FACHB-905, with inhibitory mechanism being disruption of photosynthetic activity, overwhelming of the antioxidant system and activation of programmed cell death (PCD). H. akashiwo displayed resistance to 1,2-BD during exposure, and the growth inhibition was mainly attributed to PCD. Therefore, the species-specific allelopathic responses provide new insights for controlling HABs using 1,2-BD and 3-IDC.

Natural Algaecide Sphingosines Identified in Hybrid Straw Decomposition Driven by White-Rot Fungi

Harmful algal blooms (HABs), which are promoted by eutrophication and intensified by global warming, occur worldwide. Allelochemicals, which are natural chemicals derived from plants or microbes, are emerging weapons to eliminate these blooms. However, the cost and technical challenges have limited the discovery of novel antialgal allelochemicals. Herein, the decomposition of agricultural straws is manipulated by white-rot fungi and achieved elevated antialgal efficiency. The transcriptomic analysis reveals that nutrient limitation activated fungal decomposition. By using a comparative nontarget metabolomics approach, a new type of allelochemical sphingosines (including sphinganine, phytosphingosine, sphingosine, and N-acetylsphingosine) is identified. These novel natural algaecides exhibit superior antialgal capability, with as high as an order of magnitude lower effective concentration on blooming species than other prevalent allelochemicals. The co-expression relationship between transcriptomic and metabolomic results indicate that sphinganine is strongly correlated with the differentially expressed lignocellulose degradation unigenes. The algal growth suppression is triggered by the activation of programmed cell death, malfunction of algal photosystem and antioxidant system, the disruption on CO2 assimilation and light absorption. The sphingosines reported here are a new category of allelochemicals in addition to the well-known antialgal natural chemicals, which are potential species-specific agents for HABs control identified by multi-omics methodology.

Algicidal characteristics of novel algicidal compounds, cyclic lipopeptide surfactins from Bacillus tequilensis strain D8, in eliminating Heterosigma akashiwo blooms

Heterosigma akashiwo blooms have caused severe damage to marine ecosystems, the aquaculture industry and human health worldwide. In this study, Bacillus tequilensis D8 isolated from an H. akashiwo bloom area was found to exert high algicidal activity via extracellular metabolite production. This activity remained stable after exposure to different temperatures and light intensities. Scanning electron microscopy observation and fluorescein diacetate staining indicated that the algicidal substances rapidly destroyed algal plasma membranes and decreased esterase activity. Significant decreases in the maximum photochemical quantum yield and relative electron transfer rate were observed, which indicated photosynthetic membrane destruction. Subsequently, the algicidal compounds were separated and purified by high-performance liquid chromatography and identified as three surfactin homologues by interpreting high-resolution electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy data. Among these, surfactin-C13 and surfactin-C14 exhibited strong algicidal activity against three HAB-causing species, namely, H. akashiwo, Skeletonema costatum, and Prorocentrum donghaiense, with 24 h-LC50 values of 1.2-5.31 μg/ml. Surfactin-C15 showed strong algicidal activity against S. costatum and weak algicidal activity against H. akashiwo but little activity against P. donghaiense. The present study illuminates the algicidal characteristics and mechanisms of action of surfactins on H. akashiwo and their potential applicability in controlling harmful algal blooms.

Algicidal Bacteria: A Review of Current Knowledge and Applications to Control Harmful Algal Blooms

Interactions between bacteria and phytoplankton in aqueous ecosystems are both complex and dynamic, with associations that range from mutualism to parasitism. This review focuses on algicidal interactions, in which bacteria are capable of controlling algal growth through physical association or the production of algicidal compounds. While there is some evidence for bacterial control of algal growth in the field, our understanding of these interactions is largely based on laboratory culture experiments. Here, the range of these algicidal interactions is discussed, including specificity of bacterial control, mechanisms for activity, and insights into the chemical and biochemical analysis of these interactions. The development of algicidal bacteria or compounds derived from bacteria for control of harmful algal blooms is reviewed with a focus on environmentally friendly or sustainable methods of application. Potential avenues for future research and further development and application of bacterial algicides for the control of algal blooms are presented.

Isolation and characterization of an algicidal bacterium against the bloom-forming algae raphidophyte Heterosigma akashiwo

Harmful algae blooms (HABs) have increased in intensity and frequency worldwide, causing negative effects on public health and marine ecosystems. This study isolated and identified the bloom causing species and its associated algicidal bacterium during a phytoplankton bloom in coastal waters of Lianyungang, China. Morphological observations and DNA barcoding analysis indicate that the studied phytoplankton bloom was caused by the raphidophyte Heterosigma akashiwo, and the algicidal bacterium, strain LD-B1, was identified as a species belonging to the genus Pseudoalteromonas. Furthermore, the algicidal effects of strain LD-B1 against H. akashiwo were characterized; revealing strain LD-B1 show strong algicidal activity against H. akashiwo. After 48 h of bacterium culture addition, the algicidal rate reached up to 98.8% with a 1% final volume rate. Moreover, our findings indicate strain LD-B1's extracellular compounds involved in algicidal activity are likely not proteinaceous. These findings indicate that the isolated strain, LD-B1, is a promising algicidal bacterium to control H. akashiwo blooms.

Design and evaluation of glutathione responsive glycosylated camptothecin nanosupramolecular prodrug

A novel tumor-targeted glutathione responsive Glycosylated-Camptothecin nanosupramolecular prodrug (CPT-GL NSp) was designed and fabricated via a disulfide bond. The effects of glycoligand with different polarities on solubility, self-assembly, stability, cellular uptake, and glutathione responsive cleaving were explored, and an optimal glycosylated ligand was selected for nanosupramolecular prodrug. It has been found that CPT-GL NSp exhibited higher drug loading than traditional nanoparticles. Among of which maltose modified NSp had the strongest anti-tumor effects than that of glucose and maltotriose. CPT-SS-Maltose had a similar anti-tumor ability to Irinotecan (IR), but the superior performance in solubility, hemolysis, and uptake of HepG2 cells.