Killing effect of deinoxanthins on cyanobloom-forming Microcystis aeruginosa: Eco-friendly production and specific activity of deinoxanthins

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.

Insights into the synthesis, engineering, and functions of microbial pigments in Deinococcus bacteria

The ability of Deinococcus bacteria to survive in harsh environments, such as high radiation, extreme temperature, and dryness, is mainly attributed to the generation of unique pigments, especially carotenoids. Although the limited number of natural pigments produced by these bacteria restricts their industrial potential, metabolic engineering and synthetic biology can significantly increase pigment yield and expand their application prospects. In this study, we review the properties, biosynthetic pathways, and functions of key enzymes and genes related to these pigments and explore strategies for improving pigment production through gene editing and optimization of culture conditions. Additionally, studies have highlighted the unique role of these pigments in antioxidant activity and radiation resistance, particularly emphasizing the critical functions of deinoxanthin in D. radiodurans. In the future, Deinococcus bacterial pigments will have broad application prospects in the food industry, drug production, and space exploration, where they can serve as radiation indicators and natural antioxidants to protect astronauts' health during long-term space flights.

Sustainable control of Microcystis aeruginosa, a harmful cyanobacterium, using Selaginella tamariscina extracts

Eco-friendly reagents derived from plants represent a promising strategy to mitigate the occurrence of toxic cyanobacterial blooms. The use of an amentoflavone-containing Selaginella tamariscina extract (STE) markedly decreased the number of Microcystis aeruginosa cells, thus demonstrating significant anti-cyanobacterial activity. In particular, the Microcystis-killing fraction obtained from pulverized S. tamariscina using hot-water-based extraction at temperatures of 40 °C induced cell disruption in both axenic and xenic M. aeruginosa. Liquid chromatographic analysis was also conducted to measure the concentration of amentoflavone in the STE, thus supporting the potential M. aeruginosa-specific killing effects of STE. Bacterial community analysis revealed that STE treatment led to a reduction in the relative abundance of Microcystis species while also increasing the 16S rRNA gene copy number in both xenic M. aeruginosa NIBR18 and cyanobacterial bloom samples isolated from a freshwater environment. Subsequent testing on bacteria, cyanobacteria, and algae isolated from freshwater revealed that STE was not toxic for other taxa. Furthermore, ecotoxicology assessment involving Aliivibrio fischeri, Daphnia magna, and Danio rerio found that high STE doses immobilized D. magna but did not impact the other organisms, while there was no change in the water quality. Overall, due to its effective Microcystis-killing capability and low ecotoxicity, aqueous STE represents a promising practical alternative for the management of Microcystis blooms.

Biological and Chemical Approaches for Controlling Harmful Microcystis Blooms

The proliferation of harmful cyanobacterial blooms dominated by Microcystis aeruginosa has become an increasingly serious problem in freshwater ecosystems due to climate change and eutrophication. Microcystis-blooms in freshwater generate compounds with unpleasant odors, reduce the levels of dissolved O2, and excrete microcystins into aquatic ecosystems, potentially harming various organisms, including humans. Various chemical and biological approaches have thus been developed to mitigate the impact of the blooms, though issues such as secondary pollution and high economic costs have not been adequately addressed. Red clays and H2O2 are conventional treatment methods that have been employed worldwide for the mitigation of the blooms, while novel approaches, such as the use of plant or microbial metabolites and antagonistic bacteria, have also recently been proposed. Many of these methods rely on the generation of reactive oxygen species, the inhibition of photosynthesis, and/or the disruption of cellular membranes as their mechanisms of action, which may also negatively impact other freshwater microbiota. Nevertheless, the underlying molecular mechanisms of anticyanobacterial chemicals and antagonistic bacteria remain unclear. This review thus discusses both conventional and innovative approaches for the management of M. aeruginosa in freshwater bodies.

Antagonistic actions of Paucibacter aquatile B51 and its lasso peptide paucinodin toward cyanobacterial bloom-forming Microcystis aeruginosa PCC7806

Superior antagonistic activity against axenic Microcystis aeruginosa PCC7806 was observed with Paucibacter sp. B51 isolated from cyanobacterial bloom samples among 43 tested freshwater bacterial species. Complete genome sequencing, analyzing average nucleotide identity and digital DNA-DNA hybridization, designated the B51 strain as Paucibacter aquatile. Electron and fluorescence microscopic image analyses revealed the presence of the B51 strain in the vicinity of M. aeruginosa cells, which might provoke direct inhibition of the photosynthetic activity of the PCC7806 cells, leading to perturbation of cellular metabolisms and consequent cell death. Our speculation was supported by the findings that growth failure of the PCC7806 cells led to low pH conditions with fewer chlorophylls and down-regulation of photosystem genes (e.g., psbD and psaB) during their 48-h co-culture condition. Interestingly, the concentrated ethyl acetate extracts obtained from B51-grown supernatant exhibited a growth-inhibitory effect on PCC7806. The physical separation of both strains by a filter system led to no inhibitory activity of the B51 cells, suggesting that contact-mediated anti-cyanobacterial compounds might also be responsible for hampering the growth of the PCC7806 cells. Bioinformatic tools identified 12 gene clusters that possibly produce secondary metabolites, including a class II lasso peptide in the B51 genome. Further chemical analysis demonstrated anti-cyanobacterial activity from fractionated samples having a rubrivinodin-like lasso peptide, named paucinodin. Taken together, both contact-mediated inhibition of photosynthesis and the lasso peptide secretion of the B51 strain are responsible for the anti-cyanobacterial activity of P. aquatile B51.

The β-Lactamase Activity at the Community Level Confers β-Lactam Resistance to Bloom-Forming Microcystis aeruginosa Cells

Many freshwater cyanobacteria, including Microcystis aeruginosa, lack several known antibiotic resistance genes; however, both axenic and xenic M. aeruginosa strains exhibited high antibiotic resistance against many antibiotics under our tested concentrations, including colistin, trimethoprim, and kanamycin. Interestingly, axenic PCC7806, although not the xenic NIBR18 and NIBR452 strains, displayed susceptibility to ampicillin and amoxicillin, indicating that the associated bacteria in the phycosphere could confer such antibiotic resistance to xenic strains. Fluorescence and scanning electron microscopic observations revealed their tight association, leading to possible community-level β-lactamase activity. Combinatory treatment of ampicillin with a β-lactamase inhibitor, sulbactam, abolished the ampicillin resistance in the xenic stains. The nitrocefin-based assay confirmed the presence of significant community-level β-lactamase activity. Our tested low ampicillin concentration and high β-lactamase activity could potentially balance the competitive advantage of these dominant species and provide opportunities for the less competitive species, thereby resulting in higher bacterial diversity under ampicillin treatment conditions. Non-PCR-based metagenome data from xenic NIBR18 cultures revealed the dominance of blaOXA-related antibiotic resistance genes followed by other class A β-lactamase genes (AST-1 and FAR-1). Alleviation of ampicillin toxicity could be observed only in axenic PCC7806, which had been cocultured with β-lactamase from other freshwater bacteria. Our study suggested M. aeruginosa develops resistance to old-class β-lactam antibiotics through altruism, where associated bacteria protect axenic M. aeruginosa cells.

Highly Water-Dispersed and Stable Deinoxanthin Nanocapsule for Effective Antioxidant and Anti-Inflammatory Activity

Introduction

Deinoxanthin (DX), a carotenoid, has excellent antioxidant and anti-inflammatory properties. However, owing to its lipophilicity, it is unfavorably dispersed in water and has low stability, limiting its application in cosmetics, food, and pharmaceuticals. Therefore, it is necessary to study nanoparticles to increase the loading capacity and stability of DX.

Methods

In this study, DX-loaded nanocapsules (DX@NCs) were prepared by nanoprecipitation by loading DX into nanocapsules. The size, polydispersity index, surface charge, and morphology of DX@NCs were confirmed through dynamic light scattering and transmission electron microscopy. The loading content and loading efficiency of DX in DX@NCs were analyzed using high-performance liquid chromatography. The antioxidant activity of DX@NCs was evaluated by DPPH assay and in vitro ROS. The biocompatibility of DX@NCs was evaluated using an in vitro MTT assay. In vitro NO analysis was performed to determine the effective anti-inflammatory efficacy of DX@NCs.

Results

DX@NCs exhibited increased stability and antioxidant efficacy owing to the improved water solubility of DX. The in situ and in vitro antioxidant activity of DX@NCs was higher than that of unloaded DX. In addition, it showed a strong anti-inflammatory effect by regulating the NO level in an in vitro cell model.

Conclusion

This study presents a nanocarrier to improve the water-soluble dispersion and stability of DX. These results demonstrate that DX@NC is a carrier with excellent stability and has a high potential for use in cosmetic and pharmaceutical applications owing to its antioxidant and anti-inflammatory effects.

Recent Advances in the Research on the Anticyanobacterial Effects and Biodegradation Mechanisms of Microcystis aeruginosa with Microorganisms

Harmful algal blooms (HABs) have attracted great attention around the world due to the numerous negative effects such as algal organic matters and cyanobacterial toxins in drinking water treatments. As an economic and environmentally friendly technology, microorganisms have been widely used for pollution control and remediation, especially in the inhibition/biodegradation of the toxic cyanobacterium Microcystis aeruginosa in eutrophic water; moreover, some certain anticyanobacterial microorganisms can degrade microcystins at the same time. Therefore, this review aims to provide information regarding the current status of M. aeruginosa inhibition/biodegradation microorganisms and the acute toxicities of anticyanobacterial substances secreted by microorganisms. Based on the available literature, the anticyanobacterial modes and mechanisms, as well as the in situ application of anticyanobacterial microorganisms are elucidated in this review. This review aims to enhance understanding the anticyanobacterial microorganisms and provides a rational approach towards the future applications.