The common bloom-forming cyanobacterium Microcystis is prone to a wide array of microbial antagonists

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.

Coupling effect of cyanobacterial blooms with migration and transformation of typical pollutants in lake or reservoir: Enhanced or decreased?

Eutrophication of lake and reservoir caused by cyanobacterial harmful algal blooms (cyanoHABs) become a global ecological problem because of massive destruction of ecosystems, which have attracted attentions widely. In addition to the production of cyanotoxins by certain bloom-forming species, there may also be direct or indirect interactions between cyanobacteria blooms and various pollutants in lakes or reservoirs. Based on bibliometrics, 19110 papers in Web of Science (WOS) and 2998 papers in the China National Knowledge Infrastructure (CNKI) on eutrophication and cyanobacterial blooms in lakes and reservoirs were analyzed, which showed that research on this topic has been ongoing for nearly 80 years with a gradual increase in its popularity. The research on the coupling process of cyanobacterial blooms with five typical pollutants, including microcystins (MCs), heavy metals, viruses, antibiotics and antibiotic resistance genes (ARGs), indicate that the coupling process between cyanobacteria blooms and certain pollutants is indeed generated through direct or indirect interactions by adsorption, changing the physical and chemical conditions of water environment, and changing the structure of microbial community. For instance, the production, toxicity would be likely enhanced by cyanobacteria blooms directly. And the microorganisms may play a significant role in the interaction between cyanobacteria blooms and ARGs. Generally, the risk of some typical pollutants would be likely enhanced or decreased directly or indirectly by these processes. It is recommended that further attention be paid to the interrelationships between the process of cyanobacterial bloom and typical pollutants' migration and transformation, to provide the scientific basis for the risk assessment and thus multi-objective synergistic control and management of nutrients and typical pollutants in eutrophic lakes or reservoirs.

Bacteriophages carry auxiliary metabolic genes related to energy, sulfur and phosphorus metabolism during a harmful algal bloom in a freshwater lake

Cyanophages play an important role in nutrient cycling in lakes since they can modulate the metabolism of cyanobacteria. A proper understanding of the impact of cyanophage infection on the metabolism and ecology of cyanobacteria is critical during a complete cycle of harmful algal bloom (HAB). The ecology of cyanophages in marine environments has been well-delineated, but cyanophages in freshwater lakes remain less studied. Here, we studied the diversity of cyanophages and their impact on host ecology and metabolism through the succession of HAB in Utah Lake, which is a shallow eutrophic freshwater lake, in 2019. We collected water samples at three different periods from two locations in freshwater Utah Lake. The three sampling periods represented the pre-bloom, peak-bloom, and post-bloom events. We observed that the Utah Lake virome was dominated by families Myoviridae, Siphoviridae, and Podoviridae under the order Caudovirales. We detected photosystem-related genes, sulfur assimilation genes, and pho regulon (phosphorus metabolism) genes in genomes of predicted cyanophages. We were able to capture the changes in relative abundance and expression of functional genes in genomes of cyanophage at different stages of the bloom. We observed higher relative abundance and expression of cyanophage-encoded pho-regulon genes in the "pre-bloom" period. The higher expression of pho-regulon genes in P-limited ecosystem of Utah Lake indicated the possible contribution of cyanophage to enhance the fitness of the host cyanobacteria. Our study provides some insightful findings on the role of cyanophages in controlling the ecology and relative abundance of host cyanobacteria in freshwater lakes.

Scientists' call to action: Microbes, planetary health, and the Sustainable Development Goals

Microorganisms, including bacteria, archaea, viruses, fungi, and protists, are essential to life on Earth and the functioning of the biosphere. Here, we discuss the key roles of microorganisms in achieving the United Nations Sustainable Development Goals (SDGs), highlighting recent and emerging advances in microbial research and technology that can facilitate our transition toward a sustainable future. Given the central role of microorganisms in the biochemical processing of elements, synthesizing new materials, supporting human health, and facilitating life in managed and natural landscapes, microbial research and technologies are directly or indirectly relevant for achieving each of the SDGs. More importantly, the ubiquitous and global role of microbes means that they present new opportunities for synergistically accelerating progress toward multiple sustainability goals. By effectively managing microbial health, we can achieve solutions that address multiple sustainability targets ranging from climate and human health to food and energy production. Emerging international policy frameworks should reflect the vital importance of microorganisms in achieving a sustainable future.

Diverse interactions between bacteria and microalgae: A review for enhancing harmful algal bloom mitigation and biomass processing efficiency

The interactions between bacteria and microalgae play pivotal roles in resource allocation, biomass accumulation, nutrient recycling, and species succession in aquatic systems, offering ample opportunities to solve several social problems. The escalating threat of harmful algal blooms (HABs) in the aquatic environment and the lack of cheap and eco-friendly algal-biomass processing methods have been among the main problems, demanding efficient and sustainable solutions. In light of this, the application of algicidal bacteria to control HABs and enhance algal biomass processing has been promoted in the past few decades as potentially suitable mechanisms to solve those problems. Hence, this comprehensive review aims to explore the diverse interaction modes between bacteria and microalgae, ranging from synergistic to antagonistic, and presents up-to-date information and in-depth analysis of their potential biotechnological applications, particularly in controlling HABs and enhancing microalgal biomass processing. For instance, several studies revealed that algicidal bacteria can effectively inhibit the growth of Microcystis aeruginosa, a notorious freshwater HAB species, with an antialgal efficiency of 24.87 %-98.8 %. The review begins with an overview of the mechanisms behind algae-bacteria interactions, including the environmental factors influencing these dynamics and their broader implications for aquatic ecosystems. It then provides a detailed analysis of the role of algicidal bacteria in controlling harmful algal blooms, as well as their role in bioflocculation and the pretreatment of microalgal biomass. Additionally, the review identifies and discusses the constraints and challenges in the biotechnological application of these interactions. By exploring the strategic use of algicidal bacteria, this review not only underscores their importance in maintaining aquatic environmental health but also in enhancing biomass processing efficiency. It offers valuable insights into future research avenues and the potential scalability of these applications, both in situ and at an industrial level.

Physiological and toxicological response of Microcystis aeruginosa BCCUSP232 exposed to Salvinia auriculata extracts

Microcystis aeruginosa is one of the most predominant freshwater bloom-forming cyanobacterium found globally which is capable of producing toxic secondary metabolites including microcystins that might intoxicate animals and humans when contaminated water or food is ingested. Salvinia auriculata Aubl is one of the plants that might possess bioactive compounds capable of controlling growth and reproduction of M. aeruginosa. The present study aimed to determine the presence of bioactive compounds in S. auriculata extracts and determine alterations occurred in growth and reproduction of M. aeruginosa when exposed to these plant extracts. In addition, this investigation aimed to examine the influence of S. auriculata on antioxidant enzymes detected in M. aeruginosa. The results obtained demonstrated that the aqueous and ethanolic extracts of S. auriculata presented potential for control of cyanobacteria populations, exhibiting algicidal action on M. aeruginosa as well as interfering in antioxidant enzymes activities and parameters associated with oxidative stress. Phytochemical analyses demonstrated the presence of polyphenols and flavonoids content in both extracts. In addition, application of S. auriculata extracts did not produce cytogenotoxicity and/or mutagenicity utilizing Allium cepa test. Therefore, further studies are needed in order to identify and characterize the compounds responsible for these effects on M. aeruginosa and provide information regarding the possible application of S. auriculata in the treatment of drinking water.

Phylogenic diversity of bacteria associated with potentially toxic cyanobacteria Microcystis aeruginosa: a synthesis on its bloom dynamics

The occurrence of toxic bloom-forming cyanobacteria, Microcystis aeruginosa, has been frequently reported worldwide. These colony forming toxic cyanobacteria harbour a wide range of heterotrophic bacterial communities. The present study has attempted to understand the bloom dynamics of M. aeruginosa along with isolating their colony-associated culturable heterotrophic bacteria from two freshwater ponds in south India with a persisting cyanobacterial bloom. The monthly monitoring of these study areas revealed the conducive role of warm, stagnant waters with high nutrients in forming M. aeruginosa bloom. The peak values of temperature, nitrate, and phosphate at station 1 reached up to 30.5 °C, 4.48 mg/L, 1.64 mg/L, and at station 2, 31 °C, 3.45 mg/L, and 0.62 mg/L, respectively. Twenty-eight bacterial isolates belonging to Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Actinobacteria, and Firmicutes were obtained during the study. Among these 28 isolates, Firmicutes was dominant with the M. aeruginosa bloom from both the study areas.

Harmful algal blooms in Cayuga lake, NY: From microbiome analysis to eDNA monitoring

The global increase in harmful algal blooms (HABs) has become a growing concern over the years, and New York State (NYS) is no exception. The Finger Lakes region in NYS has been identified as a hotspot for HABs, with Cayuga Lake having the highest number of blooms reported. The Cayuga Lake HABs Monitoring Program has been tracking cHABs (dominant bloom taxa, chlorophyll A, and microcystin levels) since 2018. However, limited research has been conducted on the microbiome of HABs in this region. In this study, the microbiome of HABs in the Cayuga Lake was surveyed and compared with non-HAB baseline samples. Using 16S rDNA community analysis, common bloom-forming cyanobacteria, were identified, with Microcystis being the dominant taxa in high toxin blooms. Further, this study evaluated the ability of Microcystis mcyA qPCR to detect elevated levels of potential toxigenic Microcystis in water samples using both benchtop and handheld qPCR devices. The results showed good performance of the qPCR assay as a screening for high toxin versus low/no toxin blooms. Additionally, the handheld qPCR device holds potential for in-field rapid (<1 h) screenings for high toxin blooms. This study provides insights into the microbiome of HABs in Cayuga Lake and offers a potential tool for rapid screening of high toxin blooms.

Grazing preferences of three species of amoebae on cyanobacteria and green algae

Twenty species/isolates of cyanobacteria and green algae were isolated from cyanobacterial bloom samples in lakes associated with the upper Qu'Appelle River drainage system in southern Saskatchewan, Canada. Three amoebae species (Cochliopodium sp., Vannella sp. and Vermamoeba vermiformis) were also isolated from one of these samples, and were subjected to grazing assays to determine which species of cyanobacteria or algae could potentially serve as a food source. Amoeba grazing rates were quantified based on the diameter of the plaque after 12 days on agar plate assays, and by estimation of the amoeba population growth rate from the rate of increase of plaque area. The common cyanobacterial bloom-formers Dolichospermum sp. and Aphanizomenon flos-aquae supported high growth rates for all three amoebae, while green algae, with the exception of one green alga/amoeba combination, did not support growth of the tested amoebae. Many of the cyanobacterial and algal isolates that did not support amoebae growth were ingested, suggesting that ingestion did not determine grazing success. Overall, while the cyanobacteria Dolichospermum sp. and Aphanizomenon flos-aquae were suitable food sources for the amoebae, the other cyanobacteria were grazed in an unpredictable manner, with some species/strains grazed by some amoebae and some species not grazed at all.

Comparative genomic analysis of Microcystis strain diversity using conserved marker genes

Microcystis-dominated cyanobacterial harmful algal blooms (cyanoHABs) have a global impact on freshwater environments, affecting both wildlife and human health. Microcystis diversity and function in field samples and laboratory cultures can be determined by sequencing whole genomes of cultured isolates or natural populations, but these methods remain computationally and financially expensive. Amplicon sequencing of marker genes is a lower cost and higher throughput alternative to characterize strain composition and diversity in mixed samples. However, the selection of appropriate marker gene region(s) and primers requires prior understanding of the relationship between single gene genotype, whole genome content, and phenotype. To identify phylogenetic markers of Microcystis strain diversity, we compared phylogenetic trees built from each of 2,351 individual core genes to an established phylogeny and assessed the ability of these core genes to predict whole genome content and bioactive compound genotypes. We identified single-copy core genes better able to resolve Microcystis phylogenies than previously identified marker genes. We developed primers suitable for current Illumina-based amplicon sequencing with near-complete coverage of available Microcystis genomes and demonstrate that they outperform existing options for assessing Microcystis strain composition. Results showed that genetic markers can be used to infer Microcystis gene content and phenotypes such as potential production of bioactive compounds , although marker performance varies by bioactive compound gene and sequence similarity. Finally, we demonstrate that these markers can be used to characterize the Microcystis strain composition of laboratory or field samples like those collected for surveillance and modeling of Microcystis-dominated cyanobacterial harmful algal blooms.

Coordinated proteome change precedes cell lysis and death in a mat-forming cyanobacterium

Cyanobacteria form dense multicellular communities that experience transient conditions in terms of access to light and oxygen. These systems are productive but also undergo substantial biomass turnover through cell death, supplementing heightened heterotrophic respiration. Here we use metagenomics and metaproteomics to survey the molecular response of a mat-forming cyanobacterium undergoing mass cell lysis after exposure to dark and anoxic conditions. A lack of evidence for viral, bacterial, or eukaryotic antagonism contradicts commonly held beliefs on the causative agent for cyanobacterial death during dense growth. Instead, proteogenomics data indicated that lysis likely resulted from a genetically programmed response triggered by a failure to maintain osmotic pressure in the wake of severe energy limitation. Cyanobacterial DNA was rapidly degraded, yet cyanobacterial proteins remained abundant. A subset of proteins, including enzymes involved in amino acid metabolism, peptidases, toxin-antitoxin systems, and a potentially self-targeting CRISPR-Cas system, were upregulated upon lysis, indicating possible involvement in the programmed cell death response. We propose this natural form of cell death could provide new pathways for controlling harmful algal blooms and for sustainable bioproduct production.

A novel cyanolytic bacterium, Pseudomonas fluorescens BG-E as a potential biological control agent for freshwater bloom-forming cyanobacteria Pseudanabaena spp

The majority of bacterial antagonists identified to date are active against Microcystis. Therefore, this study aimed to isolate and characterize novel cyanolytic bacterial strains antagonistic against bloom-forming filamentous cyanobacteria. The bacterial strain BG-E isolated from the Bandagiriya Wewa in Sri Lanka was identified as Pseudomonas fluorescens (MZ007859) based on the 16S rRNA gene sequencing. BG-E showed 82% and 73% cyanolytic activity (CA) against Pseudanabaena sp. LW2 (MW288948) and Pseudanabaena lonchoides LW1 (MW288940), respectively, after 10 days of inoculation. The light microscopic images affirmed the complete disintegration in the filamentous structures of the tested Pseudanabaena species. The bacterial cell density of 15% v/v showed the CA with 95% and 89% cell lysis, respectively, in P. lonchoides and Pseudanabaena sp. LW2. Moreover, the results showed that >50% CA could be achieved by 0.100 and 1.00 (OD₇₃₀ ) cell densities for these same species. The highest CA of the cell-free supernatant of BG-E against P. lonchoides and bacterial culture against Pseudanabaena sp. LW2 illustrated the species-specific mode of action of BG-E. Although BG-E efficiently lysed the tested cyanobacterial species, the results of the MC-biodegradation assay confirmed its inability to degrade MC-LR cyanotoxin. Further, the BG-E strain lacks the mlrABCD gene cluster which is known to be responsible for the enzymatic degradation of MCs. The overall findings highlighted the applicability of P. fluorescens BG-E as a biological controlling agent to terminate blooms of freshwater filamentous cyanobacteria genus Pseudanabaena. The incorporation of cyanotoxin-degrading heterotrophic bacteria is recommended as a means of controlling toxic Pseudanabaena blooms.

Freshwater Cyanobacterial Toxins, Cyanopeptides and Neurodegenerative Diseases

Cyanobacteria produce a wide range of structurally diverse cyanotoxins and bioactive cyanopeptides in freshwater, marine, and terrestrial ecosystems. The health significance of these metabolites, which include genotoxic- and neurotoxic agents, is confirmed by continued associations between the occurrence of animal and human acute toxic events and, in the long term, by associations between cyanobacteria and neurodegenerative diseases. Major mechanisms related to the neurotoxicity of cyanobacteria compounds include (1) blocking of key proteins and channels; (2) inhibition of essential enzymes in mammalian cells such as protein phosphatases and phosphoprotein phosphatases as well as new molecular targets such as toll-like receptors 4 and 8. One of the widely discussed implicated mechanisms includes a misincorporation of cyanobacterial non-proteogenic amino acids. Recent research provides evidence that non-proteinogenic amino acid BMAA produced by cyanobacteria have multiple effects on translation process and bypasses the proof-reading ability of the aminoacyl-tRNA-synthetase. Aberrant proteins generated by non-canonical translation may be a factor in neuronal death and neurodegeneration. We hypothesize that the production of cyanopeptides and non-canonical amino acids is a more general mechanism, leading to mistranslation, affecting protein homeostasis, and targeting mitochondria in eukaryotic cells. It can be evolutionarily ancient and initially developed to control phytoplankton communities during algal blooms. Outcompeting gut symbiotic microorganisms may lead to dysbiosis, increased gut permeability, a shift in blood-brain-barrier functionality, and eventually, mitochondrial dysfunction in high-energy demanding neurons. A better understanding of the interaction between cyanopeptides metabolism and the nervous system will be crucial to target or to prevent neurodegenerative diseases.

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.

Temporal variation of 2-MIB and geosmin production by Pseudanabaena galeata and Phormidium ambiguum exposed to high-intensity light

This study demonstrated the temporal variation of 2-methylisoborneol (2-MIB) and geosmin (GSM) production of two filamentous cyanobacteria species Pseudanabaena galeata (NIES-512; planktonic) and Phormidium ambiguum (NIES-2119; benthic) exposed to high light intensity (950-1000 μmol m-2  s-1 photosynthetically active radiation). The production of 2-MIB and GSM was quantified together with oxidative stress, chlorophyll content, and cellular protein content. The relative chlorophyll bleaching and cell degradations were compared through microscopic images. The 2-MIB production of P. galeata increased by over 42 ± 17% on the second day of exposure and remained leveled through the exposure period. P. ambiguum showed a continuous increase of 2-MIB until the 10th day, recording a 95 ± 4% increment. The GSM production was elevated until the fourth day of exposure by 46 ± 10% for P. galeata and by 74 ± 21% on the second day for P. ambiguum and reduced with prolonged exposure for both species. The chlorophyll content of P. galeata was reduced by 62 ± 7% on the second day, and that of P. ambiguum was reduced by 52 ± 9% on the fourth day and remained low. Protein and H2 O2 contents of both species were changed inconsistently. Exposure to high-intensity light can photobleach and deteriorate cells of both species, but elevations in odorous compounds can be expected.

Bioremoval of Cylindrospermopsis raciborskii cells and cylindrospermopsin toxin in batch culture by the yeast Aureobasidium pullulans

This study describes the ability of a yeast strain, Aureobasidium pullulans KKUY0701 isolated from eutrophic lake to eliminate Cylindrospermopsis raciborskii and cylindrospermopsin (CYN) toxin. The anti-cyanobacterial activity of this yeast strain was evaluated by growing with living cells and filtrate of C. raciborskii. CYN bioremoval was assayed using living and heat-inactivated yeast cells. Both living cells and filtrate of this yeast strain were able to suppress the growth of C. raciborskii, with total cell death occurring at day 2 and day 3, respectively. Living and inactivated yeast cells, but not yeast filtrate, reduced CYN concentrations released into cyanobacterial cultures, indicating that this toxin might be removed from the culture medium via absorption onto yeast surface rather than enzymatic biodegradation. The adsorption experiments also confirmed the elimination of CYN by living and heat-inactivated yeast. Nevertheless, inactivated yeast exhibited higher capacity (K = 3.3) and intensity (n = 1.4) than living yeast (K = 1.9, n = 1) for CYN adsorption. The study suggests that this yeast strain could be employed for bioremediation of Cylindrospermopsis blooms in freshwaters. Additionally, heat-inactivated yeast biomass could be used in slow sand filters for elimination of CYN in drinking water treatment plants.

Algicidal activity of Morganella morganii against axenic and environmental strains of Microcystis aeruginosa: Compound combination effects

Cyanobacterial harmful algal blooms (cyanoHABs) are a global problem with serious consequences for public health and many sectors of the economy. The use of algicidal bacteria as natural antagonists to control bloom-forming cyanobacteria is a topic of growing interest. However, there are still unresolved questions that need to be addressed to better understand their mode of action and to implement effective mitigation strategies. In this study, thirteen bacterial strains isolated from both scums and concentrated bloom samples exhibited algicidal activity on three Microcystis aeruginosa strains with different characteristics: the axenic microcystin (MC)-producing strain M. aeruginosa PCC7820 (MaPCC7820), and two environmental (non-axenic) M. aeruginosa strains isolated from two different water bodies in Poland, one MC-producer (MaSU) and another non-MC-producer (MaPN). The bacterial strain SU7S0818 exerted the highest average algicidal effect on the three cyanobacterial strains. This strain was identified as Morganella morganii (99.51% similarity) by the 16S rRNA gene analyses; hence, this is the first study that demonstrates the algicidal properties of these ubiquitous bacteria. Microscopic cell counting and qPCR analyses showed that M. morganii SU7S0818 removed 91%, 96%, and 98.5% of MaPCC7820, MaSU and MaPN cells after 6 days of co-culture, respectively. Interestingly, the ultra-high-performance liquid chromatography-tandem mass spectrometer (UHPLC-MS/MS) analyses showed that this bacterium was involved on the release of several substances with algicidal potential. It was remarkable how the profile of some compounds evolved over time, as in the case of cadaverine, tyramine, cyclo[Pro-Gly] and cyclo[Pro-Val]. These dynamic changes could be attributed to the action of M. morganii SU7S0818 and the presence of associated bacteria with environmental cyanobacterial strains. Therefore, this study sheds light on how algicidal bacteria may adapt their action on cyanobacterial cells by releasing a combination of compounds, which is a crucial insight to exploit them as effective biological tools in the control of cyanoHABs.

The cyanobactericidal bacterium Paucibacter aquatile DH15 caused the decline of Microcystis and aquatic microbial community succession: A mesocosm study

Microcystis blooms pose a major threat to the quality of drinking water. Cyanobactericidal bacteria have attracted much attention in the research community as a vehicle for controlling Microcystis blooms because of their ecological safety. Nonetheless, most studies on cyanobactericidal bacteria have been conducted on a laboratory scale but have not been scaled-up as field experiments. Thus, our understanding of the microbial response to cyanobactericidal bacteria in natural ecosystems remains elusive. Herein, we applied Paucibacter aquatile DH15 to control Microcystis blooms in a 1000 L mesocosm experiment and demonstrated its potential with the following results: (1) DH15 reduced Microcystis cell density by 90.7% within two days; (2) microcystins released by Microcystis death decreased to the control level in four days; (3) during the cyanobactericidal processes, the physicochemical parameters of water quality remained safe for other aquatic organisms; and (4) the cyanobactericidal processes promoted the growth of eukaryotic microalgae, replacing cyanobacteria. The cyanobactericidal processes accelerated turnover rates, decreased stability, and altered the functional profile of the microbial community. Network analysis demonstrated that this process resulted in more complex interactions between microbes. Overall, our findings suggest that strain DH15 could be considered a promising candidate for controlling Microcystis blooms in an eco-friendly manner.

Microcystis colony formation: Extracellular polymeric substance, associated microorganisms, and its application

Microcystis sp., amongst the most prevalent bloom-forming cyanobacteria, is typically found as a colonial form with multiple microorganisms embedded in the mucilage known as extracellular polymeric substance. The colony-forming ability of Microcystis has been thoroughly investigated, as has the connection between Microcystis and other microorganisms, which is crucial for colony development. The following are the key subjects to comprehend Microcystis bloom in depth: 1) key issues related to the Microcystis bloom, 2) features and functions of extracellular polymeric substance, as well as diversity of associated microorganisms, and 3) applications of Microcystis-microorganisms interaction including bloom control, polluted water bioremediation, and bioactive compound production. Future research possibilities and recommendations regarding Microcystis-microorganism interactions and their significance in Microcystis colony formation are also explored. More information on such interactions, as well as the mechanism of Microcystis colony formation, can bring new insights into cyanobacterial bloom regulation and a better understanding of the aquatic ecosystem.

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

Harmful cyanobacterial blooms (HCBs) caused by Microcystis aeruginosa are of great concern as they negatively affect the aquatic environment and human health. Chemical methods could rapidly eradicate HCBs and have been used for many decades. However, many chemical reagents are not recommended to eliminate HCBs in the long term, given the possible destructive and toxic effects of the chemicals employed on non-target aquatic organisms. We developed a new algaecide, 2-((1,3,4-thiadiazol-2-yl)thio)-N-(4-chlorophenyl) acetamide (Q2), to control harmful cyanobacteria while being environmentally friendly and selective. In our study, Q2 effectively inhibited cyanobacterial growth, especially of M. aeruginosa, but did not affect eukaryotic algae in test concentrations. A critical mechanism was revealed by transcriptome and metagenomic results showing that Q2 affects multiple cellular targets of cyanobacteria for HCB control, including the destruction of organelles, damage in the photosynthesis center, as well as inhibition of gas vesicle growth, and these changes can be highly relevant to the decrease of quorum-sensing functional KEGG pathways. Furthermore, Q2 did not affect the microbial composition and could recover the disrupted aquatic functional pathways in a short period. This is different from the impact on ecosystem functioning of the traditionally used harmful algaecide diuron. All these results verified that Q2 could be friendly to the aquatic environment, providing a new directional choice in managing HCBs in the future.

To Die or Not to Die-Regulated Cell Death and Survival in Cyanobacteria

Regulated cell death (RCD) is central to the development, integrity, and functionality of multicellular organisms. In the last decade, evidence has accumulated that RCD is a universal phenomenon in all life domains. Cyanobacteria are of specific interest due to their importance in aquatic and terrestrial habitats and their role as primary producers in global nutrient cycling. Current knowledge on cyanobacterial RCD is based mainly on biochemical and morphological observations, often by methods directly transferred from vertebrate research and with limited understanding of the molecular genetic basis. However, the metabolism of different cyanobacteria groups relies on photosynthesis and nitrogen fixation, whereas mitochondria are the central executioner of cell death in vertebrates. Moreover, cyanobacteria chosen as biological models in RCD studies are mainly colonial or filamentous multicellular organisms. On the other hand, unicellular cyanobacteria have regulated programs of cellular survival (RCS) such as chlorosis and post-chlorosis resuscitation. The co-existence of different genetically regulated programs in cyanobacterial populations may have been a top engine in life diversification. Development of cyanobacteria-specific methods for identification and characterization of RCD and wider use of single-cell analysis combined with intelligent image-based cell sorting and metagenomics would shed more light on the underlying molecular mechanisms and help us to address the complex colonial interactions during these events. In this review, we focus on the functional implications of RCD in cyanobacterial communities.

Identification and feeding characteristics of the mixotrophic flagellate Poterioochromonas malhamensis, a microalgal predator isolated from planting water of Pontederia cordata

The microorganisms and allelochemicals in Pontederia cordata planting water may have a synergistic inhibitory effect on algae. To study this synergy, an algae-inhibiting organism was isolated and identified, and its growth and feeding characteristics were studied. The organism was identified as Poterioochromonas malhamensis yzs924 based on both its morphology and molecular barcoding employing 18S rDNA gene sequences.The growth and feeding of P. malhamensis were affected by environmental factors and the state of its prey. (1) P. malhamensis is a mixotrophic flagellate. Its heterotrophic growth was the fastest in a wheat grain medium, and its growth rate in this study reached 2.5 day^-1. (2) Within a short period of time (2 days), P. malhamensis growth was slower under continuous dark conditions than under alternating light and dark conditions, but it fed on Microcystis aeruginosa more rapidly under dark conditions. (3) High pH was disadvantageous to the growth and grazing of P. malhamensis. When the pH was kept stable at 9, P. malhamensis could not grow continuously. (4) When the initial density of M. aeruginosa was 5 × 10⁷ cells/mL or is in a period of decline, P. malhamensis could not remove all M. aeruginosa. The combined use of P. malhamensis and allelochemicals may represent a method of M. aeruginosa control, but this approach requires further research.

Linear Six-Carbon Sugar Alcohols Induce Lysis of Microcystis aeruginosa NIES-298 Cells

Cyanobacterial blooms are a global concern due to their adverse effects on water quality and human health. Therefore, we examined the effects of various compounds on Microcystis aeruginosa growth. We found that Microcystis aeruginosa NIES-298 cells were lysed rapidly by linear six-carbon sugar alcohols including mannitol, galactitol, iditol, fucitol, and sorbitol, but not by other sugar alcohols. Microscopic observations revealed that mannitol treatment induced crumpled inner membrane, an increase in periplasmic space, uneven cell surface with outer membrane vesicles, disruption of membrane structures, release of intracellular matter including chlorophylls, and eventual cell lysis in strain NIES-298, which differed from the previously proposed cell death modes. Mannitol metabolism, antioxidant-mediated protection of mannitol-induced cell lysis by, and caspase-3 induction in strain NIES-298 were not observed, suggesting that mannitol may not cause organic matter accumulation, oxidative stress, and programmed cell death in M. aeruginosa. No significant transcriptional expression was induced in strain NIES-298 by mannitol treatment, indicating that cell lysis is not induced through transcriptional responses. Mannitol-induced cell lysis may be specific to strain NIES-298 and target a specific component of strain NIES-298. This study will provide a basis for controlling M. aeruginosa growth specifically by non-toxic substances.

Multi-Soil-Layering Technology: A New Approach to Remove Microcystis aeruginosa and Microcystins from Water

Eutrophication of surface waters caused by toxic cyanobacteria such as Microcystis aeruginosa leads to the release of secondary metabolites called Microcystins (MCs), which are heptapeptides with adverse effects on soil microbiota, plants, animals, and human health. Therefore, to avoid succumbing to the negative effects of these cyanotoxins, various remediation approaches have been considered. These techniques involve expensive physico-chemical processes because of the specialized equipment and facilities required. Thus, implementing eco-technologies capable of handling this problem has become necessary. Indeed, multi-soil-layering (MSL) technology can essentially meet this requirement. This system requires little space, needs simple maintenance, and has energy-free operation and high durability (20 years). The performance of the system is such that it can remove 1.16 to 4.47 log10 units of fecal contamination from the water, 98% of suspended solids (SS), 92% of biological oxygen demand (BOD), 98% of chemical oxygen demand (COD), 92% of total nitrogen (TN), and 100% of total phosphorus (TP). The only reported use of the system to remove cyanotoxins has shown a 99% removal rate of MC-LR. However, the mechanisms involved in removing this toxin from the water are not fully understood. This paper proposes reviewing the principal methods employed in conventional water treatment and other technologies to eliminate MCs from the water. We also describe the principles of operation of MSL systems and compare the performance of this technology with others, highlighting some advantages of this technology in removing MCs. Overall, the combination of multiple processes (physico-chemical and biological) makes MSL technology a good choice of cyanobacterial contamination treatment system that is applicable in real-life conditions, especially in rural areas.

Physiological and metabolic responses of Microcystis aeruginosa to a salinity gradient

Microcystis is a well-known toxic cyanobacterium in eutrophic environments, and an increasing number of Microcystis blooms have emerged in salty reservoirs and coastal rivers. This study observed that many Microcystis were identified in a coastal river in June 2020. The relative abundance of Microcystis decreased from 81.2 to 10.2% in the sampling sites from a salinity of 0 (Sal. 0) to a salinity of 12 (Sal. 12). Hepatotoxic microcystins (MCs) were identified in the coastal river and its estuary. Of the samples, those with a salinity of 5 (Sal. 5) had the highest concentration of MCs at 7.81 ± 0.67 μg L^-1. In a saline water simulation experiment, the results showed that salt inhibited Microcystis (M.) aeruginosa growth, enhanced the activity levels of superoxide dismutase (SOD) and catalase (CAT) and stimulated microcystin production. Transcription analysis showed that the expression levels of the psaB and rbcL genes controlling photosymbiotic processes were downregulated, and capD and csaBgene-related polysaccharide productions were upregulated by salt incubation. Notably, metabolism analysis showed that the total polysaccharides, proteins and small molecular matter, such as sucrose, methionine and N-acetyl-D-glucosamine, in the Microcystis cells increased substantially to resist the extracellular hyperosmotic pressure caused by the high salinity levels in culture. These findings indicate that increased salt in a natural aquatic body shifts the phytoplankton community by influencing the physiological metabolism of cyanobacteria and poses a high risk of microcystin exposure during cyanobacterial blooms in coastal rivers.

Algicidal effect of tryptoline against Microcystis aeruginosa: Excess reactive oxygen species production mediated by photosynthesis

Cyanobacterial blooms significantly decrease water quality and can damage ecosystems and, as such, require efficient control methods. Algicidal bacteria and their associated substances are promising tools for controlling cyanobacterial blooms; however, their specific algicidal mechanisms remain unclear. Therefore, the current study sought to investigate the algicidal mechanism of tryptoline (1,2,3,4-tetrahydro-9 h-pyrido[3,4-b]indole) against Microcystis aeruginosa, with a specific focus on the contribution made by reactive oxygen species (ROS), the underlying mechanisms of ROS increase, as well as the photosystem response. Results show that the algicidal ratio of tryptoline significantly and positively correlates with algal ROS. Moreover, 93.79% of the algicidal ratio variation is attributed to ROS in the tryptoline group, while only 47.75% can be attributed to ROS in the tryptoline + N-acetyl-L-cysteine (NAC) group, where ROS are partially scavenged by NAC. In the presence of tryptoline, algicidal effect and ROS levels were significantly enhanced in the presence of light as compared to those in the dark (P < 0.001). Hence, the increase in ROS production attributed to tryptoline is primarily affected by the presence of light and photosynthesis. Additionally, tryptoline significantly reduces F_v/F_m, PI_ABS, ET_o/RC, and the expression of psaB and psbA genes related to photosynthesis, while increasing V_j and DI_o/RC (P < 0.05). These results suggest that tryptoline hinders algal photosynthesis by significantly decreasing photosynthetic efficiency and carbon assimilation, inhibiting photochemical electron transfer, and increasing closed reaction centers and energy loss. Moreover, following partial blockade of the photosynthetic electron transfer from Q_A to Q_B by diuron (3-(3-4-dichlorophenyl)-1,1-dimethylurea), the ROS of algae exposed to tryptoline is significantly decreased. Thus, tryptoline inhibits electron transfer downstream of Q_A, which increase the number of escaping electron and thereby increase ROS generation. Collectively, this study describes the algicidal mechanism of tryptoline against M. aeruginosa and highlights the critical factors associated with induction of algicidal activity.

Simultaneous biodegradation of harmful Cylindrospermopsis raciborskii and cylindrospermopsin toxin in batch culture by single Bacillus strain

This study investigates the capability of a Bacillus flexus strain isolated from decayed cyanobacterial blooms for the bioremediation of Cylindrospermopsis raciborskii and cylindrospermopsin (CYN) toxin. The algicidal activity of this strain was tested by co-cultivation with C. raciborskii cultures. CYN biodegradation was investigated in the presence of living and heat-inactivated bacterial cells or bacterial filtrate. Living bacterial cells inhibited C. raciborskii growth after 2 days of incubation with complete cell death at day 5. Bacterial filtrate caused a rapid reduction in C. raciborskii growth at the first day, with complete cell lysis at day 3. Only living cells of SSZ01 caused reduction in CYN released into the medium during the bacterial decay of C. raciborskii cells. The biodegradation rate of CYN by SSZ01 relied on initial toxin concentrations. The highest rate (42 μg CYN L^-1 day^-1) was obtained at the higher initial concentration (300 μg L^-1), and the lowest (4μg CYN L^-1 day^-1) was at lower concentration (50 μg L^-1). These results suggest that this bacterial strain could be employed to bioremediate cyanobacterial blooms in freshwaters. Also, the application of this bacterium in slow sand filters would give possibilities for degradation and bioremediation of cyanotoxins in drinking water treatment plants.

Antimicrobial activity against Microcystis aeruginosa and degradation of microcystin-LR by bacteria isolated from Antarctica

Cyanobacteria massive proliferations are common in freshwater bodies worldwide, causing adverse effects on aquatic ecosystems and public health. Numerous species develop blooms. Most of them correspond to the toxic microcystin-producing cyanobacterium Microcystis aeruginosa. Microorganisms recovered from Antarctic environment can be considered an unexploited source of antimicrobial compounds. Data about their activity against cyanobacteria are scant or inexistent. This study aimed to evaluate the capacity of Antarctic bacteria to inhibit the proliferation of M. aeruginosa BCPUSP232 and to degrade microcystin-LR (MC-LR). Cell-free extracts of seventy-six bacterial strains were initially tested for antimicrobial activity. Unidentified (UN) strains 62 and ES7 and Psychromonas arctica were able to effectively lyse M. aeruginosa. Eight strains showed MIC ranging from 0.55 to 3.00 mg mL^-1, with ES7 showing the best antimicrobial activity. Arthrobacter sp. 443 and UN 383 were the most efficient in degrading MC-LR, with 24.87 and 23.85% degradation, respectively. To our knowledge, this is the first report of antimicrobial and MC-LR degradation activities by Antarctic bacteria, opening up perspectives for their future application as an alternative or supporting approach to help mitigate cyanobacterial blooms.

Fungal biodegradation and removal of cyanobacteria and microcystins: potential applications and research needs

Harmful cyanobacterial blooms (HCB) have severe impacts on marine and freshwater systems worldwide. They cause oxygen depletion and produce potent cyanotoxins that have detrimental effects on human and environmental health and deteriorate the water quality. Biological treatment of the water for control of cyanobacterial blooms and removal of cyanotoxins can be a more economical and environment-friendly way, as they do not result in production of undesirable by-products. Most biological treatments of cyanobacteria and cyanotoxins have concentrated largely on bacteria, with little attention paid to algicidal fungi. Therefore, this review aims to provide an overview of the current status and the main progresses achieved in fungal biodegradation of HCB and cyanotoxin research. The available data revealed that 15 fungal species had high lytic activity against cyanobacteria, and 6 species were capable of degrading microcystins (MCs). Some fungal species (e.g., Aurobasidium pullulans and Trichoderma citrinoviride) have been identified to selectively inhibit the growth of cyanobacteria rather than beneficial species of other algal groups. Interestingly, some fungal strains (Trichaptum abietinum, Trichoderma citrinoviride) exhibited di-functional trait, being efficient in lysing cyanobacteria and degrading MCs released from the cells after decay. Beyond a comprehensive review of algicidal and toxin-degrading activities of fungi, this paper also identifies and prioritizes research gaps in algicidal fungi. The review also gives insights to the potential applications of algicidal fungi for removal of cyanobacterial blooms and their cyanotoxins from the aquatic environment.

Harmful algal blooms and their eco-environmental indication

Harmful algal blooms (HABs) in freshwater lakes and oceans date back to as early as the 19th century, which can cause the death of aquatic and terrestrial organisms. However, it was not until the end of the 20th century that researchers had started to pay attention to the hazards and causes of HABs. In this study, we analyzed 5720 published literatures on HABs studies in the past 30 years. Our review presents the emerging trends in the past 30 years on HABs studies, the environmental and human health risks, prevention and control strategies and future developments. Therefore, this review provides a global perspective of HABs and calls for immediate responses.

The genetic and ecophysiological diversity of Microcystis

Microcystis is a cyanobacterium that forms toxic blooms in freshwater ecosystems around the world. Biological variation among taxa within the genus is apparent through genetic and phenotypic differences between strains and via the spatial and temporal distribution of strains in the environment, and this fine-scale diversity exerts strong influence over bloom toxicity. Yet we do not know how varying traits of Microcystis strains govern their environmental distribution, the tradeoffs and links between these traits, or how they are encoded at the genomic level. Here we synthesize current knowledge on the importance of diversity within Microcystis and on the genes and traits that likely underpin ecological differentiation of taxa. We briefly review spatial and environmental patterns of Microcystis diversity in the field and genetic evidence for cohesive groups within Microcystis. We then compile data on strain-level diversity regarding growth responses to environmental conditions and explore evidence for variation of community interactions across Microcystis strains. Potential links and tradeoffs between traits are identified and discussed. The resulting picture, while incomplete, highlights key knowledge gaps that need to be filled to enable new models for predicting strain-level dynamics, which influence the development, toxicity and cosmopolitan nature of Microcystis blooms.

Occurrence and diversity of viruses associated with cyanobacterial communities in a Brazilian freshwater reservoir

As part of the phytoplankton of marine and freshwater environments around the world, cyanobacteria interact with viruses (cyanophages) that affect their abundance and diversity. Investigations focusing on cyanophages co-occurring with freshwater cyanobacteria are scarce, particularly in Brazil. The aim of this study was to assess the diversity of cyanophages associated with a Microcystis-dominated cyanobacterial bloom in a tropical reservoir. Samples were processed as viral fractions of water and cellular fractions, and temporal fluctuations in the abundance of Ma-LMM01-type cyanophages and their Microcystis hosts were determined by qPCR. We applied shotgun metagenomics to obtain a wider characterization of the cyanophage community. During the study period, Microcystis gene copies were quantified in all cellular fractions, and the copy number of the Ma-LMM01 phage gene tended to increase with host abundance. Metagenomic analysis demonstrated that Caudovirales was the major viral order associated with the cyanophage families Myoviridae (34-88%), Podoviridae (3-42%), and Siphoviridae (6-23%). The metagenomic analysis results confirmed the presence of Microcystis cyanophages in both viral and cellular fractions and demonstrated a high relative abundance of picocyanobacteria-related viruses and Prochlorococcus (36-52%) and Synechococcus (37-50%) phages. For other main cyanobacterial genera, no related cyanophages were identified, which was probably due to the scarce representation of cyanophage sequences in databanks. Thus, the studied reservoir hosted a diverse cyanophage community with a remarkable contribution of phages related to picoplanktonic cyanobacteria. These results provide insights that motivate future sequencing efforts to assess cyanophage diversity and recover complete genomes.

Examining the Evidence for Regulated and Programmed Cell Death in Cyanobacteria. How Significant Are Different Forms of Cell Death in Cyanobacteria Population Dynamics?

Cyanobacteria are ancient and versatile members of almost all aquatic food webs. In freshwater ecosystems some cyanobacteria form “bloom” populations containing potent toxins and such blooms are therefore a key focus of study. Bloom populations can be ephemeral, with rapid population declines possible, though the factors causing such declines are generally poorly understood. Cell death could be a significant factor linked to population decline. Broadly, three forms of cell death are currently recognized – accidental, regulated and programmed – and efforts are underway to identify these and standardize the use of cell death terminology, guided by work on better-studied cells. For cyanobacteria, the study of such differing forms of cell death has received little attention, and classifying cell death across the group, and within complex natural populations, is therefore hard and experimentally difficult. The population dynamics of photosynthetic microbes have, in the past, been principally explained through reference to abiotic (“bottom-up”) factors. However, it has become clearer that in general, only a partial linkage exists between abiotic conditions and cyanobacteria population fluctuations in many situations. Instead, a range of biotic interactions both within and between cyanobacteria, and their competitors, pathogens and consumers, can be seen as the major drivers of the observed population fluctuations. Whilst some evolutionary processes may theoretically account for the existence of an intrinsic form of cell death in cyanobacteria, a range of biotic interactions are also likely to frequently cause the ecological incidence of cell death. New theoretical models and single-cell techniques are being developed to illuminate this area. The importance of such work is underlined by both (a) predictions of increasing cyanobacteria dominance due to anthropogenic factors and (b) the realization that influential ecosystem modeling work includes mortality terms with scant foundation, even though such terms can have a very large impact on model predictions. These ideas are explored and a prioritization of research needs is proposed.

Functions of mineral-solubilizing microbes and a water retaining agent for the remediation of abandoned mine sites

There has been a rapid increase in abandoned mines across China, Consequently, external-soil spray seeding technologies have emerged as a common method for their remediation. However, slope soils are typically unstable and easily collapsed and the nutrients absorbed by plants are insufficient, which complicate ecological restoration. For this study, we added mineral-solubilizing microbes and a water retaining agent to an external-soil spray seeding substrate in Lespedeza bicolor pots. We investigated the soil nutrients, soil enzyme activities, root growth parameters, root tensile properties, and root-reinforced soil shear strengths. The results revealed that the addition of microbes enhanced soil nutrients, soil enzyme activities, and the content of lignin and hemicellulose, which promoted root growth. Further, the addition of a water retaining agent promoted Lespedeza bicolor root growth but decreased the root tensile strength and force. Shear stress under the microbe treatment was more robust than without it. Finally, root growth was correlated with soil nutrients and enzyme activities, whereas the root tensile force and strength were correlated with lignin and cellulose. Our results suggested that the addition of mineral-solubilizing microbes had the capacity to enhance the quality of soils to facilitate the growth of plants. These results provide a new and viable strategy for the ecological restoration of abandon mine sites.

Effects of Mineral-Solubilizing Microorganisms on Root Growth, Soil Nutrient Content, and Enzyme Activities in the Rhizosphere Soil of Robinia pseudoacacia

Background: Abandoned mining sites are becoming increasingly common due to anthropogenic activities. Consequently, external-soil spray seeding technology has attracted increasing attention as a strategy to remediate them. However, significant challenges remain that greatly inhibit the efficacy of such technologies, such as insufficient nutrients available for plants. Methods: For this study, we designed an experiment, which involved the addition of mineral-solubilizing microorganisms and R. pseudoacacia seedlings to the external-soil spray seeding (ESSS) substrate, and measured the soil nutrients, enzyme activities, and root growth of R. pseudoacacia. Results: First, the combination of certain mineral-solubilizing microorganisms with ESSS advanced its efficiency by increasing the availability of soil nutrients and soil enzymatic activities in association with R. pseudoacacia. Furthermore, the improvement of root growth of R. pseudoacacia was intimately related to soil nutrients, particularly for soil total nitrogen (TN) and total sulfur (TS). In general, the effects of the J2 (combined Bacillus thuringiensis and Gongronella butleri) treatment for soil nutrients, enzyme activities, and plant growth were the strongest. Conclusion: In summary, the results of our experiment revealed that these mineral-solubilizing microorganisms conveyed a promotional effect on R. pseudoacacia seedlings by increasing the soil nutrient content. These results provide basic data and microbial resources for the development and applications of mineral-solubilizing microorganisms for abandoned mine remediation.

Moroccan actinobacteria with promising activity against toxic cyanobacteria Microcystis aeruginosa

In recent decades, harmful cyanobacterial blooms (HCBs) have become a severe hazard for human health mainly in drinking water resources and are responsible for serious ecological disturbances in freshwater ecosystems. The present study aims to explore the potential of actinobacteria isolated from sediment samples collected from Moroccan salt river to control HCBs mainly through Microcystis aeruginosa lysis. In order to investigate the possible anti-cyanobacterial response mechanisms, the antioxidant enzyme activities of M. aeruginosa cells were analysed. Anti-cyanobacterial activity was tested using the agar cylinder method against the toxic cyanobacteria Microcystis aeruginosa. Amongst the twenty-three isolates tested, only one showed promising anti-cyanobacterial activities with inhibition zone (ZI) equal to 22.00 mm, minimum inhibitory concentration (MIC) equal to 19.53 mg/L and minimum bactericidal concentration MBC equal to 39.06 mg/L. Phylogenetic analysis of the near-complete 16S rRNA gene sequence indicated that the strain DS1R1 belongs to the genus Streptomyces and has the highest similarity (100%) to Streptomyces sp. Indeed, M. aeruginosa growth, chlorophyll-a and protein content were significantly reduced by Streptomyces sp. DS1R1 extract. Superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA) were significantly elevated after treatment with Streptomyces sp. DS1R1 extract. These experimental findings provided insights in the development of a new eco-friendly procedure based on the use of actinobacteria for toxic cyanobacterial bloom bio-control.

Diversity Assessment of Toxic Cyanobacterial Blooms during Oxidation

Fresh-water sources of drinking water are experiencing toxic cyanobacterial blooms more frequently. Chemical oxidation is a common approach to treat cyanobacteria and their toxins. This study systematically investigates the bacterial/cyanobacterial community following chemical oxidation (Cl₂, KMnO₄, O₃, H₂O₂) using high throughput sequencing. Raw water results from high throughput sequencing show that Proteobacteria, Actinobacteria, Cyanobacteria and Bacteroidetes were the most abundant phyla. Dolichospermum, Synechococcus, Microcystis and Nostoc were the most dominant genera. In terms of species, Dolichospermum sp.90 and Microcystis aeruginosa were the most abundant species at the beginning and end of the sampling, respectively. A comparison between the results of high throughput sequencing and taxonomic cell counts highlighted the robustness of high throughput sequencing to thoroughly reveal a wide diversity of bacterial and cyanobacterial communities. Principal component analysis of the oxidation samples results showed a progressive shift in the composition of bacterial/cyanobacterial communities following soft-chlorination with increasing common exposure units (CTs) (0–3.8 mg·min/L). Close cyanobacterial community composition (Dolichospermum dominant genus) was observed following low chlorine and mid-KMnO₄ (287.7 mg·min/L) exposure. Our results showed that some toxin producing species may persist after oxidation whether they were dominant species or not. Relative persistence of Dolichospermum sp.90 was observed following soft-chlorination (0.2–0.6 mg/L) and permanganate (5 mg/L) oxidation with increasing oxidant exposure. Pre-oxidation using H₂O₂ (10 mg/L and one day contact time) caused a clear decrease in the relative abundance of all the taxa and some species including the toxin producing taxa. These observations suggest selectivity of H₂O₂ to provide an efficient barrier against toxin producing cyanobacteria entering a water treatment plant.

Disentangling the drivers of Microcystis decomposition: Metabolic profile and co-occurrence of bacterial community

In aquatic ecosystems, water microbial communities can trigger the outbreak or decline of cyanobacterial blooms. However, the microbiological drivers of Microcystis decomposition in reservoirs remain unclear. Here, we explored the bacterial community metabolic profile and co-occurrence dynamics during Microcystis decomposition. The results showed that the decomposition of Microcystis greatly altered the metabolic characteristics and composition of the water bacterial community. Significant variations in bacterial community composition were observed: the bacterial community was mainly dominated by Proteobacteria, Actinobacteria, Planctomycetes, and Bacteroidetes during Microcystis decomposition. Additionally, members of Exiguobacterium, Rhodobacter, and Stenotrophomonas significantly increased during the terminal stages. Dissolved organic matters (DOM) primarily composed of fulvic-like, humic acid-like, and tryptophan-like components, which varied distinctly during Microcystis decomposition. Additionally, the metabolic activity of the bacterial community showed a continuous decrease during Microcystis decomposition. Functional prediction showed a sharp increase in the cell communication and sensory systems of the bacterial communities from day 12 to day 22. Co-occurrence networks showed that bacteria responded significantly to variations in the dynamics of Microcystis decomposition through close interactions between each other. Redundancy analysis (RDA) indicated that Chlorophyll a, nitrate nitrogen (NO₃^--N), dissolved oxygen (DO), and dissolved organic carbon (DOC) were crucial drivers for shaping the bacterial community structure. Taken together, these findings highlight the dynamics of the water bacterial community during Microcystis decomposition from the perspective of metabolism and community composition, however, further studies are needed to understand the algal degradation process associated with bacteria.

Growth inhibition of Microcystis aeruginosa and adsorption of microcystin toxin by the yeast Aureobasidium pullulans, with no effect on microalgae

This study evaluates the inhibitory effect of a yeast strain, Aureobasidium pullulans KKUY0701, isolated from decayed cyanobacterial bloom against harmful cyanobacterium Microcystis aeruginosa and determines the ability of this strain to remove microcystin (MC) toxin from the water. The antialgal activity of this yeast strain was assayed by co-cultivation with M. aeruginosa, diatom, and green algal species. The MC adsorption experiment was conducted in the presence of living and heat-inactivated yeast cells. Both yeast cells and filtrates caused a rapid reduction in the growth of M. aeruginosa, with complete death and cell lysis occurring after 3 days. The yeast strain did not exhibit any inhibitory effect on either green algae or diatoms. Both living and heat-inactivated yeast cells were capable of adsorption of MC on their surfaces. Inactivated yeast exhibited higher adsorption capacity and lower intensity than living yeast for the adsorption of MC toxin. The results of this study suggest that this yeast strain could be employed to selectively reduce cyanobacterial blooms in freshwaters. Moreover, the application of heat-inactivated yeast's biomass for toxin adsorption gives new possibilities in drinking water treatment plants.

Exploring microcystin-degrading bacteria thriving on recycled membranes during a cyanobacterial bloom

Microcystins (MC) are highly toxic secondary metabolites produced by cyanobacterial blooms in many freshwater ecosystems used for recreational and drinking water purposes. So far, biological processes remain to be optimized for an efficient cyanotoxin removal, and new approaches are necessary to compete with physical-chemical treatments. In previous studies we provided a new concept of membrane biofilm reactor made of recycled material, in which a single MC-degrading bacterial strain was inoculated. The present study evaluates the capacity of bacterial consortia associated with freshwater cyanobacterial blooms to form biofilms on recycled membranes and remove MC. Three different discarded reverse osmosis (RO) membranes, previously used in desalination plants after treating brackish water (BWd), seawater (SWd) and brackish water but transformed into nanofiltration (BWt-NF), were exposed to a cyanobacterial bloom in San Juan reservoir (central Spain). Results showed that the three recycled membranes developed a bacterial community with MC removal capacity. Little differences in bacterial coverage and MC removal efficiency between membranes were observed after their exposure in the reservoir. High-throughput sequencing of 16S rRNA gene analysis showed similar bacterial community composition at the phylum level but dissimilar at the order level between the three membranes. This suggests possible surface selectivity on the attached bacterial community. The mlr^- candidates such as Burkholderiales and Methylophilales were highly abundant in BWt-NF and BWd, respectively, while mlr⁺ candidates (e.g. Sphingomonadales) were low abundant in all membranes. Analysis of mlrA and mlrB genes used as markers for MC degradation following mlr-pathway confirmed the presence of this pathway in all membranes. These results suggest the co-existence of both genotypes in membrane-attached native biofilms. Therefore, this study confirms that recycled membranes are suitable support for many MC-degrading bacteria, thus giving value to discarded membranes for eco-friendly and low-cost biological filters.

Seaweed Essential Oils as a New Source of Bioactive Compounds for Cyanobacteria Growth Control: Innovative Ecological Biocontrol Approach

The application of natural compounds extracted from seaweeds is a promising eco-friendly alternative solution for harmful algae control in aquatic ecosystems. In the present study, the anti-cyanobacterial activity of three Moroccan marine macroalgae essential oils (EOs) was tested and evaluated on unicellular Microcystis aeruginosa cyanobacterium. Additionally, the possible anti-cyanobacterial response mechanisms were investigated by analyzing the antioxidant enzyme activities of M. aeruginosa cells. The results of EOs GC-MS analyses revealed a complex chemical composition, allowing the identification of 91 constituents. Palmitic acid, palmitoleic acid, and eicosapentaenoic acid were the most predominant compounds in Cystoseira tamariscifolia, Sargassum muticum, and Ulva lactuca EOs, respectively. The highest anti-cyanobacterial activity was recorded for Cystoseira tamariscifolia EO (ZI = 46.33 mm, MIC = 7.81 μg mL-1, and MBC = 15.62 μg mL-1). The growth, chlorophyll-a and protein content of the tested cyanobacteria were significantly reduced by C. tamariscifolia EO at both used concentrations (inhibition rate >67% during the 6 days test period in liquid media). Furthermore, oxidative stress caused by C. tamariscifolia EO on cyanobacterium cells showed an increase of the activities of superoxide dismutase (SOD) and catalase (CAT), and malondialdehyde (MDA) concentration was significantly elevated after 2 days of exposure. Overall, these experimental findings can open a promising new natural pathway based on the use of seaweed essential oils to the fight against potent toxic harmful cyanobacterial blooms (HCBs).

Harmful Cyanobacterial Blooms (HCBs): innovative green bioremediation process based on anti-cyanobacteria bioactive natural products

Over the last decades, Harmful Cyanobacterial Blooms (HCBs) represent one of the most conspicuous hazards to human health in freshwater ecosystems, due to the uses of the water for drinking, recreation and aquaculture. Cyanobacteria are one of the main biological components in freshwater ecosystems and they may proliferate in nutrients rich ecosystems causing severe impacts at different levels. Therefore, several methods have been applied to control cyanobacterial proliferation, including physical, chemical and biological strategies. However, the application of those methods is generally not very efficient. Research on an eco-friendly alternative leading to the isolation of new bioactive compounds with strong impacts against harmful cyanobacteria is a need in the field of water environment protection. Thus, this paper aims to give an overview of harmful cyanobacterial blooms and reviews the state of the art of studying the activities of biological compounds obtained from plants, seaweeds and microorganisms in the cyanobacterial bloom control.

Cyanobacterial Abundance and Microcystin Profiles in Two Southern British Lakes: The Importance of Abiotic and Biotic Interactions

Freshwater cyanobacteria blooms represent a risk to ecological and human health through induction of anoxia and release of potent toxins; both conditions require water management to mitigate risks. Many cyanobacteria taxa may produce microcystins, a group of toxic cyclic heptapeptides. Understanding the relationships between the abiotic drivers of microcystins and their occurrence would assist in the implementation of targeted, cost-effective solutions to maintain safe drinking and recreational waters. Cyanobacteria and microcystins were measured by flow cytometry and liquid chromatography coupled to tandem mass spectrometry in two interconnected reservoirs varying in age and management regimes, in southern Britain over a 12-month period. Microcystins were detected in both reservoirs, with significantly higher concentrations in the southern lake (maximum concentration >7 µg L^-1). Elevated microcystin concentrations were not positively correlated with numbers of cyanobacterial cells, but multiple linear regression analysis suggested temperature and dissolved oxygen explained a significant amount of the variability in microcystin across both reservoirs. The presence of a managed fishery in one lake was associated with decreased microcystin levels, suggestive of top down control on cyanobacterial populations. This study supports the need to develop inclusive, multifactor holistic water management strategies to control cyanobacterial risks in freshwater bodies.

Selective Inhibition on Growth and Photosynthesis of Harmful Cyanobacteria (Microcystis aeruginosa) by Water Soluble Substances of Dendranthema indicum Flowers

Harmful cyanobacterial blooms become serious environmental issues in various waterbodies, including aquaculture ponds, which inherently need a high biomass and healthy composition of phytoplankton to sustain their high productivity. Indoor bioassays were conducted to investigate the effects of an aqueous extract of Dendranthema indicum flowers on cyanobacteria and green algae species. The thermal stability and polarity of the water-soluble active substances of D. indicum flowers were also assessed based on the growth and photosynthesis responses of Microcystis aeruginosa. There was obvious growth promotion of green algae, including Chlorella vulgaris, Kirchneriella sp. and Haematococcus pluvialis and strong growth inhibition of toxigenic and non-toxigenic M. aeruginosa by aqueous extracts of D. indicum flowers at concentrations ranging from 0.5 to 2.0 g·DW·L−1. The cell concentrations of M. aeruginosa and C. vulgaris were 46.5% and 242.2% of those in the corresponding controls after a 10-day exposure to aqueous extracts of D. indicum flowers at 1.0 g·DW·L−1. There must be some water-soluble active allelochemicals released from D. indicum flowers that are responsible for the selective inhibition of M. aeruginosa rather than green algae. The inhibition ratio of the growth and photosynthesis of M. aeruginosa by aqueous extracts of D. indicum flowers at 2.0 g·DW·L−1 prepared with water at 25 °C and 100 °C were above 90% and 80% compared to the cell density and performance index on absorption basis (PIABS) value of M. aeruginosa in the control on day 6, without significant differences. It indicates that the active substances of D. indicum flowers were thermally stable. The methanol fraction eluted from solid phase extraction (SPE)-enriched aqueous extracts of D. indicum flowers showed the strongest inhibition of the growth and photosynthesis of M. aeruginosa compared to the other four fractions. It indicates that the most polar substances of D. indicum flowers were responsible for the selective inhibition of M. aeruginosa. More experiments are required to identify the responsible active substances and reveal the underlying mechanisms of aqueous extracts of D. indicum flowers that selectively inhibit cyanobacteria and regulate the phytoplankton community structure.

Effects of mineral-solubilizing microbial strains on the mechanical responses of roots and root-reinforced soil in external-soil spray seeding substrate

There are a large number of abandoned mining areas in China, where external-soil spray seeding is a common technique used to assist with the restoration of these areas. However, the soil component of external-soil spray seeding is deficient, and they are prone to collapse, which complicates ecological restoration. In this study, we added a mineral-solubilizing microbial strain to an external-soil spray seeding substrate in Robinia pseudoacacia and Lespedeza bicolor pots, which were monitored from December 2018 to November 2019. We investigated their root growth and root tensile properties, as well as root-reinforced soil shear strength. The results revealed that the addition of the microbial strain in the substrate improved root growth of Robinia pseudoacacia. The root-reinforced soil shear strength, tensile force and strength were also strengthened by the added microbial strain. Although the growth rate of Robinia pseudoacacia was faster than that of Lespedeza bicolor, the shear strength of the root-reinforced Robinia pseudoacacia soil was lower than that of the Lespedeza bicolor root-reinforced soil of the same diameter. Finally, compared with the cohesion, the change in the friction angle is relatively small, and differences in cohesion resulted in shear strength changes under the same treatment. Our results suggested that the addition of a mineral-solubilizing microbial strain to the external-soil spray seeding substrate could help plants strengthen the soil and positively enhance its effects. These results might also enrich the existing data on the effects of mineral-solubilizing microbial strains on plant roots, while guiding further studies toward improving the efficacy of external-soil spray seeding technologies.

The Composition and Function of Microbiomes Within Microcystis Colonies Are Significantly Different Than Native Bacterial Assemblages in Two North American Lakes

The toxic cyanobacterium Microcystis is one of the most pervasive harmful algal bloom (HAB) genera and naturally occurs in large colonies known to harbor diverse heterotrophic bacterial assemblages. While colony-associated microbiomes may influence Microcystis blooms, there remains a limited understanding of the structure and functional potential of these communities and how they may be shaped by changing environmental conditions. To address this gap, we compared the dynamics of Microcystis-attached (MCA), free-living (FL), and whole water (W) microbiomes during Microcystis blooms using next-generation amplicon sequencing (16S rRNA), a predictive metagenome software, and other bioinformatic approaches. Microbiomes were monitored through high resolution spatial-temporal surveys across two North American lakes, Lake Erie (LE) and Lake Agawam (LA; Long Island, NY, United States) in 2017, providing the largest dataset of these fractions to date. Sequencing of 126 samples generated 7,922,628 sequences that clustered into 7,447 amplicon sequence variants (ASVs) with 100% sequence identity. Across lakes, the MCA microbiomes were significantly different than the FL and W fractions being significantly enriched in Gemmatimonadetes, Burkholderiaceae, Rhizobiales, and Cytophagales and depleted of Actinobacteria. Further, although MCA communities harbored > 900 unique ASVs, they were significantly less diverse than the other fractions with diversity inversely related to bloom intensity, suggesting increased selection pressure on microbial communities as blooms intensified. Despite taxonomic differences between lakes, predicted metagenomes revealed conserved functional potential among MCA microbiomes. MCA communities were significantly enriched in pathways involved in N and P cycling and microcystin-degradation. Taxa potentially capable of N2-fixation were significantly enriched (p < 0.05) and up to four-fold more abundant within the MCA faction relative to other fractions, potentially aiding in the proliferation of Microcystis blooms during low N conditions. The MCA predicted metagenomes were conserved over 8 months of seasonal changes in temperature and N availability despite strong temporal succession in microbiome composition. Collectively, these findings indicate that Microcystis colonies harbor a statistically distinct microbiome with a conserved functional potential that may help facilitate bloom persistence under environmentally unfavorable conditions.

Connections and Feedback: Aquatic, Plant, and Soil Microbiomes in Heterogeneous and Changing Environments

Plant, soil, and aquatic microbiomes interact, but scientists often study them independently. Integrating knowledge across these traditionally separate subdisciplines will generate better understanding of microbial ecological properties. Interactions among plant, soil, and aquatic microbiomes, as well as anthropogenic factors, influence important ecosystem processes, including greenhouse gas fluxes, crop production, nonnative species control, and nutrient flux from terrestrial to aquatic habitats. Terrestrial microbiomes influence nutrient retention and particle movement, thereby influencing the composition and functioning of aquatic microbiomes, which, themselves, govern water quality, and the potential for harmful algal blooms. Understanding how microbiomes drive links among terrestrial (plant and soil) and aquatic habitats will inform management decisions influencing ecosystem services. In the present article, we synthesize knowledge of microbiomes from traditionally disparate fields and how they mediate connections across physically separated systems. We identify knowledge gaps currently limiting our abilities to actualize microbiome management approaches for addressing environmental problems and optimize ecosystem services.

Increased algicidal activity of Aeromonas veronii in response to Microcystis aeruginosa: interspecies crosstalk and secondary metabolites synergism

Toxic Microcystis spp. blooms constitute a serious threat to water quality worldwide. Aeromonas veronii was isolated from Microcystis sp. colonies collected in Lake Kinneret. Spent Aeromonas media inhibits the growth of Microcystis aeruginosa MGK isolated from Lake Kinneret. The inhibition was much stronger when Aeromonas growth medium contained spent media from MGK suggesting that Aeromonas recognized its presence and produced secondary metabolites that inhibit Microcystis growth. Fractionations of the crude extract and analyses of the active fractions identified several secondary metabolites including lumichrome in Aeromonas media. Application of lumichrome at concentrations as low as 4 nM severely inhibited Microcystis growth. Inactivation of aviH in the lumichrome biosynthetic pathway altered the lumichrome level in Aeromonas and the extent of MGK growth inhibition. Conversely, the initial lag in Aeromonas growth was significantly longer when provided with Microcystis spent media but Aeromonas was able to resume normal growth. The longer was pre-exposure to Microcystis spent media the shorter was the lag phase in Aeromonas growth indicating the presence of, and acclimation to, secondary MGK metabolite(s) the nature of which was not revealed. Our study may help to control toxic Microcystis blooms taking advantage of chemical languages used in the interspecies communication.