Identification and characterization of a novel indigenous algicidal bacterium Chryseobacterium species against Microcystis aeruginosa

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.

Spatio-temporal connectivity of a toxic cyanobacterial community and its associated microbiome along a freshwater-marine continuum

Due to climate changes and eutrophication, blooms of predominantly toxic freshwater cyanobacteria are intensifying and are likely to colonize estuaries, thus impacting benthic organisms and shellfish farming representing a major ecological, health and economic risk. In the natural environment, Microcystis form large mucilaginous colonies that influence the development of both cyanobacterial and embedded bacterial communities. However, little is known about the fate of natural colonies of Microcystis by salinity increase. In this study, we monitored the fate of a Microcystis dominated bloom and its microbiome along a French freshwater-marine gradient at different phases of a bloom. We demonstrated changes in the cyanobacterial genotypic composition, in the production of specific metabolites (toxins and compatible solutes) and in the heterotrophic bacteria structure in response to the salinity increase. In particular M. aeruginosa and M. wesenbergii survived salinities up to 20. Based on microcystin gene abundance, the cyanobacteria became more toxic during their estuarine transfer but with no selection of specific microcystin variants. An increase in compatible solutes occurred along the continuum with extensive trehalose and betaine accumulations. Salinity structured most the heterotrophic bacteria community, with an increased in the richness and diversity along the continuum. A core microbiome in the mucilage-associated attached fraction was highly abundant suggesting a strong interaction between Microcystis and its microbiome and a likely protecting role of the mucilage against an osmotic shock. These results underline the need to better determine the interactions between the Microcystis colonies and their microbiome as a likely key to their widespread success and adaptation to various environmental conditions.

Acetylacetone effectively controlled the secondary metabolites of Microcystis aeruginosa under simulated sunlight irradiation

Inactivation of cyanobacterial cells and simultaneous control of secondary metabolites is of significant necessity for the treatment of cyanobacteria-laden water. Acetylacetone (AcAc) has been reported a specific algicide to inactivate Microcystis aeruginosa (M. aeruginosa) and an effective light activator to degrade pollutants. This study systematically investigated the photodegradation ability of AcAc under xenon (Xe) irradiation on the secondary metabolites of M. aeruginosa, mainly algal organic matter (AOM), especially toxic microcystin-LR (MC-LR). Results showed that AcAc outperformed H2O2 in destructing the protein-like substances, humic acid-like matters, aromatic proteins and fulvic-like substances of AOM. For MC-LR (250 µg/L), 0.05 mmol/L AcAc attained the same degradation efficiency (87.0%) as 0.1 mmol/L H2O2. The degradation mechanism of Xe/AcAc might involve photo-induced energy/electron transfer and formation of carbon center radicals. Alkaline conditions (pH > 9.0) were detrimental to the photoactivity of AcAc, corresponding to the observed degradation rate constant (k1 value) of MC-LR drastically decreasing to 0.0013 min-1 as solution pH exceeded 9.0. The PO43- and HCO3- ions had obvious inhibition effects, whereas NO3- slightly improved k1 value from 0.0277 min-1 to 0.0321 min-1. The presence of AOM did not significantly inhibit MC-LR degradation in Xe/AcAc system. In addition, the biological toxicity of MC-LR was greatly reduced after photoreaction. These results demonstrated that AcAc was an alternative algicidal agent to effectively inactivate algal cells and simultaneously control the secondary metabolites after cell lysis. Nevertheless, the concentration and irradiation conditions should be further optimized in practical application.

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.

Impacts of a bacterial algicide on metabolic pathways in Chlorella vulgaris

Chlorella is a dominant species during harmful algal blooms (HABs) worldwide, which bring about great environmental problems and are also a serious threat to drinking water safety. Application of bacterial algicides is a promising way to control HABs. However, the identified bacterial algicides against Chlorella and the understanding of their effects on algal metabolism are very limited. Here, we isolated a novel bacterium Microbacterium paraoxydans strain M1 that has significant algicidal activities against Chlorella vulgaris (algicidal rate 64.38 %, at 120 h). Atrazine-desethyl (AD) was then identified from strain M1 as an effective bacterial algicide, with inhibition or algae-lysing concentration values (EC50) of 1.64 μg/mL and 1.38 μg/mL, at 72 h and 120 h, respectively. LAD (2 μg/mL AD) or HAD (20 μg/mL AD) causes morphology alteration and ultrastructure damage, chlorophyll a reduction, gene expression regulation (for example, psbA, 0.05 fold at 24 h, 2.97 fold at 72 h, and 0.23 fold of the control in HAD), oxidative stress, lipid oxidation (MDA, 2.09 and 3.08 fold of the control in LAD and HAD, respectively, at 120 h) and DNA damage (average percentage of tail DNA 6.23 % at 120 h in HAD, slight damage: 5∼20 %) in the algal cells. The impacts of AD on algal metabolites and metabolic pathways, as well as the algal response to the adverse effects were investigated. The results revealed that amino acids, amines, glycosides and urea decreased significantly compared to the control after 24 h exposure to AD (p < 0.05). The main up-regulated metabolic pathways implied metabonomic resistance and defense against osmotic pressure, oxidative stress, photosynthesis inhibition or partial cellular structure damage, such as phenylalanine metabolism, arginine biosynthesis. The down-regulated glycine, serine and threonine metabolism is a major lead in the algicidal mechanism according to the value of pathway impact. The down-regulated glycine, and serine are responsible for the downregulation of glyoxylate and dicarboxylate metabolism, aminoacyl-tRNA biosynthesis, glutathione metabolism, and sulfur metabolism, which strengthen the algae-lysing effect. It is the first time to highlight the pivotal role of glycine, serine and threonine metabolism in algicidal activities, which provided a new perspective for understanding the mechanism of bacterial algicides exerting on algal cells at the metabolic level.

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.

Algicide capacity of Paucibacter aquatile DH15 on Microcystis aeruginosa by attachment and non-attachment effects

The excessive proliferation of Microcystis aeruginosa can lead to ecological damage, economic losses, and threaten animal and human health. For controlling Microcystis blooms, microorganism-based methods have attracted much attention from researchers because of their eco-friendliness and species-specificity. Herein, we first found that a Paucibacter strain exhibits algicidal activity against M. aeruginosa and microcystin degradation capability. The algicidal activity of DH15 (2.1 × 10⁴ CFU/ml) against M. aeruginosa (2 × 10⁶ cells/ml) was 94.9% within 36 h of exposure. DH15 also degraded microcystin (1.6 mg/L) up to 62.5% after 72 h. We demonstrated that the algicidal activity of DH15 against M. aeruginosa can be mediated by physical attachment and indirect attack: (1) Both washed cells and cell-free supernatant could kill M. aeruginosa efficiently; (2) Treatment with DH15 cell-free supernatants caused oxidative stress, altered the fatty acid profile, and damaged photosynthetic system, carbohydrate, and protein metabolism in M. aeruginosa. The combination of direct and indirect attacks supported that strain DH15 exerts high algicidal activity against M. aeruginosa. The expression of most key genes responsible for photosynthesis, antioxidant activity, microcystin synthesis, and other metabolic pathways in M. aeruginosa was downregulated. Strain DH15, with its microcystin degradation capacity, can overcome the trade-off between controlling Microcystis blooms and increasing microcystin concentration. Our findings suggest that strain DH15 possesses great potential to control outbreaks of Microcystis blooms.

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.

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

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

Transcriptional Analysis of Microcystis aeruginosa Co-Cultured with Algicidal Bacteria Brevibacillus laterosporus

Harmful algal blooms caused huge ecological damage and economic losses around the world. Controlling algal blooms by algicidal bacteria is expected to be an effective biological control method. The current study investigated the molecular mechanism of harmful cyanobacteria disrupted by algicidal bacteria. Microcystis aeruginosa was co-cultured with Brevibacillus laterosporus Bl-zj, and RNA-seq based transcriptomic analysis was performed compared to M. aeruginosa, which was cultivated separately. A total of 1706 differentially expressed genes were identified, which were mainly involved in carbohydrate metabolism, energy metabolism and amino acid metabolism. In the co-cultured group, the expression of genes mainly enriched in photosynthesis and oxidative phosphorylation were significantly inhibited. However, the expression of the genes related to fatty acid synthesis increased. In addition, the expression of the antioxidant enzymes, such as 2-Cys peroxiredoxin, was increased. These results suggested that B. laterosporus could block the electron transport by attacking the PSI system and complex I of M. aeruginosa, affecting the energy acquisition and causing oxidative damage. This further led to the lipid peroxidation of the microalgal cell membrane, resulting in algal death. The transcriptional analysis of algicidal bacteria in the interaction process can be combined to explain the algicidal mechanism in the future.

Molecular detection of some toxogenic cyanobacteria in Tigris River in Baghdad-Iraq

Cyanobacteria and their pollution are being increasingly commonly reported worldwide that cause a serious hazard to environmental and human health. Cyanotoxin was the most algal toxin reported to be produced by several orders of cyanobacteria. This study aimed to provide a technique to detect cylindrosprmopsin and saxitoxin biosynthesis genes in the river. In November, December 2019, and January 2020. Cyanobacteria were isolated from freshwater of Tigris River and identified by compound microscope also conventional PCR. Five isolates of cyanobacteria that successfully amplified a gene fragment from the phycocyanin were found in all cyanobacteria (Microcystis flosaquae, Microcystis sp, anabaena circinalis, nostoc commune and westiellopsis prolifica) and all isolates successfully amplified aoaC gene to detecting the cylidrospemopsin and the saxitoxin. Our results concluded that PCR assay can be used for early detection of cylidrospemopsin and the saxitoxin producing cyanobacteria in river water that useful to stations responsible for the preparation of drinking water to public.

All-Dielectric Metasurface for Sensing Microcystin-LR

Sensing Microcystin-LR (MC-LR) is an important issue for environmental monitoring, as the MC-LR is a common toxic pollutant found in freshwater bodies. The demand for sensitive detection method of MC-LR at low concentrations can be addressed by metasurface-based sensors, which are feasible and highly efficient. Here, we demonstrate an all-dielectric metasurface for sensing MC-LR. Its working principle is based on quasi-bound states in the continuum mode (QBIC), and it manifests a high-quality factor and high sensitivity. The dielectric metasurface can detect a small change in the refractive index of the surrounding environment with a quality factor of ~170 and a sensitivity of ~788 nm/RIU. MC-LR can be specifically identified in mixed water with a concentration limit of as low as 0.002 μg/L by a specific recognition technique for combined antigen and antibody. Furthermore, the demonstrated detection of MC-LR can be extended to the identification and monitoring of other analytes, such as viruses, and the designed dielectric metasurface can serve as a monitor platform with high sensitivity and high specific recognition capability.

Nitrogen Fertilization. A Review of the Risks Associated with the Inefficiency of Its Use and Policy Responses

Nitrogen (N) is a key input to food production. Nearly half of N fertilizer input is not used by crops and is lost into the environment via emission of gases or by polluting water bodies. It is essential to achieve production levels, which enable global food security, without compromising environmental security. The N pollution level expected by 2050 is projected to be 150% higher than in 2010, with the agricultural sector accounting for 60% of this increase. In this paper, we review the status of the pollution from N fertilizers worldwide and make recommendations to address the situation. The analysis reviews the relationship between N fertilizer use, N use efficiency, no-point pollution, the role of farmer management practices, and policy approaches to address diffuse pollution caused by N fertilization. Several studies show a lack of information as one of the main hurdles to achieve changes in habits. The objective of this study is to highlight the gravity of the current global non-point pollution as well as the need for a communication effort to make farmers aware of the relationship between their activity and N pollution and, therefore, the importance of their fertilizer management practices.

A Mini-Review on Detection Methods of Microcystins

Cyanobacterial harmful algal blooms (CyanoHABs) produce microcystins (MCs) which are associated with animal and human hepatotoxicity. Over 270 variants of MC exist. MCs have been continually studied due of their toxic consequences. Monitoring water quality to assess the presence of MCs is of utmost importance although it is often difficult because CyanoHABs may generate multiple MC variants, and their low concentration in water. To effectively manage and control these toxins and prevent their health risks, sensitive, fast, and reliable methods capable of detecting MCs are required. This paper aims to review the three main analytical methods used to detect MCs ranging from biological (mouse bioassay), biochemical (protein phosphatase inhibition assay and enzyme linked immunosorbent assay), and chemical (high performance liquid chromatography, liquid chromatography-mass spectrometry, high performance capillary electrophoresis, and gas chromatography), as well as the newly emerging biosensor methods. In addition, the current state of these methods regarding their novel development and usage, as well as merits and limitations are presented. Finally, this paper also provides recommendations and future research directions towards method application and improvement.

A Mini Review on Microcystins and Bacterial Degradation

Microcystins (MCs) classified as hepatotoxic and carcinogenic are the most commonly reported cyanobacterial toxins found in the environment. Microcystis sp. possessing a series of MC synthesis genes (mcyA-mcyJ) are well documented for their excessive abundance, numerous bloom occurrences and MC producing capacity. About 246 variants of MC which exert severe animal and human health hazards through the inhibition of protein phosphatases (PP1 and PP2A) have been characterized. To minimize and prevent MC health consequences, the World Health Organization proposed 1 µg/L MC guidelines for safe drinking water quality. Further the utilization of bacteria that represent a promising biological treatment approach to degrade and remove MC from water bodies without harming the environment has gained global attention. Thus the present review described toxic effects and bacterial degradation of MCs.

Identification and characterization of the dominant Microcystis sp. cyanobacteria detected in Lake Dong Ting, China

The presence of cyanobacteria in drinking water, aquatic foods and bathing water has created a significant major problem to global public health as these toxins induce damage in various organ including liver, cardiovascular, intestinal and central nervous systems. Although the morphologic, phylogenetic and toxicogenetic characteristics of cyanobacteria were identified in several lakes in China, many freshwater sources such as Dong Ting Lake, Hunan Province, China remain to be determined. Since the presence of these cyanobacteria may potentially affect human health, the aim of this study was to isolate, identify and characterize the most frequent occurring bloom-forming cyanobacteria in Dong Ting Lake, Hunan Province, China, which can provide information on the safety of utilization of this water source for drinking water, agriculture and recreation. Samples collected from the surface water of Dong Ting Lake were subjected to serial dilution in the lab for morphological analysis. Data demonstrated the morphological features were 2-5 µm diameters with rounded shapes and green color resembling Microcystis sp. The isolated cyanobacterial strain obtained from surface water samples in Dong Ting Lake was termed Microcystis sp. YFM2. The MC concentration was detected by enzyme-linked immunosorbent assay (ELISA) and found to be 92.88 µg/10⁷ cells in Microcystis sp. YFM2. By polymerase chain reaction (PCR) results indicated that Microcystis sp. YFM2 isolated from Dong Ting Lake contained synthetase genes (mcyA-C). Our findings indicated that the dominant cyanobacteria Microcystis sp. YFM2 isolated from the freshwater Dong Ting Lake demonstrated morphologic, phylogenetic and toxicogenetic properties resembling a toxin generating cyanobacterium. Based upon this knowledge, it is essential to monitor the use of this Lake for future domestic, agricultural and recreational purposes.

Aromatic hydrocarbon compound degradation of phenylacetic acid by indigenous bacterial Sphingopyxis isolated from Lake Taihu

The aromatic compound phenylacetic acid (PAA) is present in the environment, and released in the catabolism of phenylalanine, 2-phenylethylamine, or environmental contaminants such as ethylbenzene and styrene. PAA was also proposed to be involved in human chronic kidney disease development. Several bacteria and fungi utilize these aromatic acids as sole carbon source either during aerobic or anaerobic conditions. The aromatic structure of PAA makes this compound resistant toward oxidation or reduction, because the stabilizing resonance energy of the aromatic ring system is difficult to overcome. In the case of bacteria that utilize aromatic compounds as growth substrates, the aromatic ring system limits survival due to a lack of carbon source. Sphingopyxis sp. YF1 isolated from Lake Taihu was found to be beneficial in bioremediation of aromatic compounds. This study thus aimed to examine the influence of environmental factors such as temperature, PAA concentration, and pH on the effectiveness of Sphingopyxis sp. YF1 to degrade aromatic compounds using PAA as model compound. Data showed the highest PAA-degrading rate of strain Sphingopyxis sp. YF1 was 7.6 mg/L·h under the condition of 20°C, pH 9 with a 1000 μg/ml concentration of PAA. Evidence indicates that PAA-degrading ability of strain Sphingopyxis sp. YF1 appears to be primarily influenced by the concentration of PAA, followed by temperature and pH. PAA-degrading gene PAAase was identified in this strain using polymerase chain reaction (PCR) method. These results illustrate that the bacteria Sphingopyxis sp. YF1 removes PAA effectively at certain environmental conditions and this proves beneficial in bioremediation of aromatic compounds.