Microcystis Species Research Articles

Double effects of mitigating cyanobacterial blooms using modified clay technology: regulation and optimization of the microbial community structure.

Harmful algal blooms (HABs) are global hazards under global climate change and eutrophication conditions. Modified clay (MC) method is widely used to control HABs in Asian and American coastal waters. However, little research has been conducted on the underlying mechanisms by which MC controls blooms in freshwater environments. Herein, experiments and bioinformatics analyses were conducted for MC-based control of freshwater blooms in a closed water body with an area of approximately 240 m2 in the Fuchun River, China. Results revealed that the dominant bloom species were Microcystis, and an 87.68-97.01% removal efficiency of whole algal biomass was achieved after 3 h of MC treatment. The weaker zeta potentials of Microcystis species and hydrophilic groups such as O-H and P-O-P in the extracellular polymeric substances (EPS) surrounding Microcystis cells made them easier to be flocculated and removed by MC particles, and the relative abundance of Microcystis decreased to 29.12% and that of Cyanobium increased to 40.97%. Therefore, MC changes the cyanobacterial community structure, which is accompanied by the elimination of Microcystis sp. apical dominance and enhanced competition between Cyanobium and Microcystis in the phytoplankton community, increasing cyanobacterial community diversity. Under MC treatment, residual microorganisms, including cyanobacteria, had a high potential for DNA damage repair and were more likely to survive after being subjected to oxidative stress. In the meanwhile, the abundance of genes involved in genetic information processing, signal transduction, and photosynthesis was decreased indicating that the residual microbiome was week in proliferation and light energy harvesting. Therefore, accompanied with the destruction of Microcystis colonies, MC changes the function of cyanobacteria and phycosphere microbiome, further hindering bloom development. These findings illustrate that MC can regulate and optimize the microbial community structure through which MC controls cyanobacterial blooms in ecosystems.

Potential of selected microalgae in the bioremediation of wastewater impacted dam water: A case of Goreangab Dam in Windhoek, Namibia

The study was aimed at determining the efficacy of freshwater microalgae in the treatment of polluted dam water with respect to the reduction of pathogen loads, as well as heavy metals and nutrients concentrations. Microalgae were collected from the Klein Windhoek River, as well as the Avis and Goreangab Dams in Windhoek, Namibia. Identification of the microalgae species revealed the presence of the Microcystis species in the Goreangab Dam (control), Anabaena species in the Klein Windhoek River (treatment 1) and the Scenesdesmus species as well as the Anabaena species in the Avis Dam (treatment 2). During treatment, the water samples were assessed on day 0, day 6 and day 12 for faecal and total coliform bacteria, heavy metals (Pb and Cd) as well as nutrients (phosphorous and nitrates). A one-way analysis of variance (ANOVA) indicated that there were no statistical differences between the mean values of Pb (p = 0.346) and Cd (p = 0.940) concentrations after treatment with microalgae. The Kruskal Wallis tests indicated statistical differences between the mean values of the nitrate levels (H(3) = 8.597, p = 0.035) before and after treatment with microalgae. However, the ANOVA indicated that there were no significant differences between the mean values of total phosphate uptake (p = 0.052) after treatment with microalgae. The results for pathogen loads in the wastewater samples indicated statistically significant differences between the mean values of total coliforms ((H(3) = 10.352, p = 0.015) as well as faecal coliforms (H(3) = 10.421, p = 0.015) before and after treatment with microalgae. We conclude that while our microalgae species were not effective in the removal of heavy metals from the dam water, they were nonetheless effective in the removal of microbial contaminants as well as excessive nutrients from wastewater.

Seasonal dynamics of toxigenic Microcystis in a large, shallow Lake Peipsi (Estonia) using microcystin mcyE gene abundance.

Large and temperate Lake Peipsi is the fourth largest lake in Europe, where the massive cyanobacterial blooms are composed mostly of Microcystis spp., which have been common for several decades now. The seasonal dynamics of potentially toxic Microcystis were studied using microscopy and quantitative polymerase chain reaction (qPCR) by assessing the microcystin-encoding microcystin synthetase gene E (mcyE) abundances. Water samples were analyzed over the lake areas, varying in depth, trophic level, and cyanobacterial composition during the growing period of 2021. The Microcystis mcyE genes were detected through the growing period (May-October), forming peak abundances in September with decreasing temperatures (8.9-11.1°C). Total phosphorus (TP) and nitrate (NO3-) were the most relevant environmental variables influencing the Microcystis biomass as well as mcyE abundances. Comparison with previous years (2011, 2012) indicated that the abundance and seasonal dynamics of toxigenic Microcystis can be highly variable between the years and lake areas, varying also in dominant Microcystis species. Contrary to expectations, based on mcyE abundances, the increased risk of toxin-producing Microcystis can occur in Peipsi through the growing period, independently of the water temperature and biomasses of Microcystis.

Physiological and transcriptome level responses of Microcystis aeruginosa and M. viridis to environmental concentrations of triclosan

The toxicity of triclosan (TCS) to various aquatic organisms has been demonstrated at environmental concentrations. However, the effects and mechanisms of TCS on toxic cyanobacteria remains largely unexplored. This study investigated the physiological and molecular variations in two representative toxic Microcystis species (M. aeruginosa and M. viridis) under exposure to TCS for 12 d. Our findings demonstrated that the median effective concentration (EC50) of TCS for both Microcystis species were close to the levels detected in the environment (M. aeruginosa: 9.62 μg L−1; M. viridis: 27.56 μg L−1). An increased level of reactive oxygen species (ROS) was observed in Microcystis, resulting in oxidative damage when exposed to TCS at concentrations ranging from 10 μg L−1 to 50 μg L−1. The photosynthetic activity of Microcystis had a certain degree of recovery capability at low concentrations of TCS. Compared to M. aeruginosa, the higher recovery capability of the photosynthetic system in M. viridis would be mainly attributed to the increased ability for PSII repair and phycobilisome synthesis. Additionally, the synthesis of microcystins in the two species and the release rate in M. viridis significantly increased under 10–50 μg L−1 TCS. At the molecular level, exposure to TCS at EC50 for 12 d induced the dysregulation of genes associated with photosynthesis and antioxidant system. The upregulation of genes associated with microcystin synthesis and nitrogen metabolism further increased the potential risk of microcystin release. Our results revealed the aquatic toxicity and secondary ecological risks of TCS at environmental concentrations, and provided theoretical data with practical reference value for TCS monitoring.

Can a shift in dominant species of Microcystis alter growth and reproduction of waterfleas?

The bloom-forming species Microcystis wesenbergii and M. aeruginosa occur in many lakes globally, and may exhibit alternating blooms both spatially and temporally. As environmental changes increase, cyanobacteria bloom in more and more lakes and are often dominated by M. wesenbergii. The adverse impact of M. aeruginosa on co-existing organisms including zooplanktonic species has been well-studied, whereas studies of M. wesenbergii are limited. To compare effects of these two species on zooplankton, we explored effects of exudates from different strains of microcystin-producing M. aeruginosa (Ma905 and Ma526) and non-microcystin-producing M. wesenbergii (Mw908 and Mw929), on reproduction by the model zooplankter Daphnia magna in both chronic and acute exposure experiments. Specifically, we tested physiological, biochemical, molecular and transcriptomic characteristics of D. magna exposed to Microcystis exudates. We observed that body length and egg and offspring number of the daphnid increased in all treatments. Among the four strains tested, Ma526 enhanced the size of the first brood, as well as total egg and offspring number. Microcystis exudates stimulated expression of specific genes that induced ecdysone, juvenile hormone, triacylglycerol and vitellogenin biosynthesis, which, in turn, enhanced egg and offspring production of D. magna. Even though all strains of Microcystis affected growth and reproduction, large numbers of downregulated genes involving many essential pathways indicated that the Ma905 strain might contemporaneously induce damage in D. magna. Our study highlights the necessity of including M. wesenbergii into the ecological risk evaluation of cyanobacteria blooms, and emphasizes that consequences to zooplankton may not be clear-cut when assessments are based upon production of microcystins alone.

A non-microcystin-producing Microcystis wesenbergii strain alters fish food intake by disturbing neuro-endocrine appetite regulation

Cyanobacterial harmful algal blooms (cHABs) are pervasive sources of stress resulting in neurotoxicity in fish. A member of the widely distributed Microcystis genus of bloom-forming cyanobacteria, Microcystis wesenbergii can be found in many freshwater lakes, including Dianchi Lake (China), where it has become one of the dominant contributors to the lake's recurrent blooms. However, unlike its more well-known counterpart M. aeruginosa, the effects of dense non-microcystin-containing M. wesenbergii blooms are seldom studied. The disturbance of appetite regulation and feeding behaviour can have downstream effects on the growth of teleost fish, posing a significant challenge to aquaculture and conservation efforts. Here we examined the effects of M. wesenbergii blooms on the food intake of Acrossocheilus yunnanensis, a native cyprinid in southern China. This fish species has disappeared in Dianchi Lake, and its reintroduction might be negatively affected by the presence of this newly-dominant Microcystis species. We co-cultured juvenile A. yunnanensis with a non-microcystin-producing strain of M. wesenbergii at initial densities between 5 × 104 and 1 × 106 cells/mL and monitored fish feeding behaviour and changes in neurotransmitter and hormone protein levels. High-density M. wesenbergii cultures increased the feeding rate of co-cultured fish, elevating concentrations of appetite-stimulating signalling molecules (Agouti-related protein and γ-aminobutyric acid), while decreasing inhibitory ones (POMC). These changes coincided with histopathological alterations and reduced somatic indices in brain and intestinal tissues. Given this potential for detrimental effects and dysregulation of food intake, further studies are necessary to determine the impacts of chronic exposure of M. wesenbergii in wild fish.

Cyanobacterial bloom affects structural and functional succession of microbial communities in urban wetland sediments in the Qinghai Plateau

Abstract Algal blooms significantly affect microbial communities in wetland ecosystems. However, little is known about the succession of sediment microbial communities during algal blooms. This study aimed to investigate the temporal patterns of sediment bacterial community structure and function succession during algal blooms (March to May 2022) with high-throughput sequencing technology. To this end, algal blooms were divided into the bloom stage (BS), decomposition stage (DS) and end stage (ES). The results showed that: (i) The algal blooms were dominated by Microcystis species within Cyanobacteria. Both phytoplankton abundance and biomass reached the peak in the BS, with 45.78 × 105 cells/L and 5.97 mg/L, respectively. (ii) The alpha diversity indices of the sediment bacterial community showed a monotonically increasing trend, with the lowest value in the BS. Cyanobacterial blooms reduced the relative abundance of Actinobacteria and Chloroflexi, and raised that of Firmicutes, Proteobacteria and Bacteroidetes. (iii) Cyanobacterial blooms remarkably decreased the complexity of the co-occurrence network of the sediment bacterial community, which resisted extreme environmental conditions in the BS and DS by increasing positive relationships. (iv) Mantel test showed that phytoplankton biomass, T, dissolved oxygen and organic carbon had significant effects on the sediment bacterial community. The results of this study are important for the ecological management of algal blooms through microorganisms.

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

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

Стрессорное воздействие биоцидных метаболитов актинобактерии Streptomyces geldanamycininus Z374 на цианобактерии Microcystis aeruginosa

Over the past decades, as a result of anthropogenic pollution and global warming, the frequency, intensity and geographical distribution of the mass development of microalgae and cyanobacteria in water bodies have significantly increased. The Microcystis species are responsible for most cases of the cyanobacterial blooms in freshwater bodies worldwide. Microcystis aeruginosa is the most commonly observed of them. In this work, we assessed the stress effect of isolated from actinobacteria Streptomyces geldanamycininus cyanocidal crude biocide Z374 (CB Z374) on the cyanobacteria M. aeruginosa. The results showed that CB Z374 significantly inhibited M. aeruginosa biomass. The CB Z374 half maximal effective concentration (EC50) for M. aeruginosa after 96 hours of treatment was 5 mg/L. The growth of M. aeruginosa with CB Z374 is characterized by an increase in the duration of the lag-phase, a decrease in the specific growth rate and biomass yield compared to the control. CB Z374 caused oxidative stress in cyanobacteria cells, determined by the elevated levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA) up to 1.6 times, as well as an increased permeability of M. aeruginosa cell membranes by 1.5 times. The levels of superoxide dismutase (SOD) and catalase (CAT) activities and reduced glutathione (GSH) content raised in response to oxidative stress. M. aeruginosa growth inhibition was accompanied by a photosynthesis modification: the photosynthetic pigments phycobiliproteins and carotenoids content increases by 2.3 and 1.6 times respectively and the chlorophyll a content decreases by 1.2 times. CB Z374 inhibited M. aeruginosa photosynthesis, which was expressed in a decline in the maximum quantum efficiency of photosystem II – Fv/Fm by 10% and a reduction in the electron transfer rate (ETR) by 18%. We assume that oxidative stress and, as a result, cell membranes damage and photosynthesis inhibition are the main mechanisms of the cyanocidal action of CB Z374 on M. aeruginosa.

Seasonal community dynamics and toxicity potential of cyanobacteria in Lough Arrow, an oligo-mesotrophic lake in the north-west of Ireland

Favourable water quality is paramount to ensuring the protection of natural habitats and the resources they provide. Phytoplankton are an important assessor of the health of aquatic ecosystems, particularly in lakes. As such, the characterisation of phytoplankton communities over time enables a detailed assessment of a water body’s ecological condition. This study examined the characteristics of cyanobacteria in Lough Arrow, a lake in Ireland’s northwest, over the course of a year to ascertain their community dynamics as well as potential for cyanotoxin production. DGGE analysis of 16 S rRNA gene amplicons for spherical cyanobacteria revealed seasonal shifts in Lough Arrow, with greater diversity in the summer and autumn. Non-metric multidimensional scaling showed that seasonal changes in the cyanobacterial community were largely driven by changes in environmental factors such as temperature and conductivity. The presence of the toxigenic species Microcystis sp. was confirmed from DGGE profiles. Analysis for the potential production of microcystin toxins in the lake was undertaken via qPCR analysis of the mcyE gene. No significant difference between the summer and autumn seasons was observed. Microcystin concentrations, estimated via the application of an ELISA assay, showed very low concentrations in the lake (max conc. 0.027 µg/l), which were not significantly different between the summer and autumn. The species richness and abundance of cyanobacteria in Lough Arrow was seasonal; responding dynamically to changes in environmental factors. The presence of Microcystis sp. and potential for microcystin production detected in the summer and autumn seasons indicating that the establishment of a tailored monitoring plan could be of benefit for better ascertaining and managing water quality parameters and potential risks to human and animal health.

The Effect of Microcystis on the Monitoring of Faecal Indicator Bacteria.

The survival of Escherichia coli (E. coli) bacteria, the most common faecal indicator bacteria (FIB), may be significantly affected by cyanobacteria present during a harmful algal bloom (HAB). Therefore, the effect of Microcystis on the survival of FIB E.coli and coliforms was investigated. Microcosms containing two species of Microcystis (M. aeruginosa and M. smithii) were established and then inoculated with four reference strains of E. coli (ATCC 25922, 8739, 51813, and 11775) to explore the cyanobacteria-bacteria dynamics at a laboratory setting. Monitoring over several days showed normal growth of Microcystis, with or without the presence of E. coli. However, Microcystis was shown to dramatically decrease the survival of E. coli over time. Analysis of microcystin production by Microcystis was found to correlate with loss of E. coli, suggesting a toxic effect of microcystins on E. coli bacteria. This phenomenon was also demonstrated for a natural consortium of E. coli and coliform bacteria by inoculating with contaminated lake water. The results indicate that the use of E. coli as FIB may be greatly compromised in the presence of Microcystis spp. such as during a HAB when associated toxins are produced.

Isopropylthiol emission by bloom-forming Microcystis: Biochemistry, ecophysiology and semiochemistry of a volatile organosulfur compound

Microcystis species not only produce toxic cyanobacterial blooms, but can be a significant source of taste and odour. Previous studies have associated foul-smelling volatile organic sulfur compounds (VOSCs) with Microcystis blooms, but have largely attributed these compounds to bacterial bloom decomposition. However, earlier reports of the production of isopropylthio compounds by several Microcystis strains suggests that these cyanobacteria may themselves be a source of these VOSCs. Sulphur compounds have been shown to play important semiochemical roles in algal cell protection and grazer interactions in marine systems, but little is known about the production and chemical ecology of freshwater cyanobacterial VOSCs. To address this knowledge gap, we undertook the first detailed investigation of the biochemistry, ecophysiology and semiochemistry of these compounds and their production by Microcystis, and tested the hypothesis that they act as multifunctional semiochemicals in processes related to cell protection and grazer defence. Using short-term incubations and an adapted headspace-GC–MS technique, we investigated VOSC production by axenic and non-axenic strains, and verified that isopropylthio compounds are in fact produced by these cyanobacteria, identifying 5 isopropyl moiety-containing VOSCs (isopropylthiol (ISH), isopropylmethyl sulfide, isopropyl methyl disulfide, diisopropyl disulfide (ISSI) and diisopropyl trisulfide) as well as methanethiol in three strains. Further studies with the axenic strain Microcystis PCC 7806 using different light regimes, metabolic inhibitors (sodium azide, DCMU), the antioxidant enzyme catalase and stable labelled precursors (hydrogencarbonate, acetates and sulfate) demonstrated that ISH is a true exo-metabolite, synthesized via the acetate pathway. It is actively produced and continuously excreted by the cyanobacteria during growth, with minimal internal storage or post-lysis catalytic generation. The molar ratios of the redox pair ISH/ISSI are not directly involved in the photosynthetic and respiratory electron transport chains, but dependant on the redox state of the cell - likely mediated by reactive oxygen species (ROS), as shown by a marked effect of catalase. These results, along with toxicological and behavioural assays using the two aquatic invertebrates Thamnocephalus platyurus and Daphnia magna indicate that ISH plays multiple important physiological and ecological roles. It acts as an effective antioxidant against high ROS levels, as often experienced in surface blooms, it elicits avoidance-related behavioural responses in grazer communities and at high levels, it can be toxic to some invertebrates.

Summer dynamics of cyanobacteria in an oligo-mesotrophic temperate lake in Northwest Ireland

Despite the potential adverse consequences they can impart on biotopes, cyanobacteria are an understudied component of lake plankton communities in Ireland. This study, in summer 2019, examined cyanobacterial diversity and associated environmental variables in a lake previously impacted by algal blooms, in north-west Ireland. Vertical profiling showed that photosynthetic pigment concentrations were spatially heterogenous for the majority of the survey. However, water column homogeneity was observed towards the end of the survey, coinciding with increases in pigment concentrations. Sunshine hours, nutrient concentrations and wind speed were stable throughout the survey. Spatial homogeneity in pigments was attributed to an increase in minimal temperatures observed in the water column. PCR-DGGE analysis identified patterns in community composition, indicating a rise in cyanobacterial richness concomitant to increase in temperature and photosynthetic pigments. Band sequencing analysis identified phylotypes similar to the toxigenic species Microcystis sp. These were prominent at the end of the survey and coincided with the presence of the mcyE gene and low levels of microcystins, as indicated by real time PCR and ELISA analyses. The summer background presence of toxigenic cyanobacteria with potential bloom-forming capacity highlights the importance of annual lake cyanotoxin monitoring to inform resource management to protect human and animal health.

Environmental concentrations of anionic surfactants in lake surface microlayers enhance the toxicity of Microcystis blooms: Insight from photosynthesis, interspecies competition, and MC production

Anionic surfactants represented by linear alkylbenzene sulfonate (LAS) exhibit vertical heterogeneity of concentrations in aquatic environments owing to their amphiphilic structure. Field investigations showed that the concentration of anionic surfactants (mainly LAS) in the water surface microlayer (SML) of Lake Taihu reached 580 μg/L, higher than that in the lower layer. Floating Microcystis blooms overlap in space with the high concentration of anionic surfactants in SML. However, few studies have focused on the effects of anionic surfactants (e.g., LAS) on the interspecies competition between toxic and nontoxic Microcystis. In this study, coculture and monoculture experiments were conducted with both toxic and nontoxic Microcystis species to explore how the environmental concentration of LAS regulates the dominance of toxic Microcystis and toxicity from the perspective of photosynthesis, species dominance, and MC production. The results showed that LAS concentrations above 0.267 or 0.431 mg/L (depending on light conditions) selectively promoted the photosynthetic competitive advantage of toxic Microcystis, leading to its higher population proportion in the community. Additionally, LAS concentrations above 0.5 mg/L induced the synthesis and release of microcystins (MCs). The results of chlorophyll fluorescence analysis, electron microscopy and transcriptome sequencing suggested that compared with nontoxic Microcystis, toxic Microcystis can better resist LAS stress by dissipating excess light, maintaining an intact membrane structure and maintaining cellular homeostasis. Transcriptome sequencing revealed that the photosynthetic damage of nontoxic Microcystis might be attributed to the impacts of LAS on the absorption and assimilation of nitrogen, which finally resulted in the degradation of phycobilisomes. This study can provide novel insight for establishing standards and safety management of wastewater discharge.

A microcystin synthesis mcyE/ndaF gene assay enables early detection of microcystin production in a tropical wastewater pond

Cyanobacteria can dominate the algal community in wastewater ponds, which can lead to the production of cyanotoxins and their release into the environment. We applied traditional and molecular techniques to identify cyanotoxin hazards and high-risk periods in a tropical wastewater treatment system. Potentially toxic cyanobacteria were identified by microscopy and amplicon sequencing over the course of a year. Toxin gene levels were monitored and compared to toxin production to identify likely toxin producing species and high-risk periods. Cyanobacteria were persistent in the effluent year-round, with Planktothrix and Microcystis the most abundant genera; Microcystis could not be resolved beyond genus using amplicon sequencing, but M. flos-aquae was identified as a dominant species by microscopy. Microcystin toxin was detected for the first time in treated effluent at the beginning of the wet season (December 2018), which correlated with an increase in Microcystis amplicon sequence abundance and elevated microcystin toxin gene (mcyE/ndaF) levels. Concomitantly, microscopy data showed an increase in M. flos-aquae but not M. aeruginosa. These data informed a refined sampling campaign in 2019 and results showed a strong correlation between mcyE/ndaF gene abundance, microcystin toxin levels and Microcystis amplicon sequence abundance. Microscopy data showed that in addition to M. flos-aquae, M. aeruginosa was also abundant in February and March 2019, with highest levels coinciding with toxin detection and toxin gene levels. M. aeruginosa was the most abundant Microcystis species detected in selected treated effluent samples by metagenomics analysis, and elevated levels coincided with toxin production. All microcystin genes in the biosynthesis pathway were detected, but microcystin genes from Planktothrix agardhii were not detected.Gene toxin assays were successfully used to predict microcystin production in this wastewater system. Changes in amplicon sequence relative abundance were a useful indicator of changes in the cyanobacterial community. We found that metagenomics was useful not just for identifying the most abundant Microcystis species, but the detection of microcystin biosynthesis genes helped confirm this genus as the most likely toxin producer in this system. We recommend toxin gene testing for the early detection of potential toxin producing cyanobacteria to manage the risk of toxicity and allow the implementation of risk management strategies.

Biodegradability of algal-derived dissolved organic matter and its influence on methylmercury uptake by phytoplankton

Methylmercury (MeHg) uptake by phytoplankton represents a key step in determining the exposure risks of aquatic organisms and human beings to this potent neurotoxin. Phytoplankton uptake is believed to be negatively related to dissolved organic matter (DOM) concentration in water. However, microorganisms can rapidly change DOM concentration and composition and subsequent impact on MeHg uptake by phytoplankton has rarely been tested. Here, we explored the influences of microbial degradation on the concentrations and molecular compositions of DOM derived from three common algal sources and tested their subsequent impacts on MeHg uptake by the widespread phytoplankton species Microcystis elabens. Our results indicated that dissolved organic carbon was degraded by 64.3‒74.1% within 28 days of incubating water with microbial consortia from a natural meso‑eutrophic river. Protein-like components in DOM were more readily degraded, while the numbers of molecular formula for peptides-like compounds had increased after 28 days’ incubation, probably due to the production and release of bacterial metabolites. Microbial degradation made DOM more humic-like which was consistent with the positive correlations between changes in proportions of Peaks A and C and bacterial abundance in bacterial community structures as illustrated by 16S rRNA gene sequencing. Despite rapid losses of the bulk DOM during the incubation, we found that DOM degraded after 28 days still reduced the MeHg uptake by Microcystis elabens by 32.7‒52.7% relative to a control without microbial decomposers. Our findings emphasize that microbial degradation of DOM would not necessarily enhance the MeHg uptakes by phytoplankton and may become more powerful in inhibiting MeHg uptakes by phytoplankton. The potential roles of microbes in degrading DOM and changing the uptakes of MeHg at the base of food webs should now be incorporated into future risk assessments of aquatic Hg cycling.

Cyanometabolites: molecules with immense antiviral potential

Cyanometabolites are active compounds derived from cyanobacteria that include small low molecular weight peptides, oligosaccharides, lectins, phenols, fatty acids, and alkaloids. Some of these compounds may pose a threat to human and environment. However, majority of them are known to have various health benefits with antiviral properties against pathogenic viruses including Human immunodeficiency virus (HIV), Ebola virus (EBOV), Herpes simplex virus (HSV), Influenza A virus (IAV) etc. Cyanometabolites classified as lectins include scytovirin (SVN), Oscillatoria agardhii agglutinin (OAAH), cyanovirin-N (CV-N), Microcystis viridis lectin (MVL), and microvirin (MVN) also possess a potent antiviral activity against viral diseases with unique properties to recognize different viral epitopes. Studies showed that a small linear peptide, microginin FR1, isolated from a water bloom of Microcystis species, inhibits angiotensin-converting enzyme (ACE), making it useful for the treatment of coronavirus disease 2019 (COVID-19). Our review provides an overview of the antiviral properties of cyanobacteria from the late 90s till now and emphasizes the significance of their metabolites in combating viral diseases, particularly severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which has received limited attention in previous publications. The enormous medicinal potential of cyanobacteria is also emphasized in this review, which justifies their use as a dietary supplement to fend off pandemics in future.

Spatio-temporal dynamic diversity of bacterial alkaline phosphatase phoD gene and its environmental drivers in sediments during algal blooms: A case study of shallow Lake Taihu

Bacterial alkaline phosphatase encoded by the phoD gene is essential for phosphorus (P) cycling in ecosystems. Until now, knowledge of the phoD gene diversity in shallow lake sediments is still lacking. In this study, from early to late stage of cyanobacterial blooms, we investigated the dynamic changes of the abundance of phoD gene (hereafter phoD abundance) and phoD-harboring bacterial community composition (hereafter phoD-harboring BCC) in sediments from different ecological regions of Lake Taihu, the third-largest shallow freshwater lake in China, as well as explored their environmental driving factors. Results showed that phoD abundance in the sediments of Lake Taihu showed spatiotemporal heterogeneity. The highest abundance was found in macrophyte-dominated area (mean 3.25*106copies/g DW), where Haliangium and Aeromicrobium were identified as the major contributors. Due to the negative impact of Microcystis species, phoD abundance decreased significantly (by 40.28% on average) during cyanobacterial blooms in all other regions except the estuary area. The phoD abundance in sediment was positively correlated with total organic carbon (TOC) and total nitrogen (TN). However, the relationship between phoD abundance and alkaline phosphatase activity (APA) varied with time, showing positive correlation (R2 = 0.763, P < 0.01) in the early stage of cyanobacterial blooms, but not (R2 = −0.052, P = 0.838) in the later stage. The predominant phoD-harboring genera in sediments were Kribbella, Streptomyces and Lentzea, all of which belong to Actinobacteria. Non-metric multidimensional scaling (NMDS) analysis revealed that the spatial heterogeneity of phoD-harboring BCC in the sediments of Lake Taihu was significantly higher than the temporal heterogeneity. TP and sand were the principle environmental factors affecting the phoD-harboring BCC in the sediments of the estuary area, while DO, pH, organic phosphorus (Po) and diester phosphorus were the key driving factors for other lake regions. We concluded that the C, N, and P cycles in sediments might work in concert. This study extends the understanding of the phoD gene diversity in shallow lake sediments.

Introducing Cyanodorina gen. nov. and Cyanodorina ovale sp. nov. (Microcystaceae, Chroococcales), a Novel Coccoid Cyanobacterium Isolated from Caohai Lake in China Based on a Polyphasic Approach

The Chroococcales is one of the least studied cyanobacterial orders comprising the non-baeocyte-producing coccoids cyanobacteria with stacked and fasciculated thylakoids. During a survey of aquatic biodiversity in Caohai Lake in Guizhou Province, China, a coccoid-like cyanobacterium was isolated. It was characterized using a polyphasic approach, based on morphology, electron microscopy, and molecular phylogenetic analyses. This species’ colonies exhibited morphological similarity to those of Microcystis species but differed in their larger colony sizes and widely oval cells. The 16S rRNA gene sequence of this species had the maximum homology, corresponding to 93.10%, to that of the genus Microcystis. The results of 16S rRNA gene threshold value and 16S rRNA phylogenetic analyses confirmed that the studied species belongs to the family Microcystaceae but is phylogenetically distinct from the other species of Microcystaceae. Furthermore, The D1–D1′, Box–B helix, and V3 helix of the 16S–23S ITS region were also different from those previously described in Microcystaceae taxa. Combining the morphological, ecological, and molecular features of the coccoid-like cyanobacterium, we here propose the establishment of the Cyanodorina gen. nov. and the Cyanodorina ovale sp. nov.

Patterns in sources and forms of nitrogen in a large eutrophic lake during a cyanobacterial harmful algal bloom

AbstractWestern Lake Erie experiences an annual, toxic cyanobacterial harmful algal bloom (cyanoHAB), primarily caused by excess anthropogenic inputs of nitrogen (N) and phosphorous (P). Because the non‐N fixing cyanobacteria species Microcystis dominates these blooms, N availability is hypothesized to play a central role in cyanoHAB progression, as well as production of the N‐rich toxin microcystin. Many previous studies focused on nitrate because it is the most abundant N substrate during bloom initiation. However, recent work implicated reduced N substrates like ammonium and dissolved organic N (DON) in promoting greater bloom biomass and longevity. To examine the relative importance of oxidized and reduced N substrates to phytoplankton during different bloom stages, we measured concentrations and natural abundance δ15N isotope values of dissolved N substrates and phytoplankton biomass throughout the entirety of the 2020 cyanoHAB in Western Lake Erie. The results provide the first data on DON dynamics and composition in Western Lake Erie, and suggest that phytoplankton, including Microcystis, likely relied on N regenerated from the DON pool in later bloom stages. In addition, the stable isotope data confirm the importance of nitrate delivered via the Maumee River to cyanobacterial growth and toxin production.