Influence of polyethylene-type microplastics on long-term exposure to heavy metals in freshwater phytoplankton.

The use of plastic materials has brought about significant social benefits but has also led to negative consequences, particularly their accumulation in aquatic environments. Studies have shown that small plastic particles, known as microplastics (MPs), can carry various harmful pollutants, such as heavy metals (HMs). Therefore, the aim of this research is to investigate the impact of polyethylene-type MPs on the long-term exposure of different HMs on freshwater microalgae Scenedesmus armatus and cyanobacteria Microcystis aeruginosa, in both isolated cultures and phytoplanktonic community conditions. Over a period of 28 days, the strains were subjected to concentrations of Ag+, Cu+2, and Cr+6 corresponding to their respective 72 h-EC10, with or without the presence of MPs. Throughout this period, the growth cell ratio, photosynthetic activity, and reactive oxygen species (ROS) were monitored. The findings indicated a substantial inhibitory impact on cell growth during the initial 7-14 days of exposure, followed by a reduction until reaching values like the controls after 28 days of exposure. There was a disturbance in photosynthetic activity during the first 72 h of exposure, which gradually returned to control levels, mainly significantly affected the respiration phase. Reactive oxygen species (ROS) activity was also affected during the initial 14 days of exposure. The presence or absence of MPs in the culture medium did not significantly alter the observed effects. However, interspecies competition created a more favorable environment for M. aeruginosa over the freshwater microalgae S. armatus. These findings suggest that the formation of MP-HMs complexes may have a limited impact on reducing the adverse effects of HMs in long-term exposures. However, because the impact depends on the specific HM involved, further studies are needed to gain a better understanding of the interaction between these pollutants.

Biotechnological approaches for suppressing Microcystis blooms: insights and challenges.

Cyanobacterial harmful algal blooms, particularly those dominated by Microcystis, pose significant ecological and health risks worldwide. This review provides an overview of the latest advances in biotechnological approaches for mitigating Microcystis blooms, focusing on cyanobactericidal bacteria, fungi, eukaryotic microalgae, zooplankton, aquatic plants, and cyanophages. Recently, promising results have been obtained using cyanobactericidal bacteria: not through the inoculation of cultured bacteria, but rather by nurturing those already present in the periphyton or biofilms of aquatic plants. Fungi and eukaryotic microalgae also exhibit algicidal properties; however, their practical applications still face challenges. Zooplankton grazing on Microcystis can improve water quality, but hurdles exist because of the colonial form and toxin production of Microcystis. Aquatic plants control blooms through allelopathy and nutrient absorption. Although cyanophages hold promise for Microcystis control, their strain-specificity hinders widespread use. Despite successful laboratory validation, field applications of biological methods are limited. Future research should leverage advanced molecular and bioinformatic techniques to understand microbial interactions during blooms and offer insights into innovative control strategies. Despite progress, the efficacy of biological methods under field conditions requires further verification, emphasizing the importance of integrating advanced multi-meta-omics techniques with practical applications to address the challenges posed by Microcystis blooms. KEY POINTS: • A diverse range of biotechnological methods is presented for suppressing Microcystis blooms. • Efficacy in laboratory experiments needs to be proved further in field applications. • Multi-meta-omics techniques offer novel insights into Microcystis dynamics and interactions.

Microbial nitrogen cycling in Microcystis colonies and its contribution to nitrogen removal in eutrophic Lake Taihu, China.

Cyanobacterial blooms induced by excessive loadings of nitrogen (N) and other nutrients are a severe ecological problem in aquatic ecosystems. Previous studies of N removal have primarily focused on sediment-water interface, yet the role of cyanobacterial colonies has recently been attracting more research attention. In this study, N cycling processes were quantified for cyanobacterial colonies (primarily Microcystis colonies) and their contribution to N removal was estimated for a large, shallow eutrophic lake in China, Lake Taihu. Various N cycling processes were determined via stable 15N isotope, together with 16S rRNA gene sequencing and quantitative microbial element cycling (QMEC) chip. Denitrification was found to be the most prominent process, estimated to be 36.63, 9.85, 3.35, and 3.15 times higher than dissimilatory nitrate reduction to ammonium (DNRA), nitrification, ammonium (NH4+) uptake and nitrate (NO3-) uptake rates, respectively. Denitrifiers accounted for a large part of the bacterial taxa (35.50 ± 24.65%), and the nirS gene was the most abundant among N cycling-related genes, with (2.54 ± 0.51) × 109 copies g-1Microcystis colonies. A field investigation revealed a positive correlation between the potential denitrification rate and the Chl-a concentration (mostly derived from Microcystis colonies). Based on a multiple stepwise regression model and historical data from 2007 to 2015 for Lake Taihu, the total amount of N removed via denitrification by Microcystis colonies was estimated at 171.72 ± 49.74 t yr-1; this suggests that Microcystis colonies have played an important role in N removal in Lake Taihu since the drinking water crisis in 2007. Overall, this study revealed the importance of denitrification within Microcystis colonies for N removal in eutrophic lakes, like Lake Taihu.

ß-ionone inhibits the grazing of Daphnia sinensis by reducing the activity of acetylcholinesterase.

ß-ionone is a volatile metabolite of Microcystis aeruginosa that is toxic to aquatic organisms. Using Daphnia sinensis as model, our present study found that ß-ionone could significantly reduce heart rate and feeding rate, and induce intestinal emptying. Transcriptomic analysis showed that ß-ionone could significantly inhibit the expression of acetylcholinesterase (AchE) mRNA, while metabolomics further revealed that ß-ionone could significantly increase the level of acetylcholine (Ach) in D. sinensis. These results indicated that ß-ionone might act as an AchE inhibitor, resulting in an increase in Ach levels. To test this hypothesis, both in vivo and in vitro experiments demonstrated that ß-ionone could significantly reduce AchE activity. Furthermore, the inhibitory effects of ß-ionone on heart rate and feeding rate could be blocked by the M-type Ach receptor (mAchR) blocker. These findings confirm that ß-ionone is a novel AchE inhibitor. ß-ionone could inhibit the activity of AchE, which in turn resulted in an increase of Ach in D. sinensis. Consequently, elevated levels of Ach could suppress the heart rate and feeding rate of D. sinensis by activating the mAchR, while concurrently accelerating the rate of intestinal emptying by stimulating intestinal peristalsis, thereby obstructing the digestion of algae within the intestinal tract.

Exploring factors that affect Microcystis abundance in the sacramento san joaquin delta.

Cyanobacteria harmful algal blooms (cHABs) are increasing in frequency, intensity and duration in estuaries worldwide. In the upper San Francisco Estuary, also known as the Sacramento San Joaquin Delta (Delta), cHABs have been a topic of concern over the past two decades. In response, managers are urgently working to understand the factors that drive cHABs and identify feasible management options to avert ecological and human health consequences. We used a six year data set to explore relationships between flow parameters, temperature, and Microcystis biovolume to determine the potential for managing large scale hydrodynamic conditions to address Delta cHABs. We also looked at the relationship between Microcystis biovolume and the low salinity zone to see if it could be used as a proxy for residence time, because residence time is positively related to cyanobacteria abundance. We found the low salinity zone is not a useful proxy for residence time in the area of the Delta that experiences the most severe cHABs. Our finding suggest that climatic conditions (i.e., temperature and water year type) have the greatest influence on Microcystis biovolume in the Delta, with higher biovolume during years with lower flow and higher temperatures. Further, there are interannual differences in Microcystis biovolume that cannot be fully explained by flow parameters or temperature, meaning other factors not included in our model may be involved. We conclude that management actions to increase flow may be ineffective at reducing Microcystis to desired levels if water temperatures remain high.

A novel strategy of bloom forming cyanobacteria Microcystis sp. in response to phosphorus deficiency: Using non-phosphorus lipids substitute phospholipids.

Despite significant reductions in phosphorus (P) loads, lakes still experience cyanobacterial blooms. Little is known regarding cellular P regulation in response to P deficiency in widely distributed bloom causing species such as Microcystis. In this study, we investigated changes in P containing and non-P lipids contents and their ratios concomitantly with the determinations of expression levels of genes encoding these lipids in cultural and field Microcystis samples. In the culture, the content of phosphatidylglycerol (PG) decreased from 2.1 µg g-1 in P replete control to 1.2 µg g-1 in P-deficient treatment, while non-P lipids, like sulfoquinovosyldiacylglycerol (SQDG) and monogalactosyldiacylglycerol (MGDG), increased dramatically from 13.6 µg g-1 to 142.3 µg g-1, and from 0.9 µg g-1 to 16.74 µg g-1, respectively. The expression of the MGDG synthesis gene, mgdE, also increased under low P conditions. Significant positive relationships between soluble reactive phosphorus (SRP) and ratios of P-containing lipids (PG) to non-P lipids, including SQDG, MGDG and digalactosyldiacylglycerol (DGDG) (P < 0.05) were observed in the field investigations. Both cultural and field data indicated that Microcystis sp. might increase non-P lipids proportion to lower P demand when suffering from P deficiency. Furthermore, despite lipid remodeling, photosynthetic activity remained stable, as indicated by comparable chlorophyll fluorescence and Fv/Fm ratios among cultural treatments. These findings suggested that Microcystis sp. may dominate in P-limited environments by substituting glycolipids and sulfolipids for phospholipids to reduce P demand without compromising the photosynthetic activity. This effective strategy in response to P deficiency meant a stricter P reduction threshold is needed in terms of Microcystis bloom control.

Application of microbubble air flotation to harvest Microcystis sp. from agriculture wastewater: The regulation and mechanisms.

The harvesting of microalgae is the main bottleneck of its large-scale biomass production, and seeking an efficient, green, and low-cost microalgae harvesting technology is one of the urgent problems to be solved. Microbubble air flotation has been proven to be an effective measure, but the mechanisms of microbubbles-algal cell attachment are still unclear. In this study, microbubble air flotation was used as a harvesting method for Microcystis cultured in agricultural wastewater. The process mechanism of microbubble air flotation harvesting microalgae in wastewater was fully revealed from three aspects (the design of bubble formation, the adhesion law, and the recovery rate of microalgae under different working conditions). The results show that the length of the release pipe is the main factor affecting the proportion of microbubbles with a particle size of less than 50 µm. In the process of adhesion, when the particle size of microbubbles is 0.6-1.7 times the size of Microcystis, the adhesion efficiency of microbubbles to Microcystis is the highest. Under the conditions of pressure 0.45 MPa, gas-liquid ratio 5%, and release pipe length 100 cm, the harvesting performance of Microcystis was the best. Microbubble air flotation has better harvesting performance (63.5%, collection rate) of Microcystis with higher density. By understanding the mechanism of microbubble flotation, the technical parameters of microbubble flotation for harvesting energy microalgae are optimized to provide support for the development of efficient and low-cost devices and equipment for collecting microalgae.

High-efficiency removal of microcystis aeruginosa using Z-scheme AgBr/NH2-MIL-125(Ti) photocatalyst with superior visible-light absorption: Performance insights and mechanisms.

Algal blooms have become a widespread concern for drinking water production, threatening ecosystems and human health. Photocatalysis, a promising advanced oxidation process (AOP) technology for wastewater treatment, is considered a potential measure for in situ remediation of algal blooms. However, conventional photocatalysts often suffer from limited visible-light response and rapid recombination of photogenerated electron-hole pairs. In this study, we prepared a Z-scheme AgBr/NH2-MIL-125(Ti) composite with excellent visible light absorption performance using co-precipitation to efficiently inactivate Microcystis aeruginosa. The degradation efficiency of AgBr/NH2-MIL-125(Ti) for chlorophyll a was 98.7 % after 180 min of visible light irradiation, significantly surpassing the degradation rate efficiency of AgBr and NH2-MIL-125(Ti) by factors of 3.20 and 36.75, respectively. Moreover, the removal rate was maintained at 91.1 % even after five times of repeated use. The experimental results indicated that superoxide radicals (•O2-) were the dominant reactive oxygen species involved. The photocatalytic reaction altered the morphology and surface charge of algal cells, inhibited their metabolism, and disrupted their photosynthetic and antioxidant systems. In conclusion, this study presents a promising material for the application of photocatalytic technology in algal bloom remediation.

Interspecific competition enhances microcystin production by Microcystis aeruginosa under the interactive influences of temperature and nutrients.

Global warming and eutrophication contribute to frequent occurrences of toxic algal blooms in freshwater systems globally, while there is a limited understanding of their combined impacts on toxin-producing algal species under interspecific competitions. This study investigated the influences of elevated temperatures, lights, nutrient enrichments and interspecific interactions on growth and microcystin (MC) productions of Microcystis aeruginosa in laboratory condition. Our results indicated that elevated temperatures and higher nutrient levels significantly boosted biomass and specific growth rates of Microcystis aeruginosa, which maintained a competitive edge over Chlorella sp. Specifically, with phosphorus levels between 0.10 and 0.70 mg P L-1, the growth rate of Microcystis aeruginosa in mixed cultures increased by 23 %-52 % compared to mono-cultures, while the growth rate of Chlorella sp. shifted from positive in mono-cultures to negative in mixed cultures. Redundancy and variance partition analyses suggested that Chlorella sp. stimulate MC production in Microcystis aeruginosa and nutrient levels outshine temperature for toxin productions during competition. Lotka‒Volterra model revealed a positive correlation between the intensities of competitions and MC concentration. Our findings indicate that future algal bloom mitigation strategies should consider combined influence of temperature, nutrients, and interspecific competition due to their synergistic effects on MC productions.

Untargeted LC-HRMS applied to microcystin-producing cyanobacterial cultures for the evaluation of the efficiency of chlorine-based treatments commonly used for water potabilization.

Cyanobacteria in water supplies are considered an emerging threat, as some species produce toxic metabolites, cyanotoxins, of which the most widespread and well-studied are microcystins. Consumption of contaminated water is a common exposure route to cyanotoxins, making the study of cyanobacteria in drinking waters a priority to protect public health. In drinking water treatment plants, pre-oxidation with chlorinated compounds is widely employed to inhibit cyanobacterial growth, although concerns on its efficacy in reducing cyanotoxin content exists. Additionally, the effects of chlorination on abundant but less-studied cyanometabolites (e.g. cyanopeptolins whose toxicity is still unclear) remain poorly investigated. Here, two chlorinated oxidants, sodium hypochlorite (NaClO) and chlorine dioxide (ClO2), were tested on the toxic cyanobacterium Microcystis aeruginosa, evaluating their effect on cell viability, toxin profile and content. Intra- and extracellular microcystins and other cyanometabolites, including their degradation products, were identified using an untargeted LC-HRMS approach. Both oxidants were able to inactivate M. aeruginosa cells at a low dose (0.5 mg L-1), and greatly reduced intracellular toxins content (>90%), regardless of the treatment time (1-3 h). Conversely, a two-fold increase of extracellular toxins after NaClO treatment emerged, suggesting a cellular damage. A novel metabolite named cyanopeptolin-type peptide-1029, was identified based on LC-HRMSn (n = 2, 3) evidence, and it was differently affected by the two oxidants. NaClO led to increase its extracellular concentration from 2 to 80-100 µg L-1, and ClO2 induced the formation of its oxidized derivative, cyanopeptolin-type peptide-1045. In conclusion, pre-oxidation treatments of raw water contaminated by toxic cyanobacteria may lead to increased cyanotoxin concentrations in drinking water and, depending on the chemical agent, its dose and treatment duration, also of oxidized metabolites. Since the effects of such metabolites on human health remain unknown, this issue should be handled with extreme caution by water security agencies involved in drinking water management.

A novel hierarchical network-based approach to unveil the complexity of functional microbial genome.

Biological networks serve a crucial role in elucidating intricate biological processes. While interspecies environmental interactions have been extensively studied, the exploration of gene interactions within species, particularly among individual microorganisms, is less developed. The increasing amount of microbiome genomic data necessitates a more nuanced analysis of microbial genome structures and functions. In this context, we introduce a complex structure using higher-order network theory, "Solid Motif Structures (SMS)", via a hierarchical biological network analysis of genomes within the same genus, effectively linking microbial genome structure with its function. Leveraging 162 high-quality genomes of Microcystis, a key freshwater cyanobacterium within microbial ecosystems, we established a genome structure network. Employing deep learning techniques, such as adaptive graph encoder, we uncovered 27 critical functional subnetworks and their associated SMSs. Incorporating metagenomic data from seven geographically distinct lakes, we conducted an investigation into Microcystis' functional stability under varying environmental conditions, unveiling unique functional interaction models for each lake. Our work compiles these insights into an extensive resource repository, providing novel perspectives on the functional dynamics within Microcystis. This research offers a hierarchical network analysis framework for understanding interactions between microbial genome structures and functions within the same genus.

Unprecedented Harmful algal bloom in the UK and Ireland's largest lake associated with gastrointestinal bacteria, microcystins and anabaenopeptins presenting an environmental and public health risk.

Harmful Algal Blooms (HABs) are outbreaks of aquatic toxic microalgae emerging as a global problem driven by nutrient enrichment, global climate change and invasive species. We uniquely describe a HAB of unprecedented duration, extent and magnitude during 2023 in Lough Neagh; the UK and Ireland's largest freshwater lake, using an unparalleled combination of satellite imagery, nutrient analysis, 16S rRNA gene sequencing and cyanotoxin profiling. The causative agent Microcystis aeruginosa accounted for over a third of DNA in water samples though common bacterioplankton species also bloomed. Water phosphate levels were hypertrophic and drove local algal biomass. The HAB pervaded the entire ecosystem with algal mats accumulating around jetties, marinas and lock gates. Over 80 % of bacterial DNA isolated from algal mat samples consisted of species associated with wildfowl or livestock faeces and human-effluent wastewater including 13 potential pathogens that can cause serious human illness including: E. coli, Salmonella, Enterobacter and Clostridium among others. Ten microcystins, nodularin and two anabaenopeptin toxins were confirmed as present (with a further microcystin and four anabaenopeptins suspected), with MC-RR and -LR in high concentrations at some locations (1,137-18,493 µg/L) with MC-LR exceeding World Health Organisation (WHO) recreational exposure guidelines in all algal mats sampled. This is the first detection of anabaenopeptins in any waterbody on the island of Ireland. Notwithstanding the ecological impacts, this HAB represented an environmental and public health risk, curtailing recreational activities in-and-around the lake and damaging local businesses. Reducing agricultural runoff and discharge from human-effluent wastewater treatment to manage nutrient loading, and the public health risk, should be the top priority of stakeholders, especially government. Key recommendations include Nature-based Solutions that avoid conflict with the productivity and profitability of the farming sector enhancing sustainability. We hope this stimulates real-world action to resolve the problems besetting this internationally important ecosystem.

Interactions between Microcystis and its associated bacterial community on electron transfer and transcriptomic processes.

Microcystis and bacteria always live together in the mucilage of Microcystis colonies. Extracellular electrons between Microcystis and bacteria can be translated from bioenergy to electric energy. Here, photosynthetic microbial fuel cells (PMFCs) were constructed to make clear the electron transfer mechanism between Microcystis and bacteria. A remarkable enhancement of current density with 2.5-fold change was detected in the coculture of Microcystis and bacteria than pure culture of Microcystis. Transcriptome analyses showed that photosynthesis efficiency of Microcystis was upregulated and may release more electron to improve extracellular electron transfer rate. Significant increase on oxidative phosphorylation of bacterial community was observed according to meta-transcriptome. Bacterial electrons were transferred out of cell membranes by enhancing VgrG and IcmF copies though the type II bacterial secretion system. Not only Microcystis and bacteria attached with each other tightly by filamentous, but also more gene copies relating to pilin and riboflavin production were detected from Microcystis culture. A confirmatory experiment found that riboflavin can upregulate the electron transfer and current density by adding riboflavin into cocultures. Thus, the direct contact and indirect interspecies electron transfer processes between Microcystis and bacteria were observed. Results enlarge knowledge for activities of Microcystis colonies in cyanobacterial blooms, and provide a better understanding for energy transformation.

Genome sequence of Bacillus pumilus RI06-95 isolated during a Microcystis bloom in lake Champlain, USA.

Here, we present the complete genome sequence of Bacillus pumilus RI06-95 isolated during a Microcystis bloom in Lake Champlain. The assembled genome comprises a 3.8 Mbp chromosome with a GC content of 42%, and two plasmids, pPZZ84 6.4 Kbp, GC content 37% and pSHB9 97Kbp, GC content 36%.

Human activities-impacted lake dissolved organic matter (DOM) affects phycosphere microbial diversity and DOM diversification via carbon metabolism.

Photosynthetic carbon sequestration and microbial carbon metabolism are major processes of algae-bacteria interactions, affecting pollutant degradation as well as fundamental biogeochemical cycles in aquatic systems. Human-induced land-use changes greatly alter the molecular composition and input of terrestrial dissolved organic matter (DOM) in inland lakes. However, how the origin of DOM leads to varying effects on phycosphere microbial communities or molecular composition of DOM, e.g., via carbon metabolism, has been little studied in freshwater. Here, we incubated the cyanobacterium Microcystis aeruginosa and a bacterial community from natural lakes to establish an alga-bacteria model system. This allowed us to investigate how DOM from different sources affects phycosphere microbial diversity and DOM diversification. We showed that Suwannee River fulvic acid (SRFA), Suwannee River natural organic matter (SRNOM) and cropland lake DOM promote algal growth, whereas DOM from an urban lake inhibits algal growth. Algal metabolites and DOM together shaped the chemotaxis response of phycosphere communities. High-resolution mass spectrometry analysis demonstrated that DOM chemo-diversity tended to become uniform after interactions of diverse DOM sources with the algae-bacteria symbiosis system. Molecular thermodynamic analysis of DOM based on a substrate-explicit model further verified that microbial interactions render DOM less bioavailable and thus increase recalcitrant DOM formation. Metabolome analysis uncovered that DOM addition intensifies metabolic pathways related to labile and recalcitrant DOM utilization (mainly lignin/carboxyl-rich alicyclic molecule (CRAM)-like DOM, unsaturated hydrocarbon), whereby cofactor and vitamin metabolism represented an extremely strong activity in all metabolic pathways. Our results highlight covariation and interactions of DOM with microbial metabolism at the molecular level and expands our understanding of microbially mediated DOM shaping aquatic carbon cycling.

Changes of vertical distribution of Microcystis colonies driven by short-term rainfall: Disappearance and reformation of surface bloom.

Global climate warming and human activities have increased the magnitude and frequency of Microcystis surface blooms, posing significant threats to freshwater ecosystems and human health over recent decades. Heavy rainfall events have been reported to cause the disappearance of these blooms. Although some studies have employed turbulence models to analyze the movement characteristics of Microcystis colonies, the impact of rainfall is complex, comprehensive investigations on their vertical migration induced by short-term rainfall are still necessary. Utilizing monitoring data from eutrophic ponds and controlled simulation experiments, this study examines the short-term impacts of rainfall on the vertical distribution of Microcystis in the water column. Our findings indicate that rainfall contributes to the disappearance of Microcystis blooms by reducing the quantity of small to medium-sized colonies (0-100 µm) at the surface, subsequently decreasing the overall Microcystis biomass. As rainfall intensity increases, larger colonies migrate deeper into the water column. At a rainfall threshold of 666 mm, the difference in the median volume diameter (DV50) of Microcystis colonies between the surface and bottom reaches a minimal value of 3.09%. Post-rainfall, these colonies rapidly ascend, aggregate into larger formations, and re-establish surface blooms. The greater the rainfall, the smaller the resultant Microcystis biomass, albeit with larger aggregated colony sizes. When rainfall exceeds 222 mm, the recovery rate of surface Microcystis biomass remains below 100%, decreasing to 19.48% at 666 mm of rainfall, while the median volume diameter (DV50) of the colonies increases to 139.07% of its pre-rainfall level. Furthermore, compared to pre-rainfall conditions, the photosynthetic activity of the surface Microcystis colonies was enhanced and the secretion of EPS was increased under heavy rainfall conditions. Our results identify a critical response time of 30 min for Microcystis colonies to rainfall, after which the response ceases to intensify. These insights are crucial for predicting post-rain Microcystis bloom dynamics and aiding management authorities in timely interventions.

Differential impacts of organic and inorganic phosphorus on the growth and phosphorus utilization of Microcystis aeruginosa.

Phytoplankton growth in freshwater is often limited by the availability of phosphorus (P), and thorough understandings of P availability are essential to prevent algal blooms. However, the differences in bioavailability and utilization mechanisms of different P forms remain unclear, especially whether organophosphorus could be used as P sources. This study investigated the effects of 0.5, 1.0, and 2.0 mg/L P on Microcystis aeruginosa, including dissolved organic P (DOP) (1-hydroxyethane 1,1-diphosphonic acid) and dissolved inorganic P (DIP) (dipotassium phosphate). Compared with DIP, intracellular P content absorbed in DOP treatment was significantly lower. DOP was more conducive to the synthesis of soluble protein and the release of extracellular polymeric substances. Alkaline phosphatase activity was generally enhanced in response to DIP deficiency. Both DIP and DOP promoted carbon uptake to the same extent. DOP groups absorbed carbon to synthesize energy and proteins in response to stress, while DIP groups were mainly used carbon for growth. They all reduced the content of microcystin releasing into the aquatic environment and therefore reduced ecological risk caused by microcystin. Compared with DIP, the expressions of photosynthesis-related genes were significantly down-regulated in DOP group, while the expressions of nucleoside phosphate catabolism, P transporter, and amino acid biosynthesis and metabolism were significantly up-regulated in response to P deficiency environment and the stress of 1.0 mg/L DOP concentration. In summary, the bioavailability of different P forms on cyanobacteria is different, so it is not sufficient to only use total P for assessing environmental risk. P forms should also be considered for risk management of freshwater ecosystems.

Microcystis abundance is predictable through ambient bacterial communities: A data-oriented approach.

The number of cyanobacterial harmful algal blooms (cyanoHABs) has increased, leading to the widespread development of prediction models for cyanoHABs. Although bacteria interact closely with cyanobacteria and directly affect cyanoHABs occurrence, related modeling studies have rarely utilized microbial community data compared to environmental data such as water quality. In this study, we built a machine learning model, the multilayer perceptron (MLP), for the prediction of Microcystis dynamics using both bacterial community and weekly water quality data from the Daechung Reservoir and Nakdong River, South Korea. The modeling performance, indicated by the R2 value, improved to 0.97 in the model combining bacterial community data with environmental factors, compared to 0.78 in the model using only environmental factors. This underscores the importance of microbial communities in cyanoHABs prediction. Through the post-hoc analysis of the MLP models, we revealed that nitrogen sources played a more critical role than phosphorus sources in Microcystis blooms, whereas the bacterial amplicon sequence variants did not have significant differences in their contribution to each other. Similar to the MLP model results, bacterial data also had higher predictability in multiple linear regression (MLR) than environmental data. In both the MLP and MLR models, Microscillaceae showed the strongest association with Microcystis. This modeling approach provides a better understanding of the interactions between bacteria and cyanoHABs, facilitating the development of more accurate and reliable models for cyanoHABs prediction using ambient bacterial data.

Effects of terrestrial dissolved organic matter on the growth, photosynthesis and colonial morphology of Microcystis aeruginosa at different levels of iron.

Terrestrial dissolved organic matter (tDOM) holds great promise for controlling cyanobacteria blooms through watershed management. To identify tDOM that could inhibit the growth, photosynthesis and colony formation, unicellular Microcystis aeruginosa Kützing (FACHB-469) was cultivated and treated with varying concentrations of gallic acid, proline and tea polyphenols at different levels of iron. The results indicated that gallic acid and tea polyphenols could inhibit Microcystis growth by suppressing photosynthesis and colony formation by reducing extracellular polysaccharides (EPS) secretion. However, proline had no significant effect on the growth, photosynthesis, colony size and EPS content of Microcystis. Transcriptome analysis showed Microcystis may optimize the internal energy transfer mode of photosynthesis through the change of phycobilisome at different levels of iron. In addition, Microcystis adapted to different iron concentration environments by regulating the expression of genes associated with iron uptake and transport. These findings suggest that the effects of plant species on algal blooms should be considered in reforestation of watershed. This consideration necessitates finding a balance between the costs and benefits of controlling cyanobacteria blooms using tDOM.

The occurrence of positive selection on BicA transporter of Microcystis aeruginosa.

The rapid growth of cyanobacteria, particularly Microcystis aeruginosa, poses a significant threat to global water security. The proliferation of toxic Microcystis aeruginosa raises concerns due to its potential harm to human health and socioeconomic impacts. Dense blooms contribute to spatiotemporal inorganic carbon depletion, promoting interest in the roles of carbon-concentrating mechanisms (CCMs) for competitive carbon uptake. Despite the importance of HCO3- transporters, genetic evaluations and functional predictions in M. aeruginosa remain insufficient. In this study, we explored the diversity of HCO3- transporters in the genomes of 46 strains of M. aeruginosa, assessing positive selection for each. Intriguingly, although the Microcystis BicA transporter became a partial gene in 23 out of 46 genomic strains, we observed significant positive sites. Structural analyses, including predicted 2D and 3D models, confirmed the structural conservation of the Microcystis BicA transporter. Our findings suggest that the Microcystis BicA transport likely plays a crucial role in competitive carbon uptake, emphasizing its ecological significance. The ecological function of the Microcystis BicA transport in competitive growth during cyanobacterial blooms raises important questions. Future studies require experimental confirmation to better understand the role of the Microcysits BicA transporter in cyanobacterial blooms dynamics.