Allelopathic interactions of linoleic acid and nitric oxide increase the competitive ability of Microcystis aeruginosa

Nanoenabled Self-Assembled Metal-Organic Algaecides Generated Photosynthetic Inhibition and Oxidative Stress for Sustainable Food Security

Achieving food sustainability is one of the biggest challenges in the new millennium. Plant factory cultivation systems provide an alternative for food sustainability, while they often suffer from algal blooms. The overuse of conventional algaecides has caused significant environmental pollution and concerns about food security. Here, we design a nanoenabled metal-organic algaecide that is self-assembled from natural polyphenols and two functional metal ions for providing shading effects and delivering active ingredients synergistically to suppress algal blooms. Black wattle tannin (BWT) and Fe3+ ions are utilized to develop self-assembled FeBWT nanoalgaecides with significant shading effects for decreasing light transmission (up to 97 %) and effectively inhibiting algal photosynthesis. Further, the FeBWT is functionalized with Cu2+ ions (bimetallic Cu/FeBWT) to target the algal cells and release Cu2+ ions via phenolic-mediated cell surface interactions, thus enhancing the inhibition efficiency. Importantly, the biosafety of Cu/FeBWT is demonstrated through toxicity tests on zebrafish and NIH3T3 cells. In our real-world field test, the Cu/FeBWT demonstrates high algal inhibition performance (>95 %, over 30 days), and enhances the accumulation of food nutrients in model plant lettuces. Collectively, the supramolecular metal-organic nanoalgaecide provides a promise for nanoagrochemical application and promotes food sustainability and security.

The allelopathic effects of Heterosigma akashiwo on Skeletonema costatum: Insights from gene expression and metabolomics analysis

The globally distributed harmful algal blooms (HAB) species, Heterosigma akashiwo, has been found to exhibit ichthyotoxicity. Previous studies have shown that H. akashiwo achieves a competitive edge during bloom occurrences by inhibiting the growth of a coexisting diatom, Skeletonema costatum, through allelopathy. However, the specific allelopathic mechanisms underlying the allelopathic effects of H. akashiwo on S. costatum remain unknown. To bridge this gap, our study utilized a combination of quantitative real-time PCR and metabolomics to examine the allelopathic processes of H. akashiwo on S. costatum. Our results demonstrate that the growth of S. costatum is hindered when co-cultured with H. akashiwo (initial cell concentration, 2 × 104 cell/mL). Gene expression investigation showed a substantial reduction in the mRNA levels of cytochrome b6, ribulose bisphosphate carboxylase large chain, and silicon transporter in S. costatum when grown in co-culture conditions. Furthermore, metabolic pathway analysis suggested that the allelopathic effects of H. akashiwo disrupted several vital metabolic pathways in S. costatum, including a reduction in purine and pyrimidine metabolism and an increase in fatty acid biosynthesis. Our investigation has revealed the intricate and substantial involvement of allelopathy in the formation of H. akashiwo blooms, demonstrating the complexity of the allelopathic interaction between H. akashiwo and S. costatum. These insights also contribute significantly to our understanding of the dynamics within HAB species.

Control of Microcystis aeruginosa by Daphnia: Experimental evidence and identification of involved infochemicals

Infochemicals refer to chemicals responsible for information exchange between organisms. We evaluated the effects of Daphnia magna and Daphnia galeata infochemicals on Microcystis aeruginosa for 15d. The Daphnia infochemicals were obtained from spent medium after culturing Daphnia in Elendt M4 medium for 48 h. Both Daphnia infochemicals significantly increased (p < 0.05) the intracellular reactive oxygen species level and microcystin-LR concentration in M. aeruginosa. This cellular effect increased colony formation of M. aeruginosa, thereby inhibiting the growth of M. aeruginosa. D. galeata infochemicals provoked significantly greater (p < 0.05) adverse effects on M. aeruginosa than those of D. magna infochemicals, which were further exaggerated by pre-exposure of Daphnia to M. aeruginosa. This result seems to be related to the different compositions and concentrations of Daphnia infochemicals. Several Daphnia infochemicals, such as methyl ferulate, cyclohexanone, 3, 5-dimethyl, hexanedioic acid, and bis(2-ethylhexyl) ester, showed a high correlation with M. aeruginosa cell concentration (|r | >0.6), suggesting that they may play a key role in controlling harmful cyanobacteria. Additionally, pre-exposure of D. magna and D. galeata to M. aeruginosa produced oleic acid, methyl ester, and n-hexadecanoic acid, with a highly correlation with M. aeruginosa cell concentration (|r | >0.6). p-tolyl acetate and linoleic acid were detected only in the pre-exposed D. galeata infochemicals. These findings suggest that some of Daphnia infochemicals identified in this study can be a promising tool to control M. aeruginosa growth. However, further studies are required to verify the specific actions of these infochemicals against cyanobacteria.

β-cyclocitral, a novel AChE inhibitor, contributes to the defense of Microcystis aeruginosa against Daphnia grazing

β-cyclocitral is one of the major compounds in cyanobacterial volatile organic compound (VOCs) and can poison other aquatic organisms. To investigate the effect of β-cyclocitral on cyanobacterial-grazer interactions, Daphnia sinensis was fed Microcystis aeruginosa and exposed to β-cyclocitral. Our present study demonstrated that M. aeruginosa could significantly inhibit D. sinensis grazing. And the grazing inhibition by Microcystis aeruginosa results from the suppression of feeding rate, heart rate, thoracic limb activity and swimming speed of D. sinensis. In addition, M. aeruginosa could also induce intestinal peristalsis and emptying in D. sinensis. Interestingly, our present study found that the exposure to β-cyclocitral could mimic a range of phenotypes induced by M. aeruginosa in D. sinensis. These results suggested that M. aeruginosa could release β-cyclocitral to inhibit Daphnia grazing. To further examine the toxic mechanism of β-cyclocitral in Daphnia, several in vivo and in vitro experiments displayed that β-cyclocitral was a novel inhibitor of acetylcholinesterase (AChE). It could induce the accumulation of acetylcholine (ACh) by inhibiting AchE activity in D. sinensis. High level of endogenous Ach could inhibit feeding rate and induce intestinal peristalsis and emptying in D. sinensis.

Competition Increases Risk of Species Extinction during Extreme Warming

AbstractTemperature and interspecific competition are fundamental drivers of community structure in natural systems and can interact to affect many measures of species performance. However, surprisingly little is known about the extent to which competition affects extinction temperatures during extreme warming. This information is important for evaluating future threats to species from extreme high-temperature events and heat waves, which are rising in frequency and severity around the world. Using experimental freshwater communities of rotifers and ciliates, this study shows that interspecific competition can lower the threshold temperature at which local extinction occurs, reducing time to extinction during periods of sustained warming by as much as 2 weeks. Competitors may lower extinction temperatures by altering biochemical characteristics of the natural environment that affect temperature tolerance (e.g., levels of dissolved oxygen, nutrients, and metabolic wastes) or by accelerating population decline through traditional effects of resource depletion on life history parameters that affect population growth rates. The results suggest that changes in community structure in space and time could drive variability in upper thermal limits.

New insights into endocrine reproductive toxicity of Microcystis aeruginosa combined with ammonia exposure in zebrafish

The ecological risk posed by MCs-producing M. aeruginosa and elevated ammonia to fish in actual aquatic environments remains uncertain. To address this knowledge gap, we conducted simulations to investigate the endocrine-reproductive toxicity of prolonged exposure (45 d) to Microcystis aeruginosa (2 × 10^6 cells/mL) and 30 mg/L total ammonia nitrogen (TAN) in zebrafish under environmentally relevant conditions. Our results showed that exposure to M. aeruginosa significantly inhibited the body weight, increased gonadosomatic index (GSI), delayed oocyte development, and disrupted endocrine hormonal balance (reduced gonadotropin-releasing hormone (GnRH), and increased estradiol (E2) and testosterone (T)). Mechanistically, it should be attributed to the over-expression of hypothalamic-pituitary-gonadal-liver (HPGL) axis-related genes (cyp11a and cyp17) induced by M. aeruginosa. On the other hand, TAN exposure caused mild damage to zebrafish ovarian tissue and promoted an increase of T levels by inducing the upregulation of steroid hormone synthesis gene (3βhsd) expression in the ovary. It is worth noting that the dysregulation of E2/T ratio in zebrafish ovaries may be attributed to the inhibition of cyp19a1a by both M. aeruginosa and TAN. These results were further confirmed by changes in steroidogenic enzymes activities in the M. aeruginosa or TAN treated groups. Our findings indicated that exposure to M. aeruginosa and TAN had adverse impacts on the reproductive system of zebrafish. And the combined exposure of M. aeruginosa and TAN had more severe effects on the body weight, GSI, pathological changes, hormone levels and HPGL-axis related gene expression in female zebrafish. These results provide compelling evidence regarding the potential risks for reproductive health associated with M. aeruginosa and TAN in eutrophic water bodies experiencing M. aeruginosa blooms, and contribute to the development of effective strategies for monitoring and managing these toxins in aquatic ecosystems.

Cell-Targeted Metal-Phenolic Nanoalgaecide in Hydroponic Cultivation to Enhance Food Sustainability

The growing global population necessitates substantial increases in food production. Hydroponic cultivation systems afford a critical alternative for food sustainability and enable stable annual production regardless of the climatic and geographical variations. However, the overgrowth of harmful algal blooms significantly threatens the crop yield by competing with nutrition in the solution and producing contaminants. The conventional practice of algaecides fails to control algal proliferation due to the limited efficiency and food safety concerns. Nanopesticides can deliver active ingredients responsively to suppress crop diseases and offer solutions to current practical challenges and difficulties. Inspired by prospects of nanotechnology for agricultural applications, we have utilized natural polyphenols and copper ions (Cu2+ ions) to develop self-assembled nanoalgaecides referred to as CuBes. The nanoalgaecide attached to algal cells via phenolic surface interactions, enabling localized Cu2+ ion release. This cell-targeted delivery suppressed Chlorella vulgaris for over 30 days (99% inhibition). Transcriptomics revealed that the nanoalgaecide disrupted algal metabolism by downregulating photosynthesis and chlorophyll pathways. In a solar-illuminated plant factory, the nanoalgaecide showed higher algal inhibition and lettuce biosafety versus the commercial Kocide 3000. Notably, the use of nanoalgaecide can enhance the nutrient value of lettuces, which meets the daily supply of Cu for adults. By integrating smart nanotechnology design with selective delivery mechanisms, this metal-phenolic nanoalgaecide provides a nanoenabled solution for controlling harmful algal blooms in hydroponics to advance food production.

Novel ecological implications of non-toxic Microcystis towards toxic ecotype in population-promoting toxic ecotype dominance at various N levels and cooperative defense against luteolin-stress

Microcystin (MC)-producing (MC+) and MC-free (MC-) Microcystis always co-exist and interact during Microcystis-dominated cyanobacterial blooms (MCBs), where MC+Microcystis abundance and extracellular MC-content (EMC) determine the hazard extent of MCBs. The current study elucidated intraspecific interaction between MC+ and MC-Microcystis at various nitrogen (N) levels (0.5-50 mg/L) and how such N-mediated interaction impacted algicidal and EMC-inhibiting effect of luteolin, a natural bioalgicide. Conclusively, MC+ and MC-Microcystis were inhibited mutually at N-limitation (0.5 mg/L), which enhanced the algicidal and EMC-inhibiting effects of luteolin. However, at N-sufficiency (5-50 mg/L), MC-Microcystis promoted MC+ ecotype growth and dominance, and such intraspecific interaction induced the cooperative defense of two ecotypes, weakening luteolin's algicidal and EMC-inhibiting effects. Mechanism analyses further revealed that MC+Microcystis in luteolin-stress co-culture secreted exopolymeric substances (EPSs) for self-protection against luteolin-stress and also released more EMC to induce EPS-production by MC-Microcystis as protectants, thus enhancing their luteolin-resistance and promoting their growth. This study provided novel ecological implications of MC-Microcystis toward MC+ ecotype in terms of assisting the dominant establishment of MC+Microcystis and cooperative defense with MC+ ecotype against luteolin, which guided the application of bioalgicide (i.e. luteolin) for MCBs and MCs pollution mitigation in different eutrophication-degree waters.

Broad spectrum and species specificity of plant allelochemicals 1,2-benzenediol and 3-indoleacrylic acid against marine and freshwater harmful algae

Allelochemicals derived from plants have shown great potential in mitigating harmful algal blooms (HABs), although different algal species can respond differently to these chemicals. Therefore, we first investigated the allelopathic effects of two newly identified plant-derived allelochemicals, 1,2-benzenediol (1,2-BD) and 3-indoleacrylic acid (3-IDC), on six algal species. Then we further evaluated the allelopathic responses of two bloom-forming species, Microcystis aeruginosa FACHB-905 and Heterosigma akashiwo to 1,2-BD. Results showed that 1,2-BD had a broader antialgal spectrum than 3-IDC. Allelopathic response analysis indicated that 1,2-BD consistently and stably inhibit the growth of M. aeruginosa FACHB-905, with inhibitory mechanism being disruption of photosynthetic activity, overwhelming of the antioxidant system and activation of programmed cell death (PCD). H. akashiwo displayed resistance to 1,2-BD during exposure, and the growth inhibition was mainly attributed to PCD. Therefore, the species-specific allelopathic responses provide new insights for controlling HABs using 1,2-BD and 3-IDC.

Phytoplankton interspecific interactions modified by symbiotic fungi and bacterial metabolites under environmentally relevant hydrogen peroxide concentrations stress

Hydrogen peroxide (H2O2), which accumulates in water and triggers oxidative stress for aquatic microbes, has been shown to have profound impacts on planktonic microbial community dynamics including cyanobacterial bloom formation. Yet, potential effects of H2O2 on interspecific relationships of phytoplankton-microbe symbiotic interactions remain unclear. Here, we investigated effects of environmentally relevant H2O2 concentrations on interspecific microbial relationships in algae-microbe symbiosis. Microbes play a crucial role in the competition between M. aeruginosa and Chlorella vulgaris at low H2O2 concentrations (∼400 nM), in which fungi and bacteria protect Microcystis aeruginosa from oxidative stress. Moreover, H2O2 stimulated the synthesis and release of extracellular microcystin-LR from Microcystis aeruginosa, while intracellular microcystin-LR concentrations remained at a relatively constant level. In the presence of H2O2, loss of organoheterocyclic compounds, organic acids and ketones contributed to the growth of M. aeruginosa, but the reduction of vitamins inhibited it. Regulation of interspecific relationships by H2O2 is achieved by its action on fungal species and bacterial secretory metabolites. This study explored the response of phytoplankton interspecific relationships in symbiotic phytoplankton-microbe interactions to environmentally relevant H2O2 concentrations stress, providing a theoretical basis for understanding the formation of harmful-algae blooming and impact of photochemical properties of water on aquatic ecological safety and stability.

Microalgal co-cultivation -recent methods, trends in omic-studies, applications, and future challenges

The burgeoning human population has resulted in an augmented demand for raw materials and energy sources, which in turn has led to a deleterious environmental impact marked by elevated greenhouse gas (GHG) emissions, acidification of water bodies, and escalating global temperatures. Therefore, it is imperative that modern society develop sustainable technologies to avert future environmental degradation and generate alternative bioproduct-producing technologies. A promising approach to tackling this challenge involves utilizing natural microbial consortia or designing synthetic communities of microorganisms as a foundation to develop diverse and sustainable applications for bioproduct production, wastewater treatment, GHG emission reduction, energy crisis alleviation, and soil fertility enhancement. Microalgae, which are photosynthetic microorganisms that inhabit aquatic environments and exhibit a high capacity for CO2 fixation, are particularly appealing in this context. They can convert light energy and atmospheric CO2 or industrial flue gases into valuable biomass and organic chemicals, thereby contributing to GHG emission reduction. To date, most microalgae cultivation studies have focused on monoculture systems. However, maintaining a microalgae monoculture system can be challenging due to contamination by other microorganisms (e.g., yeasts, fungi, bacteria, and other microalgae species), which can lead to low productivity, culture collapse, and low-quality biomass. Co-culture systems, which produce robust microorganism consortia or communities, present a compelling strategy for addressing contamination problems. In recent years, research and development of innovative co-cultivation techniques have substantially increased. Nevertheless, many microalgae co-culturing technologies remain in the developmental phase and have yet to be scaled and commercialized. Accordingly, this review presents a thorough literature review of research conducted in the last few decades, exploring the advantages and disadvantages of microalgae co-cultivation systems that involve microalgae-bacteria, microalgae-fungi, and microalgae-microalgae/algae systems. The manuscript also addresses diverse uses of co-culture systems, and growing methods, and includes one of the most exciting research areas in co-culturing systems, which are omic studies that elucidate different interaction mechanisms among microbial communities. Finally, the manuscript discusses the economic viability, future challenges, and prospects of microalgal co-cultivation methods.

Systematic exploration of transcriptional responses of interspecies interaction between Karenia mikimotoi and Prorocentrum shikokuense

Karenia mikimotoi and Prorocentrum shikokuense (also identified as P. donghaiense Lu and P. obtusidens Schiller) are two important harmful algal species which often form blooms in the coasts of China. Studies have shown that the allelopathy of K. mikimotoi and P. shikokuense plays an important role in inter-algal competition, though the underlying mechanisms remain largely unclear. Here, we observed reciprocal inhibitory effects between K. mikimotoi and P. shikokuense under co-cultures. Based on the reference sequences, we isolated RNA sequencing reads of K. mikimotoi and P. shikokuense from co-culture metatranscriptome, respectively. We found the genes involved in photosynthesis, carbon fixation, energy metabolism, nutrients absorption and assimilation were significantly up-regulated in K. mikimotoi after co-cultured with P. shikokuense. However, genes involved in DNA replication and cell cycle were significantly down-regulated. These results suggested that co-culture with P. shikokuense stimulated cell metabolism and nutrients competition activity of K. mikimotoi, and inhibited cell cycle. In contrast, genes involved in energy metabolism, cell cycle and nutrients uptake and assimilation were dramatically down-regulated in P. shikokuense under co-culture with K. mikimotoi, indicating that K. mikimotoi could highly affect the cellular activity of P. shikokuense. In addition, the expression of PLA2G12 (Group XII secretory phospholipase A2) that can catalyze the accumulation of linoleic acid or linolenic acid, and nitrate reductase that may be involved in nitric oxide production were significantly increased in K. mikimotoi, suggesting that PLA2G12 and nitrate reductase may play important roles in the allelopathy of K. mikimotoi. Our findings shed new light on the interspecies competition between K. mikimotoi and P. shikokuense, and provide a novel strategy for studying interspecific competition in complex systems.

The mechanism of different cyanobacterial responses to glyphosate

Glyphosate, the most extensively used herbicide globally, has raised ecotoxicological concerns because it can be transported into the aquatic environment and cause adverse effects on the aquatic system. However, the functional mechanism of glyphosate on cyanobacteria are not completely disentangled. In this study, we selected six common cyanobacteria to evaluate glyphosate effects on cyanobacterial growth in monoculture experiment. Results showed that the growth of five tested cyanobacterial species were promoted under different degrees, and only Pseudanabaena was inhibited by glyphosate. In the phylogenetic tree based on gene sequences of 5-enol-pyruvylshikimate-3-phosphate synthase (EPSPS), a target for glyphosate, we found that the position of Pseudanabaena is the closest to plant, which was sensitive to glyphosate, thereby explaining the inhibitory effect of Pseudanabaena following glyphosate exposure. The primary degraded metabolites or analogs did not induce cyanobacterial growth, laterally demonstrating that glyphosate was used as a source of phosphorus to accelerate cyanobacterial growth because phosphorus levels increased in the medium of glyphosate treatment. Overall, this study provides a better understanding of the influence of glyphosate on the composition of aquatic microbiota and explains the mechanism of cyanobacterial response to glyphosate.

The long overlooked microalgal nitrous oxide emission: Characteristics, mechanisms, and influencing factors in microalgae-based wastewater treatment scenarios

Microalgae-based wastewater treatment is particularly advantageous in simultaneous CO₂ sequestration and nutrients recovery, and has received increasing recognition and attention in the global context of synergistic pollutants and carbon reduction. However, the fact that microalgae themselves can generate the potent greenhouse gas nitrous oxide (N₂O) has been long overlooked, most previous research mainly regarded microalgae as labile organic carbon source or oxygenic approach that interfere bacterial nitrification-denitrification and the concomitant N₂O production. This study, therefore, summarized the amount and rate of N₂O emission in microalgae-based systems, interpreted in-depth the multiple pathways that lead to NO formation as the key precursor of N₂O, and the pathways that transform NO into N₂O. Reduction of nitrite could take place in either the cytoplasm or the mitochondria to form NO by a series of enzymes, while the NO could be enzymatically reduced to N₂O at the chloroplasts or the mitochondria respectively under light and dark conditions. The influences of abiotic factors on microalgal N₂O emission were analyzed, including nitrogen types and concentrations that directly affect the nitrogen transformation routes, illumination and oxygen conditions that regulate the enzymatic activities related to N₂O generation, and other factors that indirectly interfere N₂O emission via NO regulation. The uncertainty of microalgae-based N₂O emission in wastewater treatment scenarios were emphasized, which would be particularly impacted by the complex competition between microalgae and ammonia oxidizing bacteria or nitrite oxidizing bacteria over ammonium or inorganic carbon source. Future studies should put more efforts in improving the compatibility of N₂O emission results expressions, and adopting consistent NO detection methods for N₂O emission prediction. This review will provide much valuable information on the characteristics and mechanisms of microalgal N₂O emission, and arouse more attention to the non-negligible N₂O emission that may impair overall greenhouse gas reduction efficiency in microalgae-based wastewater treatment systems.

Effect of zinc and iron oxide nanoparticles on plant physiology, seed quality and microbial community structure in a rice-soil-microbial ecosystem

In this study, we assessed the impact of zinc oxide (ZnO) and iron oxide (FeO) (<36 nm) nanoparticles (NPs) as well as their sulphate salt (bulk) counterpart (0, 25, 100 mg/kg) on rice growth and seed quality as well as the microbial community in the rhizosphere environment of rice. During the rice growing season 2021-22, all experiments were conducted in a greenhouse (temperature: day 30 °C; night 20 °C; relative humidity: 70%; light period: 16 h/8 h, day/night) in rice field soil. Results showed that low concentrations of FeO and ZnO NPs (25 mg/kg) promoted rice growth (height (29%, 16%), pigment content (2%, 3%)) and grain quality parameters such as grains per spike (8%, 9%), dry weight of grains (12%, 14%) respectively. As compared to the control group, the Zn (2%) and Fe (5%) accumulations at their respective low concentrations of NP treatments showed stimulation. Interestingly, our results showed that at low concentration of both the NPs the soil microbes had more diversity and richness than those in the bulk treated and control soil group. Although a number of phyla were affected by the presence of NPs, the strongest effects were observed for change in the abundance of the three phyla for Proteobacteria, Actinobacteria, and Planctomycetes. The rhizosphere environment was notably enriched with potential streptomycin producers, carbon and nitrogen fixers, and lignin degraders with regard to functional groups of microorganisms. However, microbial communities mainly responsible for chitin degradation, ammonia oxidation, and nitrite reduction were found to be decreased. The results from this study highlight significant changes in several plant-based endpoints, as well as the rhizosphere soil microorganisms. It further adds information to our understanding of the nanoscale-specific impacts of important micronutrient oxides on both rice and its associated soil microbiome.

Improvement of aquaculture water quality by mixed Bacillus and its effects on microbial community structure

Microbial remediation, especially the application of probiotics, has recently gained popularity in improving water quality and maintaining aquatic animal health. The efficacy and mechanism of mixed Bacillus for improvement of water quality and its effects on aquatic microbial community structure remain unknown. To elucidate these issues, we applied two groups of mixed Bacillus (Bacillus megaterium and Bacillus subtilis (A0 + BS) and Bacillus megaterium and Bacillus coagulans (A0 + BC)) to the aquaculture system of Crucian carp. Our results showed that the improvement effect of mixed Bacillus A0 + BS on water quality was better than that of A0 + BC, and the NH₄⁺-N, NO₂^--N, NO₃^--N, and total phosphorus (TP) concentrations were reduced by 46.3%, 76.3%, 35.6%, and 80.3%, respectively. In addition, both groups of mixed Bacillus increased the diversity of the bacterial community and decreased the diversity of the fungal community. Microbial community analysis showed that mixed Bacillus A0 + BS increased the relative abundance of bacteria related with nitrogen and phosphorus removal, such as Proteobacteria, Actinobacteria, Comamonas, and Stenotrophomonas, but decreased the relative abundance of pathogenic bacteria (Acinetobacter and Pseudomonas) and fungi (Epicoccum and Fusarium). Redundancy analysis showed that NH₄⁺-N, NO₂^--N, and TP were the primary environmental factors affecting the microbial community in aquaculture water. PICRUST analysis indicated that all functional pathways in the A0 + BS group were richer than those in other groups. These results indicated that mixed Bacillus A0 + BS addition produced good results in reducing nitrogenous and phosphorus compounds and shaped a favorable microbial community structure to further improve water quality.

Evaluation of phoxim toxicity on aquatic and zebrafish intestinal microbiota by metagenomics and 16S rRNA gene sequencing analysis

Phoxim is one of the main organophosphorus pesticides used in agricultural production. However, little information is known about how it affects the aquatic microbial community and the intestinal microbiota of fish. Herein, we utilized shotgun metagenomics and 16S rRNA gene sequencing to reveal the aquatic eco-risk of phoxim. Seven days of phoxim exposure significantly changed the composition of aquatic microbial community, obliterated the interactions between microorganisms, and thus reduced the complexity and stability of the microbial community. During long-time exposure (i.e., 14 days), most of the ecological functions were restored due to the redundancy of the microbial community. However, phoxim exposure promoted the dissemination of elfamycin resistance gene. The zebrafish gut microbial community also recovered from a temporary ecological disorder of aquatic microbiota, but phoxim continually affected zebrafish growth and swimming behavior. Overall, our results demonstrated that phoxim exposure significantly changed the structure and function of the microbial community and displayed a negative impact on freshwater ecosystems in a short exposure time.

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

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

Cross-feeding among microalgae facilitates nitrogen recovery at low C/N

Although co-culture of microalgae has been found as a feasible strategy to improve biomass production, their interspecies relationships are not fully understood. Here, two algae taxa, Chlorella sp. and Phormidium sp., were mono-cultured and co-cultured in three photobioreactors for 70 days with periodically harvesting to investigate how dual-species interaction influence nitrogen recovery. Results showed that the co-culture system achieved a significantly higher protein production and nitrogen removal rate than those in the individual cultures at a C/N ratio of 3:1 (p < 0.05). Genome-Centered metagenomic analysis revealed their cooperative relationship exemplified by cross-feeding. Phormidium sp. had the ability to synthesize pseudo-cobalamin, and Chlorella sp. harbored the gene for remodeling the pseudo-cobalamin to bioavailable vitamin B12. Meanwhile, Chlorella sp. could contribute the costly amino acid and cofactors for Phormidium sp. Their symbiotic interaction facilitated extracellular polymeric substances (EPS) production and nitrogen recovery. The EPS concentration in co-culture was positively related to the settling efficiency (R² = 0.774), which plays an essential role in nitrogen recovery. This study provides new insights into microbial interactions among the photoautotrophic community and emphasizes the importance of algal interspecies interaction in algae-based wastewater treatment.

Adverse role of colonial morphology and favorable function of microcystins for Microcystis to compete with Scenedesmus

In eutrophic freshwaters, Microcystis usually becomes dominant in phytoplankton communities due to the synergistic effects of its special eco-physiological traits and environmental factors. Colonial morphology can protect Microcystis from zooplankton grazing, which indirectly favors Microcystis to outcompete other phytoplankton, although the colonial form is not conducive to the absorption of nutrients. Moreover, unicellular Microcystis usually has competitive advantages over other phytoplankton due to its efficient absorption capacity for nutrients and releasing microcystins. However, the consequence of direct competition between toxic colonial Microcystis and green algae without external grazing pressure still remained unknown. In this study, the competition between toxic colonial Microcystis aeruginosa and a common green alga Scenedesmus obliquus was explored. Results showed that: (1) colonial M. aeruginosa had a higher requirement for key macro-nutrient phosphorus than S. obliquus, and thus its population declined and was replaced by S. obliquus eventually; (2) microcystins released by colonial M. aeruginosa inhibited the photosynthetic activity and growth of S. obliquus at early stage of the competition; (3) the photosynthetic potential of colonial M. aeruginosa was stimulated in response to the competitive stress from S. obliquus, although the population of colonial M. aeruginosa declined eventually; (4) microcystin production of colonial M. aeruginosa was enhanced by phosphorus limitation due to S. obliquus competition and was positively related to photosynthetic potential of colonial M. aeruginosa. These results indicated that, in the absence of complex natural environment, colonial Microcystis cannot outcompete Scenedesmus in a pure competition, although microcystins can play a favorable role in the competition, which clarified the opposite role of colonies and microcystins in the competition of colonial Microcystis against other phytoplankton.

Synergistic toxicity to the toxigenic Microcystis and enhanced microcystin release exposed to polycyclic aromatic hydrocarbon mixtures

With the continued influx and accumulation of polycyclic aromatic hydrocarbons (PAHs) in eutrophic waters, the effects of PAHs on cyanobacteria bloom need to be clarified. PAHs usually existed as mixtures in aquatic environments, but the combined toxicity of PAH mixtures to toxigenic cyanobacteria remained unknown. This study investigated the effects of phenanthrene (Phe) and benzo [a]pyrene (BaP), alone or in combination, on the growth and physiology of Microcystis aeruginosa. The results showed that a hormesis effect on growth at low doses of the single Phe (≤1 mg/L) or PAH mixtures (≤0.279 mg/L) was observed, whereas the single BaP induced significant growth inhibitions at all concentrations (≥0.2 mg/L). The median effective concentrations (96 h) for Phe, BaP and their mixtures were 4.29, 1.29 and 1.07 mg/L, respectively. Mixture toxicity models showed that Phe and BaP elicited a synergistic interaction on M. aeruginosa. The synergy may be ascribed to the excessive oxidative stress induced by PAH mixtures, which further led to membrane structure damages, photosynthesis inhibitions and decreased metabolic activity. Moreover, the microcystins (MCs) release significantly increased by 25.3% and 31.9% upon exposure to 0.558 and 1.116 mg/L of PAH mixtures. In all, this study suggested that the enhanced release of MCs by PAH mixtures might exacerbate potential risks to the aquatic environment.

Enrofloxacin perturbs nitrogen transformation and assimilation in rice seedlings (Oryza sativa L.)

The extensive use of antibiotics worldwide has led to phytotoxicity and high risks to humans. Although research on the physiological toxicity of antibiotics is extensive, its influence on plant nitrogen uptake and assimilation remains unclear. The effect of enrofloxacin on nitrogen transformation and assimilation in rice (Oryza sativa L.) seedlings was investigated in this study. Enrofloxacin had no significant effect on rice growth, nitrogen assimilation and metabolism at low concentration, while significant changes were observed in high concentration. The growth of rice seedlings was inhibited, nitrate uptake was enhanced and nitrogen content increased significantly in both shoots and roots in enrofloxacin (800 μg L^-1) treatment. Furthermore, enrofloxacin promoted the activity of enzymes related to nitrogen assimilation, including nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, and glutamate dehydrogenase. High enzyme activity resulted in an increase in intermediate products and protein content, suggesting that rice seedlings may detoxify enrofloxacin stress through amino acid binding and nitro-oxidative stress might be one of the reasons of phenotype change. Gas chromatography-mass spectrometry results revealed that different types of metabolites in both shoots and roots increased with enrofloxacin stress. Specifically, glycine, serine, and threonine metabolism; aminoacyl-tRNA biosynthesis; alanine, aspartate, and glutamate metabolism; butanoate metabolism; glyoxylate and dicarboxylate metabolism in shoot; and tyrosine metabolism and citrate cycle in root were affected. Moreover, a significant correlation between nitrogen content, nitrogen assimilation enzyme activity, and metabolite content was observed. Collectively, these findings reveal the potential risks of using reclaimed wastewater irrigation and/or antibiotic-containing animal fertilizers on crops.

Enantioselective metabolomic modulations in Arabidopsis thaliana leaf induced by the herbicide dichlorprop

Over 40% of herbicides used today are chiral. Dichlorprop (2, 4-DCPP) is a widely used typical broad-spectrum chiral aryloxyphenoxy propionic acid (AOPP) herbicide. However, the molecular mechanism of the enantioselectivity of DCPP enantiomers (S-DCPP and R-DCPP) and their effects on non-target organisms are remain unclear. In the present study, the model plant Arabidopsis thaliana was treated by DCPP enantiomers to directly reveal the effects of DCPP enantiomers on plant growth, as well as metabolic profile. Results showed that the enantioselectivity embodied in that R-DCPP treatment led to the decrease of shoot weight, the significantly variation on morphology of shoot and root, oxidative damage, et al., while the plant morphology also changes to a certain extent associated oxidative damage after treated by S-DCPP. By using metabolomic analysis, it was found that R-DCPP had significant effects on A. thaliana leaf metabolism, including lactose metabolism, starch and sucrose metabolism, TCA cycle, fatty acid biosynthesis pathway and pentose phosphate pathway, and accumulated a lot of antioxidants in plant leaves, while the amino acids and some terpenoids increased in S-DCPP group. Our study provides a new direction to explore the relationship between chiral herbicides on leaf metabolism, and the effect of this relationship on the plant growth.

Cyanobacterial dominance and succession: Factors, mechanisms, predictions, and managements

Eutrophication of natural water bodies worldwide has led to cyanobacteria becoming the dominant species in phytoplankton communities, causing serious harm environmentally and economically. Cyanobacterial succession makes effective treatment of cyanobacterial blooms a challenge. Although there are many studies about cyanobacterial dominance and succession, it is still lack of relevant review summarizing the advances on this topic. To control cyanobacterial blooms and manage water quality effectively, we conducted a critical review and drew the following conclusions: (1) cyanobacterial dominance and succession occur from spring to summer, with changes of multiple environmental factors dominated by temperature and nutrients conditions; (2) the cyanobacterial dominance and succession are inherently attributed to the distinctive traits of cyanobacteria including colony formation, gas vesicles, toxin release, and nitrogen fixation; (3) given the current meta-omics explorations on mechanisms of cyanobacterial succession, how to combine the extensive data to draw general conclusions is a challenge in the future; (4) the dominant niche of high temperature-adapted cyanobacteria genera will be further reinforced with global warming and elevated carbon dioxide in the future; (5) considering the causes and future developments of cyanobacterial blooms, the management strategies for controlling cyanobacterial blooms include reducing external nutrient input and removing internal nutrient in sediment, artificial mixing waters to decrease buoyancy of cyanobacteria, and biological control using allelopathy of aquatic plants and/or enhancing zooplankton feeding.

ROS Metabolism Perturbation as an Element of Mode of Action of Allelochemicals

The allelopathic interaction between plants is one of the elements that influences plant communities. It has been commonly studied by applying tissue extracts onto the acceptors or by treating them with isolated allelotoxins. Despite descriptive observations useful for agricultural practice, data describing the molecular mode of action of allelotoxins cannot be found. Due to the development of -omic techniques, we have an opportunity to investigate specific reactive oxygen species (ROS)-dependent changes in proteome or transcriptome that are induced by allelochemicals. The aim of our review is to summarize data on the ROS-induced modification in acceptor plants in response to allelopathic plants or isolated allelochemicals. We present the idea of how ROS are involved in the hormesis and plant autotoxicity phenomena. As an example of an -omic approach in studies of the mode of action of allelopatic compounds, we describe the influence of meta-tyrosine, an allelochemical exudated from roots of fescues, on nitration-one of nitro-oxidative posttranslational protein modification in the roots of tomato plants. We conclude that ROS overproduction and an induction of oxidative stress are general plants' responses to various allelochemicals, thus modification in ROS metabolisms is regarded as an indirect mode of action of allelochemicals.

Nano-Sized Polystyrene at 1 mg/L Concentrations Does Not Show Strong Disturbance on the Freshwater Microbial Community

In recent years, microplastics and nanoplastics have gained public attention, but their impacts on the freshwater microbial communities is rarely evaluated. In this study, the effects of 1 mg/L nano-sized polystyrene (nPS) and its modified forms (carboxyl-modified and amino-modified nPS) on the structures and functions of freshwater microbial community were determined. The nPS were found to slightly reduce the chlorophyll-a and increase the phycocyanin contents of freshwater microbial communities. Moreover, the richness of the microbial communities temporarily decreased during this process, while their diversity remained uninfluenced by treatment with nPS. Although the three tested nPS types were found to disturb the compositions of both the prokaryotic and eukaryotic communities to some degree, they did not affect the functions of freshwater bacterial communities significantly due to functional redundancy. Our study demonstrated that the ecotoxicities of the nPS itself were found to be lower than what is generally expected.

Reviewing Interspecies Interactions as a Driving Force Affecting the Community Structure in Lakes via Cyanotoxins

The escalating occurrence of toxic cyanobacterial blooms worldwide is a matter of concern. Global warming and eutrophication play a major role in the regularity of cyanobacterial blooms, which has noticeably shifted towards the predomination of toxic populations. Therefore, understanding the effects of cyanobacterial toxins in aquatic ecosystems and their advantages to the producers are of growing interest. In this paper, the current literature is critically reviewed to provide further insights into the ecological contribution of cyanotoxins in the variation of the lake community diversity and structure through interspecies interplay. The most commonly detected and studied cyanobacterial toxins, namely the microcystins, anatoxins, saxitoxins, cylindrospermopsins and β-N-methylamino-L-alanine, and their ecotoxicity on various trophic levels are discussed. This work addresses the environmental characterization of pure toxins, toxin-containing crude extracts and filtrates of single and mixed cultures in interspecies interactions by inducing different physiological and metabolic responses. More data on these interactions under natural conditions and laboratory-based studies using direct co-cultivation approaches will provide more substantial information on the consequences of cyanotoxins in the natural ecosystem. This review is beneficial for understanding cyanotoxin-mediated interspecies interactions, developing bloom mitigation technologies and robustly assessing the hazards posed by toxin-producing cyanobacteria to humans and other organisms.

The current state of knowledge on taxonomy, modulating factors, ecological roles, and mode of action of phytoplankton allelochemicals

Allelopathy is widespread in marine, brackish, and freshwater habitats. Literature data indicate that allelopathy could offer a competitive advantage for some phytoplankton species by reducing the growth of competitors. It is also believed that allelopathy may affect species succession. Thus, allelopathy may play a role in the development of blooms. Over the past few decades, the world's coastal waters have experienced increases in the numbers of cyanobacterial and microalgal blooming events. Understanding how allelopathy is implicated with other biological and environmental factors as a bloom-development mechanism is an important topic for future research. This review focuses on a taxonomic overview of allelopathic cyanobacteria and microalgae, the biological and environmental factors that affect allelochemical production, their role in ecological dynamics, and their physiological modes of action, as well as potential industrial applications of allelopathic compounds.

Influence of cyanobacterial blooms and environmental variation on zooplankton and eukaryotic phytoplankton in a large, shallow, eutrophic lake in China

Harmful cyanobacterial blooms are a widespread destruction to the processes and function of aquatic ecosystems. To study effects of cyanobacterial blooms on plankton diversity and composition, we analyzed data of cyanobacterial, eukaryotic phytoplankton, metazoan zooplankton, and physicochemical samples collected from 24 sites for four seasons in 2017 and 2018 from the large, shallow Lake Taihu. We found that cyanobacterial abundance significantly correlated with phytoplankton biomass, species richness, functional richness and evenness, and zooplankton biomass, Shannon's diversity, Simpson's evenness, and functional evenness and richness. High cyanobacterial abundance during summer did not result in low species and functional diversities for both phytoplankton and zooplankton compared with other seasons. Species and functional diversities of sites with high cyanobacteria abundance were not significantly lower than other sites with relatively low cyanobacteria abundance. Structure equation modeling indicated that cyanobacteria had direct influence on phytoplankton and zooplankton compositions. Physicochemical and temporal-spatial factors had direct influence on phytoplankton and zooplankton, and had indirect influence on phytoplankton and zooplankton through direct influence on cyanobacteria. Variance partitioning analysis quantified that cyanobacteria alone and interactions with physicochemical and spatial-temporal factors explained about 10% of phytoplankton variation and 26% of zooplankton variation. Our results indicate that cyanobacteria have substantial effects on phytoplankton and zooplankton biodiversity and community composition. Physicochemical and spatial-temporal factors could potentially obscure the detection of cyanobacterial effects on plankton in Lake Taihu that has cyanobacterial blooms in all seasons. Our findings may improve the understanding of dynamics and responses of plankton communities to environmental changes and cyanobacterial bloom disturbance and enhance the capability of assessing the effectiveness of eutrophication management and restoration of aquatic ecosystems.

Covariance of Phytoplankton, Bacteria, and Zooplankton Communities Within Microcystis Blooms in San Francisco Estuary

Microcystis blooms have occurred in upper San Francisco Estuary (USFE) since 1999, but their potential impacts on plankton communities have not been fully quantified. Five years of field data collected from stations across the freshwater reaches of the estuary were used to identify the plankton communities that covaried with Microcystis blooms, including non-photosynthetic bacteria, cyanobacteria, phytoplankton, zooplankton, and benthic genera using a suite of analyses, including microscopy, quantitative PCR (qPCR), and shotgun metagenomic analysis. Coherence between the abundance of Microcystis and members of the plankton community was determined by hierarchal cluster analysis (CLUSTER) and type 3 similarity profile analysis (SIMPROF), as well as correlation analysis. Microcystis abundance varied with many cyanobacteria and phytoplankton genera and was most closely correlated with the non-toxic cyanobacterium Merismopoedia, the green algae Monoraphidium and Chlamydomonas, and the potentially toxic cyanobacteria Pseudoanabaena, Dolichospermum, Planktothrix, Sphaerospermopsis, and Aphanizomenon. Among non-photosynthetic bacteria, the xenobiotic bacterium Phenylobacterium was the most closely correlated with Microcystis abundance. The coherence of DNA sequences for phyla across trophic levels in the plankton community also demonstrated the decrease in large zooplankton and increase in small zooplankton during blooms. The breadth of correlations between Microcystis and plankton across trophic levels suggests Microcystis influences ecosystem production through bottom-up control during blooms. Importantly, the abundance of Microcystis and other members of the plankton community varied with wet and dry conditions, indicating climate was a significant driver of trophic structure during blooms.

Allelopathy of Alexandrium pacificum on Thalassiosira pseudonana in laboratory cultures

Alexandrium pacificum is a toxin-producing dinoflagellate with allelopathic effects. The elucidation of allelopathic mechanism of A. pacificum is of great significance for understanding A. pacificum blooms. To this end, using the model diatom Thalassiosira pseudonana as a target species, we observed changes in physiological, biochemical and gene transcription of T. pseudonana upon being co-cultured with A. pacificum. We found reciprocal effects between A. pacificum and T. pseudonana, and corroborated A. pacificum's allelopathy on T. pseudonana by observing inhibitory effects of filtrate from A. pacificum culture on the growth of T. pseudonana. We also found that co-culturing with A. pacificum, the expression of T. pseudonana genes related to photosynthesis, oxidative phosphorylation, antioxidant system, nutrient absorption and energy metabolism were drastically influenced. Coupled with the alterations in Fv/Fm (the variable/maximum fluorescence ratio), activity of superoxide dismutase, contents of malondialdehyde, neutral lipid and total protein in T. pseudonana co-cultured with A. pacificum, we propose that A. pacificum allelopathy could reduce the efficiency of photosynthesis and energy metabolism of T. pseudonana and caused the oxidative stress, while the nutrient absorption was also affected by allelopathic effects. The resultant data potentially uncovered the allelopathic molecular mechanism of A. pacificum to model alga T. pseudonana. The changes in nutrient uptake and even energy metabolism in T. pseudonana, as an adaptation to environmental conditions, may prevent it from stress-related injuries. Our finding might advance the understanding of allelopathic mechanism of A. pacificum.

The genetic and ecophysiological diversity of Microcystis

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

Co-culturing microbial consortia: approaches for applications in biomanufacturing and bioprocessing

The application of microbial co-cultures is now recognized in the fields of biotechnology, ecology, and medicine. Understanding the biological interactions that govern the association of microorganisms would shape the way in which artificial/synthetic co-cultures or consortia are developed. The ability to accurately predict and control cell-to-cell interactions fully would be a significant enabler in synthetic biology. Co-culturing method development holds the key to strategically engineer environments in which the co-cultured microorganism can be monitored. Various approaches have been employed which aim to emulate the natural environment and gain access to the untapped natural resources emerging from cross-talk between partners. Amongst these methods are the use of a communal liquid medium for growth, use of a solid-liquid interface, membrane separation, spatial separation, and use of microfluidics systems. Maximizing the information content of interactions monitored is one of the major challenges that needs to be addressed by these designs. This review critically evaluates the significance and drawbacks of the co-culturing approaches used to this day in biotechnological applications, relevant to biomanufacturing. It is recommended that experimental results for a co-cultured species should be validated with different co-culture approaches due to variations in interactions that could exist as a result of the culturing method selected.

Semi-automated classification of colonial Microcystis by FlowCAM imaging flow cytometry in mesocosm experiment reveals high heterogeneity during seasonal bloom

A machine learning approach was employed to detect and quantify Microcystis colonial morphospecies using FlowCAM-based imaging flow cytometry. The system was trained and tested using samples from a long-term mesocosm experiment (LMWE, Central Jutland, Denmark). The statistical validation of the classification approaches was performed using Hellinger distances, Bray-Curtis dissimilarity, and Kullback-Leibler divergence. The semi-automatic classification based on well-balanced training sets from Microcystis seasonal bloom provided a high level of intergeneric accuracy (96-100%) but relatively low intrageneric accuracy (67-78%). Our results provide a proof-of-concept of how machine learning approaches can be applied to analyze the colonial microalgae. This approach allowed to evaluate Microcystis seasonal bloom in individual mesocosms with high level of temporal and spatial resolution. The observation that some Microcystis morphotypes completely disappeared and re-appeared along the mesocosm experiment timeline supports the hypothesis of the main transition pathways of colonial Microcystis morphoforms. We demonstrated that significant changes in the training sets with colonial images required for accurate classification of Microcystis spp. from time points differed by only two weeks due to Microcystis high phenotypic heterogeneity during the bloom. We conclude that automatic methods not only allow a performance level of human taxonomist, and thus be a valuable time-saving tool in the routine-like identification of colonial phytoplankton taxa, but also can be applied to increase temporal and spatial resolution of the study.

Antibiotic pollution promotes dominance by harmful cyanobacteria: A case study examining norfloxacin exposure in competition experiments

Cyanobacterial harmful algal blooms (cyanoHABs) in freshwater lakes across the globe are often combined with other stressors. Pharmaceutical pollution, especially antibiotics in water bodies, poses a potential hazard in aquatic ecosystems. However, how antibiotics influence the risk of cyanoHABs remains unclear. Here, we investigated the effects of norfloxacin (NOR), one of the most widely used antibiotics globally, to a bloom-forming cyanobacterium (Microcystis aeruginosa) and a common green alga (Scenedesmus quadricauda), under both mono- and coculture conditions. Taxon-specific responses to NOR were evaluated in monoculture. In addition, the growth rate and change in ratio of cyanobacteria to green algae when cocultured with exposure to NOR were determined. In monocultures of Microcystis, exposure to low concentrations of NOR resulted in decreases in biomass, chlorophyll a and soluble protein content, while superoxide anion content and superoxide dismutase activity increased. However, NOR at high concentration only slightly affected Scenedesmus. During the co-culture trials of Microcystis and Scenedesmus, the 5 μg · L^-1 NOR treatment increased the ratio of Microcystis to co-cultured Scenedesmus by 47.2%. Meanwhile, although Scenedesmus growth was enhanced by 4.2% under NOR treatment in monoculture, it was conversely inhibited by 63.4% and 38.2% when co-cultured with Microcystis with and without NOR, respectively. Our results indicate that antibiotic pollution has a potential risk to enhance the perniciousness of cyanoHABs by disturbing interspecific interaction between cyanobacteria and green algae. These results reinforce the need for scientists and managers to consider the influence of xenobiotics in shaping the outcome of interactions among multiple species in aquatic ecosystems.

Microfluidic and mathematical modeling of aquatic microbial communities

Aquatic microbial communities contribute fundamentally to biogeochemical transformations in natural ecosystems, and disruption of these communities can lead to ecological disasters such as harmful algal blooms. Microbial communities are highly dynamic, and their composition and function are tightly controlled by the biophysical (e.g., light, fluid flow, and temperature) and biochemical (e.g., chemical gradients and cell concentration) parameters of the surrounding environment. Due to the large number of environmental factors involved, a systematic understanding of the microbial community-environment interactions is lacking. In this article, we show that microfluidic platforms present a unique opportunity to recreate well-defined environmental factors in a laboratory setting in a high throughput way, enabling quantitative studies of microbial communities that are amenable to theoretical modeling. The focus of this article is on aquatic microbial communities, but the microfluidic and mathematical models discussed here can be readily applied to investigate other microbiomes.

Synthesis and release of fatty acids under the interaction of Ulva pertusa and Heterosigma akashiwo by stable isotope analysis

Symbiosis of marine algae is inevitable in the marine environment, and species may occur interaction on the growth. In this study, the macroalgae Ulva pertusa and marine microalgae Heterosigma akashiwo were selected as target species to study the interaction mechanism between them. After the 8 days of co-cultivation, the inhibition on growth was observed for both of U. pertusa and H. akashiwo. Eight fatty acids in U. pertusa was detected, with the significant decrease in contents of polyunsaturated fatty acids (PUFAs) especially for C18:2, C18:3n-3 and C18:3n-6. Twelve fatty acids in H. akashiwo was detected, with the significant change for PUFAs. PUFA concentrations in the co-culture group were less than those in the mono-culture. Meanwhile the principal component analysis was conducted to insight into the interaction between U. pertusa and H. akashiwo by fatty acids content and carbon stable isotope ratio of fatty acids (δ¹³C_FAs). Fatty acid content could not distinguish mono and co-culture. However, δ¹³C_FAs could distinguish not only the culture time of algae, but also the living environment of algae. In addition, this study combined fatty acids content and δ¹³C_FAs to explore the release of fatty acids by algae into the seawater. The C18:3n-3 was identified as the allelochemical released by U. pertusa to inhibit the growth of H. akashiwo. The ratio of δ¹³C_FAs in seawater decreased. This study provides a theoretical basis for the symbiosis of marine algae, and a new method of compound-specific stable carbon isotopes was used to better explore the metabolism of fatty acids in algae.

Utilizing cross-species co-cultures for discovery of novel natural products

Discovery of new natural products, especially those with high biological activities and application values, is of great research significance. However, conventional methods based on the cultivation of microbial mono-cultures can hardly satisfy the increasing need of novel natural product generation. Recently, the development of co-cultures composed of different species has emerged as an effective approach for mining novel natural products. Inspired by microbial communities in nature, these co-culture systems create favorable environmental conditions to promote interactions between co-culture members for activating the natural product biosynthesis that is hard to induce otherwise. A large variety of novel natural products have been identified using this robust approach. This review summarizes the recent achievements of using cross-species co-cultures for natural products discovery and discusses the existing challenges and future directions.

Alteration of dominant cyanobacteria in different bloom periods caused by abiotic factors and species interactions

Freshwater cyanobacterial blooms have drawn public attention because they threaten the safety of water resources and human health worldwide. Heavy cyanobacterial blooms outbreak in Lake Taihu in summer annually and vanish in other months. To find out the factors impacting the cyanobacterial blooms, the present study measured the physicochemical parameters of water and investigated the composition of microbial community using the 16S rRNA gene and internal transcribed spacer amplicon sequencing in the months with or without bloom. The most interesting finding is that two major cyanobacteria, Planktothrix and Microcystis, dramatically alternated during a cyanobacterial bloom in 2016, which is less mentioned in previous studies. When the temperature of the water began increasing in July, Planktothrix appeared first and showed as a superior competitor for M. aeruginosa in NO₃^--rich conditions. Microcystis became the dominant genus when the water temperature increased further in August. Laboratory experiments confirmed the influence of temperature and the total dissolved nitrogen (TDN) form on the growth of Planktothrix and Microcystis in a co-culture system. Besides, species interactions between cyanobacteria and non-cyanobacterial microorganisms, especially the prokaryotes, also played a key role in the alteration of Planktothrix and Microcystis. The present study exhibited the alteration of two dominant cyanobacteria in the different bloom periods caused by the temperature, TDN forms as well as the species interactions. These results helped the better understanding of cyanobacterial blooms and the factors which contribute to them.

Cyanobacterial blooms contribute to the diversity of antibiotic-resistance genes in aquatic ecosystems

Cyanobacterial blooms are a global ecological problem that directly threatens human health and crop safety. Cyanobacteria have toxic effects on aquatic microorganisms, which could drive the selection for resistance genes. The effect of cyanobacterial blooms on the dispersal and abundance of antibiotic-resistance genes (ARGs) of concern to human health remains poorly known. We herein investigated the effect of cyanobacterial blooms on ARG composition in Lake Taihu, China. The numbers and relative abundances of total ARGs increased obviously during a Planktothrix bloom. More pathogenic microorganisms were present during this bloom than during a Planktothrix bloom or during the non-bloom period. Microcosmic experiments using additional aquatic ecosystems (an urban river and Lake West) found that a coculture of Microcystis aeruginosa and Planktothrix agardhii increased the richness of the bacterial community, because its phycosphere provided a richer microniche for bacterial colonization and growth. Antibiotic-resistance bacteria were naturally in a rich position, successfully increasing the momentum for the emergence and spread of ARGs. These results demonstrate that cyanobacterial blooms are a crucial driver of ARG diffusion and enrichment in freshwater, thus providing a reference for the ecology and evolution of ARGs and ARBs and for better assessing and managing water quality.

Imaging mass spectrometry of interspecies metabolic exchange revealed the allelopathic interaction between Microcystis aeruginosa and its antagonist

The frequent outbreaks of cyanobacterial blooms which caused serious societal and economic loss have become a worldwide problem. Interactions between toxic cyanobacteria and heterotrophic bacteria competitors play a pivotal role in the formation of toxic cyanobacterial bloom, but the underlying mechanisms of interactions between them await further research. The antagonist activity of Pseudomonas grimontii (P.grimontii) was confirmed by reduction in chlorophyll a concentration of Microcystis aeruginosa (M. aeruginosa) in an infected culture for a 7d period. The initial concentration of P.grimontii affected the M. aeruginosa activity significantly. When the 10% (V/V) concentration of P.grimontii A01 and P.grimontii A14 cultures were infected, the reduction of M. aeruginosa reached to 91.81% and 78.25% after 7 days, respectively. While a 0.1% (v/v) concentration of P.grimontii A01 and P.grimontii A14 cultures were infected, the M. aeruginosa increased 31.13% and 16.67% occurred, respectively. The content of reactive oxygen species (ROS) and malondialdehyde (MDA) increased with increasing of P.grimontii fermentation liquid, indicating the M. aeruginosa underwent oxidative stress. Using matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) imaging mass spectrometry (IMS) profiling of co-cultures of M. aeruginosa and its antagonist P.grimontii, we revealed novel interspecies allelopathic interactions and compete molecule. We showed the spatial secondary metabolites may mediate the interactions in which P.grimontii inhibits growth of M. aeruginosa. Additionally, we revealed how M. aeruginosa feedback to the P.grimontii, which stimulates secondary metabolites such as [D-Asp3]-microcystin-LR released by M. aeruginosa. IMS method highlights the significance of allelopathic interactions between a widely distributed toxic cyanobacteria and its bacteria competitors.

Genotype and host microbiome alter competitive interactions between Microcystis aeruginosa and Chlorella sorokiniana

Cyanobacterial harmful algal blooms (cyanoHABs) continue to increase in frequency and magnitude, threatening global freshwater ecosystems and services. In north-temperate lakes cyanobacteria appear in early summer, succeeding green algae as the dominant phytoplankton group, a pattern thought to be mediated by changes in temperature and bioavailable nutrients. To understand additional drivers of this successional pattern our study used reciprocal invasion experiments to examine the competitive interaction between Microcystis aeruginosa, a dominant contributor to cyanoHABs, and the green alga Chlorella sorokiniana. We considered two factors that may impact these interactions: (1) strain variation, with a specific emphasis on the presence or absence of the gene for the hepatotoxin microcystin, and (2) host-associated bacteria. We used toxic M. aeruginosa PCC 7806 (microcystin producing strain), a non-toxic mutant of PCC 7806, non-toxic M. aeruginosa PCC 9701 (non-microcystin producing strain), and C. sorokiniana. Each organism was available free of all bacteria (i.e., axenic) and with a re-introduced defined bacterial community to generate their xenic counterparts. Competitive interactions were assessed with reciprocal invasion experiments between paired xenic and paired axenic populations of C. sorokiniana and one of the two Microcystis strains, each assessed separately. Flow cytometry and random forest models were used to rapidly discriminate and quantify phytoplankton population densities with 99% accuracy. We found that M. aeruginosa PCC 7806, but not strain PCC 9701, could proliferate from low abundance in a steady-state population of C. sorokiniana. Further, the presence of bacteria allowed M. aeruginosa PCC 7806 to grow to a higher population density into an established C. sorokiniana population than when grown axenic. Conversely, when M. aeruginosa was dominant, C. sorokiniana was only able to proliferate from low density into the PCC 9701 strain, and only when axenic. The mutant of PCC 7806 lacking the ability to produce microcystin behaved similarly to the toxic wild-type, implying microcystin is not responsible for the difference in competitive abilities observed between the two wild-type strains. Quantification of microcystins (MCs) when PCC 7806 M. aeruginosa was introduced into the C. sorokiniana culture showed two-fold more MCs per cell when host-associated bacteria were absent compared to present in both species cultures. Our results show that the ability of M. aeruginosa to compete with C. sorokiniana is determined by genomic differences beyond genes involved in microcystin toxin generation and indicate an important role of host-associated bacteria in mediating phytoplankton interspecies interactions. These results expand our understanding of the key drivers of phytoplankton succession and the establishment and persistence of freshwater harmful cyanobacterial blooms.

Adverse effects of levofloxacin and oxytetracycline on aquatic microbial communities

The widespread use of levofloxacin (LEV) and oxytetracycline (OTC) in hospitals and farms inevitably contributes to water pollution through waste disposal processes, municipal wastewater treatment, and manure application to farmlands, which adversely affects aquatic microorganisms. Here, we evaluated the toxicity of LEV and OTC to cyanobacteria and eukaryotic algae monocultures and freshwater microcosms. Three test cyanobacteria were inhibited by both LEV and OTC at all examined concentrations. The growth of the eukaryotic organisms C. vulgaris and Monoraphidium sp. was only inhibited by high concentrations of OTC ranging from 1000 to 10,000 μg/L; however, they were less sensitive to LEV and OTC than cyanobacteria. In the aquatic microcosms, 5 μg/L of LEV and OTC did not affect the alpha diversity of prokaryotic and eukaryotic communities or the composition of the eukaryotic microbial communities after 14 d of exposure. However, this concentration of LEV and OTC significantly changed the prokaryotic microbial community structure at the genus level, and different antibiotics affected the prokaryotic microbial community differently, suggesting that different antibiotics affect prokaryotes through different molecular mechanisms, thereby leading to differences in prokaryotic microbial growth patterns. Moreover, the changes in the prokaryotic microbial community composition suggested that low antibiotic concentrations in water could disturb prokaryotic microbial communities and cause ecological risks.

Gene expression concerning fatty acid and amino acid metabolism in Chlorella vulgaris cultured with antibiotics

The green alga Chlorella vulgaris has potential as a source of clean bioenergy with abundant metabolites and a high oil content, and antibiotics are often applied to remove bacteria from culture to obtain axenic algal strains. In this work, ceftazidime and gentamicin sulphate (GS) were added separately and in combination in the aseptic processing of C. vulgaris, and gene expression and metabolites were evaluated. The results showed that ceftazidime and GS effectively inhibited the proliferation of Cyanobacteria and Bacteroidetes, respectively. Overall, the effects of antibiotics on C. vulgaris differed: GS increased the algal concentration, whereas ceftazidime alone and in combination with GS treatment decreased the specific algal growth rate. Based on comparative transcription analysis, 5917 and 5899 differentially expressed genes (DEGs) were respectively upregulated and downregulated by ceftazidime, 963 and 3921 DEGs by GS, and 4532 and 1675 DEGs by the ceftazidime and GS combination. Pathway enrichment analysis showed that the downregulated DEGs in the ceftazidime groups were enriched in the fatty acid biosynthesis pathway but that the upregulated DEGs in the GS group were enriched in the fatty acid degradation pathway. Some pathways related to amino acid metabolism were markably influenced by antibiotic treatment. The results further indicated that antibiotics affected the intracellular concentration of fatty acids and amino acids in C. vulgaris. This study provides a new viewpoint regarding the response of C. vulgaris to antibiotics in the process of obtaining axenic algal strains. KEY POINTS: • Ceftazidime and gentamicin sulphate influenced bacterial proliferation. • Downregulated differentially expressed genes mapped to the fatty acid biosynthesis pathway. • Antibiotics affected intracellular concentrations of fatty acids and amino acids.

Interspecific competition between Microcystis aeruginosa and Pseudanadaena and their production of T&O compounds

Microcystis aeruginosa and Pseudanabaena are two common cyanobacterial species/genus and they can occur coincidently in many eutrophic lakes globally. These two cyanobacteria could produce Taste & Odor (T&O) compounds, and their production of T&O compounds might be changed when they are present coincidently. The amounts of T&O compounds and their producers may influence the effectiveness of water treatment processes. Therefore, the mutual interactions between Microcystis aeruginosa (FACHB-905, M) and Pseudanabaena sp. (FACHB-1277, P) on T&O compounds in co-cultures were evaluated in this study. Different initial cell concentrations of M and P, with ratios of M:P = 1:1, M:P = 1:2 and M:P = 2:1 were applied in the co-cultures. The growth of M was enhanced under all of the cyanobacterial cell ratios. The growth of P was enhanced under the ratio of M:P = 1:1, while it was inhibited under the ratios of M:P = 1:2 and M: P = 2:1. In addition, the growth of the two cyanobacteria and their production of β-cyclocitral and 2-methylisoborneol (2-MIB) in the filtrate of P were higher than those in the filtrate of M, which may be attributed to their associated secondary metabolites. The cell integrity and photosynthetic capacity of the two studied cyanobacteria are greatly affected by exposure to β-cyclocitral and 2-MIB. The results showed that β-cyclocitral and 2-MIB had the allelopathic effects on the two cyanobacteria species which might influence the composition of co-existing cyanobacteria and their production of T&O compounds.

Simultaneous Microcystin Degradation and Microcystis aeruginosa Inhibition with the Single Enzyme Microcystinase A

Harmful Microcystis blooms (HMBs) seriously threaten the ecology of environments and human health. Microcystins (MCs) produced by Microcystis are powerful mediators of HMB induction and maintenance. In this study, microcystinase A (MlrA), an enzyme with MC-degrading ability, was successfully obtained at over 90% purity for the first time through overexpression in Escherichia coli K12 TB1. The obtained MlrA exhibited high stability at high temperature and under alkaline conditions, while also exhibiting a long half-life. MlrA selectively inhibited MC-producing Microcystis cultures, but had no effect on MC-nonproducing Synechocystis cultures. The inhibition mechanism of MlrA against Microcystis was investigated by evaluating the morphological and physiological characteristics of cultures. MlrA effectively degraded extracellular MCs and decreased the synthesis of intracellular MCs by causing downregulation of genes involved in the microcystin biosynthesis pathway. Concomitantly, MlrA inhibited Microcystis photosynthesis by causing the downregulated expression of important photosynthesis pathway genes and interrupting electron transport chain activities and pigment synthesis. Thus, MlrA achieved the inhibition of Microcystis growth by reducing its photosynthetic capacity and intracellular MC contents, while also degrading extracellular MCs. On the basis of these results, we propose a new paradigm to achieve the simultaneous removal of MCs and HMBs using the single enzyme characterized here.

Interspecific competition reveals Raphidiopsis raciborskii as a more successful invader than Microcystis aeruginosa

As a successful invasive cyanobacterial species, Raphidiopsis raciborskii is distributed globally and shows a tendency to replace Microcystis aeruginosa in many subtropical and temperate waters, but the ecological traits that contribute to its invasiveness are still unclear. In this study, we found that R. raciborskii occurred in 149 sites in 42 lakes in eastern and central China and coexisted with M. aeruginosa at most sites. Based on field results, a combination of invasion and competition experiments using a biomass gradient to evaluate the invasiveness and competitiveness of R. raciborskii compared with M. aeruginosa was conducted. In invasive groups, both R. raciborskii and M. aeruginosa were shown to have positive specific growth rates, indicating that R. raciborskii could coexist with M. aeruginosa. Furthermore, R. raciborskii was shown to grow faster from invasion while M. aeruginosa reduced growth for invasion. In competitive groups, R. raciborskii reached a higher maximum biomass and grew longer than M. aeruginosa. The specific growth rate of R. raciborskii was not inhibited by M. aeruginosa biomass, whereas the growth of M. aeruginosa was inhibited by R. raciborskii biomass. It was shown during the whole experiment that R. raciborskii tended to replace M. aeruginosa to become dominant owing to its faster growth rate and the eventual decline in growth of M. aeruginosa. With an increase in biomass of M. aeruginosa, the vegetative cell size and filament length of R. raciborskii gradually increased. This study has demonstrated that the inherent invasive traits of R. raciborskii, size differences, niche differences, and relative fitness differences between R. raciborskii and M. aeruginosa are crucial reasons for the invasive success of R. raciborskii. Our results revealed the invasiveness and domination of R. raciborskii from a new perspective.

Understanding the influence of glyphosate on the structure and function of freshwater microbial community in a microcosm

Glyphosate, one of the most popular herbicides, has become a prominent aquatic contaminant because of its huge usage. The eco-safety of glyphosate is still in controversy, and it is inconclusive how glyphosate influences aquatic microbial communities. In the present study, the effects of glyphosate on the structure and function of microbial communities in a freshwater microcosm were investigated. 16S/18S rRNA gene sequencing results showed that glyphosate treatment (2.5 mg L-1, 15 days) did not significantly alter the physical and chemical condition of the microcosm or the composition of the main species in the community, but metatranscriptomic analyses indicated that the transcriptions of some cyanobacteria were significantly influenced by glyphosate. The microbial community enhanced the gene expression in pathways related to translation, secondary metabolites biosynthesis, transport and catabolism to potentially withstand glyphosate contamination. In the low phosphorus (P) environment, a common cyanobacterium, Synechococcus, plays a special role by utilizing glyphosate as P source and thus reducing its toxicity to other microbes, such as Pseudanabaena. In general, addition of glyphosate in our artificial microcosms did not strongly affect the aquatic microbial community composition but did alter the community's transcription levels, which might be potentially explained by that some microbes could alleviate glyphosate's toxicity by utilizing glyphosate as a P source.