Strategies for regulating the intensity of different cyanobacterial blooms: Insights from the dynamics and stability of bacterioplankton communities.

The occurrence of cyanobacterial blooms is increasing in frequency and magnitude due to climate change and human activities, which poses a direct threat to drinking water security. The impacts of abiotic and biotic factors on the development of blooms have been well studied; however, control strategies for different bloom intensities have rarely been explored from the perspective of the dynamics and stability of bacterioplankton communities. Here, a network analysis was used to investigate the interactions and stability of microbial communities during different periods of R. raciborskii bloom in an inland freshwater lake. The abundance and diversity of rare taxa were significantly higher than that of abundant taxa throughout the bloom cycle. At the pre-bloom (PB) stage, microbial interactions among the different bacterial groups were weak but strongly negatively correlated, indicating low robustness and weak disturbance resistance within the community. However, community stability was better, and microbial interactions became more complicated at the high-bloom (HB) and low-bloom (LB) stages. Interestingly, rare taxa were significantly responsible for community stability and connectivity despite their low relative abundance. The Mantel test revealed that Secchi depth (SD), orthophosphate (PO43--P), and dissolved oxygen (DO) were significantly positively correlated with abundant taxa, rare taxa and PB. DO was significantly positively correlated with HB, intermediate taxa, and rare taxa, while water temperature (WT), N/P and total nitrogen (TN) were significantly positively correlated with LB, abundant taxa, intermediate taxa, and rare taxa. These findings suggest that reducing the PO43--P concentration at the PB stage may be an effective approach to preventing the development of R. raciborskii blooms, while regulating rare taxa at the HB and LB stages may be a key factor in controlling R. raciborskii blooms.

Colonial morphology weakens the response of different inorganic carbon uptake systems to CO2 levels in Microcystis population.

Rising atmospheric CO2 concentration negatively impacts aquatic ecosystems and may induce evolutionary changes in the CO2-concentrating mechanism (CCM) of cyanobacteria. As the most notorious freshwater cyanobacteria, Microcystis strains have high phenotypic plasticity to form colonies and blooms in lakes and reservoirs worldwide. However, phenotypic plasticity of Microcystis responses to elevated CO2 is still a major open question. Here, we studied how Microcystis strains with two genotype of inorganic carbon uptake systems, bicA and sbtA, and different colonial morphology response to 200 ppm, 400 ppm, and 800 ppm CO2 levels. The results revealed that sbtA genotypes showed significantly higher specific growth rates, Chl a concentration, and photosynthetic efficiency at 200 ppm CO2, whereas higher specific growth rates, Chl a concentration, and photosynthetic efficiency were found in bicA genotype at 800 ppm CO2. The highest values of specific growth rates, Chl a concentration, Fv/Fm, and maximal net photosynthesis (Pm) were observed in unicellular morphology, followed by small colony and large colonial morphology at all CO2 levels. The values of K0.5 (DIC), K0.5 (CO2), and K0.5 (HCO3-) in the large colonials increased with rising CO2 levels, but these values significantly decreased in the unicellular and small colonials. ANOSIM analysis indicated that colonial morphology reduced significantly inter-group differences between bicA and sbtA genotypes at all CO2 treatments. These results suggest that colonial morphology of Microcystis can weakens the response of different inorganic carbon uptake systems to CO2 levels. Moreover, phenotypic and genotypic plasticity is likely to broaden strongly the fitness of Microcystis from rising atmospheric CO2.

Does temperature favour the spread of Raphidiopsis raciborskii, an invasive bloom-forming cyanobacterium, by altering cellular trade-offs?

As a tropical filamentous cyanobacterium, Raphidiopsis raciborskii has attracted much attention due to its expansion and toxin production. However, the mechanisms of its expansion to temperate regions have not been studied in detail. To address the potential strategies, the physiological and metabolomic profiles of R. raciborskii FACHB 1096 isolated from a temperate lake in China were determined and measured at different temperatures (10 °C, 15 °C, 20 °C, 25 °C, and 32 °C). The results demonstrated that temperature significantly changed cell viability, chlorophyll a content, specific growth rate, Chl a fluorescence, and filamentous shape of R. raciborskii. Low temperature decreased cell viability, specific growth rate, and photosynthetic efficiency, while the proportion of akinete and carbon fixation per unit cell were significantly increased compared with high temperature (32 °C). A constructed unimodal model indicated that filament length, cell volume, and cell length/width of R. raciborskii were significantly reduced in both high and low temperature environments. Under low-temperature conditions, R. raciborskii suffered different degrees of oxidative damage and produced corresponding antioxidant substances to resist oxidative stress, suggesting that low temperature changes the metabolic level of the cells, causing the cells to gradually switch from development to defense. Metabolomic data further confirmed that temperature change induced shifts in metabolic pathways in R. raciborskii, including starch and sucrose metabolic pathways, glutathione metabolic pathways, and the pentose phosphate pathways (PPP), as well as metabolic pathways related to the tricarboxylic acid (TCA) cycle. Our results indicated that the trade-offs of R. raciborskii cells among the growth, cell size, and metabolites can be significantly regulated by temperature, with broad implications for its global expansion in temperate waterbodies.

[Influence and Driving of Environmental Heterogeneity on the Epilithic Diatom Community in Xiangxi River, a Tributary of the Three Gorges Reservoir Area].

Environmental heterogeneity can not only increase species diversity to some extent but also affect the stability of terrestrial communities. However, how environmental heterogeneity affects species diversity of epilithic diatom communities in aquatic ecosystems is rarely reported. In this study, therefore, epilithic diatoms and their roles in driving species diversity were explored by quantifying and comparing the environmental heterogeneity in Xiangxi River, a tributary of the Three Gorges Reservoir Area (TGR), on a time scale. The results showed that environmental heterogeneity, taxonomic ß-diversity, and functional ß-diversity in non-impoundment periods were significantly higher than those in impoundment periods. Moreover, the turnover components in the two hydrological periods showed the highest contribution to ß-diversity. However, the taxonomic α-diversity in impoundment periods was significantly higher than that in non-impoundment periods. In addition, functional richness in functional α-diversity was significantly higher in non-impoundment periods than that in impoundment periods, whereas there was no significant difference in other functional α-diversity, i.e., functional dispersion and functional evenness, found between the two periods. Multiple regression on (dis)similarity matrices (MRM) analysis indicated that ammonium nitrogen (NH4+-N) and silicate (SiO32--Si) were the key environmental heterogeneous factors affecting the epilithic diatom community in Xiangxi River during the non-impoundment periods, whereas the key heterogeneous factors were ammonium nitrogen (NH4+-N), silicate (SiO32--Si), and total phosphorus (TP) during the impoundment periods. These results suggested that the environmental heterogeneity during different hydrological periods in TGR can significantly affect the community structure of epilithic diatoms, resulting in the differentiation of species within the community and even affecting the stability of aquatic ecosystems.

[Impounding Impacts of the Three Gorges Reservoir on Phytoplankton Function Groups and Its Relationship with Resource Use Efficiency].

In order to investigate the relationship between phytoplankton community functional group compositions and resource use efficiency in important tributaries of the Three Gorges Reservoir, phytoplankton and environment parameters were sampled from five tributaries, the Xiangxi River, Daning River, Meixi River, Pengxi River, and Huangjin River, in August and November, 2020. There were 119 species (variants) belonging to 62 genera and 7 phyla identified in summer, whereas 118 species (variants) belonging to 7 divisions of 58 genera were found in winter. According to Padisak's theory, all phytoplankton were divided into 25 functional groups, of which there were six important functional groups in both summer and winter:L0, H1, D, Y, MP, and P in summer and L0, H1, A, M, MP, and Y in winter. The α-diversity of the phytoplankton functional group in summer was higher than that in winter. Moreover, a higher α-diversity was also found in downstream samples relative to that in upstream samples, indicating that the community structure was more complex, and the community stability was relatively better in downstream regions of the rivers. Redundancy analysis (RDA) showed that the environment factors, i.e., ν, pH, permanganate index, WT, and RUETN, significantly affected phytoplankton functional groups (P<0.05). Variance partitioning analysis (VPA) indicated that environmental factors had a higher explanatory degree for the change in functional group composition in summer (45.23%); on the contrary, resource use efficiency had a higher explanatory degree in winter (42.33%). The linear fitted model showed that functional groups L0, H1, D, and Y showed a significant positive correlation relationship with RUETN and RUETP in summer, whereas only four functional groups (M, MP, Y, and A) had a linear relationship with RUETP, and all function groups had a good linear relationship with RUETN in winter. These results indicated that the functional groups belonging to cyanobacteria, dinoflagellates, and cryptophyta were more efficient at using limited resources in summer, whereas the diatoms had a good linear relationship with resource use efficiency and formed a dominant group in the low temperature environment of winter. These results suggest that the impounding of the Three Gorges Reservoir area can significantly change the resource use efficiency of phytoplankton, resulting in changes in the phytoplankton functional group composition and community structure.

[Succession Pattern and Consequences of the Dominant Species During Cyanobacterial Bloom and Its Influencing Factors].

The succession of dominant species always occurs during cyanobacterial blooms because there are certain conditions for cyanobacterial blooms formed by different cyanobacteria; this results in more uncertain and complex effects in cyanobacterial blooms. However, the succession pattern and consequences of dominant species and its driving factors have not received enough attention during cyanobacteria blooms. In this study, the phytoplankton community characteristics and water environment factors of Nanpeng Reservoir, a drinking water source in Chongqing, were monitored and analyzed from April to September 2018. The results showed that:① a total of 108 species of phytoplankton belonging to 59 genera and 8 phyla were identified in Nanpeng Reservoir. Of this, 13 species of 4 phyla were identified as dominant species, among which the dominance index of Cylindrospermopsis raciborskii was the highest, followed by that of Pseudoanabaena sp. ② The most dominant cyanobacteria were Pseudoanabaena and Cylindrospermopsis in May and July, respectively, in which cyanobacteria density peaked, whereas the Shannon-Weiner diversity and Pielou evenness were significantly lower than those in the other months. ③ NMDS results showed that the correlation between Cylindrospermopsis or Pseudoanabaena and the ambient phytoplankton community was 0.58 and 0.48, respectively. Moreover, the VPA results showed that 47.51% of the community variation could be explained by environmental factors, and only 12.04% and 12.74% of variation in community composition could be explained by Cylindrospermopsis and Pseudoanabaena, respectively. ④ The abundance of Cylindrospermopsis was significantly positively affected by WT, pH, and RUEN and negatively affected by SD and RUEP. However, the abundance of Pseudoanabaena was significantly positively affected by permanganate index and negatively affected by EC and DO. These results suggested that both dominating cyanobacteria had significant effects on the surrounding phytoplankton community. Relative to that of Pseudoanabaena, however, Cylindrospermopsis had a more obvious impact on the aquatic ecosystem. Moreover, the synergistic effect of N limitation and warming of the water column may have caused the replacement of Pseudoanabaena with Cylindrospermopsis to form a dominant population.

Temporal heterogeneity of bacterial communities and their responses to Raphidiopsis raciborskii blooms.

To elucidate the interspecies connectivity between cyanobacteria and other bacteria (noncyanobacteria), microbial diversity and composition were investigated through high-throughput sequencing (HTS) in a drinking water reservoir in Chongqing city, Southwest China, during Raphidiopsis raciborskii blooms. Significant temporal changes were observed in microbial community composition during the sampling period, primarily reflected by variations in relative bacterial abundance. The modularity analysis of the network demonstrated that the bacterial community forms co-occurrence/exclusion patterns in response to variations in environmental factors. Moreover, five modules involved in the dynamic phases of the R. raciborskii bloom were categorized into the Pre-Bloom, Bloom, Post-Bloom, and Non-Bloom Groups. The reservoir was eutrophic (i.e., the average concentrations of total nitrogen (TN) and total phosphorus (TP) were 2.32 and 0.07 mg L-1, respectively) during the investigation; however, Pearson's correlation coefficient showed that R. raciborskii was not significantly correlated with nitrogen and phosphorus. However, other environmental factors, such as water temperature, pH, and the permanganate index, were positively correlated with R. raciborskii. Importantly, Proteobacteria (α-, γ-Proteobacteria), Acidobacteria, Chloroflexi, and Firmicutes were preferentially associated with increased R. raciborskii blooms. These results suggested that the transition of R. raciborskii bloom-related microbial modules and their keystone species could be crucial in the development and collapse of R. raciborskii blooms and could provide a fundamental basis for understanding the linkage between the structure and function of the microbial community during bloom dynamics.

Transcriptomic responses to phosphorus in an invasive cyanobacterium, Raphidiopsis raciborskii: Implications for nutrient management.

Phosphorus (P) is a vital macronutrient associated with the growth and proliferation of Raphidiopsis raciborskii, an invasive and notorious bloom-forming cyanobacterium. However, the molecular mechanisms involved in P acclimation remain largely unexplored for Raphidiopsis raciborskii. Here, transcriptome sequencing of Raphidiopsis raciborskii was conducted to reveal multifaceted mechanisms involved in mimicking dipotassium phosphate (DIP), ß-glycerol phosphate (Gly), 2-aminoethylphosphonic acid (AEP), and P-free conditions (NP). Chlorophyll a fluorescence parameters showed significant differences in the NP and AEP groups compared with the DIP and Gly-groups. Expression levels of genes related to phosphate transportation and uptake, organic P utilization, nitrogen metabolism, urea cycling, carbon fixation, amino acid metabolism, environmental information, the ATP-synthesis process in glycolysis, the tricarboxylic acid (TCA) cycle, and the pentose phosphate pathway were remarkably upregulated, while those related to photosynthesis, phycobiliproteins, respiration, oxidative phosphorylation, sulfur metabolism, and genetic information were markedly downregulated in the NP group relative to the DIP group. However, the expression of genes involved in organic P utilization, the urea cycle, and genetic information in the Gly-group, and carbon-phosphorus lyase, genetic information and environmental information in the AEP group were significantly increased compared to the DIP group. Together, these results indicate that Raphidiopsis raciborskii exhibits the evolution of coordination of multiple metabolic pathways and certain key genes to adapt to ambient P changes, which implies that if P is reduced to control Raphidiopsis raciborskii bloom, there is a risk that external nutrients (such as nitrogen, amino acids, and urea) will stimulate the growth or metabolism of Raphidiopsis.

[Analysis of Phytoplankton Community Stability and Influencing Factors in a Tributary of the Three Gorges Reservoir].

Changes in the community stability of freshwater phytoplankton not only induce a series of ecological environment problems but also influence freshwater ecosystem service functions. To understand the changes in community stability and its driving factors, phytoplankton and environmental parameters were analyzed at 11 sample sites in Huaxi River, a tributary of the Three Gorges Reservoir, in spring, summer, autumn, and winter. Moreover, the resource use efficiency (RUEPP), phytoplankton richness (S), phytoplankton evenness (J), and community turnover (BC) were also determined. Results showed that a total of 8 phyla, including 103 genera and 380 species, were identified in Huaxi River throughout the year. Among them, 264 species were collected in spring, 181 in summer, 197 in autumn, and 183 in winter. The number of Chlorophyta was the largest, followed by Bacillariophyta, Euglenophyta, and Cyanophyta. The number of species and cell density in S0 site were the smallest, while those in S2 site were the largest. The RUEPP was fluctuated in four seasons, with the maximum in summer and the minimum in autumn. BC was significantly negatively correlated with RUEPP, phytoplankton richness, total phosphorus (TP), orthophosphate (PO43--P), total nitrogen (TN), nitrate (NO3--N), permanganate index, and conductivity (Spc); however, it was significantly positively correlated with phytoplankton evenness and dissolved oxygen (DO). These results suggest that water level regulation in the Three Gorges Reservoir has a significant impact on the structure of phytoplankton community in Huaxi River, which leads to the instability of phytoplankton community and easy replacement, and the degree of community turnover is affected by the combined effect of biological and abiotic factors.

[Changes in Epilithic Algae Community and Its Relationship with Environmental Factors in the Meixi River, a Tributary of the Three Gorges Reservoir].

To explore the relationship between the community of epilithic algae and environmental factors in tributaries of the Three Gorges Reservoir region, the epilithic algae and related environment factors were investigated from 26 sampling sites in Meixi River, a tributary of the Three Gorges Reservoir region, during flood period (August 2016), drought period (November 2016), and normal water period (March 2017). Results showed that 106 species (including varieties) belonging to 47 genera and 5 families were identified from 26 sampling sites during the three periods. Among these, 73 species belonged to 38 genera and 5 families in the flood period, 67 species belonged to 36 genera and 4 families in the drought period, and 63 species belonged to 33 genera and 4 families in the normal water period. Nineteen, 17, and 18 dominant species were identified during the flood period, drought period, and normal water period, respectively. The main dominant species were Achnanthes sp., Aphanizomenon sp., and Phormidium sp. in the flood period; Achnanthes sp., Gomphonema sp., and Microcystis sp. in the drought period; and Gomphonema sp., Nitzschia sp., and Chroococcus sp. in the normal water period. Moreover, species such as Cocconeis placentula, Achnanthes sp., Gomphonema subclavatum, G. parvulum, Navicula parva, and G. constrictum were determined to be the common dominant species during the three periods. Redundancy analysis revealed that the changes in the relative abundance of dominant species in the backwater sections were significantly related to the electrical conductivity, dissolved oxygen, pH, total phosphorus, and total nitrogen, and the relative abundance of dominant species in the natural sections was mainly related to the electrical conductivity, pH, total phosphorus, temperature, and velocity. Moreover, a different relationship with the environmental factors was determined among the three periods. However, a negative correlation between total phosphorus and the relative abundances in G. parvulum, G. constrictum, and Achnanthes sp. and a positive correlation between pH and the relative abundances in G. parvulum, G. constrictum, and Achnanthes sp. were found during the three periods. These results indicated that the differences in the hydrological regime and environmental factors in the Three Gorges Reservoir played an important role on the composition of epilithic algae community and led to a significant change in the community structure of epilithic algae.

Interspecific competition between Cylindrospermopsis raciborskii and Microcystis aeruginosa on different phosphorus substrates.

Phosphorus (P) is responsible for algal growth and the structural changes in algal communities. Therefore, it is essential to know whether the different phosphorus availability to different algae can change the community structure. In this study, the interspecific competition was investigated at two bloom-forming cyanobacterium, Cylindrospermopsis raciborskii and Microcystis aeruginosa, when both were treated with five different phosphate compounds, including K2HPO4, ß-glycerol phosphate, (2-aminoethyl)-phosphinic acid, glyphosate, and P-free. The results of mono-culture experiments showed that the two species could utilize the dissolved organic phosphorus (DOP) and K2HPO4 (DIP) as the sole P resource. Moreover, the specific growth rates and the endogenous alkaline phosphatase activity in M. aeruginosa cells were much lower than those in C. raciborskii under DOP and DIP treatments. In the co-cultured experiments, however, a significant biomass increase in C. raciborskii was observed in all experimental P treatments, except for glyphosate, regardless of its initial cell density proportion. A 31.8-63.4% increase in cell number of C. raciborskii was found after incubated into K2HPO4, while the highest biomass of mixed samples, 17.72 × 106 cell mL-1, was observed in the (2-aminoethyl)-phosphinic acid treatment (50C50M). Additionally, higher specific growth rate was also found in C. raciborskii when compared with M. aeruginosa under P-free; the increasing proportion of C. raciborskii were 29.1% (50C50M), 16.4% (75C25M), and 36.7% (25C75M), respectively. When the mixed samples were co-cultivated under glyphosate, C. raciborskii cells appeared to be depressed, whereas the cell density of M. aeruginosa increased rapidly. The findings indicated that an excellent P competition might give some advantages for C. raciborskii dominance in natural waters with DIP limitation or DOP abundance.

[Dynamics of Epilithic Algae Communities and Their Relationship with Environmental Factors During Storage and Non-storage Periods in the Three Gorges Reservoir].

In order to explore the composition of epiphytic algae and its related environmental factors, 12 sampling sites in the natural reaches and the backwater reaches (including perennial backwater sections and fluctuating backwater sections) were investigated among tributaries of the Caotang River, the Meixi River, and the Daxi River in the Fengjie district of the Chongqing section of the Three Gorges Reservoir under different hydrological regimes (i.e., storage and non-storage periods). Results showed that 103 species of epilithic algae belonging to 45 genera and 4 families are found in the 3 tributaries. This included 67 species belonging to 34 genus in the natural sections and 82 species (64 species in perennial backwater sections and 41 species in fluctuating backwater sections) belonging to 34 genera in the backwater sections. During the storage period, the dominant species in the natural sections were Melosira varians, Cocconeis placentula, Diatoma vulgure, Gyrosigma scalproides, and Oscillatoria tenuis, while the dominant species in the backwater sections were M. varians, Cymbella affinis,D. vulgure, Eucapsis alpina, and M. granulata. During the non-storage period, the dominant species in the natural sections were M. varians, C. affinis, and C. placentula, whereas the dominant species in the backwater sections were O. princeps, O. rupicola,O. formosa, Synedra acus, Ulothrix sp., Merismopedia elegans, and O. tenuis. These results suggested that the compositions of dominant species showed significant differences during the non-storage period, while little difference was found during the storage period. In addition, the dominant species did not show a significant change in the natural sections, but a marked difference was observed in the backwater sections. Similar dominant species were observed in both perennial and fluctuating backwater sections during the non-storage period, but significantly different dominant species were found during the storage period. Redundancy analysis suggested that the composition of epilithic algae was influenced by different environmental factors, such as temperature, electrical conductivity, pH, total nitrogen, and total phosphorus. Indeed, changes in the cell densities of dominant algae at the different sites were mainly affected by temperature and the concentrations of nitrogen and phosphorus. These results suggest that the different hydrological regimes had an important role not only on the reservoir water environment, but also the dynamics of epilithic algal communities.

[Benthic Diatom Communities in the Main Stream of Three Gorges Reservoir Area and Its Relationship with Environmental Factors].

In order to study changes in benthic diatom communities and their relationships with environmental factors during different hydrological periods, 32 sites were sampled in the main stream of the Three Gorges Reservoir during the non-storage period (July 2015 to September 2015) and the storage period (December 2015 to March 2016). Results showed that there were significant differences in water temperature (WT), underwater light intensity (PAR), pH, conductivity (Spc), dissolved oxygen (DO), redox potential (ORP), turbidity (Tur), transparency (SD), flow rate (v), and permanganate index between the storage and non-storage periods. Ninety-six species of benthic diatoms, belonging to 28 genera, were identified during the two hydrological periods. Thirteen dominant species and three dominant species were identified during the non-storage period and the storage period, respectively, suggesting that some differences existed in the composition and distribution of dominant species between the two periods. However, Melosira varians, an α-polluting and eutrophic species, was dominant during both of the hydrological periods. Redundancy analysis (RDA) found that pH, flow rate, and orthophosphate (PO43--P) were the main environmental factors affecting the composition of benthic diatom communities, and a significant difference was found between up- and down-stream areas during the non-storage period. In comparison, water temperature, turbidity, permanganate index, and dissolved oxygen (DO) were the main environmental factors influencing the patterns of benthic diatoms communities, for which an insignificant difference was observed between up- and down-stream areas during the storage period. These results suggest that water storage in the Three Gorges Reservoir has an important impact on the composition of benthic diatom communities, and that this results in a change in community structure.

Zebra leaf 15, a receptor-like protein kinase involved in moderate low temperature signaling pathway in rice.

BACKGROUND: Zebra leaf mutants are an important resource for studying leaf colour in rice. In most such mutants, the zebra leaf phenotype results from defective chloroplast biogenesis. The molecular mechanism by which zebra leaves develop remains unclear, so additional zebra-leaf mutants need to be identified. RESULTS: We isolated a novel rice zebra-leaf mutant, named zebra leaf 15 (z15), which showed transversely striped leaves with yellow-green or white-green sectors, in which chloroplast structure was disturbed. Transmission electron microscopy revealed that the structure of various organelles was impaired in yellow/white sectors. Z15, a single-copy gene in the rice genome, encodes a receptor-like protein kinase. Subcellular localization analysis indicates that Z15 and z15 are localized on the plasma membrane. The expression of Z15 is induced by moderate low temperature (18 °C). The mutation of Z15 influenced the expression of two downstream genes, OsWRKY71 and OsMYB4, that were responsive to moderate low temperature. The results show that Z15 plays a crucial role in the early stages of the response to moderate low temperature in rice. CONCLUSIONS: We identified a novel zebra-leaf mutant (z15) that impaired chloroplast structure in rice, LOC_Os05g12680, encoding a receptor-like protein kinase. Further study indiceted that Z15 plays a crucial role in the early stages of the response to moderate low temperature in rice.

Physiological and transcriptomic analyses to determine the responses to phosphorus utilization in Nostoc sp.

Phosphorus (P) is an important factor driving algal growth in aquatic ecosystems. In the present study, the growth, P uptake and utilization, photosynthesis, and transcriptome profile of Nostoc sp. were measured when Nostoc sp. cultured in media containing ß-glycerol phosphate (ß-gly, containing COP bonds), 2-aminoethylphosphonic acid (2-amin, containing CP bonds), or orthophosphate (K2HPO4), and in P-free (NP) medium. The results revealed that NP treatment adversely affected the growth and photosynthesis of Nostoc sp. and significantly down-regulated the expression of genes related to nutrient transport and material metabolism. Furthermore, 2-amin treatment reduced the growth of Nostoc sp. but did not significantly reduce photosynthesis, and the treatments of NP and 2-amin up-regulated the expressions of genes related antioxidation and stress. Additionally, there were no obvious differences in growth, photosynthesis, and phosphorus utilization between the ß-gly and K2HPO4 treatments. These results suggested that Nostoc had a flexible ability to utilize P, which might play an important role in its widespread distribution in the environment.

Chlorophyll a fluorescence and transcriptome reveal the toxicological effects of bisphenol A on an invasive cyanobacterium, Cylindrospermopsis raciborskii.

Bisphenol A has attracted worldwide attention due to its harmful effects on humans, animals and plants. In this study, the toxicological effects of BPA on Cylindrospermopsis raciborskii were assessed based on chlorophyll a fluorescence and transcriptome analyses. The results showed that the growth of C. raciborskii was significantly inhibited when BPA exceeded 0.1 mg L-1. A marked rise of phase J was observed at a concentration greater than 0.1 mg L-1, while a K phase appeared at 20 mg L-1. The chlorophyll a fluorescence parameters of RC/CS0, F0, φP0, φE0, and ψ0, underwent a significant decline under all treatments of BPA, whereas a significant increase in both VJ and M0 occurred under all concentrations of BPA. Additionally, ABS/RC and DIo/RC markedly increased at 10 mg L-1 and 20 mg L-1. The transcriptome analysis revealed that the genes of photosynthesis, including psbA, psbB, psbC, psbD, apcA, apcB, cpcA, and cpcB, as well as those of chlorophyll and carotenoid biosynthesis, namely hemN, acsF, chlL, chlN, chlP, crtB, pds, were all down-regulated. Moreover, BPA also inhibited the oxidative phosphorylation, glycolysis/gluconeogenesis, citrate cycle (TCA cycle), and fatty acid metabolism in C. raciborskii. Taken together, these results suggest BPA can negatively affect the expression of multiple genes and the vital energy metabolism process to arrest the growth and photosynthesis of C. raciborskii.

The Effect of Bisphenol A on Growth, Morphology, Lipid Peroxidation, Antioxidant Enzyme Activity, and PS II in Cylindrospermopsis raciborskii and Scenedesmus quadricauda.

To investigate the effect of bisphenol A (BPA) on Cylindrospermopsis raciborskii (Cyanobacteria) and Scenedesmus quadricauda (Chlorophyta), we grew the two species at BPA concentrations of 0, 0.1, 1, 2, 5, 10, and 20 mg/L and examined their growth, lipid peroxidation, antioxidant enzyme activity, and chlorophyll a fluorescence. The 96-h EC50 values (effective concentration causing 50% growth inhibition) for BPA in C. raciborskii and S. quadricauda were 9.663 ± 0.047, and 13.233 ± 0.069 mg/L, respectively. A significant reduction in chlorophyll a concentration was found in C. raciborskii and S. quadricauda when BPA concentrations were greater than 1 and 2 mg/L, respectively. Furthermore, F v/F m, ΔF/F m', and qP decreased significantly at 10 mg/L BPA in C. raciborskii but started to decrease at 10 mg/L in S. quadricauda. The changes in chlorophyll fluorescence parameters (α, rETRmax) that were obtained from the rapid light response curves of both algae species showed similar responses to F v/F m, ΔF/F m', and qP under BPA-induced stress. Values for all of the chlorophyll fluorescence parameters in S. quadricauda were higher than in C. raciborskii; however, the nonphotochemical quenching measured in C. raciborskii was considerably higher than it was in S. quadricauda. In addition, lipid peroxidation (determined as MDA content) and antioxidant enzyme activities (SOD and CAT) increased in both species as the BPA concentration increased. These results suggest that C. raciborskii is more sensitive to the effects of BPA than S. quadricauda and that photosystem II might be a target for the activity of BPA in vivo.

[Functional Group Characteristics of Planktonic Diatoms and Their Relationship with Environmental Factors in the Ruxi River].

To elucidate the functional group characteristics of planktonic diatoms and their relationship with environment factors in the Ruxi River, multivariate statistical analysis and functional group classification were conducted in this study. The success pattern of a diatom functional group and its driving factor were analyzed for the Ruxi River, a typical tributary of Three Gorges Reservoir, after the phytoplankton community and environmental variables were investigated at three different stages: level water period (April 2014), dry season (December 2014), and wet season (July 2014), based on the characteristic of water level. The results showed that there were 10 diatom functional groups in the Ruxi River: the A, B, C, D, Lo, MP, P, TB, X3, and S1 groups, and among them, MP was the most groups, but the dominant group was D group. Stepwise multiple regression analysis indicated that ρ(TN) in the water column was the primary factor significantly affecting the densities in the normal water period, whereas turbidity, alkalinity, and pH significantly influenced the functional group densities in the normal water period. In the high water period, however, transparency was the most important environmental factor affecting the functional group densities. Additionally, the results of RDA analysis found that water temperature, electrical conductivity (Spc), oxidation-reduction potential (ORP), ρ(DO), and ρ(NO3--N) were the main environmental factors that influenced the diversity of diatom functional groups in the Ruxi River. These results suggested that functional groups could well reflect the habitat characteristics of the Ruxi River and the effect of the nutrient element, nitrogen, to the success of phytoplankton functional groups and changes of water quality in the Ruxi River should be paid more attention.

The response and detoxification strategies of three freshwater phytoplankton species, Aphanizomenon flos-aquae, Pediastrum simplex, and Synedra acus, to cadmium.

The response and detoxification mechanisms of three freshwater phytoplankton species (the cyanobacterium Aphanizomenon flos-aquae, the green alga Pediastrum simplex, and the diatom Synedra acus) to cadmium (Cd) were investigated. The cell growth of each species was measured over 10 days, and chlorophyll a fluorescence, Cd bioaccumulation (including surface-adsorbed and intracellular Cd), and phytochelatin (PC) synthesis were determined after 96-h exposures. The growth of the three phytoplankton species was significantly inhibited when Cd concentrations were ≥5 mg L(-1). Compared with P. simplex, greater growth inhibition in S. acus and A. flos-aquae occurred. The changes in chlorophyll fluorescence parameters including the maximal quantum yield of PSII (Fv/Fm) and relative variable fluorescence of the J point (Vj) demonstrated that the increase in Cd concentration damaged PSII in all three species. After 96-h exposures, the accumulation of surface-adsorbed Cd and intracellular Cd increased significantly in all three species, with the increase of Cd concentrations in the media; total cadmium accumulation was 245, 658, and 1670 times greater than that of the control in A. flos-aquae, P. simplex, and S. acus, respectively, after exposure to 10 mg L(-1). Total thiols exhibited a similar trend to that of Cd accumulation. PC3 was found in A. flos-aquae and P. simplex in all Cd treatments. Glutathione (GSH) and PC2 were also produced in response to exposure to high concentrations of Cd. PC4 was only discovered at exposure concentrations of 10 mg L(-1) Cd and only in S. acus. The intracellular Cd/PCs ratio increased in all three phytoplankton with an increase in Cd concentrations, and a linear relationship between the ratio and the growth inhibition rates was observed with P. simplex and S. acus. Our results have demonstrated that metal detoxification mechanisms were dependent on the species. This study suggested that the variance of metal detoxification strategies, such as cadmium accumulation and PCs, might be an explanation why algal species have different sensitivity to Cd at various levels.

Assessment of growth rate, chlorophyll a fluorescence, lipid peroxidation and antioxidant enzyme activity in Aphanizomenon flos-aquae, Pediastrum simplex and Synedra acus exposed to cadmium.

In this study, the effects of cadmium on the cyanobacterium Aphanizomenon flos-aquae, the green alga Pediastrum simplex and the diatom Synedra acus was evaluated on the basis of growth rate, chlorophyll a fluorescence, lipid peroxidation and antioxidant enzyme activity. The EC50 values (effective concentration inducing 50 % of growth inhibition) of cadmium in A. flos-aquae, P. simplex and S. acus were 1.18 ± 0.044, 4.32 ± 0.068 and 3.7 ± 0.055 mg/L, respectively. The results suggested that cadmium stress decreases growth rate and chlorophyll a concentration. The normalized chlorophyll a fluorescence transients significantly increased at cadmium concentrations of 5.0, 10.0 and 20.0 mg/L, but slightly decreased at concentrations of 0.2, 0.5 and 1.0 mg/L. The chlorophyll fluorescence parameters showed considerable variation among the three species, while lipid peroxidation and antioxidant enzyme activities showed a significant increase. Our results demonstrated that blockage of electron transport on the acceptor side of photosystem II is the mechanism responsible for cadmium toxicity in freshwater microalgae, and that the tolerance of the three species to cadmium was in the order green alga P. simplex > diatom S. acus > cyanobacterium A. flos-aquae.