Effects of nitrogen forms on the production of cyanobacterial toxin microcystin-LR by an isolated Microcystis aeruginosa

A cyanobacterial strain, which produced high content of microcystin-LR (MC-LR) but no rnicrocystin-RR (MC-RR), was isolated from the hypertrophic Dianchi Lake in China and identified as Microcystis aeruginosa DC-1. Effects of nitrogen containing chemicals and trace elements on the growth and the production of MC-LR by this strain were Studied. In the presence of bicine, compared with urea and ammonium, nitrate greatly promoted the growth and the production of MC-LR. However, leucine and arginine, which were the constitutional components in the molecular structure of MC-LR or RR, inhibited the production of MC-LR. Iron and silicon up to 10mg/L had little effects on the growth of M. aeruginosa DC-1, but the production of MC-LR was apparently enhanced. Under all conditions studied here, only MC-LR but no RR was detected within the cells of M. aeruginosa DC-1. Thus, chemical forms of nitrogen, rather than the usually concerned the total nitrogen, Lind trace elements played important roles in the production of MC toxins during cyanobacterial blooms.

铜绿微囊藻(Microcystis aeruginosa)水华毒性及毒素的研究

以巢湖铜绿微囊藻水华为材料,采用昆明鼠腹腔注射法对其毒性进行了测试,结果表明,有些时期的水华具毒性,其LDmin为60mg干藻/kg鼠重,致毒症状主要是引起实验动物肝脏淤血肿大。该藻毒素呈热稳定性。经分离纯化后,毒素回收率为16.36%,纯度达95.75%,与有毒水华的毒症状相同。毒素在240nm处有一强烈吸收峰。毒素的氨基酸组成为:天冬氨酸、谷氨酸、丙氨酸、亮氨酸和精氨酸。 以铜绿微囊藻毒株7820纯毒素为标准毒素,对该藻有毒水华的毒素进行了定量研究。结果表明,其毒素含量相当于4.45mg7820毒素/

Effects of arsenate on the growth and microcystin production of Microcystis aeruginosa isolated from Taiwan as influenced by extracellular phosphate

Arsenic pollution and eutrophication are both prominent issues in the aquaculture ponds of Taiwan. It is important to study the effects of arsenic on algal growth and toxin production in order to assess the ecological risk of arsenic pollution, or at least to understand naturally occurring ponds. The sensitivity of algae to arsenate has often been linked to the structural similarities between arsenate and phosphate. Thus, in this study we examined the effects of arsenate (10(-8) to 10(-4) M) on Microcystis aeruginosa TY-1 isolated from Taiwan, under two phosphate regimes. The present study showed that M. aeruginosa TY-1 was arsenate tolerant up to 10(-4) M, and that this tolerance was not affected by extracellular phosphate. However, it seems that extracellular phosphate contributed to microcystin production and leakage by M. aeruginosa in response to arsenate. Under normal phosphate conditions, total toxin yields after arsenate treatment followed a typical inverted U-shape hormesis, with a peak value of 2.25 +/- 0.06 mg L-1 in the presence of 10(-7) M arsenate, whereas 10(-8) to 10(-6) M arsenate increased leakage of similar to 75% microcystin. Under phosphate starvation, total toxin yields were not affected by arsenate, while 10(-6) and 10(-5) M arsenate stimulated microcystin leakage. It is suggested that arsenate may play a role in the process of microcystin biosynthesis and excretion. Given the arsenic concentrations in aquaculture ponds in Taiwan, arsenate favors survival of toxic M. aeruginosa in such ponds, and arsenate-stimulated microcystin production and leakage may have an impact on the food chain.

Avaliação dos efeitos da disponibilidade de luz sobre o crescimento e competição entre cepas de Planktothrix agardhii e Microcystis aeruginosa

As cianobactérias Microcystis aeruginosa e Planktothrix agardhii são espécies formadoras de florações comuns em ecossistemas aquáticos eutrofizados. Nestes ambientes, a disponibilidade de luz é um dos fatores determinantes para o desenvolvimento e estruturação da comunidade fitoplanctônica. O presente estudo teve como objetivo investigar o efeito da luz na fisiologia de cepas de cianobactérias (M. aeruginosa e P. agardhii), avaliando o crescimento, a variabilidade inter e intra-específica e a competição por luz. Para tanto foram realizados cultivos estanques em diferentes intensidades luminosas (10, 40, 60, 100 e 500 mol m-2 s-1) e calculadas as taxas de crescimento e os rendimentos máximos das culturas. O requerimento mínimo de luz de cada cepa foi determinado em experimentos com monoculturas em sistemas de cultivo contínuo (quimiostatos) sob condições de limitação de luz. A competição por luz foi avaliada através de experimentos com biculturas em quimiostatos. Foi observada variabilidade intra e inter-específica das cepas, nas diferentes intensidades luminosas testadas. Em 500 μmol m-2 s-1, as cepas de M. aeruginosa obtiveram maior biomassa do que P. agardhii, corroborando a maior sensibilidade de P. agardhii luz. Embora com rendimento máximo menor, P. agardhii cresceu em intensidades luminosas consideradas elevadas para a espécie, 100 e 500 μmol m-2 s-1. Estes resultados evidenciam a capacidade de P. agardhii ocorrer em ambientes com grandes amplitudes de luminosidade. Na intensidade de 10 μmol m-2 s-1, M. aeruginosa e P. agardhii apresentaram crescimento semelhante, demonstrando a habilidade das duas espécies em crescer com pouca luz. Nas monoculturas em quimiostato, sob condições de limitação de luz, as cepas de M. aeruginosa atingiram maior biomassa durante o equilíbrio (steady-state) do que P. agadhii, refletindo uma capacidade suporte mais elevada, enquanto que os valores de requerimento mínimo de luz foram semelhantes entre as duas espécies. Ao competirem, M. aeruginosa superou P. agardhii imediatamente após o início do experimento. Esse rápido crescimento resultou na dominância de M. aeruginosa em todos os pares de cepas testados e, em dois casos, ocorreu exclusão competitiva de P. agardhii. Quando não ocorreu exclusão, P. agardhii conseguiu manter-se no sistema com uma baixa biomassa (ca.15%). Estes resultados ajudam a entender a co-ocorrência destas espécies no ambiente e a dominância de M. aeruginosa mesmo em condições de baixa luminosidade.

Global transcriptional responses of the toxic cyanobacterium, Microcystis aeruginosa, to nitrogen stress, phosphorus stress, and growth on organic matter

Whole transcriptome shotgun sequencing (RNA-seq) was used to assess the transcriptomic response of the toxic cyanobacterium Microcystis aeruginosa during growth with low levels of dissolved inorganic nitrogen (low N), low levels of dissolved inorganic phosphorus (low P), and in the presence of high levels of high molecular weight dissolved organic matter (HMWDOM). Under low N, one third of the genome was differentially expressed, with significant increases in transcripts observed among genes within the nir operon, urea transport genes (urtBCDE), and amino acid transporters while significant decreases in transcripts were observed in genes related to photosynthesis. There was also a significant decrease in the transcription of the microcystin synthetase gene set under low N and a significant decrease in microcystin content per Microcystis cell demonstrating that N supply influences cellular toxicity. Under low P, 27% of the genome was differentially expressed. The Pho regulon was induced leading to large increases in transcript levels of the alkaline phosphatase phoX, the Pst transport system (pstABC), and the sphX gene, and transcripts of multiple sulfate transporter were also significantly more abundant. While the transcriptional response to growth on HMWDOM was smaller (5–22% of genes differentially expressed), transcripts of multiple genes specifically associated with the transport and degradation of organic compounds were significantly more abundant within HMWDOM treatments and thus may be recruited by Microcystis to utilize these substrates. Collectively, these findings provide a comprehensive understanding of the nutritional physiology of this toxic, bloom-forming cyanobacterium and the role of N in controlling microcystin synthesis.

铜绿微囊藻(Microcystis aeruginosa)与三种丝状蓝藻间的相互作用

研究了单细胞铜绿微囊藻和三种丝状蓝藻(水华束丝藻、水华鱼腥藻及土生席藻)间的相互作用,包括以下两个方面的内容:①铜绿微囊藻细胞滤出液对水华束丝藻、水华鱼腥藻及土生席藻生长的影响;②水华束丝藻、水华鱼腥藻及土生席藻细胞滤出液对铜绿微囊藻生长的影响．研究发现,当滤出液浓度为60％(滤出液与BG11的体积比为3:2)时,制绿微囊藻细胞滤出液对水华束丝藻、水华鱼腥藻的生长有显著促进效果,尤其对水华束丝藻的作用更加明屁;对土生席藻的生长却起着微弱的抑制作用,仅表现于100%细胞滤出液中,对铜绿微囊藻而言,土生席藻细

Physiological Responses of Microcystis aeruginosa PCC7806 to Nonanoic Acid Stress

A recent study has shown that nonanoic acid (NA) is one of the strongest allelochemicals to a cyanobacterium Microcystis aeruginosa, but the physiological responses of M. aeruginosa to NA stress remain unknown. In this study, physiological characters such as the growth rate, photosynthetic processes, phosphorus and nitrogen uptake kinetics, and the contents of intracellular microcystin of M. aeruginosa PCC7806 were studied under the NA stress. The results showed that the growth rates of M. aeruginosa PCC 7806 were significantly inhibited in all NA stress treatments during first 3 days after exposure, and the growth rate was recovered after 5-day exposure. After 2-day exposure, the contents of both phycocyanin and allophycocyanin per cell decreased at NA concentration of 4 mg L-1, and oxygen evolution was inhibited even at the concentration of 0.5 mg L-1, but carotenoid content per cell was slightly boosted in NA stress. Physiological recovery of M. aeruginosa PCC7806 was observed after 7-day exposure to NA. It was shown that NA stress had no effect on uptake of nitrogen, but could stimulate the uptake of phosphorus. The contents of intracellular microcystin have not been affected in all NA treatments in contrast with the control. (C) 2008 Wiley Periodicals, Inc. Environ Toxicol 24: 610-617, 2009.

Comparative studies on photosynthesis and phosphate metabolism of Cylindrospermopsis raciborskii with Microcystis aeruginosa and Aphanizomenon flos-aquae

The physiological differences for three bloom-forming cyanobacteria (Cylindrospermopsis raciborskii, Microcystis aeruginosa, and Aphanizomenon flos-aquae) were investigated. In comparison with M. aeruginosa and A. flos-aquae, C. raciborskii exhibited a significantly higher concentration of carotenoids, higher values in maximum photosynthesis rate (P-m), apparent photosynthetic efficieny (a), and maximum electron transport rate (ETRmax) during the growth period. In addition, higher extracellular alkaline phosphatase activities and lower light compensation point (I-c) were also detected in C raciborskii (p < 0.05, ANOVA). Therefore, it is suggested that the higher photosynthetic activities, more effective uptake and utilization to phosphate, and low light requirements might play important roles in the occurrence and invasive behavior of C. raciborskii. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.

Allelopathic mechanism of pyrogallol to Microcystis aeruginosa PCC7806 (Cyanobacteria): From views of gene expression and antioxidant system

Pyrogallol is a potent allelochemical on Microcystis aeruginosa, but its allelopathic mechanism is not fully known. In order to explore this mechanism, gene expressions for prx, mcyB, psbA, recA, grpE, fabZ under pyrogallol stress were studied, and activities of the main antioxidant enzymes were also measured. The results showed that expression of grpE and recA showed no significant change under pyrogallol stress, while psbA and mcyB were up-regulated at 4 mg L-1. Both prx and fabZ were up-regulated even under exposure to 1 mg L-1 pyrogallol concentration. The activities of superoxide dismutase (SOD) and catalase (CAT) were enhanced under pyrogallol stress. Levels of malodialdehyde (MDA) at 2 and 4 mg L-1 pyrogallol were significantly higher than those of the controls. It was concluded that oxidant damage is an important mechanism for the allelopathic effect of pyrogallol on M. aeruginosa. (c) 2009 Elsevier Ltd. All rights reserved.

Grazing on toxic and non-toxic Microcystis aeruginosa PCC7820 by Unio douglasiae and Corbicula fluminea

To explore the potential grazing effects of mussels on Microcystis aeruginosa, a common bloom-forming phytoplankton, Unio douglasiae and Corbicula fluminea were fed with Scenedesmus obliquus, toxic and non-toxic strains of Microcystis aeruginosa as single food and as mixtures in the laboratory. When fed with single foods, U. douglasiae has similar clearance rates on the three algae populations, while C. fluminea has significantly lower clearance rate on toxic M. aeruginosa than those on the other two algae populations. When fed with mixture foods, both the mussels show significantly higher clearance rates than on single foods. The clearance rates of U. douglasiae on the different food mixtures are not significantly different, and C. fluminea has a significantly lower clearance rate on the toxic food mixtures than that on non-toxic food mixtures. Although the relative lower clearance rates of C. fluminea on toxic food, we may still deduce that both the mussels can exert grazing pressure on phytoplankton. The deduction is supported by the composition of the excretion products. The excretion products (faeces and pseudofaeces) of both mussels contained mainly S. obliquus. In both mixed-food treatments, the ratios of S. obliquus to M. aeruginosa in the excrete products are significantly higher than those in the foods. Therefore, it can be concluded that both mussels prefer M. aeruginosa to S. obliquus, and can cause grazing pressure on M. aeruginosa.

Allelopathic effects of phenolic compounds present in submerged macrophytes on Microcystis aeruginosa

In laboratory studies, the allelopathic effects of 3 (Hydrocharitaceae family) submerged macrophytes (Elodea nuttallii (Planch) St. John, Hydrilla verticillata (L.f.) Royle and Vallisneria spiralis L.) were investigated on two strains of Microcystis aeruginosa. Both aqueous methanol extracts and exudates of three macrophytes inhibited the growth of both strains of Microcystis aeruginosa, After 3-days culture, E nuttallii, H. verticillata and V. spiralis excreted 0.8, 0.3 and 1.0% of total phenolic compounds (TPC), respectively, into the surrounding water. After removing phenolic compounds by polyvinylpolypyrrolidone (PVPP)), the plant exudates showed very weak activity. The inhibitory rates of exudates of E. nuttallii, H. verticillata and V. spiralis, against non-toxic M. aeruginosa were decreased by 35.7, 43.4 and 59.1% respectively. Thus 3 submerged macrophytes released the phenolic compounds into the surrounding water, to inhibit the growth of M. aeruginosa. This information may help us in understanding the mechanism of allelopathy in aquatic ecosystems and to control the algal bloom in eutrophic water bodies.

Effects of gibberellin A(3) on growth and microcystin production in Microcystis aeruginosa (cyanophyta)

Environmental. factors that affect the growth and microcystin production of microcystis have received worldwide attention because of the hazards microcystin poses to environmental safety and public health. Nevertheless, the effects of organic anthropogenic pollution on microcystis are rarely discussed. Gibberellin A(3) (GA(3)) is a vegetable hormone widely used in agriculture and horticulture that can contaminate water as an anthropogenic pollutant. Because of its common occurrence, we studied the effects of GA3 on growth and microcystin production of Microcystis aeruginosa (M. aeruginosa) PCC7806 with different concentrations (0.001-25mg/L) in batch culture. The control was obtained without gibberellin under the same culture conditions. Growth, estimated by dry weight and cell number, increased after the GA3 treatment. GA3 increased the amounts of chlorophyll a, phycocyanin and cellular-soluble protein in the cells of M. aeruginosa PCC7806, but decreased the accumulation of water-soluble carbohydrates. In addition, GA3 was observed to affect nitrogen absorption of the test algae, but to have no effect on the absorption of phosphorus. The amount of microcystin measured by enzyme-Linked immunosorbent assay (ELISA) increased in GA3 treatment groups, but the stimulatory effects were different in different culture phases. It is suggested that GA3 increases M. aeruginosa growth by stimulating its absorbance of nitrogen and increasing its ability to use carbohydrates, accordingly increasing cellular pigments and thus finally inducing accumulation of protein and microcystin. (C) 2007 Elsevier GmbH. All rights reserved.

Relationship between the allelopathic activity and molecular structure of hydroxyl derivatives of benzoic acid and their effects on cyanobacterium Microcystis aeruginosa

The antialgal activities of benzoic acid, 2-hydroxybenzoic acid (salicylic acid), 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid and 3,4,5-trihydroxybenzoic acid (gallic acid) were studied on the growth of two strains of Microcystis aeruginosa (toxic FACHB 942 and non-toxic 469). The results showed that the sequence of 50% growth inhibition concentration (ErC50) of 6- compounds for both strains of M. aeruginosa followed the same order: gallic acid > 3,5-dihydroxybenzoic acid > 4-hydroxybenzoic acid > salicylic acid > 3-hydroxybenzoic acid > benzoic acid. The position and the numbers of hydroxy groups between the hydroxy group and carboxyl influenced the antialgal effects of phenolic acids. We also investigated the joint effects of benzoic acid, 4-hydroxybenzoic acid and 3,4,5-trihydroxybenzoic acid on the growth of M. aeruginosa ( toxic FACHB 942). The mixture of phenolic allelochemicals showed the synergistic effects.

Physiological comparison between colonial and unicellular forms of Microcystis aeruginosa Kutz. (Cyanobacteria)

In order to gain insight into the bloom sustainment of colonial Microcystis aeruginosa Katz., physiological characterizations were undertaken in this study. Compared with unicellular Microcystis, colonial Microcystis phenotypes exhibited a higher maximum photosynthetic rate (Pm), a higher maximum electron transfer rate (ETRmax), higher phycocyanin content, and a higher affinity for inorganic carbon (K-0.5 DIC <= 8.4 +/- 0.7 mu M) during the growth period monitored in this study. This suggests that photosynthetic efficiency is a dominant physiological adaptation found in colonial Microcystis, thus promoting bloom sustainment. In addition, the high content of soluble and total carbohydrates in colonial Microcystis suggests that this phenotype may possess a higher ability to tolerate enhanced stress conditions when compared to unicellular (noncolonial) phenotypes. Therefore, high photosynthetic activities and high tolerance abilities may explain the bloom sustainment of colonial Microcystis in eutrophic lakes.

Antioxidant enzyme activities of Microcystis aeruginosa in response to nonylphenols and degradation of nonylphenols by M-aeruginosa

The aim of this study was to examine the effects of chemical nonylphenols (NPs) on the antioxidant system of Microcystis aeruginosa strains. The degradation and sorption of NPs by M. aeruginosa were also evaluated. High concentrations of NPs (1 and 2 mg/l) were found to cause increases in superoxidase dismutase (SOD) and glutathione-S-transferase (GST) activities and in glutathione (GSH) levels. These results suggest that toxic stress manifested by elevated SOD and GST levels and GSH contents may be responsible for the toxicity of NPs to M. aeruginosa and that the algal cells could improve their antioxidant and detoxification ability through the enhancement of enzymatic and nonenzymatic prevention substances. The observed elevations in GSH levels and GST activities were relatively higher than those in SOD activities, indicating that GSH and GST contributed more in eliminating toxic effects than SOD. Low concentrations of NPs (0.05-0.2 mg/l) enhanced cell growth and decreased GST activity in algal cells of M. aeruginosa, suggesting that NPs may have acted as a protecting factor, such as an antioxidant. The larger portion of the NPs (> 60%) disappeared after 12 days of incubation, indicating the strong ability of M. aeruginosa to degrade the moderate persistent NP compounds. The sorption ratio of M. aeruginosa after a 12-day exposure to low nominal concentrations of NPs (0.02-0.5 mg/l) was relatively high (> 30%). The fact that M. aeruginosa effectively resisted the toxic effects of NPs and strongly degraded these pollutants indicate that M. aeruginosa cells have a strong ability to adapt to variations in environmental conditions and that low and moderate concentrations of organic compounds may favor its survival. Further studies are needed to provide detailed information on the fate of persistent organic pollutants and the survival of algae and to determine the possible role of organic pollutants in the occurrence of water blooms in eutrophic lakes.