Buoyant density changes in the cyanobacterium Microcystis aeruginosa due to changes in the cellular carbohydrate content

Abstract The cyanobacterium Microcystis aeruginosa was grown in light-limited chemostat cultures with various light—dark rhythms providing a total periodicity length of 24 h. The buoyant density of the cells changed in parallel with the carbohydrate content. Short incubation experiments with different light intensities, and experiments with the inhibitors iodoacetic acid and arsenate, showed that the buoyant density changes were due to variations in the cellular carbohydrate content. It seems likely that the low dark-growth yield on carbohydrate, which had been stored during the light period, served to facilitate buoyancy changes.     

Cryopreservation of a water-bloom forming cyanobacterium, Microcystis aeruginosa f. aeruginosa

A method for the Cryopreservation of Microcystis aeruginosa f. aeruginosa is described. For the five strains tested, dimethyl sulfoxide (DMSO) (3% v/v) was the only effective cryoprotectant for freezing to, and thawing from -196°C and allowed the successful recovery (>50%) of all the strains. The viability of frozen material was independent of the period of storage in liquid nitrogen. The strain NIES-44 (National Institute for Environmental Studies) had a recovery level of greater than 90% at 3–10% (v/v) DMSO in both two step and rapid cooling methods. The other three strains, NIES-87, 88 and 89 had greater than 60% of viability after freeze/thawing in presence of both 3% and 5% DMSO concentrations. On the other hand, the strain NIES-90 showed approximately 50% of viability in only 3% DMSO solution after two step cooling to and thawing from -196°C. This strain was damaged by greater than 4% DMSO and by rapid cooling to -196°C. It was found that cold shock injury and the cytotoxicity of DMSO were different at a strain level.     

Adaptation of the toxic freshwater cyanobacterium Microcystis aeruginosa to salinity is achieved by the selection of spontaneous mutants

The cyanobacterium Microcystis aeruginosa causes most of the harmful toxic blooms in freshwater ecosystems. Some strains of M. aeruginosa tolerate low‐medium levels of salinity, and because salinization of freshwater aquatic systems is increasing worldwide it is relevant to know what adaptive mechanisms allow tolerance to salinity. The mechanisms involved in the adaptation of M. aeruginosa to salinity (acclimation vs. genetic adaptation) were tested by a fluctuation analysis design, and then the maximum capacity of adaptation to salinity was studied by a ratchet protocol experiment. Whereas a dose of 10 g NaCl L^?1 completely inhibited the growth of M. aeruginosa, salinity‐resistant genetic variants, capable of tolerating up to 14 g NaCl L^?1, were isolated in the fluctuation analysis experiment. The salinity‐resistant cells arose by spontaneous mutations at a rate of 7.3 × 10^?7 mutants per cell division. We observed with the ratchet protocol that three independent culture populations of M. aeruginosa were able to adapt to up to 15.1 g L^?1 of NaCl, suggesting that successive mutation‐selection processes can enhance the highest salinity level to which M. aeruginosa cells can initially adapt. We propose that increasing salinity in water reservoirs could lead to the selection of salinity‐resistant mutants of M. aeruginosa.     

Photoinactivation in vivo of superoxide dismutase and catalase in the cyanobacterium Microcystis aeruginosa

Abstract The planktonic cyanobacterium Microcystis aeruginosa is particularly sensitive to photoinhibition by visible light, Photosystem II and ribulose 1,5-bisphosphate (RuBP) carboxylase activities being affected. Although the organism contains superoxide dismutase (SOD) and catalase, these protective enzymes are also photoinactivated during the illumination of whole cells by visible light.     

Active release of microcystins controlled by an endogenous rhythm in the cyanobacterium Microcystis aeruginosa

The active release of microcystins in cyanobacterium Microcystis aeruginosa (Kützing) Kützing, strain BCCUSP232 was confirmed. The microcystin release is controlled by an endogenous rhythm, pointing to a biosynthetic pattern of toxins in cyanobacteria. Proofing tests for this active release were carried out by experiments at two independent 24 h cycles, light : dark and continuous light (12:12 h) along the exponential growing phase. Cultivation samples at light, temperature and photoperiod controlled conditions were collected in 2‐h intervals. Microcystin concentrations from the pellet aliquots (intracellular microcystin per cell‐quota –IMC) and supernatant (extracellular microcystin per equivalent cell‐quota – EMC) were quantified with enzyme linked immunosorbent assay. The IMC concentrations showed increases and decreases in both cycles. Decreases of IMC clearly demonstrate that the toxin was actively released to the surrounding medium and not by cell lysis. The total microcystins concentrations (IMC and EMC) between the light : dark and continuous light cycles presented similar variations between the same hours.     

Toxic and non-toxic strains of the cyanobacterium Microcystis aeruginosa contain sequences homologous to peptide synthetase genes

Abstract Toxic strains of Microcystis aeruginosa produce cyclic heptatoxins (microcystins) that are believed to be synthesized non-ribosomally by peptide synthetases. We analysed toxin-producing and non-toxic strains of M. aeruginosa with respect to the presence of DNA sequences potentially encoding peptide synthetases. Hybridizations of genomic DNA of various M. aeruginosa strains with PCR-amplificated fragments possessing homologies to adenylate-forming domains of peptide synthetase genes provided first evidence for the existence of corresponding genes in cyanobacteria. Furthermore we isolated and sequenced from genomic libraries overlapping fragments of M. aeruginosa DNA with a total length of 2982 bp showing significant homology to genes encoding peptide synthetases and hybridizing exclusively with DNA from toxic strains. Our results indicate that both toxic and non-toxic strains of M. aeruginosa possess genes coding for peptide synthetases and that hepatotoxin-producing and non-toxic strains differ in their content of genes for specific peptide synthetases.     

Cultivation and characterization of the MaMV-DC cyanophage that infects bloom-forming cyanobacterium Microcystis aeruginosa

The MaMV-DC cyanophage, which infects the bloom-forming cyanobacterium Microcystis aeruginosa, was isolated from Lake Dianchi, Kunming, China. Twenty-one cyanobacterial strains were used to detect the host range of MaMV-DC. Microcystic aeruginosa FACHB-524 and plaque purification were used to isolate individual cyanophages, and culturing MaMV-DC with cyanobacteria allowed us to prepare purified cyanophages for further analysis. Electron microscopy demonstrated that the negatively stained viral particles are tadpole-shaped with an icosahedral head approximately 70 nm in diameter and a contractile tail approximately 160 nm in length. Using one-step growth experiments, the latent period and burst size of MaMV-DC were estimated to be 24–48 hours and approximately 80 infectious units per cell, respectively. Restriction endonuclease digestion and agarose gel electrophoresis were performed using purified MaMV-DC genomic DNA, and the genome size was estimated to be approximately 160 kb. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis revealed four major structural proteins. These results support the growing interest in using freshwater cyanophages to control bloom-forming cyanobacterium.     

铜绿微囊藻的分子研究进展

中国淡水湖泊、水库众多,富营养化问题严重。铜绿微囊藻是中国湖泊、水库及其他水域生态系统发生、形成富营养化危害的主要藻类。目前对铜绿微囊藻的研究主要集中在水华成因、生长的特点、作用机理等,对其生命活动相关的分子机制研究不多。该文主要从生物节律、毒素合成、藻胆蛋白合成及其调控机制和ATP合成酶等四个方面综述了铜绿微囊藻的分子研究进展,为今后进一步研究铜绿微囊藻的分子作用机理及其防治具有重要意义。     

Identification of a Ferric uptake regulator from Microcystis aeruginosa PCC7806

Ferric uptake regulator (Fur) proteins are widely recognized as repressors that in many prokaryotes regulate a large number of genes involved in iron homeostasis and oxidative stress response. In our study, we were able to identify the complete sequence of the fur gene from Microcystis aeruginosa using inverse-polymerase chain reaction. DNA sequence analysis confirmed the presence of a 183 amino-acid open reading frame that showed high identity with Fur proteins reported for cyanobacteria. The recombinant Fur protein has been purified and electrophoretical mobility shift assays shown to be active. Mn2+ and dithiothreitol enable Fur to bind to its promoter, with dithiothreitol being more potent. The expression of Fur in Microcystis was induced about twofold in iron-deficient conditions.     

Methods for prevention of mass development of the cyanobacterium Microcystis aeruginosa Kutz emend. Elenk. in aquatic systems

Methods for prevention of mass development of the cyanobacterium Microcystis aeruginosa Kutz emend. Elenk. in continental water bodies and industrial water supply systems are reviewed. The physicochemical, chemical, and biological methods for prevention of M. aeruginosa development in water bodies and water supply systems are considered; examples of successful inhibition of M. aeruginosa growth in laboratory experiments are demonstrated. The scientific problems are outlined that are to be solved for perfecting techniques for prevention of M. aeruginosa mass development in open water bodies and in closed water supply systems.     

有机磷农药对滇池微囊藻生长和摄磷效应的影响

采集滇池水体作为铜绿微囊藻培养基,研究了两种有机磷农药(甲胺磷和辛硫磷)对微囊藻生长和摄磷效应的动力学规律。结果表明,在滇池水体中添加较低浓度的甲胺磷(0.8、1.6、3.2mg/L)和辛硫磷(0.02、0.06、0.1mg/L)均能不同程度地促进微囊藻的生长,且在HGZ培养基中抑制微囊藻生长的浓度在滇池水体中却能促进微囊藻的生长。微囊藻的生长取决于细胞内磷的浓度且对磷的吸收利用存在积累性,在微囊藻生长初期,摄取各形态磷的速率较快;随后微囊藻摄取各形态磷的速率较慢。总溶解磷(TSP)和溶解反应磷(SRP)是微囊藻优先摄取的磷形态,在生长过程中微囊藻利用了大量的溶解有机磷(DOP)作为磷源加速生长。这一特点对于微囊藻成为淡水湖泊富营养化发展过程中的一种重要优势种具有极为重要的作用。     

Buoyancy regulation in phosphate-limited cultures of Microcystis aeruginosa

Buoyancy regulation was studied in P-limited continuous cultures of Microcystis aeruginosa grown on light-dark cycles of 8–16 h. Gas-vesicle content did not vary systematically over a range of dilution rates form 0.004 to 0.015 h⁻¹. A reduction in irradiance did not cause a significant change in gas-vesicle content. The proportion of floating cells decreased during the photoperiod and increased during the dark period. At three dilution rates, parallel cultures were grown at growth-saturating irradiance and at a lower irradiance. The cultures at low irradiance had a higher proportion of floating cells and a smaller decrease in buoyancy during the light period. The buoyancy losses were not due to destruction of gas vesicles but, rather, to the accumulation of heavy substances. However, measured increases in polysaccharide ballast accounted for only 60% of the required ballast. The molecule(s) which comprised the remainder of the ballast are unknown. Upon relief of phosphate limitation, P-limited cultures increased their buoyancy when incubated in the dark or light. Buoyancy increases in the dark were correlated with a decrease in polysaccharide content, whereas there was an increase in gas vesicle content in the light.     

Physiological and Biochemical Changes in Microcystis aeruginosa Qutz. in Phosphorus Limitation

Effects of phosphorus limitation on the physiological and biochemical changes of the freshwater bloom alga Microcystis aeruginosa Qutz. are reported in the present study. As a result of phosphorus limitation, biomass was controlled to some extent and the protein content per cell in vivo decreased. However,the carbohydrate content per cell was higher in phosphorus limitation over the 8d of cultivation. Soluble proteins were distinct in the media, whereas phosphorus deficiency induced the presence of a unique protein (16.2 kDa). Under conditions of phosphorus limitation, the activities of both superoxide dismutase and peroxidase per cell in vivo were lower than under normal conditions in the last cultivation. The in vivo absorption spectra of cells showed chlorophyll absorption peaks at 676 and 436nm, over 10nm red-shifted from the normal position; cells showed an absence of a chlorophyll c with an in viva absorption peak at 623nm and an extraction absorption peak at 617nm. The chlorophyll a/carotene and chlorophyll a/xanthophylls ratios decreased under conditions of phosphorus limitation, photosynthetic efficiency (Fv/Fm) was clearly lower, and the low-temperature fluorescence emission spectra indicated a higher peak at 683nm and a lower peak at 721nm relatively, with the 721nm peak drifting slightly to the red and the 683 nm peak strengthened with a weakened 692nm shoulder peak.     

Physiological and Biochemical Changes in Microcystis aeruginosa Qutz. in Phosphorus Limitation

Effects of phosphorus limitation on the physiological and biochemical changes of the freshwater bloom alga Microcystis aeruginosa Qutz. are reported in the present study. As a result of phosphorus limitation, biomass was controlled to some extent and the protein content per cell in vivo decreased. However,the carbohydrate content per cell was higher in phosphorus limitation over the 8 d of cultivation. Soluble proteins were distinct in the media, whereas phosphorus deficiency induced the presence of a unique protein (16.2 kDa). Under conditions of phosphorus limitation, the activities of both superoxide dismutase and peroxidase per cell in vivo were lower than under normal conditions in the last cultivation. The in vivo absorption spectra of cells showed chlorophyll absorption peaks at 676 and 436 nm, over 10 nm red-shifted from the normal position; cells showed an absence of a chlorophyll c with an in vivo absorption peak at 623nm and an extraction absorption peak at 617 nm. The chlorophyll a/carotene and chlorophyll a/xanthophylls ratios decreased under conditions of phosphorus limitation, photosynthetic efficiency (Fv/Fm) was clearly lower, and the low-temperature fluorescence emission spectra indicated a higher peak at 683 nm and a lower peak at 721 nm relatively, with the 721 nm peak drifting slightly to the red and the 683 nm peak strengthened with a weakened 692 nm shoulder peak.     

Buoyancy regulation in Microcystis aeruginosa grown at different temperatures

Abstract The buoyancy regulation in light-limited cultures of the gas vacuolate cyanobacterium Microcystis aeruginosa AK1 was studied at three temperatures, 15, 20 and 28°C. At the two highest temperatures the organism remained buoyant during the entire light period, whereas at the lowest temperature the buoyancy was reduced at the start of the light period. With this temperature the buoyancy was lost during the light period. This reduced buoyancy was caused by an increase in ballast and a decrease in the gas vesicle volume. Buoyancy changes during a transient state with slow changes in temperatures, i.e., 1°C per day, were caused by changes in polysaccharide ballast. The gas vesicle volume showed no significant change during the transient state.
The maximal photosynthetic rate was dependent upon the growth and incubation temperature, whereas the light harvesting efficiency was independent of the temperature. The results are discussed in an ecological context.     

Capsular polysaccharides facilitate enhanced iron acquisition by the colonial cyanobacterium Microcystis sp. isolated from a freshwater lake

Microcystis sp., especially in its colonial form, is a common dominant species during cyanobacterial blooms in many iron‐deficient water bodies. It is still not entirely clear, however, how the colonial forms of Microcystis acclimate to iron‐deficient habitats, and the responses of unicellular and colonial forms to iron‐replete and iron‐deficient conditions were examined here. Growth rates and levels of photosynthetic pigments declined to a greater extent in cultures of unicellular Microcystis than in cultures of the colonial form in response to decreasing iron concentrations, resulting in the impaired photosynthetic performance of unicellular Microcystis as compared to colonial forms as measured by variable fluorescence and photosynthetic oxygen evolution. These results indicate that the light‐harvesting ability and photosynthetic capacity of colonial Microcystis was less affected by iron deficiency than the unicellular form. The carotenoid contents and nonphotochemical quenching of colonial Microcystis were less reduced than those of the unicellular form under decreasing iron concentrations, indicating that the colonial morphology enhanced photoprotection and acclimation to iron‐deficient conditions. Furthermore, large amounts of iron were detected in the capsular polysaccharides (CPS) of the colonies, and more iron was found to be attached to the colonial Microcystis CPS under decreasing iron conditions as compared to unicellular cultures. These results demonstrated that colonial Microcystis can acclimate to iron deficiencies better than the unicellular form, and that CPS plays an important role in their acclimation advantage in iron‐deficient waters.