The production of microcystins (MC) from Microcystis aeruginosa UTEX 2388 was investigated in a P-limited continuous culture. MC (MC-LR, MC-RR, and MC-YR) from lyophilized M. aeruginosa were extracted with 5% acetic acid, purified by a Sep-Pak C 18 cartridge, and then analyzed by high-performance liquid chromatography with a UV detector and Nucleosil C 18 reverse-phase column. The specific growth rate () of M. aeruginosa was within the range of 0.1 to 0.8/day and was a function of the cellular P content under a P limitation. The N/P atomic ratio of steady-state cells in a P-limited medium varied from 24 to 15 with an increasing . The MC-LR and MC-RR contents on a dry weight basis were highest at of 0.1/day at 339 and 774 g g ؊1 , respectively, while MC-YR was not detected. The MC content of M. aeruginosa was higher at a lower , whereas the MC-producing rate was linearly proportional to . The C fixation rate at an ambient irradiance (160 microeinsteins m ؊2 s ؊1 ) increased with . The ratios of the MC-producing rate to the C fixation rate were higher at a lower . Accordingly, the growth of M. aeruginosa was reduced under a P limitation due to a low C fixation rate, whereas the MC content was higher. Consequently, increases in the MC content per dry weight along with the production of the more toxic form, MC-LR, were observed under more P-limited conditions.The bloom of cyanobacterium Microcystis aeruginosa is a ubiquitous phenomenon in eutrophic lakes and reservoirs in many countries of the world. Many strains of Microcystis are known to produce cyanobacterial hepatotoxins called microcystins. The toxin, a soluble peptide, is lethal to many kinds of aquatic organisms and damages zooplankton, fish (14), and the liver of higher animals (2, 22).Many studies on the effects of environmental factors on microcystin production by cyanobacteria have been conducted with Microcystis (7,13,19,20,(22)(23)(24), Anabaena (15, 16), Oscillatoria (17), and Synechocystis (11) species. The toxin of M. aeruginosa is at a maximum at light intensities between 40 and 50 microeinsteins m Ϫ2 s Ϫ1 (19, 23). The microcystin contents of Anabaena and M. aeruginosa are highest at 25°C (16) and between 20 and 24°C (21), respectively. Lower and higher temperatures decrease their amounts. In contrast, the effects of N and P on the toxin production by cyanobacteria are highly variable (13). Batch-cultured M. aeruginosa decrease in toxicity when N and inorganic C are removed from the medium (2). The concentration of microcystin in Anabaena increases with P (16). Toxin production by Oscillatoria agardhii depends on a low-level concentration of P (0.1 to 0.4 mg of P per liter), and higher concentrations have no additional effect (17). It was recently reported that the net microcystin production rate decreases as the specific cell division rate decreases in N-limited M. aeruginosa cultures (13). However, information about microcystin production related to the nutrient status in cells or in ambient circumstances is still insufficient.In this study, M. ...
Physicochemical and biological water quality, including the microcystin concentration, was investigated from spring to autumn 1999 in the Daechung Reservoir, Korea. The dominant genus in the cyanobacterial blooming season was Microcystis. The microcystin concentration in particulate form increased dramatically from August up to a level of 200 ng liter ؊1 in early October and thereafter tended to decrease. The microcystin concentration in dissolved form was about 28% of that of the particulate form. The microcystins detected using a protein phosphatase (PP) inhibition assay were highly correlated with those microcystins detected by a high-performance liquid chromatograph (r ؍ 0.973; P < 0.01). Therefore, the effectiveness of a PP inhibition assay for microcystin detection in a high number of water samples was confirmed as easy, quick, and convenient. The microcystin concentration was highly correlated with the phytoplankton number (r ؍ 0.650; P < 0.01) and chlorophyll-a concentration (r ؍ 0.591; P < 0.01). When the microcystin concentration exceeded about 100 ng liter ؊1 , the ratio of particulate to dissolved total nitrogen (TN) or total phosphorus (TP) converged at a value of 0.6. Furthermore, the microcystin concentration was lower than 50 ng liter ؊1 at a particulate N/P ratio below 8, whereas the microcystin concentration varied quite substantially from 50 to 240 ng liter ؊1 at a particulate N/P ratio of >8. Therefore, it seems that the microcystin concentration in water can be estimated and indirectly monitored by analyzing the following: the phytoplankton number and chlorophyll-a concentration, the ratio of the particulate and the dissolved forms of N and P, and the particulate N/P ratio when the dominant genus is toxigenic Microcystis.Blooms of the cyanobacterium Microcystis aeruginosa are ubiquitous phenomena in eutrophic lakes and reservoirs in many countries of the world. Many strains of Microcystis are known to produce cyanobacterial hepatotoxins called microcystins (MC). These toxins are soluble peptides and are lethal to many kinds of aquatic organisms (2,23,28). MC are found in strains of the genera Microcystis, Oscillatoria, Anabaena, and Nostoc (26). To date, at least 69 MC have been structurally characterized (9).The Daechung reservoir located in the middle of South Korea was formed by the construction of a multipurpose dam in 1980 to conserve water resources for drinking, agricultural, and industrial use and for electric power supply. Since the end of the 1980s, the reservoir has shown some eutrophic phenomena, such as cyanobacterial blooms, in the summer and a deterioration in water quality. With the appearance of cyanobacterial blooms, the production of cyanobacterial toxins, particularly MC, becomes a threat to human health and natural resources (10,20,22). Therefore, the ability to detect and predict MC in water resources is very important.Normally, a high-performance liquid chromatography (HPLC) analysis is used for the detection and qualification of MC in water (7,8,9). However, thi...
Of various methods for lipid recovery in Botryococcus braunii UTEX 572, the most effective method was disruption of the cells with a bead-beater followed by extraction with chloroform/methanol (2:1, v/v). This gave a lipid content of 28.6% of dry wt. There was a significant relationship between in vivo fluorescence of cells stained with Nile Red and lipid content in B. braunii determined gravimetrically (r 2 ϭ 0.997). This suggested that the Nile Red staining as a rapid method was as good as the gravimetric method commonly used for lipid determination which requires toxic solvents and considerable time-consuming manipulations.
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