Microcystin Production by Microcystis aeruginosa in a Phosphorus-Limited Chemostat

Abstract

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. ...

Factors Shaping the Pattern of Seasonal Variations of Microcystins in Lake Xingyun, a Subtropical Plateau Lake in China

“…Many strains of Microcystis are known to produce cyanobacterial heptatoxins called microcystins (MC). Laboratory studies indicate that production of microcystin by Microcystis is affected by various environmental factors such as light, temperature, nutrients, trace elements, salinity, pH and nutrient contents in cells (Gorham 1964;Van der Westhuizen and Eloff 1985;Watanabe and Oishi 1985;Oh et al 2000;Lee et al 2000;Long et al 2001). Environmental variables are likely to influence MC concentration directly by influencing cellular microcystin production and content (Orr and Jones 1998;Long et al 2001), and indirectly by influencing cyanobacterial species and strain composition (Chorus 2001;Vézie et al 2002).…”

Use of an armored RNA standard to measure microcystin synthetase E gene expression in toxic Microcystis sp. by reverse‐transcription QPCR

“…by reversetranscription QPCR al. 2007), nitrogen and phosphorus (e.g., Orr and Jones 1998;Oh et al 2000;Vézie et al 2002), micronutrients (e.g., Lukac and Aegerter 1993;Utkilen and Gjolme 1995;Lyck et al 1996), temperature (e.g., van der Westhuizen and Eloff 1985;van der Westhuizen et al 1986;Amé and Wunderlin 2005), pH (e.g., van der Westhuizen and Eloff 1983), and photon irradiance (e.g., Kaebernick et al 2000;Kardinaal et al 2007) can affect growth and toxin production. Unfortunately, in spite of this intensive research, the regulatory mechanisms behind microcystin biosynthesis and its biological function are still largely unresolved.…”

Towards clarification of the inhibitory mechanism of wheat bran leachate on Microcystis aeruginosa NIES-843 (cyanobacteria): physiological responses

“…The toxicity of microcystins is mediated through the inhibition of eukaryotic protein phosphatases 1A and 2A in liver cells and cause liver cancer and tumors in humans and wildlife (Carmichael 1995). Many biotic and abiotic factors such as zooplankton grazing (Jang et al 2003), phosphorus concentrations (Oh et al 2000), and nitrogen concentrations (Lee et al 2000), were shown to affect the production of microcystins by Microcystis. Recently, the influence of environmental factors on microcystins synthesis was studied in levels of transcription of mcy genes and microcystins synthetase (Mcy).…”