Cellular Microcystin Content in N-Limited Microcystis aeruginosa Can Be Predicted from Growth Rate

Abstract

Cell quotas of microcystin (Q MCYST ; femtomoles of MCYST per cell), protein, and chlorophyll a (Chl a), cell dry weight, and cell volume were measured over a range of growth rates in N-limited chemostat cultures of the toxic cyanobacterium Microcystis aeruginosa MASH 01-A19. There was a positive linear relationship between Q MCYST and specific growth rate (), from which we propose a generalized model that enables Q MCYST at any nutrient-limited growth rate to be predicted based on a single batch culture experiment. The model predicts Q MCYST from , max (maximum specific growth rate), Q MCYSTmax (maximum cell quota), and Q MCYSTmin (minimum cell quota). Under the conditions examined in this study, we predict a Q MCYSTmax of 0.129 fmol cell ؊1 at max and a Q MCYSTmin of 0.050 fmol cell ؊1 at ‫؍‬ 0. Net MCYST production rate (R MCYST ) asymptotes to zero at ‫؍‬ 0 and reaches a maximum of 0.155 fmol cell The microcystins (MCYSTs) are a group of cyclic heptapeptide toxins produced by several cyanobacterial species. Of the more than 60 MCYSTs characterized to date (19,27,29), most are potent inhibitors of protein phosphatases 1 and 2A from both plants and animals (17). One of the most common MCYST-producing cyanobacteria is the bloom-forming Microcystis aeruginosa (Kützing) Lemmermann. Due to the widespread distribution and potential toxicity of this species (toxic strains have been found worldwide), M. aeruginosa has been implicated in a number of animal-poisoning incidents (e.g., reference 7) and more recently in human fatalities (11,23).M. aeruginosa is a unicellular, colonial freshwater cyanobacterium which often forms blooms during warmer months in eutrophic lakes and reservoirs (37). For this reason, much research has been concerned with the environmental factors which lead to bloom formation and toxin production in this species. A wide range of batch culture studies have shown that the variables influencing MCYST content include trace metal supply (15), nitrogen (N) and phosphorus (P) (31), light and temperature (38), and pH (34). Comparative studies on MCYST production by M. aeruginosa in continuous culture, however, have been limited to examination of the effects of photon irradiance (35), N, P, and Fe 3ϩ limitation (16, 36), and more recently P limitation (20). Despite this considerable pool of data concerning MCYST production, few studies (with the exception of the work carried out by Rapala and coworkers [25,26]) have been able to quantitatively relate MCYST content to any growth determinant.In a previous batch culture study, we presented data on the effect of N supply on the cellular production of MCYSTs (21). This work showed that the net specific rate of MCYST production was equal to the cell specific growth rate. The application of these findings to previously published batch culture studies suggested that the relationship held under a variety of culture conditions and that MCYST production was indirectly affected by environmental factors through their effects on cell division. A consequence of this l...

Mathematical modeling of Microcystis aeruginosa growth and [D-Leu1] microcystin-LR production in culture media at different temperatures

“…The constant [D-Leu 1 ] MC-LR Chl-a quota ratio found in this study supports this hypothesis and suggests that MC synthesis and/or function may be linked to the photosynthetic process. Long et al (2001) found similar results to those reported here, with values of the MC Chl-a quota at 0.59 AE 0.03 (fg ng À1 ); however, these authors also suggest that MCs may not be essential in photosynthesis. To date there has been insufficient understanding of the temperature effects on the physiology of MCs production to draw firm conclusions.…”

Cyanobacteria and their toxins in Guanting Reservoir of Beijing, China

“…Two biotic factors affect microcystins concentration in the field: cellular microcystin production and content [21], and the species composition of cyanobacteria in reservoirs [22]. Environmental conditions also indirectly influenced microcystins through their effects on these two factors.…”

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).…”