Four algae of freshwater phytoplankton were studied in monospecific culture: Chlorella vulgar-is, Fragilaria crotonensis, Staurastrum pingue and Synechocystis minima. Experiments were performed to determine the growth rate over a wide range of light intensities (5-800 PE me2 s-', 15/9 light/dark photoperiod) and temperatures (lo-35 'C). The results provide a set of parameters (particularly the maximal growth rate associated to optimal conditions of light and temperature) for a three-equation model used to described the growth rate response of a non-nutrient-limited culture.
Bioassays are little used to detect individual toxins in the environment because, compared to analytical methods, these assays are still limited by several problems, such as the sensitivity and specificity of detection. We tentatively solved these two drawbacks for detection of anatoxin-a(s) by engineering an acetylcholinesterase to increase its sensitivity and by using a combination of mutants to obtain increased analyte specificity. Anatoxin-a(s), a neurotoxin produced by some freshwater cyanobacteria, was detected by measuring the inhibition of acetylcholinesterase activity. By using mutated enzyme, the sensitivity of detection was brought to below the nanomole-per-liter level. However, anatoxin-a(s) is an organophosphorous compound, as are several synthetic molecules which are widely used as insecticides. The mode of action of these compounds is via inhibition of acetylcholinesterase, which makes the biotest nonspecific. The use of a four-mutant set of acetylcholinesterase variants, two mutants that are sensitive to anatoxin-a(s) and two mutants that are sensitive to the insecticides, allows specific detection of the cyanobacterial neurotoxin.
La croissance de huit espèces d'algues du phytoplancton d'eau douce (6 Chlorophycées, 1 Diatomée, 1 Cyanophycée) a été étudiée en culture. Plusieurs méthodes d'évaluation de la biomasse ont été comparées : poids sec, comptages cellulaires, densité optique, chlorophylle. Selon les espèces, l'extraction de pigments par l'acétone donne des valeurs inférieures de 5 à 50 % par rapport à l'éthanol. S'il n'a a pas de carence en nutriments, une assez bonne approximation du taux de croissance peut être calculée à partir des paramètres acquis par des expériences de photosynthèse (Pmax). Les variations de taille des cellules au cours du cycle de division sont également décrites. Le taux de croissance des huit espèces est décrit en fonction de la température et de la lumière selon un système d'équations inspirées de la formulation de Steele (1965). Les paramètres obtenus permettent de bien modéliser l'évolution d'une culture en tenant compte du phénomène d'ombre propre. Conditions for phytoplankton development, a comparative study of the behaviour of eight species in culture. I. Determination of growth parameters in relation to light and temperature. The growth of eight algal species from freshwater phytoplankton (6 Chlorophyceae, 1 Diatom, 1 Cyanophyceae) has been studied in culture. Several methods of biomass evaluation have been compared: dry weight, cell counts, optical density, chlorophyll. Amongst the species, the extraction of pigments by acetone provides estimates that are lower 5-50 % compared with ethanol. If there is not a lack of nutrients, a close approximation of growth rate can foe calculated beginning with the parameters acquired from the processes of photosynthesis (Pmax)' Variations in the size of cells during their division cycle are likewise described. The growth rate of eight species is described as a function of temperature and light, and according to a basic equation based on Hhat of Steele (1965). The parameters obtained can be used to model the development of a culture, taking into account the phenomenon of self-shading.
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