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(CPCC), as well as species isolated from erwironmental water samples collected in Choiniere reservoir, Eastern townships, Quebec, Canada (Deblois et al., 2013) (see table I). Ali species were cultivated in 250 ml Erlenmeyers, containing 100 ml of growth medium. The growth medium Bold Basal Medium (BBM) pH 6.8 was prepared following Stein (1973) and Modified High Salt Medium (HSM) pH 6.8 was prepared following Sueoka et al. (1967). Ali species were acclimated in growth chamber at 20°C, with a 12 hours dark-light photoperiod

and day-time light intensity of 100 pmol photons m'²s \ for a period of four weeks before the

%

beginning of the experiment. Ali assays were performed using the organisms in exponential growth phase. The glyphosate-based herbicide tested in this study was the commercial formulation Factor540°^i> (540 g l'¹ of pure glyphosate) (IPCO, Winnipeg, Manitoba, Canada). Algae and cyanobacteria were exposed to Factor540* at six glyphosate concentrations: 10, 50, 100, 300, 500 and 1000 pg I*¹, for 48 hours. Ali pesticide dilutions were madę in sterile growth medium, BBM or modified HSM, depending on the species.

Tableau 2.1 Species used for bioassays, testing growth and photosynthetic capacity of algac and cyanobacteria exposed to glyphosate-based herbicide

Groupe	Species	Growth medium
Cyanobacteria	Microcystis aeruginosea, (CPCC632) Microcystis aeruginoseu, (CPCC299) Microcystis sp.*	BBM
Chlorophytes	Scenedesmus obliąuus (CPCC5) Ankistrodesmus falcatus * Oocystis sol i tar ia*
	Chlamydomonas snowi i* Chlamydomonas reinhardtii, (CPCC 125)	HSM
Cryptophyte	Cryptomonas obovata*	BBM

♦Species isolated from Choiniere reservoir, Eastern townships, Quebec. Canada (Deblois et al., 2013)

2.5.2 Growth evaluation

Population growth ratę (p) measures were based on celi count performed with Multisizer™ 3 COULTER COUNTER® (Beckman Coulter, Inc.) and calculated as:

(2.1)

p = [ln(number of cells(t₂)) - ln(number of cells(ti))] / (t₂ - tj)