Occurrence of toxic Planktothrix rubescens blooms in lake Nantua, France.

Cyanobacteria including genus Oscillatoria are known to release toxins into waterbodies. To study the occurrence of toxic blooms in Lake Nantua, the Planktothrix rubescens species (Oscillatoria rubescens) was considered. At the same time, some physicochemical parameters were analysed to estimate their impact on toxin production. The investigations were conducted during summertime and the highest toxin concentration analysed by HPLC was detected in August (10.8 microg/l of lake water). The results of this work suggested that the toxin production increased when the light intensity, temperature, alkaline pH and phosphorus contents were at low levels. Moreover, the toxin production was positively related with NT/PT ratio. TLC analysis of the purified fractions revealed the occurrence of 4-7 polypeptide or protein bands. Two of them were shown to be toxic using Artemia bioassays and the most toxic one was identified as MCYST-RR.