Microcystis aeruginosa is a toxic cyanobacterium, which is able to bloom in a wide range of freshwater ecosystems. By sequencing the Internal Transcribed Spacer (ITS) of the ribosomal operon, we compared the genetic composition of several French bloom-forming M. aeruginosa populations from two reservoirs located on the Loire River, at two sampling points located between these reservoirs, and finally in two ponds closely linked to this river. No significant difference was found in the genetic diversity of the six Microcystis populations but we evidenced a strong genetic differentiation between most of these populations. Indeed, the Microcystis population in the Grangent reservoir was genetically differentiated from the other three populations sampled further downstream, implying that no massive transfer of population occurs from this reservoir to downstream segments. We also found genetic differentiation between the populations from the two ponds, and between these populations and those from the Loire River. On the other hand, the same dominant genotype was found in the populations sampled both in the river and in the Villerest reservoir, suggesting the selection of a distinct genotype adapted to river conditions and also an accumulation of this genotype in the downstream reservoir. Finally, by comparing our ITS sequences with those available in the GenBank, no biogeographical differentiation could be detected at a global scale, suggesting that most of the Microcystis genotypes seem to be ubiquitous.

The aroma-active and off-flavor compounds of cooked rainbow trout (Oncorhynchus mykiss) were analyzed by sensory and instrumental analyses. Sensory analysis shows that the aromatic extract obtained by vacuum steam distillation was representative of rainbow trout odor. To obtain more information on odorants of volatile compounds, analyses were conducted on two gas chromatography columns of different polarities (DB-5 and DB-Wax). The results of the gas chromatography-olfactometry analysis showed that 38 odorous compounds were perceived when the DB-5 column was used and 36 with the DB-Wax column. Of these, 31 with the DB-5 and 28 with the DB-Wax were identified. (E)-2-Nonenal, 2-ethyl-1-hexanol, 2-methylisoborneol, geosmin, 2-methylnaphthalene, and 8-heptadecene were described as off-flavor compounds by the sniffing assessors. The most powerful off-flavor compounds identified in the extract were 2-methylisoborneol and geosmin, which were described as strong musty and earthy odors, respectively.