Effects of microcystis on Daphnia pulex

Although cyanobacteria produce a wide range of natural toxins that impact aquatic organisms, food webs and water quality, the mechanisms of toxicity are still insufficiently understood. Here, we implemented a whole-genome expression microarray to identify pathways, gene networks and paralogous gene families responsive to Microcystis stress in Daphnia pulex. Therefore, neonates of a sensitive isolate were given a diet contaminated with Microcystis to contrast with those given a control diet for sixteen days. The microarray revealed 2247 differentially expressed (DE) genes (7.6% of the array) in response to Microcystis, of which 17% are lineage specific and 49% are gene duplicates (paralogs). We identified four pathways/gene networks and eight paralogous gene families affected by Microcystis. Differential regulation of the ribosome including 3 paralogous gene families encoding 40S, 60S and mitochondrial ribosomal proteins, suggests an impact of Microcystis on protein synthesis of Daphnia. In addition, differential regulation of the oxidative phosphorylation pathway, including the NADH ubquinone oxidoreductase gene family, and trypsin paralogous gene family, major component of the digestive system in Daphnia, could explain why fitness is reduced based on energy budget considerations. For others (.e.g Neurexin IV), a link with fitness remains to be established. RNA was isolated from three independent and concurrently replicated exposures of Daphnia to control and Microcystis conditions. RNA was hybridized to 4 microarrays using a standard, control vs. treated design that included dye swaps.