Does a Diet Rich in the Bacterium Improve Performance?

Background: In the wild various organisms contribute to daphnids diet. This study, intendeds to evaluate the potential of the concentration of as a single or supplementary food source for .

Methods: Feeding assays were performed according to standard guidelines for chronic assays (21 days), and life-history parameters and several biomarkers (protein content, oxidative stress, energetic reserves and pigments) were measured. Five food regimens were conducted with 20 individual replicates (A - ; 0.2 - suspension of at 0.2 arbitrary units (AU); 0.4 - suspension of at 0.4 AU; 0.2+A - suspension of at 0.2+alga; 0.2+A-suspension of at 0.4 AU + alga). Additionally, the effects of three diets (A, 0.2, and 0.2+A) on the longevity of were assessed.

Results: The five diets showed a different C, N, and carotenoids composition, with an increase in the mixed diets. The results confirmed that the mixed diets improved life-history parameters. A decrease in glycogen, and the increase of haemoglobin, protein, and gluthione-S-transferase (GST) were observed. Furthermore, fed with bacterial single diets, presented worsen life history parameters and a decrease in the protein content. An induction of oxidative stress response (increased catalase and GST), and a significant decrease in lipid peroxidation and an accumulation of glycogen and carotenoids were observed. Overall, an increase in the amount of provided to , from 0.2 AU to 0.4 AU, negatively impacted daphnid performance. No significant effects on longevity (a 110-day assay) were observed among the three diets tested. However, a significant survival percentage and fertility (cumulative offspring is more than twice) was observed when was fed with the mixed diet.

Conclusions: Results demonstrated that different diets provided a nutritional diversified food to the daphnids that induced differences in performance. The mixed diets proved to be beneficial (with increase in offspring) on performance, independently of the bacterial concentration tested. When in single diet, bacterial concentration is not nutritionally sufficient to raise even when in increased concentration.