ROS in vivo determination and antioxidant responses in rotifers Brachionus plicatilis fed with commercial yeast Saccharomyces cerevisiae or microalgae Nannochloropsis oculata

The modulation of antioxidant responses and onset of oxidative stress is due to several factors, including temperature, diets, and hypoxia followed by re-oxygenation in several aerobic organisms including rotifers. In this context, the aims of this study were (1) to establish a protocol for evaluating in vivo ROS (reactive oxygen species) concentration in rotifer Brachionus plicatilis and (2) to determine the effects on population growth and oxidative stress responses in rotifers fed with different diets: commercial baker's yeast (Saccharomyces cerevisiae) or concentrated microalgae Nannochloropsis oculata. The rotifers were stocked in five densities (200, 400, 660, 800, and 1000 rotifers mL(-1)) and exposed to four concentrations of dichlorofluorescein diacetate (H2DCF-DA) (4.4, 8.7, 17.5, and 35 nmol L-1) to optimize a protocol for in vivo ROS determination. The methodology was standardized using 8.7 nmol H2DCF-DA L-1 and it is effective when rotifer density lies within 400 and 1000 rotifers mL(-1). In the second experiment, rotifers were fed with 55 x 10(9) microalgae cells or 0.6 g yeast per million rotifers for 4 days in quadruplicate. Rotifers fed with yeast showed poorer oxidative condition as shown by (a) a higher in vivo ROS concentration; (b) a higher GST (glutathione S-transferase) activity; and (3) a reduced total antioxidant capacity. In conclusion, the methodology to measure in vivo ROS concentration using the H2DCF-DA was efficiently standardized for the first time to rotifers B. plicatilis. Although the yeast-fed rotifers showed higher population growth comparing with this concentration of microalgae, the rotifers fed with N. oculata faced a safer pro-oxidant scenario and presented a higher percentage of egg-carrying females throughout the experiment indicating a better physiological condition.