Rotifer (Brachionus “Cayman”) culture performance improvement through l-carnitine addition is not related to fatty acid metabolism

The purpose of this paper was to investigate the nature of the effect of l-carnitine on the cultures of the marine rotifer Brachionus “Cayman” and its microflora. Xenic and gnotobiotic experiments were set up with rotifers, fed axenic wild-type yeast (Saccharomyces cerevisiae) or xenic microalgae (Tetraselmis suecica) and incubated with l-carnitine concentrations of 0.1, 1, 10, 60, 100 and 1000 mg L−1. Axenic neonates were obtained by separating amictic eggs from the rotifers by blending, prior to disinfection with glutaraldehyde and hatching. The gnotobiotic cultures had a significantly lower growth rate and egg ratio (%), compared to both xenic trials. The xenic cultures fed algae performed significantly better than those fed baker's yeast, when comparing population density, growth rate and egg ratio. A significant effect of l-carnitine addition was only found in yeast-fed cultures. Microbial assays, conducted with similar doses of autoclaved l-carnitine, revealed that several bacterial species present in the community of conventional Brachionus “Cayman” cultures, could possibly utilize l-carnitine for growth. These results suggest that the improvement of population density, growth rate and egg ratio in xenic rotifer cultures supplemented with l-carnitine, is most likely due to the stimulation by this compound of certain species of (beneficial) microorganisms, which are in turn valorized by the rotifers, yielding improved culture performance. Because of the absence of a positive effect under gnotobiotic conditions, a direct effect of l-carnitine on fatty acid metabolism, as suggested in literature, is unlikely.