Avidin is evolutionarily conserved in fish but dispensable for development and resistance against Streptococcus agalactiae in zebrafish.

Biotin is a vital cofactor in cellular carboxylation reactions and avidins are biotin-binding proteins that are produced by bacteria and fungi but also by egg-laying vertebrates, including avian species and zebrafish (Danio rerio). Although avidins have proposed roles in embryonic development and immunity, their biological significance is poorly characterized. Moreover, besides zebrafish, the presence of avidins in other fish species has not been explored. Here, we cataloged avidins in fish species and demonstrate that avidins exist in lobe-finned fish (Sarcopterygii), cartilaginous fish (Chondrichthyes) and ray-finned fish (Actinopterygii), and that the biotin-binding amino acids in fish avidins are evolutionarily conserved. To evaluate the significance of avidin in embryonic development, we created avd knockout (KO) zebrafish and show that zebavidin (zebrafish avidin) is dispensable for fish development. We also assessed the survival of the avd KO embryos from Streptococcus agalactiae infection and demonstrate that the resistance of the embryos is not altered in the absence of zebavidin. Collectively, we show that avidins exist widely in fish species and provide new insights into avidin biology by demonstrating that zebavidin is not essential for zebrafish development or response to S. agalactiae.