Cultivation of Bdelloid Rotifer Adineta vaga with Synthetic Medium and Characterization of Associated Bacteria

Bdelloid rotifers are model organisms for evolutionary genetics; however, their laboratory cultivation has been limited to traditional systems that require natural food sources (e.g., lettuce juice, bacteria, or yeast) of undefined composition. This constraint impedes mechanistic studies of rotifer-microbe interactions and genetic evolution. We developed a synthetic rotifer medium (SRM) that enables axenic cultivation of <i>Adineta vaga</i>, the most commonly used model species of bdelloid rotifers in the laboratory, as a chemically controlled alternative. <i>A. vaga</i> reached a population density of 357 ± 19.95 ind./mL with a specific growth rate of 0.2131 ± 0.003 over 20 days in SRM, achieving parity with traditional food-supplemented systems while eliminating compositional variability. We further isolated 20 bacterial strains associated with SRM-cultured <i>A. vaga</i>, which were affiliated with two genera (<i>Pseudomonas</i> and <i>Aquincola</i>) on the body surface, as well as four genera (<i>Lentzea</i>, <i>Streptomyces</i>, <i>Sphingomonas</i> and <i>Spirosoma</i>) and one family (Burkholderiaceae) inside <i>A. vaga</i>. Additionally, the addition of low-concentration antibiotics over 20 days reduced the population size or specific growth rate of <i>A. vaga</i>, and cannot fully eliminate the associated bacteria. This study established the first nutritionally autonomous, compositionally stable culture system for bdelloids, enabling precise investigation of rotifer-microbe coevolution and functional genetics.