Abstract
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 Adineta vaga, the most commonly used model species of bdelloid rotifers in the laboratory, as a chemically controlled alternative. A. vaga 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 A. vaga, which were affiliated with two genera (Pseudomonas and Aquincola) on the body surface, as well as four genera (Lentzea, Streptomyces, Sphingomonas and Spirosoma) and one family (Burkholderiaceae) inside A. vaga. Additionally, the addition of low-concentration antibiotics over 20 days reduced the population size or specific growth rate of A. vaga, 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.