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

## TL;DR

Researchers created a synthetic medium to grow bdelloid rotifers in the lab and identified bacteria associated with them, enabling better study of their interactions.

## Contribution

The development of a chemically defined synthetic medium for axenic cultivation of Adineta vaga and isolation of associated bacterial strains.

## Key findings

- A synthetic medium (SRM) supports Adineta vaga population growth comparable to traditional food-based systems.
- Twenty bacterial strains were isolated from A. vaga, including both endozoic and epizoic isolates.
- Low-concentration antibiotics reduced rotifer population growth but did not fully eliminate associated bacteria.

## Abstract

Bdelloid rotifers are important model organisms for evolutionary and ecological research, yet their laboratory cultivation has traditionally relied on nutritionally variable natural food sources, limiting mechanistic studies of host–microbe interactions. This study developed a chemically defined Synthetic Rotifer Medium (SRM) that supports population growth of Adineta vaga comparable to traditional food-based systems. Using this standardized platform, we isolated and identified 20 bacterial strains from A. vaga, comprising 11 endozoic and 9 epizoic isolates. Antibiotic treatment experiments demonstrated that bacterial clearance remained incomplete while simultaneously reducing rotifer population growth. This work establishes key resources—a defined cultivation medium and a bacterial strain collection—which provide a foundation for future investigations into rotifer-microbial interactions and coevolutionary processes.

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.