A defined synthetic algal medium enables lettuce-free culturing of unfed Paramecium bursaria while preserving host-associated microbiome composition

Paramecium bursaria is widely cultured using undefined plant-based infusions such as lettuce extract, yet the variable composition of these media remains a major obstacle to experimental reproducibility and microbiome research. Here, we tested whether a chemically defined synthetic algal medium (AF-6) can replace conventional lettuce infusion while maintaining host physiology and associated microbial communities. An unfed clonal strain of P. bursaria, established in 2023 and capable of growth wi