Culture regime as an experimental variable in Caenorhabditis elegans: Cross-format evidence, reproducibility...

Caenorhabditis elegans is widely used in genetics, neurobiology, aging, toxicology, host-microbe research, and whole-animal screening, yet culture conditions are often treated as technical details rather than biologically active variables. Solid agar-based and liquid suspension systems expose animals to different spatial, nutritional, mechanical, and physicochemical environments that can influence locomotion, feeding, metabolism, stress responses, development, gene expression, and experimental reproducibility. This critical narrative review compares the principles, advantages, limitations, and applications of these two major culture regimes and evaluates how culture-dependent variables affect biological interpretation. Solid systems provide spatial organization, localized chemical and microbial cues, and high individual-level resolution, making them particularly suitable for behavioral, developmental, neurobiological, and longitudinal studies. Liquid systems facilitate more readily standardized population density, nutrient and compound exposure, synchronized biomass production, molecular analyses, automation, and high-throughput screening. However, they introduce specific sources of variability associated with swimming, oxygenation, agitation, vessel geometry, and population density. Comparative and recent studies indicate that culture and exposure conditions can alter the magnitude and, in some cases, the detectability of biological and toxicological phenotypes. Emerging approaches incorporating microfluidics, defined media, automated imaging, and controlled microbial environments increasingly combine features of both formats while improving experimental precision. We therefore propose that solid and liquid systems should be considered complementary regimes that should not be assumed to be biologically equivalent. Deliberate culture selection and comprehensive reporting of culture conditions are important for reproducibility, cross-platform comparability, and mechanistic interpretation in C. elegans research.