Background
The gut microbiome is a complex microbial ecosystem essential for intestinal barrier integrity and immune homeostasis. While food additives are widely used in modern diets, their direct effects on gut microbial growth dynamics and functional responses remain poorly characterized. Here, we systematically examined the impact of commonly used food additives on human fecal microbiome growth under anaerobic conditions.
Methods
Fecal samples from healthy donors were collected and inoculated into culture media containing graded concentrations of food additives, including monosodium glutamate (MSG), maltol and ethyl maltol. Microbial growth was monitored by optical density at 600 nm over 48 hours. Based on growth dynamics, representative concentrations were selected for downstream multi-omics analyses. Microbial pellets were collected for shotgun metagenomic sequencing, and proteins were prepared using the single-pot solid-phase-enhanced sample preparation (SP3) protocol for metaproteomic analysis.
Results
MSG did not alter overall microbial growth dynamics, whereas maltol and ethyl maltol inhibited growth in a dose-responsive manner, with effects evident within 12 hours. Principal coordinate analysis revealed a strong donor-dependent clustering, indicating that inter-individual variation was the primary determinant of microbial community structure. Family level analysis identified sex-specific changes, with decreased Oscillospiraceae and increased Odoribacteraceae in males at high MSG doses, suggesting selective compositional modulation without global disruption. Metaproteomic analysis demonstrated a clear functional shift under MSG treatment despite stable overall protein category distribution. Specifically, proteins involved in glutamate metabolism were altered, including increased glutamate dehydrogenase, glutaminase, and glutamyl-tRNA synthetase, alongside reduced glutamine synthetase, indicating reprogramming of glutamate metabolism and nitrogen handling. Maltol and ethyl maltol induced selective taxonomic changes without major global community separation. Donor effects remained dominant, while maltol at high dose caused pronounced reductions in key fermentative families such as Acetobacteraceae, Atopobiaceae, Butyricicoccaceae, Eubacteriaceae, Lachnospiraceae, Oscillospiraceae and Peptostreptococcaceae.
Conclusions
Food additives exert selective rather than global effects on the in vitro fecal microbiome., accompanied by reduced Oscillospiraceae and increased Odoribacteraceae. In contrast, maltol-derived compounds caused stronger growth inhibition and more pronounced taxonomic shifts, particularly reducing core fermentative families. These findings indicate that food additive-specific microbial responses may drive subtle ecological restructuring of gut microbial communities.