Lactic Acid Bacterial Consortia Modulate Fermentation and Microbial Communities in a Dynamic in Vitro Ruminant Gastrointestinal Model

Abstract Optimization of microbial fermentation throughout the ruminant gastrointestinal tract is important for efficient nutrient utilization and animal health. The aim of this study was to evaluate the effect of lactic acid bacteria (LAB) consortia applied to a total mixed ration (TMR) and maize silage on microbial community structure and fermentation profiles in a dynamic in vitro digestion system of the ruminant gastrointestinal tract. The model was established using fresh cow rumen fluid as the source of the microbial inoculum. Importantly, subsequent metabolite and microbiota analyses were performed on samples collected from reactors representing the respective intestinal compartments of the model, rather than on donor rumen fluid. Bacterial inoculants containing Lentilactobacillus buchneri, Pediococcus acidilactici, Lentilactobacillus parakefiri, Lentilactobacillus diolivorans and Furfurilactobacillus kisonensis were tested. A control variant receiving non-inoculated feed was compared with an experimental variant supplemented with LAB. Lactic acid, short-chain fatty acids (SCFAs), and branched-chain fatty acids (BCFAs) were quantified in the collected reactor samples. The experimental variant showed higher propionate, valerate, and lactic acid concentrations together with lower BCFA concentrations. Metagenomic and metabolomic analyses indicated that LAB supplementation was associated with distinct temporal dynamics and greater preservation of selected bacterial groups, including Bacteroidota , reduced abundance of selected taxa with opportunistic potential, and distinct metabolic profiles associated with the experimental treatment and feeding phase. These findings suggest that the selected LAB consortia were associated with altered microbial community succession and fermentation dynamics during dietary transitions within the in vitro gastrointestinal ecosystem. Further in vivo validation is required to determine whether these effects are reproduced under physiological conditions.