Screening microbial interactions during inulin utilization reveals strong competition and proteomic changes in "Lacticaseibacillus paracasei" M38

Abstract

Competition for resources is a common microbial interaction in the gut microbiome. Inulin is a well-studied prebiotic dietary fiber that profoundly shapes gut microbiome composition. Several community members and some probiotics, such as Lacticaseibacillus paracasei, deploy multiple molecular strategies to access fructans. In this work, we screened bacterial interactions during inulin utilization in representative gut microbes. Unidirectional and bidirectional assays were used to evaluate the effects of microbial interactions and global proteomic changes on inulin utilization. Unidirectional assays showed the total or partial consumption of inulin by many gut microbes. Partial consumption was associated with cross-feeding of fructose or short oligosaccharides. However, bidirectional assays showed strong competition from L. paracasei M38 against other gut microbes, reducing the growth and quantity of proteins found in the latter. L. paracasei dominated and outcompeted other inulin utilizers, such as Ligilactobacillus ruminis PT16, Bifidobacterium longum PT4, and Bacteroides fragilis HM714. The importance of strain-specific characteristics of L. paracasei, such as its high fitness for inulin consumption, allows it to be favored for bacterial competence. Proteomic studies indicated an increase in inulin-degrading enzymes in co-cultures, such as β-fructosidase, 6-phosphofructokinase, the PTS D-fructose system, and ABC transporters. These results reveal that intestinal metabolic interactions are strain-dependent and might result in cross-feeding or competition depending on total or partial consumption of inulin. Partial degradation of inulin by certain bacteria favors coexistence. However, when L. paracasei M38 totally degrades the fiber, this does not happen. The synergy of this prebiotic with L. paracasei M38 could determine the predominance in the host as a potential probiotic.