Bifidobacterium longum subsp. infantis (B. infantis) metabolism and its relationship with other infant gut microbes were majorly investigated in this work. B. infantis is one of the first colonizer in the infant gut and is widely regarded as a probiotic beneficial for infant health during early age. In this work, B. infantis utilization of human milk oligosaccharides (HMO) as nitrogen source were studied in completing B. infantis utilization of HMO as carbohydrate source. B. infantis HMO nitrogen utilization was confirmed by 15N-labeled proteomics results. Furthermore, B. infantisutilized lacto-N-tetraose (LNT) and lacto-N-neotetraose (LNnT) as inefficient nitrogen source, which can be indicated by increased intracellular 2-oxoglutarate concentration. B. infantis interactions with other infant gut commensals were investigated during LNT and LNnT fermentation using in vitro model. Previously in pure culture, B. infantis inefficient utilization of LNnT increased the signature acetate to lactate ratio. In this work, B. infantis with LNnT shaped microbial community into increased production of formate and butyrate while decreased production of acetate and lactate, compared to B. infantis with LNT. It was further speculated from the metagenomic analysis that B. infantis potentially cross-fed with another infant gut colonizer, Clostridium paraputrificum. The cross-feeding relationship was first revealed based on urea cycle pathway abundances in relative to B. infantis addition to the modeled microbiome. In addition, B. infantis and LNnT has been designated as a synergistic synbiotic pair due to their function and impact in the modeled infant gut microbiome. Likewise, cranberry xyloglucan fermentation by adult gut microbiome with perturbation of probiotic (Lactobacillus plantarum) and prebiotic (proanthocyanidins) were studied. Preliminary results in this work showed that proanthocyanidins (PAC) had little impact on L. plantarum xyloglucan fermentation in modeled adult microbiome, while L. plantarum likely experienced reduced competitive advantages in the modeled microbial community during xyloglucan fermentation.