Commensal Bacteria Impact a Protozoan's Integration into Murine Gut Microbiota in a Dietary Nutrient-dependent Manner.

Our current understanding of the host-microbiota interaction in the gut is dominated by studies focused primarily on prokaryotic bacterial communities. However, there is an underappreciated symbiotic eukaryotic protistic community that is an integral part of mammalian microbiota. How commensal protozoan-bacteria might interact to form a stable microbial community remains poorly understood. Here, we described a murine protistic commensal phylogenetically assigned as Tritrichomonas musculis, whose colonization in the gut resulted in a reduction of gut bacterial abundance and diversity in wild-type C57BL/6 mice. Meanwhile, dietary nutrient and commensal bacteria also influenced the protozoan9s intestinal colonization and stability. While mice fed on normal chow diet had abundant T. musculis, switching to a Western-type high-fat diet led to the diminishment of the protozoan from the gut. Supplementation of inulin as a dietary fiber to the high-fat diet partially restored the protozoan9s colonization. In addition, a cocktail of broad-spectrum antibiotics rendered permissive engraftment of T. musculis even under a high-fat low-fiber diet condition. Furthermore, oral administration of Bifidobacterium spp. together with dietary supplementation of inulin in the high-fat diet impacted the protozoan9s intestinal engraftment in a bifidobacterial species-dependent manner. Overall, our study described an example of dietary nutrient-dependent murine commensal protozoan-bacteria crosstalk as an important modulator of the host intestinal microbiome. Importance: Like commensal bacteria, commensal protozoan is an integral part of the vertebrate intestinal microbiome. How protozoan integrates into a commensal bacteria-enriched ecosystem remains poorly studied. Here, using a murine commensal Tritrichomonas musculis as a proof-of-concept, we studied potential factors involved in shaping the intestinal protozoan-bacteria community. Understanding the rules by which microbes form a multispecies community is crucial to prevent or correct microbial community dysfunctions to promote the host9s health or to treat diseases.