A RORγt+ cell instructs gut microbiota-specific Treg cell differentiation.

The mutualistic relationship of gut-resident microbiota and the host immune system promotes homeostasis that ensures maintenance of the microbial community and of a largely non-aggressive immune cell compartment1,2. The consequences of disturbing this balance include proximal inflammatory conditions, such as Crohn's disease, and systemic illnesses. This equilibrium is achieved in part through the induction of both effector and suppressor arms of the adaptive immune system. Helicobacter species induce T regulatory (Treg) and T follicular helper (TFH) cells under homeostatic conditions, but induce inflammatory T helper 17 (TH17) cells when induced Treg (iTreg) cells are compromised3,4. How Helicobacter and other gut bacteria direct T cells to adopt distinct functions remains poorly understood. Here we investigated the cells and molecular components required for iTreg cell differentiation. We found that antigen presentation by cells expressing RORγt, rather than by classical dendritic cells, was required and sufficient for induction of Treg cells. These RORγt+ cells-probably type 3 innate lymphoid cells and/or Janus cells5-require the antigen-presentation machinery, the chemokine receptor CCR7 and the TGFß activator αv integrin. In the absence of any of these factors, there was expansion of pathogenic TH17 cells instead of iTreg cells, induced by CCR7-independent antigen-presenting cells. Thus, intestinal commensal microbes and their products target multiple antigen-presenting cells with pre-determined features suited to directing appropriate T cell differentiation programmes, rather than a common antigen-presenting cell that they endow with appropriate functions.

Microbial Transformations of Organically Fermented Foods.

Fermenting food is an ancient form of preservation ingrained many in human societies around the world. Westernized diets have moved away from such practices, but even in these cultures, fermented foods are seeing a resurgent interested due to their believed health benefits. Here, we analyze the microbiome and metabolome of organically fermented vegetables, using a salt brine, which is a common 'at-home' method of food fermentation. We found that the natural microbial fermentation had a strong effect on the food metabolites, where all four foods (beet, carrot, peppers and radishes) changed through time, with a peak in molecular diversity after 2-3 days and a decrease in diversity during the final stages of the 4-day process. The microbiome of all foods showed a stark transition from one that resembled a soil community to one dominated by Enterobacteriaceae, such as Erwinia spp., within a single day of fermentation and increasing amounts of Lactobacillales through the fermentation process. With particular attention to plant natural products, we observed significant transformations of polyphenols, triterpenoids and anthocyanins, but the degree of this metabolism depended on the food type. Beets, radishes and peppers saw an increase in the abundance of these compounds as the fermentation proceeded, but carrots saw a decrease through time. This study showed that organically fermenting vegetables markedly changed their chemistry and microbiology but resulted in high abundance of Enterobacteriaceae which are not normally considered as probiotics. The release of beneficial plant specialized metabolites was observed, but this depended on the fermented vegetable.

Homology threading to generate RNA polymerase structures.

Homology threading is a powerful technology for generating structural models based on homologous structures. Here we use threading to generate four complex RNA polymerase models. The models appear to be as useful as x-ray crystal structures or cryo-electron microscopy structures to support research projects.