The biology of candidate divison OP3

Methanogenic cultures growing on limonene have been previously established from wastewater treatment plant sludge. The most abundant members of the microbial community were candidate division OP3, Deltaproteobacteria, Bacteroidetes, Firmicutes, as well as Archaea. Studies of the cultures suggested a syntrophy between multiple species of Bacteria and Archaea for the remineralization of limonene, and a possible predatory lifestyle of OP3. Genes associated with a type IV secretion system have been detected in the OP3 genome, and OP3-like cells have often been found attached to larger cells. This project focused on the transcriptomics of free-living OP3 cells and of those attached to the potential prey in order to identify the key virulence genes. Several predicted genes expressed exclusively in free-living cells have been identified. A highly expressed potential operon encoding a type IV secretion system was found in all of the OP3 cells. A second focus of the study was monitoring the metabolic activity of the enrichment cultures and the changes in the abundance of certain microbial groups. The OP3 abundance and methane production, used to measure metabolic activity, were inversely proportional in the initial stages of the incubation, suggesting a negative effect of OP3 on the major players involved in methanogenesis or in the production of the substrate for methanogenesis. A substantial overall increase in the relative abundance of OP3, and a perpetual decrease in that of other bacteria may indicate predator-prey relationship between them

Notch-mediated generation of monocyte-derived Langerhans cells: Phenotype and function

Langerhans cells (LCs) in the skin are a first line of defense against pathogens but also play an essential role in skin homeostasis. Their exclusive expression of the C-type lectin receptor Langerin/CD207 makes them prominent candidates for immunotherapy. For vaccine testing, an easily accessible cell platform would be desirable as an alternative to the time-consuming purification of LCs from human skin. Here we present such a model and demonstrate that monocytes in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF), transforming growth factor (TGF)-β1 and the Notch ligand Delta-like 4 (DLL4) differentiate within 3 days into CD1a+Langerin+cells containing Birbeck granules. RNA-sequencing (RNA-seq) of these monocyte-derived LCs (moLCs) confirmed gene expression of LC-related molecules, pattern recognition receptors and enhanced expression of the antigen-presenting machinery. On protein level, moLCs showed low expression of costimulatory molecules but prominent expression of C-type lectin receptors. MoLCs can be matured, secrete IL-12p70 and TNF-α and stimulate proliferation and cytokine production in allogeneic CD4+ and CD8+ T cells. In regard to vaccine testing, a recently characterized glycomimetic Langerin ligand conjugated to liposomes demonstrated specific and fast internalization into moLCs. Hence, these short-term in vitro-generated moLCs represent an interesting tool to screen LC-based vaccines in the future