Summary Host inflammation alters the availability of nutrients such as iron to limit microbial growth. However, Salmonella enterica serovar Typhimurium thrives in the inflamed gut by scavenging for iron with siderophores. By administering Escherichia coli strain Nissle 1917, which assimilates iron by similar mechanisms, we show that this non-pathogenic bacterium can outcompete and reduce S. Typhimurium colonization in mouse models of acute colitis and chronic persistent infection. This probiotic activity depends on E. coli Nissle iron acquisition as mutants deficient in iron uptake colonize the intestine but do not reduce S. Typhimurium colonization. Additionally, the ability of E. coli Nissle to overcome iron restriction by the host protein lipocalin-2, which counteracts some siderophores, is essential as S. Typhimurium is unaffected by E. coli Nissle in lipocalin-2-deficient mice. Thus, iron availability impacts S. Typhimurium growth and E. coli Nissle reduces S. Typhimurium intestinal colonization by competing for this limiting nutrient.

The human parasite Toxoplasma gondii is sensitive to dinitroaniline compounds which selectively disrupt microtubules in diverse protozoa but which have no detectable effect on vertebrate host cell microtubules or other functions. Replication of wild-type T. gondii is inhibited by 0.5 to 2.5 M oryzalin, but mutant parasites harboring amino acid substitutions in the predicted dinitroaniline binding site confer resistance up to 40 M oryzalin. However, the precise interaction between dinitroanilines and the binding site in ␣-tubulin remains unclear. We have investigated the activity of 12 dinitroanilines and the related compound amiprophos methyl on wild-type and dinitroaniline-resistant parasite lines that contain proposed binding site mutations. These data indicate that dinitramine is the most effective dinitroaniline to inhibit Toxoplasma growth in wild-type parasites and most resistant lines. Dinitramine has an amine group at the meta position not present in any of the other dinitroanilines tested here that is predicted to form hydrogen bonds with residues Arg2 and Gln133 according to docking data. Remarkably, although the binding site mutation Ile235Val confers increased resistance to most dinitroanilines, it confers increased sensitivity to GB-II-5, a compound optimized for activity against kinetoplastid tubulin. Kinetoplastid parasites have a valine at position 235 of ␣-tubulin, whereas apicomplexan parasites have an isoleucine at this site. We suggest that this heterogeneity in binding site environment influences relative dinitroaniline sensitivity in distinct protozoan lineages and hypothesize that a mutation that makes the apicomplexan dinitroaniline binding site more like the kinetoplastid site increases sensitivity to a dinitroaniline optimized for activity in the latter parasites.

Toxoplasma gondii is an obligate intracellular parasite that infects all nucleated cell types in diverse warm-blooded organisms. Many of the surface antigens and effector molecules secreted by the parasite during invasion and intracellular growth are modified by glycans. Glycosylated proteins in the nucleus and cytoplasm have also been reported. Despite their prevalence, the complete inventory and biological significance of glycosylated proteins in Toxoplasma remains unknown. In this study, we aimed to globally profile parasite glycoproteins using a bioorthogonal chemical reporter strategy. This strategy involves the metabolic incorporation of unnatural functional groups (i.e., “chemical reporters”) into Toxoplasma glycans, followed by covalent labeling with visual probes or affinity tags. The two-step approach enables the visualization and identification of newly biosynthesized glycoconjugates in the parasite. Using a buffer that mimics intracellular conditions, extracellular Toxoplasma tachyzoites were found to metabolize and incorporate unnatural sugars (equipped with bioorthogonal functional groups) into diverse proteins. Covalent chemistries were used to visualize and retrieve these labeled structures. Subsequent mass spectrometry analysis revealed 89 unique proteins. This survey identified novel proteins as well as previously characterized proteins from lectin affinity analyses.

The necessity for biological control agents has increased over the past decade. Many pathogens become resistant to drugs and chemicals, pesticides are harming the environment and genetically‐modified pest‐resistant crops are a problem (Mankau, 1880). It has been previously established that Acylated Homoserine Lactone (AHL) is essential for bacterial cell to cell communication known as quorum sensing. AHL is part of the Lux –R family of enzymes used to transcribe and translate bacterial pheromones (Tsai, Winans, 2011). Studies have shown that the fungal organism, Arthrobotrys oligospora, has a homologous AHL gene in its genome. The parasitic nematode, Caenorhabditis elegans, has been shown to move towards synthetic AHLs. Therefore, we hypothesize AHL acts as an attractant leading C. elegans to A. oligospora, where the fungus traps and kills the nematodes. The entrapment of C. elegans has been observed for many years; however, the mechanism is not understood. A biosensor will be used to detect AHL production in various fungus‐nematode interactions.Support or Funding InformationThe project was supported in part by grants from the Department of Education (Award #PO31S150199), Southern California Edison and through Vanguard University's SURP Program generously supported by the Office of the Provost and the Institute for Faculty Development.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.