dictyNews Electronic Edition Volume 41, number 4 February 6, 2015 Please submit abstracts of your papers as soon as they have been accepted for publication by using the form at http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit. Back issues of dictyNews, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. Follow dictyBase on twitter: http://twitter.com/dictybase ========= Abstracts ========= The autophagic machinery ensures nonlytic transmission of mycobacteria Lilli Gerstenmaier a,1, Rachel Pilla a,1, Lydia Herrmann a, Hendrik Herrmann a,2, Monica Prado a, Geno J. Villafano a, Margot Kolonko a, Rudolph Reimer b, Thierry Soldati c, Jason S. King d, and Monica Hagedorn a,3 a Section Parasitology, Bernhard Nocht Institute for Tropical Medicine, 20359 Hamburg, Germany; b Electronmicroscopy, Heinrich-Pette-Institute, 20251 Hamburg, Germany; c Department of Biochemistry, University of Geneva, 1211-Geneva, Switzerland; d Department of Biomedical Sciences, University of Sheffield, Sheffield S10 2TN, United Kingdom PNAS In contrast to mechanisms mediating uptake of intracellular bacterial pathogens, bacterial egress and cell-to-cell transmission are poorly understood. Previously, we showed that the transmission of path- ogenic mycobacteria between phagocytic cells also depends on nonlytic ejection through an F-actin based structure, called the ejectosome. How the host cell maintains integrity of its plasma membrane during the ejection process was unknown. Here, we reveal an unexpected function for the autophagic machinery in nonlytic spreading of bacteria. We show that ejecting mycobacteria are escorted by a distinct polar autophagocytic vacuole. If autophagy is impaired, cell-to-cell transmission is inhibited, the host plasma membrane becomes compromised and the host cells die. These findings highlight a previously unidentified, highly ordered interac- tion between bacteria and the autophagic pathway and might rep- resent the ancient way to ensure nonlytic egress of bacteria. Submitted by Monica Hagedorn [hagedorn@bnitm.de] ---------------------------------------------------------------------- Virulence determinants of the human pathogenic fungus Aspergillus fumigatus protect against soil amoeba predation Falk Hillmann, Silvia Novohradsk‡, Derek J. Mattern, Tilmann Forberger, Thorsten Heinekamp, Martin Westermann, Thomas Winckler, and Axel A. Brakhage Environmental Microbiology Filamentous fungi represent classical examples for environmentally acquired human pathogens whose major virulence mechanisms are likely to have emerged long before the appearance of innate immune systems. In natural habitats, amoeba predation could impose a major selection pressure towards the acquisition of virulence attributes. To test this hypothesis, we exploited the amoeba Dicytostelium discoideum to study its interaction with Aspergillus fumigatus, two abundant soil inhabitants for which we found co-occurrence in various sites. Fungal conidia were efficiently taken up by D. discoideum, but ingestion was higher when conidia were devoid of the green fungal spore pigment DHN-melanin, in line with earlier results obtained for immune cells. Conidia were able to survive phagocytic processing and intracellular germination was initiated only after several hours of coincubation which eventually led to a lethal disruption of the host cell. Besides phagocytic interactions, both amoeba and fungus secreted cross inhibitory factors which suppressed fungal growth or induced amoeba aggregation with subsequent cell lysis, respectively. On the fungal side, we identified gliotoxin as the major fungal factor killing Dictyostelium, supporting the idea that major virulence attributes, such as escape from phagocytosis and the secretion of mycotoxins are beneficial to escape from environmental predators. Submitted by Falk Hillmann [falk.hillmann@hki-jena.de] ---------------------------------------------------------------------- Quantitative measurement of transcription dynamics in living cells. Corrigan AM, Chubb JR. Methods in Cell Biology In a wide range of organisms the kinetics of transcription have been found to be noisy, with "bursts" or "pulses" of transcription interspersed with irregular periods of inactivity. The in vivo analysis of transcription dynamics can be most directly monitored using RNA stem loop motifs derived from MS2 and other bacteriophages. Here we describe the implementation of the MS2 RNA detection system and the steps required for precise measurement of transcription dynamics in highly motile cells. Automated image processing techniques are used to track large numbers of cells and measure transcription in a systematic and unbiased manner. We discuss popular methods for automatic image segmentation and frame-to-frame tracking of cells, and the considerations required to make measurements as quantitatively as possible. Submitted by Jonathan Chubb [j.chubb@ucl.ac.uk] ============================================================== [End dictyNews, volume 41, number 4]