dictyNews
Electronic Edition
Volume 41, number 4
February 6, 2015
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Abstracts
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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 [[log in to unmask]]
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Virulence determinants of the human pathogenic fungus Aspergillus
fumigatus protect against soil amoeba predation
Falk Hillmann, Silvia Novohradská, 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 [[log in to unmask]]
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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 [[log in to unmask]]
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[End dictyNews, volume 41, number 4]
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