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Heat-loving bacteria use various tiny surface hairs for movement and DNA reception
FRANKFURT. Bacteria of
the species Thermus thermophilus possess
two types of extensions on their surface (pili) for the purpose of motion and for
capturing and absorbing DNA from their environment. This has been discovered by
researchers at Goethe University together with researchers in Great Britain.
The discovery of the motion pilus helps to better understand the functionality
of the DNA-capturing pilus functions. (Nature Communications, DOI 10.1038/s41467-020-15650-w)
The bacteria Thermus thermophilus likes it hot. It was first discovered in the hot springs at Izu in Japan, where it thrives at an optimal temperature of about 65 degrees Celsius. Like all bacteria, Thermus thermophilus has developed mechanisms to adjust to changing environmental conditions. The bacteria changes its genetic material by exchanging DNA with other bacteria, or absorbing DNA fragments from its environment. These might come from dead bacteria cells, plants or animals. The bacteria incorporate the DNA fragments into their genetic material and keep it if the DNA proves useful.
Microbiologists at Goethe University led
by Professor Beate Averhoff from the Molecular Microbiology & Bioenergetics
of the Department of Molecular Biosciences together with a team of scientists
led by Dr Vicky Gold from the “Living Systems" Institute of the University of
Exeter in Great Britain have now studied the tiny hairs (called pili) on the
surface of the Thermus bacteria. The
scientists discovered that there are two types of pili with different
functions. High-resolution electron microscope images from Great Britain allow
thick and thin pili to be distinguished, and the Frankfurt scientists used
biochemical and molecular biological methods to demonstrate that the thick pili
are for DNA capture, and the thin pili for moving on surfaces.
“We want to find out exactly how Thermus thermophilus absorbs DNA from
its environment using its pili, as the precise mechanism is unknown," explains
Professor Beate Averhoff from the Institute for Molecular Biosciences at Goethe
University. “Through our most recent investigations we have learned that Thermus bacteria have distinct pili for
motion. Therefore, the thick pili possibly serve the purpose of DNA absorption,
which demonstrates how important this process is for the bacteria. In our
structure analyses we also found an area on the thick pili where DNA could bind."
The interplay of electron microscopy and
molecular biology also allowed the scientists to better understand the
mechanics of the pili. For both motion and DNA absorption, pili have to be
dynamic, i.e., able to be extended and retracted. “For the first time, the high
resolution structure of both pili gave us insights not only into the structure
of the pili, but also into the dynamics," Averhoff explains.
Since pili are widespread and in
pathogenic bacteria are also responsible for attaching to the host, this may
lead to new points of attack for preventing infectious processes.
Publication:
Alexander Neuhaus, Muniyandi Selvaraj, Ralf Salzer,
Julian D. Langer, Kerstin Kruse, Lennart Kirchner, Kelly Sanders, Bertram Daum,
Beate Averhoff, Vicki A. M. Gold (2020). Cryo-electron microscopy reveals two
distinct type-IV pili assembled by the same bacterium. Nature Communications, https://doi.org/10.1038/s41467-020-15650-w )
An
image may be downloaded here: http://www.uni-frankfurt.de/88063448
Caption:
Bacteria of the species Thermus thermophilus possess different tiny hairs (pili) which are
used either to capture DNA or for motion. This has been discovered by
scientists at Goethe University Frankfurt and the University of Exeter. Graphic:
aduka, Agency Frankfurt am Main(www.aduka.de) for Goethe University Frankfurt.
Further information: Prof. Beate Averhoff, Molecular Microbiology and Bioenergetics. Tel.: +49 69 798-29509, averhoff@bio.uni-frankfurt.de, https://www.mikrobiologie-frankfurt.de
Computer models of merging neutron stars predicts how to tell when this happens
FRANKFURT. According to modern particle physics, matter
produced when neutron stars merge is so dense that it could exist in a state of
dissolved elementary particles. This state of matter, called quark-gluon
plasma, might produce a specific signature in gravitational waves. Physicists
at Goethe University Frankfurt and the Frankfurt Institute for Advanced Studies
have now calculated this process using supercomputers. (Physical Review
Letters, DOI 10.1103/PhysRevLett.124.171103)
Neutron stars are among the densest objects in the universe. If our Sun, with its radius of 700,000 kilometres were a neutron star, its mass would be condensed into an almost perfect sphere with a radius of around 12 kilometres. When two neutron stars collide and merge into a hyper-massive neutron star, the matter in the core of the new object becomes incredibly hot and dense. According to physical calculations, these conditions could result in hadrons such as neutrons and protons, which are the particles normally found in our daily experience, dissolving into their components of quarks and gluons and thus producing a quark-gluon plasma.
In 2017 it was discovered for the first
time that merging neutron stars send out a gravitational wave signal that can
be detected on Earth. The signal not only provides information on the nature of
gravity, but also on the behaviour of matter under extreme conditions. When these
gravitational waves were first discovered in 2017, however, they were not
recorded beyond the merging point.
This is where the work of the Frankfurt
physicists begins. They simulated merging neutron stars and the product of the
merger to explore the conditions under which a transition from hadrons to a quark-gluon
plasma would take place and how this would affect the corresponding
gravitational wave. The result: in a specific, late phase of the life of the
merged object a phase transition to the quark-gluon plasma took place and left a clear and characteristic signature on
the gravitational-wave signal.
Professor Luciano Rezzolla from Goethe
University is convinced: “Compared to previous simulations, we have discovered
a new signature in the gravitational waves that is significantly clearer to
detect. If this signature occurs in the gravitational waves that we will receive
from future neutron-star mergers, we would have a clear evidence for the
creation of quark-gluon plasma in the present universe."
Publication: Post-merger gravitational wave signatures of phase transitions in binary mergers. Lukas R. Weih, Matthias Hanauske, Luciano Rezzolla, Physical Review Letters Physical Review Letters DOI 10.1103/PhysRevLett.124.171103 https://link.aps.org/doi/10.1103/PhysRevLett.124.171103
Video:
Visualisation of merging neutron stars: https://www.youtube.com/watch?v=rj-r-YA9d6E&t=1s
This simulation shows the density of the
ordinary matter (mostly neutrons) in red-yellow. Shortly after the two stars
merge the extremely dense centre turns green, depicting the formation of the
quark-gluon plasma.
Pictures
may be downloaded here: http://www.uni-frankfurt.de/87973606
Caption
Montage: Montage of the computer simulation of two
merging neutron stars that blends over with an image from heavy-ion collisions
to highlight the connection of astrophysics with nuclear physics. Credit: Lukas
R. Weih & Luciano Rezzolla (Goethe University Frankfurt) (right half of the
image from cms.cern)
Caption
Simulation: Shortly after two neutron stars merge a
quark gluon plasma forms in the centre of the new object. Red yellow: ordinary
matter, mostly neutrons. Credit: Lukas R. Weih & Luciano Rezzolla (Goethe
University Frankfurt)
Further information: Goethe University Frankfurt, Prof. Dr. Luciano Rezzolla, Chair of Theoretical Astrophysics, Institute for Theoretical Physics, +49-69-79847871/47879, rezzolla@itp.uni-frankfurt.de, https://astro.uni-frankfurt.de/rezzolla/
Psychologists at Goethe University Frankfurt research the short-term memory of visual impressions
FRANKFURT. When we look at
the same object in quick succession, our second glance always reflects a
slightly falsified image of the object. Guided by various object
characteristics such as motion direction, colour and spatial position, our
short-term memory makes systematic mistakes. Apparently, these mistakes help us
to stabilise the continually changing impressions of our environment. This has
been discovered by scientists at the Institute of Medical Psychology at Goethe
University. (Nature Communications, DOI 10.1038/s41467-020-15874-w)
This is, however, not at all true. Our short-term memory deceives us.
When looking to the left the second time, our eyes see something completely
different: the bicycle and the car do not have the same colour anymore because
they are just now passing through the shadow of a tree, they are no longer in
the same location, and the car is perhaps moving more slowly. The fact that we
nonetheless immediately recognise the bicycle and the car is due to the fact
that the memory of the first leftward look biases the second one.
Scientists at Goethe University, led by psychologist Christoph Bledowski
and doctoral student Cora Fischer reconstructed the traffic situation – very
abstractly – in the laboratory: student participants were told to remember the motion
direction of green or red dots moving across a monitor. During each trial, the
test person saw two moving dot fields in short succession and had to
subsequently report the motion direction of one of these dot fields. In
additional tests, both dot fields were shown simultaneously next to each other.
The test persons all completed numerous successive trials.
The Frankfurt scientists were very interested in the mistakes made by
the test persons and how these mistakes were systematically connected in
successive trials. If for example the observed dots moved in the direction of 10
degrees and in the following trial in the direction of 20 degrees, most people
reported 16 to 18 degrees for the second trial. However, if 0 degrees were
correct for the following trial, they reported 2 to 4 degrees for the second
trial. The direction of the previous trial therefore distorted the perception
of the following one – “not very much, but systematically," says Christoph
Bledowski. He and his team extended previous studies by investigating the
influence of contextual information of the dot fields like colour, spatial
position (right or left) and sequence (shown first or second). “In this way we
more closely approximate real situations, in which we acquire different types
of visual information from objects," Bledowski explains. This contextual
information, especially space and sequence, contribute significantly to the distortion
of successive perception in short-term memory. First author Cora Fischer says:
“The contextual information helps us to differentiate among different objects
and consequently to integrate information of the same object through time."
What does this mean for our traffic situation? “Initially, it doesn't
sound good if our short-term memory reflects something different from what we
physically see," says Bledowski. “But if our short-term memory were unable to
do this, we would see a completely new traffic situation when we looked to the
left a second time. That would be quite confusing, because a different car and
a different cyclist would have suddenly appeared out of nowhere. The slight 'blurring'
of our perception by memory ultimately leads us to perceive our environment,
whose appearance is constantly changing due to motion and light changes, as stable.
In this process, the current perception of the car, for example, is only
affected by the previous perception of the car, but not by the perception of
the cyclist."
Publication:
Context information
supports serial dependence of multiple visual objects across memory episodes.
Cora Fischer, Stefan Czoschke, Benjamin Peters, Benjamin Rahm, Jochen Kaiser,
Christoph Bledowski. Nat. Commun. 11, 1932
(2020). https://doi.org/10.1038/s41467-020-15874-w
Further information:
Goethe University Frankfurt
Dr Christoph Bledowski
Institute for Medical Psychology
Tel.: +49 69-6301-4533
bledowski@em.uni-frankfurt.de
http://imp-frankfurt.de/bledowski.html#welcome
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