Download Chromosome segregation in the Archaea domain of life

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Chromosome segregation in the Archaea domain of life
Archaea evolved as the third domain
of life billions of years ago, but they
are a relatively recent addition to
the map of the universal tree of
living organisms. Their discovery
34 years ago represented a major
biological milestone. Archaea are
unicellular organisms that populate
our planet together with bacteria
and eukaryotes. Both bacteria and
Archaea are prokaryotes, i.e. their
genetic material is not wrapped
by a membrane into a separate
compartment, called nucleus, which
is instead a defining hallmark of
eukaryotes (baker yeast, fungi,
algae, plants, animals and humans
to mention some). Initially isolated
from extreme ecosystems, Archaea
are now known to be ubiquitous,
constituting a considerable fraction
of the biosphere. For example, it
has been reported that the world
ocean alone contains approximately
1.3 x 1028 archaeal cells; this is an
enormous number. To provide a
comparison, the estimated number
of grains of sand on all the beaches
on earth is 7.5 x 1018, a quantity
still much smaller as compared
with that of marine archaeal cells.
Their ubiquity and abundance make
them key players in regulating
global biogeochemical cycles
on Earth. From a functional and
mechanistic standpoint, Archaea are
a mosaic of tesserae from bacteria
and eukaryotes, but they are also
characterised by unique molecular
features like methane production.
Hyperthermophilic archaea are
super microbes thriving at 80ºC and
higher temperatures in hot springs,
volcanoes, deep sea vents and
exhibiting unusual properties, which
make these organisms valuable
for the development of novel
biotechnological applications, but
also extremely interesting for basic
studies on life pushed to extremes.
Despite the significant progress
made in decoding molecular
mechanisms in these organisms
in the last three decades, to date
no information is available on the
fundamental process of chromosome
segregation in Archaea and the
subject remains a black box awaiting
investigation. Genome segregation
is a crucial stage of the life cycle
of every cell; the genetic material
is first duplicated, then separated
and equally distributed into the two
daughter cells. We intend to analyse
this process in the hyperthermophilic
archaeon Sulfolobus solfataricus
(see figure below), whose genome
harbours genes that encode
excellent candidates for a minimalist
chromosome segregation machine.
The project will exploit in vivo and
in vitro approaches to construct
a multifaceted picture of the
chromosome segregation engine
of S. solfataricus. We will start with
genetics: the classic genetic method
to discover the function of a gene
is to delete it from the genome and
examine which defects emerge in
the organism under scrutiny. We
will delete the candidate genes and
inspect the phenotype (‘observable
characteristics’ from the Greek verb
‘phainein’ meaning ‘to appear’)
of the mutant S. solfataricus cells
by fluorescence microscopy. The
proteins encoded by the candidate
genes will then be probed by
undertaking biochemical and
biophysical investigations. The blend
of interdisciplinary approaches will
ensure exciting contributions to
unravel the molecular mechanisms
underpinning chromosome
segregation in Sulfolobus species,
paving the way toward a more
systematic exploration of this topic in
the third domain of life.
Dr Daniela Barillà
University of York
Daniela was awarded a Research
Project Grant in June 2011; providing
£143,618 over 36 months.
Sulfolobus solfataricus cells. (A) Cells stained
with a fluorescent dye called DAPI that
binds to their chromosome. (B) Bright field
micrograph of the same cells. (C) Overlay of
DAPI-stained and bright field images. Scale
bar = 1µm. Images courtesy of Brett McLeod.