SULFOLOBUS is a genus of microorganism in the family
It belongs to the archaea domain.
Sulfolobus species grow in volcanic springs with optimal growth
occurring at pH 2-3 and temperatures of 75-80 °C, making them
acidophiles and thermophiles respectively.
Sulfolobus cells are
irregularly shaped and flagellar .
Sulfolobus are generally named after the location from
which they were first isolated, e.g.
Sulfolobus solfataricus was first
isolated in the Solfatara volcano. Other species can be found
throughout the world in areas of volcanic or geothermal activity, such
as geological formations called mud pots , which are also known as
solfatare (plural of solfatara).
Sulfolobus as a model to study the molecular mechanisms of DNA
* 2 Role in biotechnology
* 5 Cell structure and metabolism
* 6 Ecology
* 7 DNA damage response
* 7.1 The ups operon
Sulfolobus as a viral host
* 9 See also
* 10 References
* 11 Further reading
* 11.1 Scientific journals
* 11.2 Scientific books
* 11.3 Scientific databases
* 12 External links
SULFOLOBUS AS A MODEL TO STUDY THE MOLECULAR MECHANISMS OF DNA
When the first Archaeal genome, Methanococcus jannaschii, had been
sequenced completely in 1996, it was found that the genes in the
genome of Methanococcus jannaschii involved in DNA replication,
transcription, and translation were more related to their counterparts
in eukaryotes than to those in other prokaryotes. In 2001, the first
genome sequence of Sulfolobus,
Sulfolobus solfataricus P2, was
published. In P2's genome, the genes related to chromosome replication
were likewise found to be more related to those in eukaryotes. These
genes include DNA polymerase, primase (including two subunits), MCM,
CDC6/ORC1, RPA, RPC, and
PCNA . In 2004, the origins of DNA
Sulfolobus solfataricus and
were identified. It showed that both species contained two origins in
their genome. This was the first time that more than a single origin
of DNA replication had been shown to be used in a prokaryotic cell.
The mechanism of DNA replication in archaea is evolutionary conserved,
and similar to that of eukaryotes.
Sulfolobus is now used as a model
to study the molecular mechanisms of DNA replication in Archaea. And
because the system of DNA replication in
Archaea is much simpler than
that in Eukaryota, it was suggested that
Archaea could be used as a
model to study the much more complex DNA replication in Eukaryota.
ROLE IN BIOTECHNOLOGY
Sulfolobus proteins are of interest for biotechnology and industrial
use due to their thermostable nature. One application is the creation
of artificial derivatives from S. acidocaldarius proteins, named
affitins . Intracellular proteins are not necessarily stable at low pH
Sulfolobus species maintain a significant pH gradient
across the outer membrane.
Sulfolobales are metabolically dependent on
sulfur: heterotrophic or autotrophic , their energy comes from the
oxidation of sulfur and/or cellular respiration in which sulfur acts
as the final electron acceptor. For example, S. tokodaii is known to
oxidize hydrogen sulfide to sulfate intracellularly.
The complete genomes have been sequenced for S. acidocaldarius DSM
639 (2,225,959 nucleotides ), S. solfataricus P2 (2,992,245
nucleotides), and S. tokodaii str. 7 (2,694,756 nucleotides).
Sulfolobus solfataricus has a circular chromosome that
consists of 2,992,245 bp. Another sequenced species, S. tokodaii has a
circular chromosome as well but is slightly smaller with 2,694,756 bp.
Both species lack the genes ftsZ and minD, which has been
characteristic of sequenced Crenarchaeota. They also code for citrate
synthase and two subunits of 2-oxoacid:ferredoxin oxidoreductase,
which plays the same role as alpha-ketoglutarate dehydrogenase in the
TCA (tricarboxylic/Krebs/citric acid) cycle. This indicates that
Sulfolobus has a TCA cycle system similar to that found in
mitochondria of eukaryotes. Other genes in the respiratory chain which
partake in the production of ATP were not similar to what is found in
eukaryotes. Cytochrome c is one such example that plays an important
role in electron transfer to oxygen in eukaryotes. This was also found
in A. pernix K1. Since this step is important for an aerobic
microorganism like Sulfolobus, it probably uses a different molecule
for the same function or has a different pathway.
CELL STRUCTURE AND METABOLISM
Sulfolobus can grow either lithoautotrophically by oxidizing sulfur,
or chemoheterotrophically using sulfur to oxidize simple reduced
carbon compounds. Heterotrophic growth has only been observed,
however, in the presence of oxygen. The principle metabolic pathways
are a glycolytic pathway, a pentose phosphate pathway, and the TCA
Archaea have lipids with ether links between the head group and
side chains, making the lipids more resistant to heat and acidity than
bacterial and eukaryotic ester-linked lipids. The
known for unusual tetraether lipids.In Sulfolobales, the ether-linked
lipids are joined covalently across the "bilayer," making tetraethers.
Technically, therefore, the tetraethers form a monolayer, not a
bilayer. The tetraethers help
Sulfolobus species survive extreme acid
as well as high temperature.
S. solfataricus has been found in different areas including
Yellowstone National Park, Mount St. Helens, Iceland, Italy, and
Russia to name a few.
Sulfolobus is located almost wherever there is
volcanic activity. They thrive in environments where the temperature
is about 80 °C with a pH at about 3 and sulfur present. Another
species, S. tokodaii, has been located in an acidic spa in Beppu Hot
Springs, Kyushu, Japan. Sediments from ~90m below the seafloor on the
Peruvian continental margin are dominated by intact archaeal
tetraethers, and a significant fraction of the community is
sedimentary archaea taxonomically linked to the crenarchaeal
Sulfolobales (Sturt, et al., 2004).
DNA DAMAGE RESPONSE
Sulfolobus solfataricus or
Sulfolobus acidocaldarius to
the DNA damaging agents UV-irradiation, bleomycin or mitomycin C
induced cellular aggregation. Other physical stressors, such as pH
or temperature shift, did not induce aggregation, suggesting that
induction of aggregation is caused specifically by DNA damage. Ajon
et al. showed that UV-induced cellular aggregation mediates
chromosomal marker exchange with high frequency in S. acidocaldarius.
Recombination rates exceeded those of uninduced cultures by up to
three orders of magnitude. Wood et al. also showed that
UV-irradiation increased the frequency of recombination due to genetic
exchange in S. acidocaldarius. Frols et al. and Ajon et al.
hypothesized that the UV-inducible DNA transfer process and subsequent
homologous recombinational repair represents an important mechanism to
maintain chromosome integrity in S. acidocaldarius and S.
solfataricus. This response may be a primitive form of sexual
interaction, similar to the more well-studied bacterial transformation
that is also associated with DNA transfer between cells leading to
homologous recombinational repair of DNA damage.
THE UPS OPERON
The ups operon of
Sulfolobus species is highly induced by UV
irradiation . The pili encoded by this operon are employed in
promoting cellular aggregation, which is necessary for subsequent DNA
exchange between cells, resulting in homologous recombination . A
study of the
Sulfolobales acidocaldarius ups operon showed that one of
the genes of the operon, saci-1497, encodes an endonuclease III that
nicks UV-damaged DNA; and another gene of the operon, saci-1500,
encodes a RecQ-like helicase that is able to unwind homologous
recombination intermediates such as
Holliday junctions . It was
proposed that Saci-1497 and Saci-1500 function in an homologous
recombination-based DNA repair mechanism that uses transferred DNA as
a template. Thus it is thought that the ups system in combination
with homologous recombination provide a DNA damage response which
Sulfolobales from DNA damaging threats.
SULFOLOBUS AS A VIRAL HOST
Lysogenic viruses infect
Sulfolobus for protection. The viruses
cannot survive in the extremely acidic and hot conditions that
Sulfolobus lives in, and so the viruses use
Sulfolobus as protection
against the harsh elements. This relationship allows the virus to
replicate inside the archaea without being destroyed by the
Sulfolobus viruses are temperate or permanent
lysogens. Permanent lysogens differ from lysogenic bacteriophages in
that the host cells are not lysed after the induction of
Fuselloviridae production and eventually return to the lysogenic
state. They are also unique in the sense that the genes encoding the
structural proteins of the virus are constantly transcribed and DNA
replication appears to be induced. The viruses infecting archaea like
Sulfolobus have to use a strategy to escape prolonged direct exposure
to the type of environment their host lives in, which may explain some
of their unique properties.
Evolution of sexual reproduction
* ^ See the NCBI webpage on Sulfolobus. Data extracted from the
"NCBI taxonomy resources" . National Center for Biotechnology
Information . Retrieved 2007-03-19.
* ^ Chen, L; Brügger, K; Skovgaard, M; Redder, P; She, Q;
Torarinsson, E; Greve, B; Awayez, M; Zibat, A; Klenk, HP; Garrett, RA
(July 2005). "The genome of