''Haloquadratum walsbyi'' is of the genus ''Haloquadratum,'' within the
archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
domain known for its square halophilic nature.
First discovered in a
brine
Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for br ...
pool in the
Sinai peninsula
The Sinai Peninsula, or simply Sinai (now usually ) (, , cop, Ⲥⲓⲛⲁ), is a peninsula in Egypt, and the only part of the country located in Asia. It is between the Mediterranean Sea to the north and the Red Sea to the south, and is a l ...
of
Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Mediter ...
, ''H. walsbyi'' is noted for its flat, square-shaped cells, and its unusual ability to survive in aqueous environments with high concentrations of
sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
and
magnesium chloride
Magnesium chloride is the family of inorganic compounds with the formula , where x can range from 0 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which occur in natu ...
.
The
species' genus name ''Haloquadratum'' translates from
Greek and Latin as "salt square". This archaean is also commonly referred to as "Walsby's Square Bacterium" because of its identifying square shape which makes it very unique.
In accordance with its name, ''Haloquadratum walsbyi'' are most abundantly observed in salty environments.
''Haloquadratum walsbyi'' is a
phototroph
Phototrophs () are organisms that carry out photon capture to produce complex organic compounds (e.g. carbohydrates) and acquire energy. They use the energy from light to carry out various cellular metabolic processes. It is a common misconcep ...
ic
halophilic
The halophiles, named after the Greek word for "salt-loving", are extremophiles that thrive in high salt concentrations. While most halophiles are classified into the domain Archaea, there are also bacterial halophiles and some eukaryotic species, ...
archaeon. It was the only recognized species of the genus ''Haloquadratum'' until 1999 when
Haloarcula quadrata
''Haloarcula quadrata'' is a species of archaea discovered in a brine pool in the Sinai peninsula of Egypt. It was one of the first strains of prokaryotes whose cells show a flat, box-like shape.
They were categorized as Haloarcula on the b ...
was reported as recovered from a brine pool.
''Haloquadratum walsbyi'' is very unusual because of its unique cellular structure that resembles an almost-perfectly flat-shaped figure.
The genus was first observed in 1980 by a British microbiologist,
Prof. Anthony E. Walsby, from samples taken from the Sabkha Gavish, a brine lake in southern Sinai, Egypt. This discovery is formally described in 2007 by Burns ''
et al''. Attempts to
cultivate the archaea were unsuccessful until 2004 and resulted in the identification of ''
Haloarcula quadrata
''Haloarcula quadrata'' is a species of archaea discovered in a brine pool in the Sinai peninsula of Egypt. It was one of the first strains of prokaryotes whose cells show a flat, box-like shape.
They were categorized as Haloarcula on the b ...
'', another species of square archaea of the genus ''Haloarcula'', distinct from ''H. walsbyi'', less abundant and genetically quite different.
Description
''Haloquadratum walsbyi'' cells size at 2 to 5
microns
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...
and 100 to 200
nanometers
330px, Different lengths as in respect to the molecular scale.
The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...
thick. The archaea generally contain
granules of
polyhydroxyalkanoates
Polyhydroxyalkanoates or PHAs are polyesters produced in nature by numerous microorganisms, including through bacterial fermentation of sugars or lipids. When produced by bacteria they serve as both a source of energy and as a carbon store. M ...
and hold a number of
refractive
In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomeno ...
vacuoles
A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...
filled with gas that ensure
buoyancy
Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the p ...
in an
aqueous
An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be re ...
environment, and allow for maximum
light absorption
In physics, absorption of electromagnetic radiation is how matter (typically electrons bound in atoms) takes up a photon's energy — and so transforms electromagnetic energy into internal energy of the absorber (for example, thermal energy). A ...
. These gas vacuoles were discovered by Wallaby in 1980 when determining the identity of intracellular refractive bodies in the archaean's structure.
They gather in sheets up to 40 μm wide, but the
connections between the cells are fragile and can easily be broken.
These
organisms
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fungi; ...
can be found in any stretch of very salty water. During the
evaporation of seawater,
calcium carbonate (CaCO
3) and
calcium sulfate
Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula CaSO4 and related hydrates. In the form of γ-anhydrite (the anhydrous form), it is used as a desiccant. One particular hydrate is better known as plaster of Pari ...
(CaSO
4) precipitate first, leading to a brine rich in
sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
NaCl. If evaporation continues, NaCl precipitates in the form of
halite
Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...
, leaving a brine rich in
magnesium chloride
Magnesium chloride is the family of inorganic compounds with the formula , where x can range from 0 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which occur in natu ...
(MgCl
2). ''H. walsbyi'' prospers during the final phase of the precipitation of halite, and can constitute 80% of the
biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
of this medium. ''Haloquadratum walsbyi'' cells have been determined to be Gram-negative through staining and when grown in a laboratory the best determined conditions for growth is a media with 18% salts at a neutral pH
The
genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
of ''H. walsbyi'' has been
completely sequenced, allowing access to a better understanding of the
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
and
taxonomic classification
In biology, taxonomy () is the scientific study of naming, defining ( circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are give ...
of this organism and its role in the
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
. A
genomic comparison of Spanish and Australian
isolates {{About, , the linguistics term dealing with languages unrelated to any other language in the world, Language isolate, other uses, Isolate (disambiguation){{!Isolate
Isolates is a term used in developmental psychology and family studies, to describ ...
(
strains HBSQ001 and C23
T) strongly suggests a rapid global dispersion, as they are remarkably similar and have maintained the
order of genes.
Its growth in the laboratory was obtained in a medium with very high chloride concentrations (greater than 2 mol · L
−1 of MgCl
2 and greater than 3 mol · L
−1of NaCl ), making this organism among the most
haloresistant known. Its
optimum growth temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
is 40
°C, making this archaea a
Mesophile
A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, with an optimum growth range from . The optimum growth temperature for these organisms is 37°C. The term is mainly applied to microorganisms. Organi ...
.
File:Optical phase-contrast microscopy image of a Haloquadratum walsbyi square cell - PLoS ONE.png, Optical phase-contrast microscopy image of a ''Haloquadratum walsbyi'' square cell. The numerous light dots are gas vesicle
Gas vesicles, also known as gas vacuoles, are nanocompartments in certain prokaryotic organisms, which help in buoyancy. Gas vesicles are composed entirely of protein; no lipids or carbohydrates have been detected.
Function
Gas vesicles occur ...
s that allow flotation to the surface, most likely to acquire oxygen.
File:Microorganisms from the hypersaline Lake Tyrrell.jpg, Microscopic image from the hypersaline Lake Tyrrell
Lake Tyrrell (also known as Lake Tyrrell Wildlife Reserve) is a shallow, salt-crusted depression in the Mallee district of north-west Victoria, in Australia. The name 'Tyrrell' is derived from the local Wergaia word for 'sky', the Boorong ...
, in which orange chlorophyte ''Dunaliella salina
''Dunaliella salina'' is a type of halophile green unicellular micro-algae especially found in hypersaline environments, such as salt lakes and salt evaporation ponds. Known for its antioxidant activity because of its ability to create large ...
'' can be tentatively identified, accompanied by a number of smaller ''Haloquadratum walsbyi'', showing their flat square-shaped cells.
Diversity
A surprisingly high amount of cells in salt brines around the world are ''Haloquadratum walsbyi.'' Up to 80% of the cells in the brines can be identified as ''Haloquadratum walsbyi.'' Experiments have been done to examine the genetic diversity in the salt brine environment. Seven different types of ''H. walsbyi's'' genomic island have been discovered in natural environments.
After examining the
metogenomic fosmid Fosmids are similar to cosmids but are based on the bacterial F-plasmid. The cloning vector is limited, as a host (usually '' E. coli'') can only contain one fosmid molecule. Fosmids can hold DNA inserts of up to 40 kb in size; often the source of t ...
library for ''H. walsbyi,'' two types of the cell-wall associated islands were identified. The genes in these islands include those responsible for the synthesis of surface layer structures such as
glycoprotein
Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycos ...
s and genes responsible for the synthesis of
cell envelope
The cell envelope comprises the inner cell membrane and the cell wall of a bacterium. In gram-negative bacteria an outer membrane is also included. This envelope is not present in the Mollicutes where the cell wall is absent.
Bacterial cell env ...
s.
Homologous recombination
Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...
is responsible for the maintaining the genes mentioned above and also the diversity of the metagenome in its natural environment. Surface structures on different ''H. walsbyi'' cells help to differentiate sources of lineage for the population as a whole. These differing structures also increase the diversity of the cells in their natural environment. These changes in cell structure may be due to the cells' attempts to reduce their susceptibility to attack by
virus
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsky's 1 ...
es.
In 2009 an experiment was conducted in Australia to determine the diversity of ''H. walsbyi'' in three distinct saltern crystallizer ponds. In all three of the pools that were located in different regions they all shared two 97%-OTU of both ''Haloquadratum'' and ''Halorubrum'' -like sequences.
Genomics and structure
''H. walsbyi'' is classified as an
oligotroph
An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates o ...
ic microorganism, as it grows in nutrient deficient conditions where concentrations of organic substances are minimal. To combat, ''H. walsbyi'' maintains a high
surface to volume ratio
The surface-area-to-volume ratio, also called the surface-to-volume ratio and variously denoted sa/vol or SA:V, is the amount of surface area per unit volume of an object or collection of objects.
SA:V is an important concept in science and engin ...
by flattening to maximize nutrient uptake. Because of their
square shape, they are more capable of flattening than
spherical
A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the ce ...
shaped microorganisms are.
''H. walsbyi'' can flatten an extreme amount of about 0.1-0.5μm. The overall size of the cell structure ranges from 1.5 to 11 μm. However, larger cells have been observed. The largest recorded H. walsbyi cell was measured as 40 x 40 μm.
The square shape of ''H. walsbyi'' has been the focus of many studies. It is able to maintain this structure due to its
adaptive traits.
These traits can be found in both ''H. walsbyi's''
genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
composition as well as its protein sequences. For example, ''H.walsbyi’s'' expression of the
halomucin protein creates an aqueous protective layering that helps prevent
desiccation
Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container.
...
of the cells.
These adaptations allow ''H. walsbyi'' to thrive in environments such as saturated brines while also maintaining a defined square structure.
''H. walsbyi’s'' cellular structure consists of highly refractive
gas vesicle
Gas vesicles, also known as gas vacuoles, are nanocompartments in certain prokaryotic organisms, which help in buoyancy. Gas vesicles are composed entirely of protein; no lipids or carbohydrates have been detected.
Function
Gas vesicles occur ...
s,
poly-β-hydroxyalkanoate granules, and a unique cellular wall.
This microbe has displayed cell walls that range from 15 to 25 nm in thickness. The genome of ''H.walsbyi'' encodes S-layered
glycoprotein
Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycos ...
s of the cell wall. Additionally,
photoactive
Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 nm), visible light (400–7 ...
retinal proteins are also encoded for the membrane.
The HBSQ001 strain, discovered in 2004, showed these same internal cellular structures. However, this specific strain showed a complex trichotomous structured cell wall.
A typical Genome of ''H. walsbyi'' has a 3,132,494 bp chromosome. The strain HBSQ001, DSM 16790 was analyzed to obtain this data. ''H. walsbyi'' is distinguished by the abnormally low
Guanine-Cytosine (GC) content compared to other haloarchaea. ''H. walsbyi'' has an average of 47.9% GC content compared to the expected 60-70%. Additionally, the proteins encoded are
highly conserved specifically in the amino acid sequence. It is understood that ''H. walsbyi'' evolved from a typical GC rich, moderately conserving ancestor.
History
The ''Haloquadratum walsbyi'' archaea was first discovered in 1980 by a microbiology professor
Anthony E. Walsby.
The microbe was initially named after him as “Walsby's square bacterium," as it was discovered before the
archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
domain was acknowledged in full. It is now formally known as ''Haloquadratum walsbyi'', and considered a well known
halophilic
The halophiles, named after the Greek word for "salt-loving", are extremophiles that thrive in high salt concentrations. While most halophiles are classified into the domain Archaea, there are also bacterial halophiles and some eukaryotic species, ...
archaea. Additionally, it is accredited to be one of first archaea discovered with a square cellular shape.
Upon the observation of the unique shape of ''H. walsbyi'', cultivation has been a goal for scientists studying the species. Hyper-saline media has been found to be a substantial medium to maintain the pure cultures.
''H. walsbyi'' remains one of the largest
prokaryote
A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...
s known today and contains roughly 3 million basepairs.
As mentioned earlier, the location site of this distinctive microbe's discovery was in the transcontinental country of
Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Mediter ...
within the
Sinai peninsula
The Sinai Peninsula, or simply Sinai (now usually ) (, , cop, Ⲥⲓⲛⲁ), is a peninsula in Egypt, and the only part of the country located in Asia. It is between the Mediterranean Sea to the north and the Red Sea to the south, and is a l ...
.
However, with this discovery also came an extended period that consisted of intensive
trial and error
Trial and error is a fundamental method of problem-solving characterized by repeated, varied attempts which are continued until success, or until the practicer stops trying.
According to W.H. Thorpe, the term was devised by C. Lloyd Morgan (18 ...
attempts to achieve complete isolation of ''H. walsbyi.'' Because of how difficult it was to fully isolate this microorganism, there existed a vast gap in known information on ''H. walsbyi's'' physiological processes and genomic composition.
However in 2004, two
strains of ''H. walsbyi'' were successfully isolated and able to be
sequenced
In genetics and biochemistry, sequencing means to determine the primary structure (sometimes incorrectly called the primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which suc ...
.
The second strain was an Australian isolate, called C23.
Five strains were additionally isolated, totaling in seven total isolates of ''H. walsbyi.'' In a specific
hypersaline
A hypersaline lake is a landlocked body of water that contains significant concentrations of sodium chloride, brines, and other salts, with saline levels surpassing that of ocean water (3.5%, i.e. ).
Specific microbial species can thrive in hi ...
environment, Lake Tyrrell, ''Haloquadratum walsbyi'' made up nearly 38% of the community of
archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
found when the ecosystem was cultured.
Normal microbiota
The Archaeon ''Haloquadratum walsbyi'' is abundant in red brines, in salt lakes and solar salter crystallizer ponds,
shallow ponds that are connected to each other and increase in salinity.
Bacteriorhodopsin
Bacteriorhodopsin is a protein used by Archaea, most notably by haloarchaea, a class of the Euryarchaeota. It acts as a proton pump; that is, it captures light energy and uses it to move protons across the membrane out of the cell. The resulting ...
, a membrane protein that uses energy from light to drive the hydrogen-ion pump, which are found in ''Haloquadratum walsbyi'' absorbs energy from light and are found in communities within these brines.
The use of these
bacteriorhodopsin
Bacteriorhodopsin is a protein used by Archaea, most notably by haloarchaea, a class of the Euryarchaeota. It acts as a proton pump; that is, it captures light energy and uses it to move protons across the membrane out of the cell. The resulting ...
shows the
photoheterotroph
Photoheterotrophs ('' Gk'': ''photo'' = light, ''hetero'' = (an)other, ''troph'' = nourishment) are heterotrophic phototrophs – that is, they are organisms that use light for energy, but cannot use carbon dioxide as their sole carbon source. Con ...
nature of ''Haloquadratum walsbyi.'' The salt saturated environments that this archaean inhabits, along with being rich in magnesium chloride, have very low activity within the water which causes
desiccation
Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container.
...
stress. These salt saturated environments can have a salinity of more than ten-times that of average seawater. The magnesium saturation in these ecosystems, what is also referred to as
bitterns, are most often found with very little to no life present.
This environment is very hostile and ''H. walsbyi'' is only able to survive in it due to its unique genomic make up and while other organisms would perish in similar conditions.
References
Further reading
*
*
External links
Type strain of ''Haloquadratum walsbyi'' at Bac''Dive'' - the Bacterial Diversity Metadatabase"Friday Fellow: Walsby's Square Holoarcheon"at Earthling Nature.
{{Taxonbar, from=Q3782773
Halobacteria
Archaea described in 2007