Arxula adeninivorans
Encyclopedia
Arxula adeninivorans is a dimorphic
yeast
with unusual characteristics. The first description of A. adeninivorans was provided in the mid-eighties. The species was initially designated as Trichosporon adeninovorans. After the first identification in the Netherlands
, strains of this species were later on also found in Siberia
and in South Africa
in soil and in wood hydrolysates. Recently, A. adeninivorans was renamed as Blastobotrys adeninivorans after a detailed phylogenetic comparison with other related yeast species. However, many scientists desire to maintain the popular name A. adeninivorans.
(hence the name A. adeninivorans) and several other purine
compounds as sole energy and carbon source, they all share properties like nitrate
assimilation, they are thermo-tolerant (they can grow at temperatures of up to 48 °C or 118.4 °F). A special feature of biotechnological impact is a temperature-dependent dimorphism. At temperatures above 42 °C (107.6 °F) a reversible transition from budding
cells to mycelial
forms is induced. Budding is re-established when cultivation temperature is decreased below 42 °C (107.6 °F).
, lipase
, phosphatase
s and many others. On the other hand it is a very robust and safe organism that can be genetically engineered to produce foreign proteins. Suitable host strains can be transformed
with plasmid
s. The basic design of such plasmids is similar to that described under Hansenula polymorpha
and yeast expression platforms.
Here two special examples of recombinant
strains and their application: in both cases several plasmids with different foreign product genes were introduced into the yeast. In a first case this recombinant yeast strain acquired the capability to produce natural plastics, namely PHA (polyhydroxyalkanoates). For this purpose a new synthetic pathway had to be transferred into this organism consisting of three enzymes. The respective genes phbA, phbB and phbC were isolated from the bacterium Ralstonia eutropha
and integrated into plasmids. These plasmids were introduced into the organism. The resulting recombinant strain was able to produce the plastic material.
In the second example a biosensor
for the detection of estrogen
ic activities in wastewater has been developed. In this case the route how estrogens act in nature was mimicked. A gene for the human estrogen receptor alpha
(hERalpha) contained on a first plasmid was initially introduced. The protein encoded by this gene recognizes and binds estrogens. The complex is then bound to a second gene contained on a second plasmid that becomes activated upon binding. In this case a gene sequence of a reporter gene
(the gene product can be easily monitored by simple assays) was fused to a control sequence (a promoter) responsive to the estrogen/receptor complex. Such strains can be cultured in the presence of wastewater and the estrogens present in such samples can be easily quantified by the amount of the reporter gene product.
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...
yeast
Yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
with unusual characteristics. The first description of A. adeninivorans was provided in the mid-eighties. The species was initially designated as Trichosporon adeninovorans. After the first identification in the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
, strains of this species were later on also found in Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
and in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
in soil and in wood hydrolysates. Recently, A. adeninivorans was renamed as Blastobotrys adeninivorans after a detailed phylogenetic comparison with other related yeast species. However, many scientists desire to maintain the popular name A. adeninivorans.
Characteristics
All A. adeninivorans strains share unusual biochemical activities being able to assimilate a range of amines, adenineAdenine
Adenine is a nucleobase with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate and the cofactors nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and protein synthesis, as a chemical component of DNA...
(hence the name A. adeninivorans) and several other purine
Purine
A purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines, including substituted purines and their tautomers, are the most widely distributed kind of nitrogen-containing heterocycle in nature....
compounds as sole energy and carbon source, they all share properties like nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
assimilation, they are thermo-tolerant (they can grow at temperatures of up to 48 °C or 118.4 °F). A special feature of biotechnological impact is a temperature-dependent dimorphism. At temperatures above 42 °C (107.6 °F) a reversible transition from budding
Budding
Budding is a form of asexual reproduction in which a new organism grows on another one. The new organism remains attached as it grows, separating from the parent organism only when it is mature. Since the reproduction is asexual, the newly created organism is a clone and is genetically identical...
cells to mycelial
Mycelium
thumb|right|Fungal myceliaMycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or within many other...
forms is induced. Budding is re-established when cultivation temperature is decreased below 42 °C (107.6 °F).
Biotechnological potential
The unusual characteristics described above render A. adeninivorans very attractive for biotechnological applications. On one hand it is a source for many enzymes with interesting properties and the respective genes, for instance glucoamylase, tannaseTannase
In enzymology, a tannase is an enzyme that catalyzes the chemical reactionThus, the two substrates of this enzyme are digallate and H2O, whereas its product is gallate....
, lipase
Lipase
A lipase is an enzyme that catalyzes the formation or cleavage of fats . Lipases are a subclass of the esterases.Lipases perform essential roles in the digestion, transport and processing of dietary lipids in most, if not all, living organisms...
, phosphatase
Phosphatase
A phosphatase is an enzyme that removes a phosphate group from its substrate by hydrolysing phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl group . This action is directly opposite to that of phosphorylases and kinases, which attach phosphate groups to their...
s and many others. On the other hand it is a very robust and safe organism that can be genetically engineered to produce foreign proteins. Suitable host strains can be transformed
Transformation (genetics)
In molecular biology transformation is the genetic alteration of a cell resulting from the direct uptake, incorporation and expression of exogenous genetic material from its surroundings and taken up through the cell membrane. Transformation occurs naturally in some species of bacteria, but it can...
with plasmid
Plasmid
In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...
s. The basic design of such plasmids is similar to that described under Hansenula polymorpha
Hansenula polymorpha
Ogataea polymorpha is a methylotrophic yeast with unusual characteristics. It is used as a protein factory for pharmaceuticals.Ogataea polymorpha belongs to a limited number of methylotrophic yeast species – yeasts that can grow on methanol...
and yeast expression platforms.
Here two special examples of recombinant
Recombinant DNA
Recombinant DNA molecules are DNA sequences that result from the use of laboratory methods to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in biological organisms...
strains and their application: in both cases several plasmids with different foreign product genes were introduced into the yeast. In a first case this recombinant yeast strain acquired the capability to produce natural plastics, namely PHA (polyhydroxyalkanoates). For this purpose a new synthetic pathway had to be transferred into this organism consisting of three enzymes. The respective genes phbA, phbB and phbC were isolated from the bacterium Ralstonia eutropha
Ralstonia eutropha
Ralstonia eutropha is a gram-negative soil bacterium of the betaproteobacteria class.-Taxonomy:R. eutropha has gone through a series of name changes. In the first half of the 20th century many microorganisms were isolated for their ability to utilize hydrogen. Hydrogen metabolizing...
and integrated into plasmids. These plasmids were introduced into the organism. The resulting recombinant strain was able to produce the plastic material.
In the second example a biosensor
Biosensor
A biosensor is an analytical device for the detection of an analyte that combines a biological component with a physicochemical detector component.It consists of 3 parts:* the sensitive biological element A biosensor is an analytical device for the detection of an analyte that combines a biological...
for the detection of estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
ic activities in wastewater has been developed. In this case the route how estrogens act in nature was mimicked. A gene for the human estrogen receptor alpha
Estrogen receptor alpha
Estrogen receptor alpha , also known as NR3A1 , is a nuclear receptor that is activated by the sex hormone estrogen...
(hERalpha) contained on a first plasmid was initially introduced. The protein encoded by this gene recognizes and binds estrogens. The complex is then bound to a second gene contained on a second plasmid that becomes activated upon binding. In this case a gene sequence of a reporter gene
Reporter gene
In molecular biology, a reporter gene is a gene that researchers attach to a regulatory sequence of another gene of interest in cell culture, animals or plants. Certain genes are chosen as reporters because the characteristics they confer on organisms expressing them are easily identified and...
(the gene product can be easily monitored by simple assays) was fused to a control sequence (a promoter) responsive to the estrogen/receptor complex. Such strains can be cultured in the presence of wastewater and the estrogens present in such samples can be easily quantified by the amount of the reporter gene product.