Podospora anserina | |
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Wild-type strain on a Petri dish | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Fungi |
Division: | Ascomycota |
Class: | Sordariomycetes |
Order: | Sordariales |
Family: | Podosporaceae |
Genus: | Podospora |
Species: | P. anserina |
Binomial name | |
Podospora anserina | |
Synonyms | |
Podospora anserina is a filamentous ascomycete fungus from the order Sordariales. It is considered a model organism for the study of molecular biology of senescence (aging), prions, sexual reproduction, and meiotic drive. [1] [2] It has an obligate sexual and pseudohomothallic life cycle. It is a non-pathogenic coprophilous fungus that colonizes the dung of herbivorous animals such as horses, rabbits, cows and sheep. [1] [3]
Podospora anserina was originally named Malinvernia anserina Rabenhorst (1857). Podospora anserina was subsequently published in Niessl (1883), [4] which is used today to reference the common laboratory strain therefrom, 'Niessl'. It is also known as Pleurage anserina (Ces.) Kuntze. [5] [6] Genetics of P. anserina were characterized in Rizet and Engelmann (1949) and reviewed by Esser (1974). P. anserina is estimated to have diverged from Neurospora crassa 75 million years ago based on 18S rRNA and protein orthologous share 60-70% homology. [7] Gene cluster orthologs between Aspergillus nidulans and Podospora anserina have 63% identical primary amino acid sequence (even though these species are from distinct classes) and the average amino acid of compared proteomes is 10% less, giving rise to hypotheses of distinct species yet shared genes.
Podospora is a model organism to study genetics, aging (senescence, cell degeneration), ascomycete development, heterokaryon incompatibility, [8] mating in fungi, prions, and mitochondrial and peroxisomal physiology. [9] Podospora is easily culturable on complex (full) potato dextrose, cornmeal agar/broth, or even synthetic medium, and, using modern molecular tools, is easy to manipulate. Its optimal growth temperature is 25–27 °C (77–81 °F) and can complete its life cycle in 7 to 11 days under laboratory conditions. [1] [10]
Most research has been done in a small collection of French strains sampled in the 1920s, in particular the strains named S and s. [11] These two strains are known to be very similar except for the het-s locus. The reference genome published in 2008 corresponds to S+, a haploid derivate of the S strain with a + mating type. [7]
In addition, two other populations have been sampled, one in Usingen, Germany, [12] and the other in Wageningen, the Netherlands, [13] [14] [15] [16] both of which have been used to study spore killing, the phenotypic expression of meiotic drive in fungi. [2]
In addition there are multiple lab-derived strains:
Podospora anserina has a definite life span and shows senescence phenotypically (by slower growth, less aerial hyphae, and increased pigment production in distal hyphae). However, isolates show either increased life span or immortality, as to study the process of aging many genetic manipulations have been done to produce immortal strains or increase life-span. In general, the mitochondrion and mitochondrial chromosome is investigated. [21] [22]
Senescence occurs because during respiration reactive oxygen species are produced that limit the life span and over time defective mitochondrial DNA can accumulate. [19] [23] With this knowledge, focus turned to nutrition availability, respiration (ATP synthesis) and oxidases, such as cytochrome c oxidase. Carotenoids, pigments that are also found in plants and provide health benefits to humans, [24] are known to be in fungi like Podospora's divergent ancestor Neurospora crassa; in N. crassa (and other fungi) cartenoids al genes namely provide UV radiation protection. Over-expression of al-2Podospora anserina increased life span by 31%. [25]
Calorie restriction studies show that decreasing nutrients, such as sugar, increased life span, likely due to slower metabolism and thus decreased reactive oxygen species production or induced survival genes. Also, intracellular copper levels were found to be correlated with growth. This was studied in Grisea-deleted and ex1-deleted strains, as well as in a wild type s strain. Podospora without Grisea, a copper transcription factor, had decreased intracellular copper levels which lead to use of an alternative respiratory pathway that consequently produced less oxidative stress. [20]
In the P. anserina aging model, autophagy, a pathway for the degradation of damaged biomolecules and organelles, was shown to be a longevity assurance mechanism. [26]
The following genes, both allelic and nonallelic, are found to be involved in vegetative incompatibility (only those cloned and characterized are listed): het-c, het-c, het-s, idi-2, idi-1, idi-3, mod-A, mode-D, mod-E, psp-A. Podospora anserina contains at least 9 het loci. [27]
Podospora anserina is known to produce laccases, a type of phenoloxidase. [28]
Original genetic studies by gel electrophoresis led to the finding of the genome size, c. 35 megabases, with 7 chromosomes and 1 mitochondrial chromosome. In the 1980s the mitochondrial chromosome was sequenced. Then, in 2003, a pilot study was initiated to sequence regions bordering chromosome V's centromere using BAC clones and direct sequencing. [29] In 2008, a 10x whole genome draft sequence was published. [7] The genome size is now estimated to be 35-36 megabases. [7]
Genetic manipulation in fungi is difficult due to low homologous recombination efficiency and ectopic integrations [30] which hinders genetic studies using allele replacement and knock-outs. [9] In 2005, a method for gene deletion was developed based on a model for Aspergillus nidulans that involved cosmid plasmid transformation. A better system for Podospora was developed in 2008 by using a strain that lacked nonhomologous end joining proteins (Ku (protein), known in Podospora as PaKu70). This method claimed to have 100% of transformants undergo desired homologous recombination leading to allelic replacement, and after the transformation, the PaKu70 deletion can be restored by crossing over with a wild-type strain to yield progeny with only the targeted gene deletion or allelic exchange (e.g. point mutation). [9]
It is well known that many organisms across all domains produce secondary metabolites, and fungi are prolific in this regard. Product mining was well underway in the 1990s for the genus Podospora. From Podospora anserina two new natural products classified as pentaketides, specifically derivatives of benzoquinones, were discovered; these showed antifungal, antibacterial, and cytotoxic activities. [31] Horizontal gene transfer is common in bacteria and between prokaryotes and eukaryotes yet is more rare between eukaryotic organisms. Between fungi, secondary metabolite clusters are good candidates for horizontal gene transfer, for example, a functional ST gene cluster that produces sterigmatocystin was found in Podospora anserina and originally derived from Aspergillus. This cluster is well-conserved, including, notably, the transcription-factor binding sites. Sterigmatocystin itself is toxic and is a precursor to another toxic metabolite, aflatoxin. [32]
Candida albicans is an opportunistic pathogenic yeast that is a common member of the human gut flora. It can also survive outside the human body. It is detected in the gastrointestinal tract and mouth in 40–60% of healthy adults. It is usually a commensal organism, but it can become pathogenic in immunocompromised individuals under a variety of conditions. It is one of the few species of the genus Candida that cause the human infection candidiasis, which results from an overgrowth of the fungus. Candidiasis is, for example, often observed in HIV-infected patients. C. albicans is the most common fungal species isolated from biofilms either formed on (permanent) implanted medical devices or on human tissue. C. albicans, C. tropicalis, C. parapsilosis, and C. glabrata are together responsible for 50–90% of all cases of candidiasis in humans. A mortality rate of 40% has been reported for patients with systemic candidiasis due to C. albicans. By one estimate, invasive candidiasis contracted in a hospital causes 2,800 to 11,200 deaths yearly in the US. Nevertheless, these numbers may not truly reflect the true extent of damage this organism causes, given new studies indicating that C. albicans can cross the blood–brain barrier in mice.
In molecular biology and genetics, transformation is the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous genetic material from its surroundings through the cell membrane(s). For transformation to take place, the recipient bacterium must be in a state of competence, which might occur in nature as a time-limited response to environmental conditions such as starvation and cell density, and may also be induced in a laboratory.
Neurospora crassa is a type of red bread mold of the phylum Ascomycota. The genus name, meaning 'nerve spore' in Greek, refers to the characteristic striations on the spores. The first published account of this fungus was from an infestation of French bakeries in 1843.
Sordaria fimicola is a species of microscopic fungus. It is commonly found in the feces of herbivores. Sordaria fimicola is often used in introductory biology and mycology labs because it is easy to grow on nutrient agar in dish cultures. The genus Sordaria, closely related to Neurospora and Podospora, is a member of the large class Sordariomycetes, or flask-fungi. The natural habitat of the three species of Sordaria that have been the principal subjects in genetic studies is dung of herbivorous animals. The species S. fimicola is common and worldwide in distribution. The species of Sordaria are similar morphologically, producing black perithecia containing asci with eight dark ascospores in a linear arrangement. These species share a number of characteristics that are advantageous for genetic studies. They all have a short life cycle, usually 7–12 days, and are easily grown in culture. Most species are self-fertile and each strain is isogenic. All kinds of mutants are easily induced and readily obtainable with particular ascospore color mutants. These visual mutants aid in tetrad analysis, especially in analysis of intragenic recombination.
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