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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.
The most common form of S. fimicola is a dark brown. Certain mutants are grey or tan. A common experiment for an introductory biology lab class is to cross one of the mutant types with a wild type and observe the ratio of coloring in the offspring. This experiment illustrates the concepts of genetic inheritance in a haploid organism. The eight ascospores are produced inside an ascus. Sordaria squashes can give us information about crossing over during meiosis. If no crossing over occurs a 4:4 pattern is produced: four black spores, and four tan spores all lined up. If crossing over does occur there is a 2:2:2:2 pattern visible, or a 2:4:2 pattern.
Another common lab use is to observe meiosis and mitosis in the fruit bodies, called perithecia. An interesting feature of S. fimicola is that its fruit body is phototrophic. Thus, as it grows the stalk will bend toward a light source and when the sac bursts, the spores are shot towards the light.
Taxonomy
Research to update Sordariomycete fungal taxonomy is ongoing, and the position of Sordaria fimicola within the taxonomy of the Sordariomycetes is being researched and updated. The sordariomycetes are known as the flask fungi because they are characterized by flask-shaped perithecia and unitunicate asci. Phylogenetic studies of partial 18s ribosomal DNA strands has illuminated the phylogeny of the Sordariomycetes. Morphological features that characterize the Sordariaceae include the differentiation of the hyphal envelope that surrounds the ascogonium into peripheral wall layers and a pseudoparenchymatous centrum. Broad paraphyses composed of delicate, multinucleate cells arise from the cells of the centrum and completely fill the perithecium, crushing the remaining pseudoparenchymatous cells against the perithecial wall. S. fimicola differs from other species of Sordariaceae studied in the aggregation of the ascogenous cells to form a placenta‐like mass in the base of the centrum. Consequently, the asci arise in a cluster rather than in a uniform wall layer. S. fimicola grows septate hyphae which at the macro level look like small dark brown fibers forming a fluffy sheet over the substrate. Small black spots will form when sexual reproduction occurs, as these spots are the location of the ascii. Additionally, there are tan and grey mutant strains of S. fimicola. In sterilized and unsterilized soil, S. fimicola promoted host growth and prevented mortality. Research shows that S. fimicola in potato dextrose cultures is capable of producing triacontanol and indole-3-carboxaldehyde, both of which have antibacterial properties that may help prevent host disease.
S. fimicola has also been shown to inhibit the growth of other species of fungi which are pathogenic to plants including Pestalotiopsis guepinii, Colletotrichum capsici, Curvularia lunata [Cochliobolus lunatus], Alternaria alternata and Fusarium oxysporum.
S. fimicola has also been shown to negatively affect the health of some plants that it can be found growing on. When S. fimicola was first isolated from maize researchers believed that it was most likely an opportunistic pathogen. Healthy maize plants in the laboratory did not grow S. fimicola indicating that healthy maize plants may exclude it. S. fimicola did colonize healthy B. tectorum resulting in reduced fecundity and reduced growth. S. fimicola with a non-functional mutant SfWC-1 receptor had delayed and less-pronounced fruiting-body formation, was defective in phototropism of the perithecial beaks, and lacked the fruiting-body zonation pattern compared with the wild type. Olive considered that these gene conversion events resulted from "trans replication, by which a locus is copied more than the normal number of times during replication at meiotic prophase." Since then many studies on the gene conversion phenomenon were carried out with S. fimicola and other organisms, particularly other ascomycetes [see review by Whitehouse (1982)]. Efforts to understand gene conversion at the molecular level have provided important insights into the mechanism and adaptive function of meiotic recombination, which in turn bears on the adaptive function of sexual reproduction.
Images
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Image:Sordaria fimicola mating plate.png|A mating between wild-type (dark brown) and mutant (tan) Sordaria fimicola colonies
Image:Sordaria fimicola perithecium (heterozygote) 40X.png|Sordaria fimicola perithecia with both mutant and wild-type ascospores
Image:Sordaria fimicola ascus (heterozygote) 160X.png|A Sordaria fimicola ascus with an unusual 2:1:1:1:1:2 pattern
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