Ashbya gossypii

From MicrobeWiki, the student-edited microbiology resource

Classification

Higher Order Taxa:

Fungi, Ascomycota, Saccharomycetes, Saccharomycetales, Saccharomycetaceae

Species:

A. gossypii

Description and Significance

Fungus Ashbya gossypii. Nuclei are shown in green. Jaspersen Lab, 2007.

Ashbya gossypii (Eremothecium gossypii) is a filamentous fungus, meaning that it is an infectious agent of the fungus kingdom consisting of a long series of attached cells. It is closely related to unicellular yeasts, especially Saccharomyces cerevisiae, a yeast with which it shares more than 90% of its genome.


Ashbya gossypii is an effective fungus in which to study the growth of long and multinucleate (more than one nucleus) fungal cells. It has a small genome, haploid nuclei, and efficient gene targeting methods, characteristics that make it favorable in studies. Through the work of Professor Peter Philippsen and research team, basic yet essential knowledge was gained on the species which is now applied to problems in medicine and agriculture [1].


In addition, because this fungal species is so closely related to yeasts (especially Saccharomyces cerevisiae,) it acts as a model for studying regulatory networks. Explorations of these networks reveal the functional differences between filamentous growth and yeast growth. This is important to understanding diseases that affect the environment and humans, such as Candida albicans. [2]. Candida albicans, a human fungal pathogen, switches in morphology from yeast to filamentous form in response to specific environmental stimuli, which is important in studying pathology.







Genome Structure

A comparison of the genomes for Ashbya gossypii and Saccharomyces cerevisiae. Nature Publishing Group 2013.

The genome for Ashbya gossypii is the smallest genome of a free-living eukaryote thus far, coming up to only 9.2 megabases. It contains a total of 4718 protein-coding genes. As mentioned above, more than 90% of its genes are similar to that of Saccharomyces cerevisiae. Importantly, the gene order was conserved (in evolution.)


The comparison of these genes reveals shared homology and synteny (the condition of two or more genes being located on the same chromosome) between the two species.


Professor Peter Philippsen, Ordinarius of Microbiology at the Biozentrum Basel, was the first scientist to fully examine Ashbya Gossypii (a few years they completed the sequencing of the Saccahromyces cerevisiae genome in 1996.)[3] In these explorations of the two species, these scientists were able to find such extensive similarities.





Growth, Cell Structure and Metabolism

Growth

Ashbya gossypii grows isotropically. Its isotropic growth involves the haploid spore's germination and the formation of a germ bubble. Once the germ bubble is formed, two germ tubes grow from opposite sites of the bubble. Apical growth follows, which allows fungi to extend into their environment and release enzymes from the tips for nutrient intake.


The fungus is made up of hyphae, or long, thin, branch-like filamentous structures. The nuclei lined up inside the hyphae act independently though they are contained in one cytoplasm. As the nuclei flow through the hyphae, they undergo mitosis at sites of branch formation (where a hyphae will branch off into two, etc.) The two daughter cells will then flow through the new hypha. According to MATLAB-based tracking methods, diffusions of proteins allow communication between nuclei. There are ongoing studies addressing the question of whether the nuclei are competing for resources or if they are functionally independent of one another. [4].

Cell Structure

To the naked eye, Ashbya gossypii colonies are flat and similar in size and appearance to hair. Under a microscope, they range in color from pale-yellow to vibrant yellow. Their asci, or sexual spore-bearing cells, are long and thin, like thread, and translucent. The ascospores are long and thin as well and also have hooked appendages. [5].

Metabolism

Ecology

As briefly mentioned under Growth, Ashbya gossypii and fungi in general involve apical growth. This form of growth allows it to extend into fresh zones of substrate, (which its enzymes will erode.) This is especially important for growth when the fungi cells encounter an insoluble polymer such as cellulose, which decreases the organism's rate of enzyme diffusion.


Pathology

Ashbya gossypii is a pathogen in certain crops that causes stigmatomycosis. (Ashby and Novell, 1926.) This fungal disease, discovered in cotton, affects the development of hair cells in cotton bolls. It can then transfer to citrus fruits, causing dry rot disease in which the fruits dry out and collapse. In the early 1900s, the pathogen, along with two other fungi, caused stigmatomycosis in cotton crops, making it nearly impossible to grow cotton in certain regions and causing huge economical damage. (Frederic P. Miller, Agnes F. Vandome, John McBrewster 2010.)




References



Edited by Jenna Cartusciello, student of Joan Slonczewski for BIOL 116 Information in Living Systems, 2013, Kenyon College.