Ashbya gossypii

Fluorescence microscopy images of the mycelium of Ashbya gossypii ( nuclei labeled)

Ashbya gossypii (also Eremothecium gossypii ) is a mold that is closely related to baker's yeast. It was first described in 1926 by Ashby and Nowell as a pathogen of cotton plants in which it causes the so-called Stigmatomykose. The disease affects the development of hair cells in the bolls of cotton and can be transmitted to citrus fruits that dry and then coincide ( dry rot ). A. gossypii is a natural producer of About riboflavin (vitamin B2), which is why he was industrially interesting.

Description

Growth, development and morphology

The life cycle of A. gossypii begins with the uniform in all directions ( isotropy ) on growth of the haploid spore germination. This is followed by apical growth, which produces two seed tubes consecutively to opposite sides of the germinal vesicle. Further axes are formed during lateral branching in young mycelium. Maturation is characterized by apical junctions (separation of peaks ), and a dramatic increase in the speed of growth (up to 200 microns / hour at 30 ° C ), which is A. gossypii allows it to fill in a petri dish of 8 cm in diameter in about 7 days. Sporulation is likely to be caused by deprivation of food and leads to a contraction of the septum, cytokinesis and subsequent secretion of the sporangia, which may contain up to eight haploid spores. The hyphae themselves are generally divided by septa, which initially appear as a ring that allows the transfer of nuclear material; later, the appearance of the septa changes to a closed disc. Each Hyphenkompartiment contains about eight nuclei.

Karyotype and genome

The genetic information is present in A. gossypii 7 autosomes as well as the core of the mitochondria in the cell nucleus. The genome of strain ATCC 10895 was first fully analyzed in 2004; it consists of 9 million base pairs and an estimated 4,750 genes. This makes it the smallest known genome of a free-living eukaryotes. Ninety percent of the genes in A. gossypii are both homologous and in the same order ( synteny ) as in Saccharomyces cerevisiae. The ancestor of the two organisms lived 100 million years ago. While A. gossypii only slightly altered, a gene duplication occurred in the subsequent evolution of baker's yeast.

Pathology

A. gossypii and two other fungi that cause Stigmatomykose ( Eremothecium coryli, Aureobasidium pullulans ), made it in the first half of the 20th century to cultivate almost impossible cotton in some subtropical regions. Only the control of the spore -carrying insects Dysdercus species suturellus and Antestia angulosa could then prevent the infection of cotton.

A. gossypii as a model organism

Due to its small size and also haploid genome and existing efficient methods for gene targeting A. gossypii is recognized as a model organism, particularly for the study of the growth of long and multinucleate fungal cells. It is generally believed that a better understanding of the hyphal growth will enable the development of novel fungicides. Particularly promising Ashbya gossypii as a model organism due to the high conservation of gene order ( synteny ) between the genomes of A. gossypii and Saccharomyces cerevisiae.

Taxonomic position

In recent works, the genera Ashbya, Holleya, and Nematospora are synonymous to Eremothecium. The four genera are characterized by needle-like ascospores, which may be straight or curved. The taxa are pathogenic in various plant species and Ashbya and Eremothecium are used worldwide for the production of riboflavin. Phylogenetic analysis of ribosomal RNA and DNA in the 1990s, in the opinion agreed that the four species are congeners.