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Title: Mating type and sexual reproduction in the black Aspergilli
Author: Darbyshir, Heather Louise
ISNI:       0000 0004 6349 735X
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2014
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The black aspergilli refers to members of the genus Aspergillus that are typically characterised by the production of dark or black asexual conidia (classified as section Nigri). The group includes Aspergillus niger and Aspergillus awamori, which are of particular industrial importance because of their safe use status and ability to produce a wide range of enzymes and organic acids. Prior to the onset of these Ph.D studies all members of the black aspergilli were only known to reproduce by asexual means. Given their economic and ecological importance, studies were therefore undertaken to determine whether members of the black aspergilli showed characteristics consistent with the possibility for sexual reproduction, and whether it was possible to induce sex in any of these species. Firstly, PCR diagnostic tests were developed which enabled members of the black aspergilli to be screened for the presence of mating-type (/VMT) genes, which are key transcriptional regulators of sexual reproduction. Screenings revealed the presence of complementary MAT1- 1 and MAT1-2 isolates in approximately even numbers for many species, consistent with an extant or historical heterothallic breeding system, although a MAT1-1 bias was detected in A. niger and A. uvarum and a MAT1-2 bias in A. carbonarius. Secondly, members of the black aspergilli were examined for the ability to form sclerotia, which were believed to be prerequisites for sexual reproduction based on data from the Aspergillus teleomorph genus Petromyces. Experimental work was undertaken to determine optimal conditions to induce sclerotial development, and it was found to be possible to reliably induce sclerotial formation in certain species of black aspergilli. Next, attempts were made to induce sexual reproduction in vitro by crossing target species under a range of different conditions. Of high significance, it was found that at least one member of the black aspergilli, Aspergillus sclerotiicarbonarius, was able to complete a sexual cycle. This was achieved by crossing known MAT1-1 and MAT1-2 isolates on oatmeal agar with an extended period of incubation. This resulted in the production of sclerotia which developed into stroma containing multiple ascocarps, with asci and viable ascospores, within the stromal matrix. Ascospore progeny were isolated and recombination confirmed by the detection of novel genotypes, which were characterised using single nucleotide polymorphic (SNP) markers which had been obtained from comparative genome sequencing of the parental isolates. The discovery of a heterothallic sexual cycle in A. sclerotiicarbonarius provides insights into the evolution of asexuality in the black aspergilli, and provides a model for induction of sexual cycles in other members of the black aspergilli. It is hoped that future molecular genetic studies might lead to the induction of sexuality in other black aspergilli, such as the industrially important species A. niger, with the sexual cycle providing a valuable tool for classical genetic analysis and strain improvement purposes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available