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Seekles, S.J. (2022)

Genetic and environmental factors determining heterogeneity in preservation stress resistance of Aspergillus niger conidia

Doctoral Thesis
Fungal food spoilage often starts with a contamination with spores. Experimental data strongly indicate the existence of subpopulations of spores with different levels of resistance to preservation methods. In this thesis, the extent of this heterogeneity and the underlying mechanisms using fungal model systems is studied. The role of the genetic background, environmental conditions and the developmental state of the spores were studied, using quantitative imaging, genome and RNA/protein sequencing as well as functional gene analysis. 
The role of transcription factors in weak acid stress resistance of Aspergillus niger is described. Next, heat resistance of fungal spores of three food spoilage species was quantified and compared. The genomes of Aspergillus niger strains were sequenced and compared revealing the existence of a possible sexual cycle. Melanin of fungal spores impacts UV-C resistance, but not heat resistance and a functional CRISPR/Cas9 genome editing system for...Show moreFungal food spoilage often starts with a contamination with spores. Experimental data strongly indicate the existence of subpopulations of spores with different levels of resistance to preservation methods. In this thesis, the extent of this heterogeneity and the underlying mechanisms using fungal model systems is studied. The role of the genetic background, environmental conditions and the developmental state of the spores were studied, using quantitative imaging, genome and RNA/protein sequencing as well as functional gene analysis. 
The role of transcription factors in weak acid stress resistance of Aspergillus niger is described. Next, heat resistance of fungal spores of three food spoilage species was quantified and compared. The genomes of Aspergillus niger strains were sequenced and compared revealing the existence of a possible sexual cycle. Melanin of fungal spores impacts UV-C resistance, but not heat resistance and a functional CRISPR/Cas9 genome editing system for Paecilomyces variotii and Penicillium roqueforti is described. Older spores are more heat resistant than younger spores, which can be contributed to differences in compatible solute composition. Additionally, a high cultivation temperature results in fungal spores with high heat resistance, possibly due to heat shock proteins.

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Aspergillus niger
Conidia
Food preservation
Heterogeneity
Weak acids
Heat resistance
Fungal spores
Stress resistance
Food spoilage
All authors
Seekles, S.J.
Supervisor
Ram, A.F.J.; Punt, P.J.
Committee
Winde, J.H. de; Wezel, G.P. van; Claessen, D.; Brul, S.; Meyer, V.; Rozen, D.E.
Qualification
Doctor (dr.)
Awarding Institution
Institute of Biology Leiden (IBL), Faculty of Science, Leiden University
Date
2022-01-18
ISBN (print)
9789464580181

Funding

Sponsorship
This work was performed within the framework of TIFN, financed by Agri & Food: AF-15507 | Heterogeneity in spores of food spoilage fungi