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... 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. Show less
The filamentous bacteria Streptomyces are widespread inhabitants of terrestrial soils. Streptomycetes are not only among the most potent producers of valuable secondary metabolites (e.g.... Show moreThe filamentous bacteria Streptomyces are widespread inhabitants of terrestrial soils. Streptomycetes are not only among the most potent producers of valuable secondary metabolites (e.g. antibiotics), but also the source of various industrially relevant hydrolytic enzymes. The mode-of-growth of streptomycetes under industrial conditions is markedly different to that observed in their natural habitat. Most species form dense particles called pellets. Pellets are heterogeneous in size; more specifically at least two populations of differently-sized pellets exist in submerged cultures. Importantly, pellet size and production have been shown to be to be tightly correlated in streptomycetes. The study and control of pellet size heterogeneity in streptomycetes is the subject of the research presented in this thesis. Here, the various phenomena occurring throughout growth are characterized with the aim of understanding the factors underlying this phenomenon. Subsequently, the obtained knowledge is applied to obtain homogeneously-sized pellets of the industrial workhorse Streptomyces lividans. The work described in this thesis also addresses the fate of pellets at late stages of growth and a growth strategy representing a valuable alternative to conventional liquid cultures. Show less