Heterogeneity of food spoilage fungi

The world population is projected to reach up to 11 billion inhabitants this century. As a consequence, the demand for food will rise up to 70 % in 2050. One of the methods to meet this demand is by limiting the amount of food wasted each year, which is currently about one third of all food produced. Microorganisms such as fungi cause microbiological spoilage. Fungal spoilage is predominantly caused by mould or yeast-like fungi that belong to the Ascomycota. The moulds grow by means of vegetative hyphae and after a period of vegetative growth, a mycelium can produce asexual reproduction structures known as conidia. Conidia are considered to be the main cause of food spoilage because colonies produce enormous numbers of these spores that are easily dispersed. Conidia are generally more stress-resistant than vegetative mycelium enabling them to survive post-harvest treatments of food and subsequently spoil food. A single spore is sufficient to cause spoilage. Formation of heterogeneous spores is a strategy to increase the chance of successful colonization of food products. Heterogeneity can not only be found between species and strains but also between spore populations of colonies of the same strain that have been exposed to different environmental conditions. In this thesis, the heterogeneity of two common food spoilage fungi, Aspergillus niger and Penicillium roqueforti, towards germination, heat resistance and sorbic acid resistance is studied. Within conidia derived from a single strain, germination was found to be highly variable, even in rich media. In addition, a 100-fold difference in conidial heat resistance between strains was observed for P. roqueforti and through a genome-wide association study the presence of a specific gene cluster was identified to result in significantly increased sorbic acid resistance.