Quantitative analysis of protein profile of ascospores of Neosartorya pseudofischeri subjected to heat treatment.

Heat-resistant fungi can survive pasteurization processes for high-acid fruit products, and subsequently germinate and grow to cause spoilage during shelf life period, leading to significant economic losses for the producers and potential health threat for the consumers. Neosartorya pseudofischeri, a heat- resistant fungus, was isolated from contaminated blueberry juice in our laboratory. To obtain a better understanding of its heat-resistant property, a quantitative proteomic approach employing stable isotope labeling by peptide demethylation was used to investigate the intracellular protein changes of N. pseudofischeri ascospores subjected to heat treatment at 93°C for 0, 1 or 8 min. Our results showed that 811 proteins were identified and quantified and among them, 417 non-redundant proteins were classified into 16 functional categories. Using the normalized ratio of protein abundance, proteins that changed more than two-fold were identified as increased or decreased ones during heat process. Therefore, 150 significantly changed proteins were grouped into four clusters based on their quantitative changes. Decreased proteins were mainly involved in the central carbon metabolism, heat stress responses, reactive oxygen intermediates elimination and translation events. These proteins were stored during the spore formation rather than synthesized under short stress condition, and their decrease was in agreement with the reduction of ascospores found following the heat treatment. A group of proteins in relation to toxicant degradation and antibiotic neutralization, which link to environmental adaptability and tolerance of heat-resistant fungus, were also identified. Our research findings provide insights into possible molecular target for antifungal therapy. This is the first report for proteomic study on N. pseudofischeri that lays the foundation for further investigations on heat- resistant molds using targeted quantitative studies.