Quantitative proteomic analysis of Neosartorya pseudofischeri ascospores subjected to heat treatment.

Neosartorya pseudofischeri, a heat- resistant fungus, was isolated from contaminated blueberry juice in our laboratory. To obtain a better understanding of the cellular process of heat- resistant fungus, a quantitative proteomic investigation employing stable isotope labeling by peptide demethylation was conducted on changes in intracellular proteins of N. pseudofischeri ascospores subjected to heat treatment at 93 °C for 0, 1 or 8 min. In total, 811 proteins were identified and quantified. Using the normalized ratio of protein abundance, proteins that changed more than two- fold after heat treatment were identified as significantly increased or decreased proteins and grouped into four clusters based on their quantitative changes. Decreased proteins were found mainly involved in the central carbon metabolism, heat stress responses, reactive oxygen intermediates elimination and translation events. A group of proteins in relation to toxicant degradation and antibiotic neutralization linking to environmental adaptability and tolerance of heat- resistant, was also identified. These findings provide insights into protein changes of N. pseudofischeri ascospores and lay foundations for further investigations on heat- resistant molds using targeted quantitative approaches. SIGNIFICANCE OF THE RESEARCH: Heat- resistant fungi can survive pasteurization processes, and subsequently germinate and grow to cause spoilage of food products, leading to significant economic losses for the food industry and potential health risk for the consumers. To obtain a better understanding of the cellular process of heat- resistant fungi, a quantitative proteomic approach employing stable isotope labeling by peptide demethylation has been used to investigate the intracellular protein changes of N. pseudofischeri ascospores isolated from blueberry juice and subjected to heat treatment. 150 significantly changed proteins were grouped into four clusters based on their quantitative changes. The significant decrease in protein abundance in response to heat treatment revealed possible mechanism that N. pseudofischeri ascospores could survive the heat treatment. This is the first proteomic profile report for N. pseudofischeri. These findings provide insights into protein changes of N. pseudofischeri and lay foundations for further investigations on heat- resistant fungi using targeted quantitative approaches to evaluate the efficiency of thermal treatment for processed food products.

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