Characterization of chromate-sensitive and -tolerant mutants of Schizosaccharomyces pombe

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.

Interference of chromium with biological systems in yeasts and fungi: a review

This paper deals with the interactions of chromium (Cr) with biological systems, focusing in particular on yeasts and fungi. These interactions are analysed with primarily regard to biochemical functions, but higher levels of organization are also considered. Thus, the morphological and cytological characteristics of selected microorganisms in response to exposure to chromium ions are evaluated. The different oxidation states of chromium and reactive oxygen species (ROS) generated in redox reactions with chromium ions are presented and characterized. The interactions of the most exposed subcellular structures, including the cell wall, plasma membrane and nuclei, have been deeply investigated in recent years, for two major reasons. The first is the toxicity of chromium ions and their strong impact on the metabolism of many species, ranging from microbes to humans. The second is the still disputed usefulness of chromium ions, and in particular trivalent chromium, in the glucose and fat metabolisms. Chromium pollution is still an important issue in many regions of the world, and various solutions have been proposed for the bioremediation of soil and water with selected microbial species. Yeasts and especially moulds have been most widely investigated from this aspect, and the biosorption and bioaccumulation of chromium for bioremediation purposes have been demonstrated. Accordingly, the mechanisms of chromium tolerance or resistance of selected microbes are of particular importance in both bioremediation and waste water treatment technologies. The mechanisms of chromium toxicity and detoxification have been studied extensively in yeasts and fungi, and some promising results have emerged in this area.

Gene expressions and enzyme analyses in the Schizosaccharomyces pombe Deltapap1 transcription factor mutant exposed to Cd(2+)

The objective of this study was to investigate the role of the Pap1 transcription factor in response to long-term Cd(2+) stress. The Schizosaccharomyces pombe wild-type strain and the Deltapap1 mutant, treated with 0.5 mM CdSO(4), were used in antioxidant enzyme and gene expression experiments. The Deltapap1 mutant proved to be sensitive to Cd(2+) in the spot test assay, suggesting that the Pap1 transcription factor plays an important role in the response to Cd(2+) stress. The Cd(2+) uptake was the same in both strains. Determination of the superoxide level in the wild-type strain proved that superoxide was generated, suggesting that long-term Cd(2+) treatment could trigger oxidative stress. Furthermore, the Deltapap1 mutant displayed higher amounts of superoxide. These results were supported by the significantly lower amount of peroxide generated in the reaction catalyzed by superoxide dismutase (SOD). The Deltapap1 mutant had a significantly lower glutathione S-transferase specific activity than that of the wild-type strain during long-term Cd(2+) stress, caused by the lower GSH and sulfide assimilation. We have demonstrated that GST III activity was not induced by Cd(2+) stress in the Deltapap1 mutant. The overall low GST activity was not sufficient for the cell to eliminate Cd(2+) caused damage and could result in a Cd(2+)-sensitive phenotype of the Deltapap1 mutant. The RT-PCR and Northern blot experiments proved that gst2 was not induced either by short-term or by long-term Cd(2+) treatment. The SPCC965.06 (a putative K(+) ion channel subunit) gene expression increased, while the hmt1 (an ABC-type vacuolar transporter protein) expression decreased in both strains. No detectable alteration in the mRNA levels of, gpx1, hmt2, sod1, sod, and trx1 was observed. SOD enzyme analyses revealed that the absence of Pap1 protein could result in a lower SODs activity and affect the sulfate assimilation. This is the first report on the fact that the Pap1 transcription factor could play an important role in the cellular post-transcriptional/post-translational enzyme activity induction processes of SODs that occur in response to Cd(2+).