Salt stress improves thermotolerance and high-temperature bioethanol production of multi-stress-tolerant Pichia kudriavzevii by stimulating intracellular metabolism and inhibiting oxidative damage

Abstract

Background High-temperature bioethanol production benefits from yeast thermotolerance. Salt stress could induce obvious cross-protection against heat stress of Pichia kudriavzevii, contributing to the improvement of its thermotolerance and bioethanol fermentation. However, the underlying mechanisms of the cross-protection remain poorly understood. Results Salt stress showed obvious cross-protection for thermotolerance and high-temperature ethanol production of P. kudriavzevii observed by biomass, cell morphology and bioethanol production capacity. The biomass and ethanol production of P. kudriavzevii at 45 °C were, respectively, improved by 2.6 and 3.9 times by 300 mmol/L NaCl. Metabolic network map showed that salt stress obviously improved the key enzymes and intermediates in carbohydrate metabolism, contributing to the synthesis of bioethanol, ATP, amino acids, nucleotides, and unsaturated fatty acids, as well as subsequent intracellular metabolisms. The increasing trehalose, glycerol, HSPs, and ergosterol helped maintain the normal function of cell components. Heat stress induced serious oxidative stress that the ROS-positive cell rate and dead cell rate, respectively, rose from 0.5% and 2.4% to 28.2% and 69.2%, with the incubation temperature increasing from 30 to 45 °C. The heat-induced ROS outburst, oxidative damage, and cell death were obviously inhibited by salt stress, especially the dead cell rate which fell to only 20.3% at 300 mmol/L NaCl. The inhibiting oxidative damage mainly resulted from the abundant synthesis of GSH and GST, which, respectively, increased by 4.8 and 76.1 times after addition of 300 mmol/L NaCl. The improved bioethanol production was not only due to the improved thermotolerance, but resulted from the up-regulated alcohol dehydrogenases and down-regulated aldehyde dehydrogenases by salt stress. Conclusion The results provide a first insight into the mechanisms of the improved thermotolerance and high-temperature bioethanol production of P. kudriavzevii by salt stress, and provide important information to construct genetic engineering yeasts for high-temperature bioethanol production. Graphical Abstract

Molecular and Physiological Diversity of Indigenous Yeasts Isolated from Spontaneously Fermented Wine Wort from Ilfov County, Romania

“…The members of the P. kudriavzevii species present as the main mechanism of resistance to thermal stress, the accumulation of trehalose and glycerol. In fact, their ability to tolerate temperatures higher than 37 °C recommends them for a series of industrial processes aimed at obtaining valuable compounds for the food and cosmetic industries, as well as for biomedical applications [ 53 , 54 ].…”

Nakazawaea atacamensis f.a., sp. nov. a novel nonconventional fermentative ascomycetous yeast species from the Atacama Desert

“…Notably, N. atacamensis exhibited an increased number of genes associated with oxidative phosphorylation and the TCA cycle, likely suggesting that this yeast may rely on the electron transport chain for ATP production and energy generation via cellular respiration. These differences may correlate with the hyperarid conditions where N. atacamensis is present, where high salt concentrations may increase gene expression in TCA cycle genes due to an increase ATP demand (Lahtvee et al, 2016; Li et al, 2021). Conversely, N. peltata displayed a higher number of genes involved in sulfur metabolism, suggesting an augmented capacity for sulfur assimilation, utilization, and regulation when compared to N. atacamensis .…”

“…Branch lengths denote amino acid substitutions per site. correlate with the hyperarid conditions where N. atacamensis is present, where high salt concentrations may increase gene expression in TCA cycle genes due to an increase ATP demand (Lahtvee et al, 2016;Li et al, 2021). Conversely, N. peltata displayed a higher number of genes involved in sulfur metabolism, suggesting an augmented capacity for sulfur assimilation, utilization, and regulation when compared to N. atacamensis.…”

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