Heat Adaptation Induced Cross Protection Against Ethanol Stress in Tetragenococcus halophilus: Physiological Characteristics and Proteomic Analysis

Abstract

Ethanol is a toxic factor that damages membranes, disturbs metabolism, and may kill the cell. Tetragenococcus halophilus, considered as the cell factory during the manufacture of traditional fermented foods, encounters ethanol stress, which may affect the viability and fermentative performance of cells. In order to improve the ethanol tolerance of T. halophilus, a strategy based on cross protection was proposed in the current study. The results indicated that cross protection induced by heat preadaptation (45°C for 1.5 h) could significantly improve the stress tolerance (7.24-fold increase in survival) of T. halophilus upon exposure to ethanol (10% for 2.5 h). Based on this result, a combined analysis of physiological approaches and TMT-labeled proteomic technology was employed to investigate the protective mechanism of cross protection in T. halophilus. Physiological analysis showed that the heat preadapted cells exhibited a better surface phenotype, higher membrane integrity, and higher amounts of unsaturated fatty acids compared to unadapted cells. Proteomic analysis showed that a total of 163 proteins were differentially expressed in response to heat preadaptation. KEGG enrichment analysis showed that energy metabolism, membrane transport, peptidoglycan biosynthesis, and genetic information processing were the most abundant metabolic pathways after heat preadaptation. Three proteins (GpmA, AtpB, and TpiA) involved in energy metabolism and four proteins (ManM, OpuC, YidC, and HPr) related to membrane transport were up-regulated after heat preadaptation. In all, the results of this study may help understand the protective mechanisms of preadaptation and contribute to the improvement of the stress resistance of T. halophilus during industrial processes.

Microbial Adaptation to Enhance Stress Tolerance

“…In prokaryotes, Tetragenococcus halophilus underwent short-term acclimation at 45°C for 1.5 h. Not only did the adaptability to high temperature improve, but its ability to resist osmotic stress also increased. When T. halophilus was transferred to a 10% ethanol environment and cultivated for 2.5 h, its survival rate increased by sevenfold ( Yang et al, 2021 ). Similarly, short-term adaptation of the eukaryotic microorganism Rhodotorula mucilaginosa at 40°C for 30 min not only increased high temperature tolerance, but also enhanced tolerance to H 2 O 2 , NaCl and high heat stress, and the survival rate of their cells increased about 1.2-fold ( Cheng et al, 2016 ).…”

“…The cause of microbial cross-tolerance may also be the common stimulation targets or the same ability to excrete harmful substances under different stress environments. T. halophilus strains subjected to high temperature stress not only improved their temperature tolerance but also ethanol tolerance ( Yang et al, 2021 ). Ethanol is a toxicity factor that disrupts cell metabolism and damages the cell plasma membrane ( Wijesundara and Rupasinghe, 2019 ).…”

“…However, microorganisms can use membrane transport and take up extracellular organic compounds to improve stress tolerance under different stress conditions ( Tang et al, 2014 ; Huang et al, 2016 ). Analysis revealed that the membrane protein insertion enzyme YidC of T. halophilus strains was significantly up-regulated after high temperature acclimation, which may be beneficial to the absorption of extracellular nutrients ( Yang et al, 2021 ). Therefore, high temperature may enhance the performance of T. halophilus cytoplasmic membrane, thereby increasing resistance to ethanol.…”

Application of pre-adaptation strategies to improve the growth of probiotic lactobacilli under food-relevant stressful conditions

“…[15][16][17] Moreover, bacterial strains can develop cross-tolerance, which means that cells preadapted under mild stress conditions increased their tolerance towards diverse harsher conditions such as high temperatures, acidity, as well as oxygen presence. [18][19][20][21][22] The improvement of viability after pre-adaptation has been demonstrated also in foods, e.g., yogurt and skimmed milk. 23,24 The bacterial response to sublethal stress is strictly related to the microbial strain and to the growth limits for each parameter (sublethal level).…”

“…15–17 Moreover, bacterial strains can develop cross-tolerance, which means that cells preadapted under mild stress conditions increased their tolerance towards diverse harsher conditions such as high temperatures, acidity, as well as oxygen presence. 18–22…”