Mitophagy Improves Ethanol Tolerance in Yeast: Regulation by Mitochondrial Reactive Oxygen Species in Saccharomyces cerevisiae

Abstract

Ethanol often accumulates during the process of wine fermentation, and mitophagy has critical role in ethanol output. However, the relationship between mitophagy and ethanol stress is still unclear. In this study, the expression of ATG11 and ATG32 genes exposed to ethanol stress was accessed by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). The result indicated that ethanol stress induced expression of the ATG11 and ATG32 genes. The colony sizes and the alcohol yield of atg11 and atg32 were also smaller and lower than those of wild type strain under ethanol whereas the mortality of mutants is higher. Furthermore, compared with wild type, the membrane integrity and the mitochondrial membrane potential of atg11 and atg32 exhibited greater damage following ethanol stress. In addition, a greater proportion of mutant cells were arrested at the G1/G0 cell cycle. There was more aggregation of peroxide hydrogen (H 2 O 2 ) and superoxide anion (O 2 •- ) in mutants. These changes in H 2 O 2 and O 2 •- in yeasts were altered by reductants or inhibitors of scavenging enzyme by means of regulating the expression of ATG11 and ATG32 genes. Inhibitors of the mitochondrial electron transport chain (mtETC) also increased production of H 2 O 2 and O 2 •- by enhancing expression of the ATG11 and ATG32 genes. Further results showed that activator or inhibitor of autophagy also activated or inhibited mitophagy by altering production of H 2 O 2 and O 2 • . Therefore, ethanol stress induces mitophagy which improves yeast the tolerance to ethanol and the level of mitophagy during ethanol stress is regulated by ROS derived from mtETC.

Blocking mitophagy does not improve fuel ethanol production in Saccharomyces cerevisiae

“…A combination of the absence of these internal building blocks and the concomitant excess of the external carbon and energy source – the sugar in the cultivation medium – would channel more of this carbon towards the fermentative pathway (36). In a different work, Jing and co-workers (35) report that deletion of ATG32 not only decreased tolerance to ethanol stress in haploid BY 4742, but also led to a lower ethanol titre (7.25 %v/v) compared to the WT (7.5 %v/v) in standard YPD medium, which is nutrient rich. For their ethanol measurement, they relied on densitometry, just like Shiroma and co-workers, but this study used an enzymatic assay (16, 35).…”

“…In a different work, Jing and co-workers (35) report that deletion of ATG32 not only decreased tolerance to ethanol stress in haploid BY 4742, but also led to a lower ethanol titre (7.25 %v/v) compared to the WT (7.5 %v/v) in standard YPD medium, which is nutrient rich. For their ethanol measurement, they relied on densitometry, just like Shiroma and co-workers, but this study used an enzymatic assay (16, 35). The improvement (or the decrease) reported in these studies are quite marginal (0.2% v/v), and it beckons us to question whether the accuracy of the measurement is reliable to claim physiological significance.…”

“…However, these authors did not observe higher ethanol yields or specific production rates in the atg32 mutant, with respect to the values displayed by the parental strain, although deletion of ATG32 significantly increased the maximum specific growth rate. It should be noted that these experiments were performed using a commercial synthetic yeast medium with 20 g/L initial glucose, meaning that nutrient limitation is much less prone to occur, when compared to the use of the same medium base, but with 150 g/L initial glucose, as performed by Shiroma et al (16, 35,36).…”

“…For their ethanol measurement, they relied on densitometry, just like Shiroma and coworkers, but this study used an enzymatic assay (16,35). The improvement (or the decrease)…”

Protective Effects of Melatonin on Saccharomyces cerevisiae under Ethanol Stress

“…•− ) [12][13][14][15], which can induce lipid peroxidation, DNA damage, and oxidative stress [12,16,17]. Therefore, upon ethanol stress, the response to oxidative stress is activated.…”