High Osmolarity Environments Activate the Mitochondrial Alternative Oxidase in Debaryomyces Hansenii

Abstract

The oleaginous yeast Debaryomyces hansenii is a good model to understand molecular mechanisms involved in halotolerance because of its impressive ability to survive under a wide range of salt concentrations. Several cellular adaptations are implicated in this response, including the presence of a cyanide-insensitive ubiquinol oxidase (Aox). This protein, which is present in several taxonomical orders, has been related to different stress responses. However, little is known about its role in mitochondria during transitions from low to high saline environments. In this report, we analyze the effects of Aox in shifts from low to high salt concentrations in the culture media. At early stages of a salt insult, we observed that this protein prevents the overflow of electrons on the mitochondrial respiratory chain, thus, decreasing the production of reactive oxygen species. Interestingly, in the presence of high osmolite concentrations, Aox activity is able to sustain a stable membrane potential when coupled to complex I, despite a compromised cytochrome pathway. Taken together, our results suggest that under high osmolarity conditions Aox plays a critical role regulating mitochondrial physiology.

Fine-tuning mitochondrial activity in Yarrowia lipolytica for citrate overproduction

“…This is in good agreement with the proposed association/dissociation mechanism of NADH2e/CIV channeling electron from the external NADH to cytochrome pathway or towards the alternative oxidase 35 . In agreement with the literature we propose AOX activity as a protective mechanism against mitochondrial ROS production in Y. lipolytica and some other yeasts and plants species 51 , 54 . Indeed, OxPhos is considered as the main ROS producer, specially through CI and CIII 54 .…”

“…Another way to confirm these predictions would have been to add salicylhydroxamic acid (SHAM), another well-known and used inhibitor of AOX 51 . The dFBA model of Y. lipolytica also was also used to predict the effect of adding various Krebs intermediates such as α-ketoglutarate, malate and oxaloacetate for citrate optimization.…”

A Physiological Characterization in Controlled Bioreactors Reveals a Novel Survival Strategy forDebaryomyces hanseniiat High Salinity and Confirms its Halophilic Behavior

“…Although it worths mentioning that this previous work (Calahorra et al 2009) was performed using a different D. hansenii strain in other culture conditions, and their measurements correspond to ethanol production using enzyme extracts from previously cultured cells, a follow up study performed by García-Neto et al (2017) contradicted such observation using the same strain. Our observations align well with the latter study, confirming that no ethanol production is occurring in our strain either, thus further proving that D. hansenii is crabtree negative.…”

A physiological characterization in controlled bioreactors reveals a novel survival strategy for Debaryomyces hansenii at high salinity

“…To date, nobody has conducted an in-depth physiological analysis of this yeast in a controlled environment (e.g., using bioreactors), and there is a lack of consensus about its capacity to produce ethanol in high saline environments or its cell performance in the presence of high salt concentrations. While some studies point to a beneficial role of salts on D. hansenii's performance (Almagro et al, 2000;García-Neto, Cabrera-Orefice, Uribe-Carvajal, Kowaltowski, & Luévano-Martínez, 2017;Navarrete et al, 2009;Papouskova & Sychrova, 2007), others claim that sodium is detrimental in terms for the fitness of this yeast in general (Capusoni et al, 2019;Sánchez, Calahorra, Ramírez, & Peña, 2018).…”