A shift to 50°C provokes death in distinct ways for glucose- and oleate-grown cells of Yarrowia lipolytica

Abstract

Based on the observation that shocks provoked by heat or amphiphilic compounds present some similarities, this work aims at studying whether cells grown on oleate (amphiphilic pre-stress) acquire a tolerance to heat shock. In rich media, changing glucose for oleate significantly enhanced the cell resistance to the shock, however, cells grown on a minimal oleate medium lost their ability to grow on agar with the same kinetic than glucose-grown cells (more than 7-log decrease in 18 min compared with 3-log for oleate-grown cells). Despite this difference in kinetics, the sequence of events was similar for oleate-grown cells maintained at 50°C with a (1) loss of ability to form colonies at 27°C, (2) loss of membrane integrity and (3) lysis (observed only for some minimal-oleate-grown cells). Glucose-grown cells underwent different changes. Their membranes, which were less fluid, lost their integrity as well and cells were rapidly inactivated. But, surprisingly, their nuclear DNA was not stained by propidium iodide and other cationic fluorescent DNA-specific probes but became stainable by hydrophobic ones. Moreover, they underwent a dramatic increase in membrane viscosity. The evolution of lipid bodies during the heat shock depended also on the growth medium. In glucose-grown cells, they seemed to coalesce with the nuclear membrane whereas for oleate-grown cells, they coalesced together forming big droplets which could be released in the medium. In some rare cases of oleate-grown cells, lipid bodies were fragmented and occupied all the cell volume. These results show that heat triggers programmed cell death with uncommon hallmarks for glucose-grown cells and necrosis for methyl-oleate-grown cells.

Production of Dicarboxylic Acids and Flagrances by Yarrowia lipolytica

“…Although some authors have noted a toxicity of oleic acid on yeast cells Lockshon et al 2007) and many processes of production of lactones propose the utilisation of esterified forms of the substrates (methyl ricinoleate or castor oil), it seems that these sources are rapidly hydrolysed by Y. lipolytica's lipases, but the toxicity of these acids is not obvious. However, methyl oleate when added to the culture medium increases rapidly the membrane fluidity (Ta et al 2012). This increase is due to the immediate incorporation of oleate moieties into the membrane, but, as a response to this stress, the sterol homeostasis is modified, resulting in a higher concentration of ergosterol.…”

Tropical traditional fermented food, a field full of promise. Examples from the Tropical Bioresources and Biotechnology programme and other related French–Vietnamese programmes on fermented food

“…Beside biocatalytic properties, cells properties of interest include a better tolerance to unfavourable media such as the presence of toxic amphiphilic compounds, which can depend on the membrane physiology (Ta et al, 2010(Ta et al, , 2012 and the ability of microbes to locate in the right place (next to their substrate and away from toxical compounds in heterogeneous media) (Ly et al, 2007(Ly et al, , 2008aLy-Chatain et al, 2010), which depends on the highly diverse and adaptable surface properties (Wach e et al, 2000;Aguedo et al, 2003;Ly et al, 2006a,b).…”