Enrichment of a continuous culture of Saccharomyces cerevisiae with the yeast Issatchenkia orientalis in the production of ethanol at increasing temperatures

Abstract

A fermentation system was continuously fed with sugar-cane syrup and operated with recycling of Saccharomyces cerevisiae cells at temperatures varying from 30 to 47 °C. The aim of the present work was to obtain and study the colonies of isolates showing elongated cells of yeasts which were sporadically observed at the end of this continuous process. Based on a sequence of assays involving methods of classical taxonomy and RAPD-PCR, two groups of isolates showing characteristics of non-Saccharomyces yeasts were identified in the yeast population where S. cerevisiae was the dominant yeast. The largest group of non-Saccharomyces yeasts, resulting from a slow proliferation over the 2 months, reached a final level of 29.6% at the end of the process. RAPD-PCR profiles obtained for the isolates of this dominant non-Saccharomyces yeast indicated that they were isolates of Issatchenkia orientalis. Pichia membranifaciens was the only species of non-Saccharomyces yeast detected together with I. orientalis but at a very low frequency. The optimum temperature for ethanol formation shown by the isolate 195B of I. orientalis was 42 °C. This strain also showed a faster ethanol formation and biomass accumulation than the thermotolerant strain of S. cerevisiae used as the starter of this fermentation process. Some isolates of I. orientalis were also able to grow better at 40 °C than at 30 °C on plates containing glycerol as carbon source. Yeasts able to grow and produce ethanol at high temperatures can extend the fermentation process beyond the temperature limits tolerated by S. cerevisiae.

Ethanol production from alkali-treated rice straw via simultaneous saccharification and fermentation using newly isolated thermotolerant Pichia kudriavzevii HOP-1

“…Although the mechanism behind formation of pseudohyphae or their role in cell metabolism is not clear, it is thought that the pseudohyphae are formed during depletion of nutrients, especially the nitrogen source. Most of the morphological and physiological characteristics and the ability of the yeast cells used in the present study to assimilate specific sugars and nitrogen sources resembled the characteristics shown by the group-I non-Saccharomyces isolates belonging to I. orientalis reported previously [11]. They also identified a gene FLO11 that encodes a cell wall protein, which is critically required for both invasion and pseudohyphae formation in response to nitrogen starvation.…”

“…Gallardo et al [11] observed the pseudohyphae formation for non-Saccharomyces isolates after 3 days of growth. Although the mechanism behind formation of pseudohyphae or their role in cell metabolism is not clear, it is thought that the pseudohyphae are formed during depletion of nutrients, especially the nitrogen source.…”

Characterization of isolated yeast growth response to methionine analogs

“…It is possible that strains K1 and C1 produced sufficient ethanol at levels to be somewhat inhibitory and thus cause a decrease in biomass synthesis compared to previous studies. Gallardo et al [38] and Shin et al [39] detected ethanol during I. orientalis fermentation. Some yeast species produce ethanol even in aerobic cultures at sugar concentrations of more than approximately 0.04 g L −1 glucose.…”

“…[19,22,[38][39][40] Yeast biomass in this study was between 0.12 and 1.33 g L −1 (0.0001 to 0.0013%). It is possible that strains K1 and C1 produced sufficient ethanol at levels to be somewhat inhibitory and thus cause a decrease in biomass synthesis compared to previous studies.…”

Comparison study on copper bioaccumulation by growing Pichia kudriavzevii and Saccharomyces cerevisiae

“…The precultured P. kudriavzevii or S. cerevisiae was cultivated in YEPD liquid medium under various environmental stresses: high NaCl concentrations (10,20,40 and 60 g/L), low pH (pH 4, 3, 2 and 1), high Cu concentrations (0.5, 1, 3 and 4 mmol/L), high Zn concentrations (0.5, 1, 3 and 4 mmol/L) and high Cd concentrations (0.05, 0.1, 0.2 and 0.5 mmol/L). The initial biomass concentration was 0.1 g dry weight/L.…”