Isolation and characterization of thermotolerant yeasts for the production of second-generation bioethanol

Abstract

The purpose of this study was to isolate, identify, and characterize the thermotolerant yeasts for use in high-temperature ethanol fermentation. Thermotolerant yeasts were isolated and screened from soil samples collected from the Mekong Delta, Vietnam, using the enrichment method. Classification and identification of the selected thermotolerant yeasts were performed using matrixassisted laser desorption ionization/time-of-fight mass spectrometry (MALDI-TOF/MS) and nucleotide sequencing of the D1/D2 domain of the 26S rDNA and the internal transcribed spacer (ITS) 1 and 2 regions. The ethanol production by the selected thermotolerant yeast was carried out using pineapple waste hydrolysate (PWH) as feedstock. A total of 174 yeast isolates were obtained from 80 soil samples collected from 13 provinces in the Mekong Delta, Vietnam. Using MALDI-TOF/MS and nucleotide sequencing of the D1/D2 domain and the ITS 1 and 2 regions, six different yeast species were identified, including Meyerozyma caribbica, Saccharomyces cerevisiae, Candida tropicalis, Torulaspora globosa, Pichia manshurica, and Pichia kudriavzevii. Among the isolated thermotolerant yeasts, P. kudriavzevii CM4.2 displayed great potential for high-temperature ethanol fermentation. The maximum ethanol concentration (36.91 g/L) and volumetric ethanol productivity (4.10 g/L h) produced at 45°C by P. kudriavzevii CM4.2 were achieved using PWH containing 103.08 g/L of total sugars as a feedstock. These findings clearly demonstrate that the newly isolated thermotolerant yeast P. kudriavzevii CM4.2 has a high potential for secondgeneration bioethanol production at high temperature.

Identification and Growth Characterization of a Novel Strain of Saccharomyces boulardii Isolated From Soya Paste

“…In the current study, some technological and in vitro probiotic properties of the selected strain were investigated according to the suggestion of FAO/WHO (14,25). As shown in Figure 2A, the isolated yeast strains have a strong ability to tolerate high temperatures and S. boulardii is viable at 45 • C, which agrees with the previous reports (35). Bile resistance is an important criterion in the selection of culture as a dietary adjunct because it could allow the growth of the ingested probiotic microorganism in the intestinal tract (6,7).…”

“…To determine the thermal stability of the yeast strain, SDB (Sabouraud dextrose broth) medium (Difco, Thermo Fisher Scientific) was prepared and transferred to tubes in 5 ml. An inoculum of yeast strain was prepared in SDB medium by overnight incubation and 1% (v/v) fresh culture was added to each tube and incubated for 24, 48, and 72 h at 25, 30, 35, 37, 40, 45, and 50 • C. After incubation, the survival rate of the isolate was measured by taking absorbance at 660 nm by a spectrophotometer (Thermo Multiskan EX) (19,35).…”

“…The yeast isolate was tested for tolerance against different NaCl concentrations. The growth rate of yeast culture in the SDB medium containing different levels (1-7%) of NaCl was determined (35).…”

Functional Biodiversity of Yeasts Isolated from Colombian Fermented and Dry Cocoa Beans

“…Some earlier studies were addressed to the characterization of yeasts by identifying thermotolerant strains belonging to P. kudriavzevii and S. cerevisiae from fermented cocoa beans [ 28 , 33 ], and in industrial processes to improve the production of ethanol from sugar cane [ 46 , 47 , 48 ]. The thermotolerance of P. manshurica and C. parapsilosis isolated from fermented cocoa beans has never been reported before but a previous study found this characteristic in strains from soil samples collected from the Mekong Delta, in Vietnam [ 49 ], and from sugar cane from Brazil [ 48 ]. In addition, the thermotolerance of C. parapsilosis isolated from soil has been previously documented by El-Gamal et al, [ 50 ].…”

Optimization of ethanol production using newly isolated ethanologenic yeasts

“…The DNA was sequenced using NL1 (5′-GCATATCAATAAGCGGAGGAAAAG-3′) and NL4 (5′-GGTCCGTGTTTCAAGACGG-3′) as PCR primers for amplification of D1/D2 region of LSU rDNA [ 24 ]. PCR amplification was performed in 20 μL reaction, containing 10 μL of GoTaq® Green Master Mix (Promega), 10 pmol of each primer, and 2 μL of 1–20 ng/μL extracted DNA, on GeneAmp® PCR System 9700 (Applied Biosystems) or iCycler (BioLad).…”