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A new search for thermotolerant yeasts, its characterization and optimization using response surface methodology for ethanol production.

Arora R, Behera S, Sharma NK, Kumar S - Front Microbiol (2015)

Bottom Line: After optimization using Face-centered Central Composite Design (FCCD), the growth parameters like temperature and pH were found to be 45.17°C and 5.49, respectively for K. marxianus NIRE-K1 and 45.41°C and 5.24, respectively for K. marxianus NIRE-K3.Further, batch fermentations were carried out under optimized conditions, where K. marxianus NIRE-K3 was found to be superior over K. marxianus NIRE-K1.Ethanol yield (Y x∕s ), sugar to ethanol conversion rate (%), microbial biomass concentration (X) and volumetric product productivity (Q p ) obtained by K. marxianus NIRE-K3 were found to be 9.3, 9.55, 14.63, and 31.94% higher than that of K. marxianus NIRE-K1, respectively.

View Article: PubMed Central - PubMed

Affiliation: Biochemical Conversion Division, Sardar Swaran Singh National Institute of Bio-Energy Kapurthala, India ; I.K Gujral Punjab Technical University Kapurthala, India.

ABSTRACT
The progressive rise in energy crisis followed by green house gas (GHG) emissions is serving as the driving force for bioethanol production from renewable resources. Current bioethanol research focuses on lignocellulosic feedstocks as these are abundantly available, renewable, sustainable and exhibit no competition between the crops for food and fuel. However, the technologies in use have some drawbacks including incapability of pentose fermentation, reduced tolerance to products formed, costly processes, etc. Therefore, the present study was carried out with the objective of isolating hexose and pentose fermenting thermophilic/thermotolerant ethanologens with acceptable product yield. Two thermotolerant isolates, NIRE-K1 and NIRE-K3 were screened for fermenting both glucose and xylose and identified as Kluyveromyces marxianus NIRE-K1 and K. marxianus NIRE-K3. After optimization using Face-centered Central Composite Design (FCCD), the growth parameters like temperature and pH were found to be 45.17°C and 5.49, respectively for K. marxianus NIRE-K1 and 45.41°C and 5.24, respectively for K. marxianus NIRE-K3. Further, batch fermentations were carried out under optimized conditions, where K. marxianus NIRE-K3 was found to be superior over K. marxianus NIRE-K1. Ethanol yield (Y x∕s ), sugar to ethanol conversion rate (%), microbial biomass concentration (X) and volumetric product productivity (Q p ) obtained by K. marxianus NIRE-K3 were found to be 9.3, 9.55, 14.63, and 31.94% higher than that of K. marxianus NIRE-K1, respectively. This study revealed the promising potential of both the screened thermotolerant isolates for bioethanol production.

No MeSH data available.


Growth of K. marxianus NIRE-K1 and NIRE-K3 in YEPD medium, (---) K. marxianus NIRE-K1; (—) K. marxianus NIRE-K3; (■) Glucose; (▴) Dry cell weight (DCW); (•) Ethanol.
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Figure 1: Growth of K. marxianus NIRE-K1 and NIRE-K3 in YEPD medium, (---) K. marxianus NIRE-K1; (—) K. marxianus NIRE-K3; (■) Glucose; (▴) Dry cell weight (DCW); (•) Ethanol.

Mentions: Aerobic batch fermentations were carried out using both the yeast strains of K. marxianus NIRE-K1 and NIRE-K3 on YEP medium containing 2% glucose and xylose solely and further mixture of both in equal ratio at 45°C. Both the strains of K. marxianus NIRE-K1 and NIRE-K3 could produce maximum ethanol concentration with ethanol yield of 0.31 ± 0.023 and 0.36 ± 0.022 g g−1, respectively in YEPD medium with complete utilization of glucose (20 g l−1) in 16 h (Figure 1). However, both the strains could utilize xylose for the production of ethanol with concomitant xylitol production. In case of xylose containing YEPX media using cells of K. marxianus NIRE-K1, maximum ethanol and xylitol concentration of 0.3 ± 0.01 and 4.34 ± 0.03 g l−1 were obtained in 24 h of duration through the utilization of 13.18 ± 0.029 g l−1 xylose sugar (Figure 2). Similarly with the same duration of fermentation, K. marxianus NIRE-K3 could be able to utilize 11.18 ± 0.04 g l−1 of xylose for the production of 0.88 ± 0.01 and 0.80 ± 0.01 g l−1 of ethanol and xylitol, respectively (Figure 2). In other hand, both the strains of K. marxianus NIRE-K1 and NIRE-K3 was capable of simultaneously using mixture of glucose and xylose in YEPDX medium, achieving maximum ethanol concentration of 3.4 ± 0.051 and 3.5 ± 0.057 g l−1, respectively in 24 h of fermentation. Both the strains could be able to completely utilize glucose, while 6.63 ± 0.1 and 4.39 ± 0.01 g l−1 of residual xylose was left in case of K. marxianus NIRE-K1 and NIRE-K3, respectively (Figure 3).


A new search for thermotolerant yeasts, its characterization and optimization using response surface methodology for ethanol production.

Arora R, Behera S, Sharma NK, Kumar S - Front Microbiol (2015)

Growth of K. marxianus NIRE-K1 and NIRE-K3 in YEPD medium, (---) K. marxianus NIRE-K1; (—) K. marxianus NIRE-K3; (■) Glucose; (▴) Dry cell weight (DCW); (•) Ethanol.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4555967&req=5

Figure 1: Growth of K. marxianus NIRE-K1 and NIRE-K3 in YEPD medium, (---) K. marxianus NIRE-K1; (—) K. marxianus NIRE-K3; (■) Glucose; (▴) Dry cell weight (DCW); (•) Ethanol.
Mentions: Aerobic batch fermentations were carried out using both the yeast strains of K. marxianus NIRE-K1 and NIRE-K3 on YEP medium containing 2% glucose and xylose solely and further mixture of both in equal ratio at 45°C. Both the strains of K. marxianus NIRE-K1 and NIRE-K3 could produce maximum ethanol concentration with ethanol yield of 0.31 ± 0.023 and 0.36 ± 0.022 g g−1, respectively in YEPD medium with complete utilization of glucose (20 g l−1) in 16 h (Figure 1). However, both the strains could utilize xylose for the production of ethanol with concomitant xylitol production. In case of xylose containing YEPX media using cells of K. marxianus NIRE-K1, maximum ethanol and xylitol concentration of 0.3 ± 0.01 and 4.34 ± 0.03 g l−1 were obtained in 24 h of duration through the utilization of 13.18 ± 0.029 g l−1 xylose sugar (Figure 2). Similarly with the same duration of fermentation, K. marxianus NIRE-K3 could be able to utilize 11.18 ± 0.04 g l−1 of xylose for the production of 0.88 ± 0.01 and 0.80 ± 0.01 g l−1 of ethanol and xylitol, respectively (Figure 2). In other hand, both the strains of K. marxianus NIRE-K1 and NIRE-K3 was capable of simultaneously using mixture of glucose and xylose in YEPDX medium, achieving maximum ethanol concentration of 3.4 ± 0.051 and 3.5 ± 0.057 g l−1, respectively in 24 h of fermentation. Both the strains could be able to completely utilize glucose, while 6.63 ± 0.1 and 4.39 ± 0.01 g l−1 of residual xylose was left in case of K. marxianus NIRE-K1 and NIRE-K3, respectively (Figure 3).

Bottom Line: After optimization using Face-centered Central Composite Design (FCCD), the growth parameters like temperature and pH were found to be 45.17°C and 5.49, respectively for K. marxianus NIRE-K1 and 45.41°C and 5.24, respectively for K. marxianus NIRE-K3.Further, batch fermentations were carried out under optimized conditions, where K. marxianus NIRE-K3 was found to be superior over K. marxianus NIRE-K1.Ethanol yield (Y x∕s ), sugar to ethanol conversion rate (%), microbial biomass concentration (X) and volumetric product productivity (Q p ) obtained by K. marxianus NIRE-K3 were found to be 9.3, 9.55, 14.63, and 31.94% higher than that of K. marxianus NIRE-K1, respectively.

View Article: PubMed Central - PubMed

Affiliation: Biochemical Conversion Division, Sardar Swaran Singh National Institute of Bio-Energy Kapurthala, India ; I.K Gujral Punjab Technical University Kapurthala, India.

ABSTRACT
The progressive rise in energy crisis followed by green house gas (GHG) emissions is serving as the driving force for bioethanol production from renewable resources. Current bioethanol research focuses on lignocellulosic feedstocks as these are abundantly available, renewable, sustainable and exhibit no competition between the crops for food and fuel. However, the technologies in use have some drawbacks including incapability of pentose fermentation, reduced tolerance to products formed, costly processes, etc. Therefore, the present study was carried out with the objective of isolating hexose and pentose fermenting thermophilic/thermotolerant ethanologens with acceptable product yield. Two thermotolerant isolates, NIRE-K1 and NIRE-K3 were screened for fermenting both glucose and xylose and identified as Kluyveromyces marxianus NIRE-K1 and K. marxianus NIRE-K3. After optimization using Face-centered Central Composite Design (FCCD), the growth parameters like temperature and pH were found to be 45.17°C and 5.49, respectively for K. marxianus NIRE-K1 and 45.41°C and 5.24, respectively for K. marxianus NIRE-K3. Further, batch fermentations were carried out under optimized conditions, where K. marxianus NIRE-K3 was found to be superior over K. marxianus NIRE-K1. Ethanol yield (Y x∕s ), sugar to ethanol conversion rate (%), microbial biomass concentration (X) and volumetric product productivity (Q p ) obtained by K. marxianus NIRE-K3 were found to be 9.3, 9.55, 14.63, and 31.94% higher than that of K. marxianus NIRE-K1, respectively. This study revealed the promising potential of both the screened thermotolerant isolates for bioethanol production.

No MeSH data available.