Abstract
BackgroundAlthough bioethanol production has been gaining worldwide attention as an alternative to fossil fuel, ethanol productivities and yields are still limited due to the susceptibility of fermentation microorganisms to various stress and inhibitory substances. There is therefore an unmet need to search for multi-stress-tolerant organisms to improve ethanol productivity and reduce production cost, particularly when lignocellulosic hydrolysates are used as the feedstock.ResultsHere, we have characterized a previously isolated Pichia kudriavzevii LC375240 strain which is thermotolerant to high temperatures of 37 °C and 42 °C. More excitingly, growth and ethanol productivity of this strain exhibit strong tolerance to multiple stresses such as acetic acid, furfural, formic acid, H2O2 and high concentration of ethanol at 42 °C. In addition, simple immobilization of LC375240 on corncobs resulted to a more stable and higher efficient ethanol production for successive four cycles of repeated batch fermentation at 42 °C.ConclusionThe feature of being thermotolerant and multi-stress-tolerant is unique to P. kudriavzevii LC375240 and makes it a good candidate for second-generation bioethanol fermentation as well as for investigating the molecular basis underlying the robust stress tolerance. Immobilization of P. kudriavzevii LC375240 on corncobs is another option for cheap and high ethanol productivity.
Highlights
Bioethanol production has been gaining worldwide attention as an alternative to fossil fuel, ethanol productivities and yields are still limited due to the susceptibility of fermentation microorganisms to various stress and inhibitory substances
The drawback is the different temperature requirement between saccharification and fermentation, as high temperature is usually required for the hydrolysis step, whereas most fermentation organisms are inhibited at high temperatures
When fermentation was prolonged to 72 h the ethanol concentration produced from 160 g/l and 200 g/l glucose decreased (Fig. 1c), probably due to ethanol consumption by the yeast cells when glucose was depleted at the late stage
Summary
Bioethanol production has been gaining worldwide attention as an alternative to fossil fuel, ethanol productivities and yields are still limited due to the susceptibility of fermentation microorganisms to various stress and inhibitory substances. There is an unmet need to search for multi-stress-tolerant organisms to improve ethanol productivity and reduce production cost, when lignocellulosic hydrolysates are used as the feedstock. Simultaneous saccharification and fermentation (SSF) is usually preferred for bioethanol production based on the advantages of combining enzymatic hydrolysis and fermentation in a single fermenter, simpler operation, less cost and shorter completion time. Using thermotolerant microorganisms for ethanol production provides solution to this limitation and a great strategy for reducing the cooling and sterilization cost, as well as lower the risk of bacterial contamination during SSF
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