Effects of various inhibitory substances and immobilization on ethanol production efficiency of a thermotolerant Pichia kudriavzevii

Abstract

Background Although 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. Results Here, 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. Conclusion The 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.

Whole genome sequencing and metabolomics analyses reveal the biosynthesis of nerol in a multi-stress-tolerant Meyerozyma guilliermondii GXDK6

“…In addition, when the incubation temperature increased to 50 ℃, GXDK6 stopped to reproduce. A similar result was reported by Ndubuisi et al [ 19 ], who found that the growth of heat-resistant Pichia was significantly inhibited by increasing temperature, and the ethanol production efficiency of Pichia was lowered.…”

Whole genome sequencing and metabolomics analyses reveal the biosynthesis of nerol in a multi-stress-tolerant Meyerozyma guilliermondii GXDK6

“…In addition, when the incubation temperature was increased to 50 ℃, GXDK6 stopped to reproduce. A similar result was reported by Ndubuisi et al [14], who found that the growth of heat-resistant Pichia is signi cantly inhibited by increasing the temperature, and the ethanol production e ciency of Pichia is lowered.…”

Ethanol Production from Wheat Straw Hydrolysate by Issatchenkia Orientalis Isolated from Waste Cooking Oil

“…As demonstrated in Figure 3, a complete inhibition of growth was observed at 50 mM and higher. Likewise growth of I. orientalis LC375240, another thermotolerant strain isolated by Ndubuisi et al, was inhibited by 30 mM formic acid [46], whereas the strain isolated by Dandi et al, was completely blocked at 2 g L −1 (44 mM) [49]. Moreover, LC375240 tolerated up to 20 mM furfural, whereas the growth of I. orientalis KJ27-7 was clearly inhibited by 10 mM furfural.…”

“…I. orientalis KJ27-7 grew almost unhampered in 10% ethanol, and a distinct growth inhibition was observed only at 15% ethanol (Figure 3). While some thermotolerant I. orientalis strains exhibited a very similar ethanol tolerance profile [46,51], others show a clear growth limitation in the presence of 10% [52] or even 8% ethanol [7].…”

“…Hydrolysates derived from steam exploded lignocellulosic material such as wheat straw contain several substances that are generally considered as inhibitors of microbial growth and fermentation, among them acetic acid, formic acid, HMF and furfural [45]. It has been described that I. orientalis can be fairly tolerant to many of these classical inhibitory substances [7,46]. To evaluate I. orientalis KJ27-7′s capability to tolerate the inhibitory substances, which are typically present in steam explosion-derived lignocellulosic hydrolysates, a spot drop test was performed.…”