Table 1 Adaptive laboratory evolution of S. passalidarum and other techniques to improve furfural tolerance in S. passalidarum

S. passalidarum NRRL Y-27907= (ATCC MYA-4345, CBS 10155), which is mesophile yeast (T_max =40 °C) that presents glucose repression and cannot assimilate L-arabinose [7, 37].

1. Improved co-assimilation of glucose and xylose

Spc3

UV mutagenesis and ALE (2-DOG)

Spc3 showed a slight improvement in glucose and xylose co-fermentation compared to WT, however, the consumption rate of both sugars was slower than WT.

[30]

X2, X5

Genome shuffling between S. cerevisiae and S. passalidarum and ALE (YP medium containing 20 g/l xylose at 40 °C)

Under mixed sugars of glucose-xylose condition at 40 °C, X2 and X5 could utilize glucose and xylose faster than WT. Both adapted strains produced ethanol 1.5-fold higher than WT.

[31]

E7

ALE (wood hydrolysate under O₂-limiting conditions)

Fermentation ability of E7 in both MHH and SM media was performed. Adapted strain could co-metabolize glucose and xylose at similar rates in both media, however xylose utilization was delayed. Ethanol production in MHH required 21 h longer than that in SM. Ethanol production in MHH was 39 g/l with a yield of 0.34 g/g, which was slightly lower than that in SM (did not compare with WT).

[32]

AF2

ALE (wood hydrolysate and AFEX corn stover hydrolysate under O₂-limiting conditions)

Fermentation of AF2 in an AFEX hydrolysate took a long time. Xylose was largely delayed. It was utilized after glucose was nearly finished. Ethanol production was rich to the highest level of 23 g/l with a yield of 0.45 at 7 days (did not compare with WT).

2. Increased hydrolysate inhibitors tolerance

A5

ALE (sugarcane hydrolysate)

Adapted strain, A5 was capable of fermenting hydrolysate efficiently, reaching ethanol yield and productivity of 0.404 g/g and 0.357 g/l/h, respectively, while the WT was not able to ferment.

[33]

mutA4

UV mutagenesis and ALE (acetic acid and Eucalyptus globulus auto-hydrolysate)

Adapted strain, mutA4 was tolerant to acetic acid. In presence of 4.5 g/l acetic acid, it produced ethanol volumetric productivity and ethanol yield of 7-fold (0.23 g/l/h) and 2-fold (0.48 g/g) higher than WT, respectively. When Eucalyptus globulus auto-hydrolysate was used as a culture medium, mutA4 resisted inhibitors usually found in this hydrolysate and was able to co-ferment glucose, xylose and cellobiose under microaerobic condition without lag phase.

[34]

FS22

(hybrid strain)

UV mutagenesis (furfural) and protoplast fusion

Hybrid strain, FS22 was able to grow and produce ethanol at a yield of 0.4 g/g in 75% liquid fraction of pretreated wheat straw (WSLQ) medium with addition of 30 g/l xylose.

[14]

3. Increased fermentation ability

E11

Cell recycling, cell mating and high-throughput screening and ALE (various types of hydrolysates)

Adapted strain, E11 showed a 3-fold increase in specific fermentation rate compared to WT and an ethanol yield greater than 0.45 g/g substrate while co-utilizing cellobiose, glucose and xylose.

[35]

S. passalidarum CMUWF1−2, which is thermotolerant yeast (T_max = 42 °C that presents no glucose repression and can assimilate L-arabinose [6].

Improved furfural tolerance

AF2.5

ALE (furfural)

Adapted strain, AF2.5 showed improvement of furfural tolerance together with ethanol and HMF tolerances compared with WT, while maintaining the ability of simultaneous utilization of glucose and other sugars.

This study