Aerobic Fermentation of D-Xylose to Ethanol by Clavispora sp

Xylose and yeasts: A story beyond xylitol production

Six different yeasts were used to study their metabolism of glucose and xylose, and mainly their capacity to produce ethanol and xylitol. The strains used were Candida guilliermondii, Debaryomyces hansenii, Saccharomyces cerevisiae, Kluyveromyces marxianus, Meyerozyma guilliermondii and Clavispora lusitaniae, four isolated from a rural mezcal fermentation facility. All of them produced ethanol when the substrate was glucose. When incubated in a medium containing xylose instead of glucose, only K. marxianus and M. guilliermondii were able to produce ethanol from xylose. On the other hand, all of them could produce some xylitol from xylose, but the most active in this regard were K. marxianus, M. guilliermondii, Candida lusitaniae, and C. guilliermondii with the highest amount of xylitol produced. The capacity of all strains to take up glucose and xylose was also studied. Xylose, in different degrees, produced a redox imbalance in all yeasts. Respiration capacity was also studied with glucose or xylose, where C. guilliermondii, D. hansenii, K. marxianus and M. guilliermondii showed higher cyanide resistant respiration when grown in xylose. Neither xylose transport nor xylitol production were enhanced by an acidic environment (pH 4), which can be interpreted as the absence of a proton/sugar symporter mechanism for xylose transport, except for C. lusitaniae. The effects produced by xylose and their magnitude depend on the background of the studied yeast and the conditions in which these are studied.

Using fermentation waste of ethanol-producing yeast for bacterial riboflavin production and recycling of spent bacterial mass for enhancing the growth of oily plants

AIM

This study aims to use fermentation waste of ethanol production (solid and liquid) for riboflavin and recycling of bacterial biomass as biofertilizers to enhance the growth of some oily crop plants.

METHODS AND RESULTS

Out of ten yeast isolates from fresh milk, Clavispora lusitaniae ASU 33 (MN583181) was able to ferment different concentrations of glucose (2.5, 5, 7.5, 10, 15, and 20 %) into ethanol with high efficiency at 10%. Among seven non-Lactobacillus bacterial isolates recovered from cheese samples, two bacterial isolates Bacillus subtlis-SR2 (MT002768) and Novosphingobium panipatense-SR3 (MT002778) were selected for their high riboflavin production. Different media (control medium, fermentation waste medium, and a mixture of the fermentation waste medium and control medium (1:1)) were used for riboflavin production. These media were inoculated by a single or mixture of B. subtlis-SR2, N. panipatense-SR3. The addition of the waste medium of ethanol production to the control medium (1:1) had a stimulatory effect on riboflavin production whether inoculated either with a single strain or mixture of B. subtlis-SR2, N. panipatense-SR3. A mixture of fermentation waste and control media inoculated with N. panipatense produced a high riboflavin yield in comparison with other media. Inoculation of Zea mays and Ocimum basilicum plants either with the bacterial biomass waste of riboflavin production (B. subtlis or N. panipatense or a mixture of B. subtlis and N. panipatense) shows a stimulatory effect on the plant growth in comparison with control (uninoculated plants).

CONCLUSIONS

These results demonstrate the possibility of minimizing the cost of riboflavin and biofertilizer manufacturing via interlinking ethanol and riboflavin with the biofertilizer production technology.

SIGNIFICANCE AND IMPACT OF STUDY

This study outlines methods of evaluating the strength of spent media by applying procedures developed in the vitamins production industries. Furthermore, bacterial biomass waste can act as an environmentally friendly alternative for agrochemicals.

Cellulose Biorefinery Based on a Combined Catalytic and Biotechnological Approach for Production of 5-HMF and Ethanol

In this study, a combination of catalytic and biotechnological processes was proposed for the first time for application in a cellulose biorefinery for the production of 5-hydroxymethylfurfural (5-HMF) and bioethanol. Hydrolytic dehydration of the mechanically activated microcrystalline cellulose over a carbon-based mesoporous Sibunt-4 catalyst resulted in moderate yields of glucose and 5-HMF (21.1-25.1 and 6.6-9.4 %). 5-HMF was extracted from the resulting mixture with isobutanol and subjected to ethanol fermentation. A number of yeast strains were isolated that also revealed high thermotolerance (up to 50 °C) and resistance to inhibitors found in the hydrolysates. The strains Kluyveromyces marxianus C1 and Ogataea polymorpha CBS4732 were capable of producing ethanol from processed catalytic hydrolysates of cellulose at 42 °C, with yields of 72.0±5.7 and 75.2±4.3 % from the maximum theoretical yield of ethanol, respectively.

Bioconversion of water-hyacinth (Eichhornia crassipes) hemicellulose acid hydrolysate to motor fuel ethanol by xylose-fermenting yeast

Water-hyacinth (Eichhornia crassipes) hemicellulose acid hydrolysate has been utilized as a substrate for ethanol production using Pichia stipitis NRRL Y-7124. Hydrolysate fermentability was considerable improved by boiling, and overliming up to pH 10.0 with solid Ca(OH)(2) in combination with sodium sulfite. The percent total sugar utilized and ethanol yield (Y(p/s)) for the untreated hydrolysate were 20.15+/-0.17% and 0.19+/-0.003 g(p) g(s)(-1), respectively, compared with 76.0+/-0.32% and 0.35 g(p) g(s)(-1), respectively for the treated material. The fermentation was very effective at an aeration rate of 0.02 v/v/m, temperature 30+/-0.2 degrees C and pH 6.0+/-0.2. However, the volumetric productivity (Q(p)) was still considerably less than observed in a simulated synthetic hydrolysate medium with a sugar composition similar to the hemicellulose acid hydrolysate. L-Arabinose was not fermented but assimilated. The presence of acetic acid in the hydrolysate decreased the ethanol yield and productivity considerably.

Ethanol production from wheat straw hemicellulose hydrolysate by Pichia stipitis

Ethanol production was evaluated from wheat straw (WS) hemicellulose acid hydrolysate using an adapted and parent strain of Pichia stipitis. NRRL Y-7124. The treatment by boiling and overliming with Ca(OH)(2) significantly improved the fermentability of the hydrolysate. Ethanol yield (Yp/s) and productivity (Qp av) were increased 2.4+/-0.10 and 5.7+/-0.24 folds, respectively, compared to neutralized hydrolysate. Adaptation of the yeast to the hydrolysate resulted further improvement in yield and productivity. The maximum yield was 0.41+/-0.01 g(p) g(s)(-1), equivalent to 80.4+/-0.55% theoretical conversion efficiency. Acetic acid, furfurals and lignins present in the hydrolysate were inhibitory to microbial growth and ethanol production. The addition of these inhibitory components individually or in various combinations at a concentrations similar to that found in hydrolysate to simulated medium resulted a reduction in ethanol yield (Yp/s) and productivity (Qp av). The hydrolysate used had the following composition (expressed in g x l(-1)): xylose 12.8+/-0.25; glucose 1.7+/-0.3; arabinose 2.6+/-0.21 and acetic acid 2.7+/-0.33.

Development of xylose-fermenting yeast Pichia stipitis for ethanol production through adaptation on hardwood hemicellulose acid prehydrolysate

AIMS

The objective of this study was to develop a mutant from Pichia stipitis NRRL Y-7124, tolerant of high concentrations of acetic acid and other inhibitory components present in acid hydrolysates, to improve ethanol yield and productivity.

METHODS AND RESULTS

The mutant was developed through adaptation in acid hydrolysate supplemented with nutrients and minerals at 30 +/- 0.5 degrees C. When it was tested for its ability to ferment acid hydrolysate, it showed shorter fermentation time, better tolerance to acid and could ferment at lower pH. The ethanol yield (Yp/s) and productivity (Qp) were increased 1.6- and 2.1-fold, respectively.

CONCLUSION

The development of a mutant and its tolerance to acetic acid present in hydrolysates is described. The selected mutant is capable of fermenting both hexoses and pentoses present in hydrolysate at lower pH in comparison with the parent strain.

SIGNIFICANCE AND IMPACT OF THE STUDY

The mutant could play a significant role in reducing environmental pollution by using sugars present in pulp mill effluent and, at the same time, could produce a marketable liquid fuel ethanol.

Conversion of pentoses to ethanol by yeasts and fungi

Fermentation of D-xylose is of interest in enhancing the yield of ethanol obtainable from lignocellulosic hydrolysates. Such hydrolysates can contain both pentoses and hexoses, and while technology to convert hexoses to ethanol is well established, the fermentation of pentoses had been problematical. To overcome the difficulty, yeasts and fungi have been sought and identified in recent years that can convert D-xylose into ethanol. However, operation of their cultures in the presence of the pentose to obtain rapid and efficient ethanol production is somewhat more complex than in the archetype alcoholic fermentation, Saccharomyces cerevisiae on D-glucose. The complexity stems, in part, from the association of ethanol accumulation in cultures where D-xylose is the sole carbon source with conditions that limit growth, by oxygen in particular, although limitation by other nutrients might also be implicated. Aspects of screening for appropriate organisms and of the parameters that play a role in determining culture variables, especially those associated with ethanol productivity, are reviewed. Performance with D-xylose as sole carbon source, in sugar mixtures, and in lignocellulosic hydrolysates is discussed. A model that involves biochemical considerations of D-xylose metabolism is presented that rationalizes the effects of oxygen on cultures where D-xylose is the sole carbon source, notably effects of the specific rate of oxygen use on the rate and extent of ethanol accumulation. Alternate methods to direct fermentation of D-xylose have been developed that depend on its prior isomerization to D-xylose, followed by fermentation of the pentulose by certain yeasts and fungi. Factors involved in the biochemistry, use, and performance of these methods, which with some organisms involves sensitivity to oxygen, are reviewed.