Detailed Explanation:

Question:
The major drawback in using wild type S. cerevisiae for producing ethanol from biomass hydrolysate is:

• (1) Low biomass yield of hexose sugars

• (2) Presence of solid residues

• (3) Low concentration of sugars

• (4) Non-utilization of pentose sugars

Correct Answer:

(4) Non-utilization of Pentose sugars

Explanation:

Saccharomyces cerevisiae, commonly known as baker’s yeast, is widely used in the production of ethanol. However, when it comes to producing ethanol from biomass hydrolysate, which is derived from the breakdown of plant material (lignocellulosic biomass), the wild-type S. cerevisiae exhibits several limitations. These limitations impact its efficiency in converting all sugars in the hydrolysate into ethanol.

Let’s go through the options:

1. Low biomass yield of hexose sugars:

Hexose sugars (such as glucose) are crucial for ethanol production. However, wild-type S. cerevisiae does not have a specific problem with low biomass yield of hexose sugars. In fact, S. cerevisiae can efficiently ferment hexose sugars into ethanol.

2. Presence of solid residues:

While solid residues can occur after biomass hydrolysis (from plant fibers or lignin), this is not a specific drawback of the yeast itself. This issue is related more to the hydrolysis process rather than a limitation of the yeast strain in question.

3. Low concentration of sugars:

Wild-type S. cerevisiae can handle a reasonable concentration of sugars in the biomass hydrolysate. While higher concentrations of sugars could inhibit fermentation due to osmotic stress, the primary issue is not the low sugar concentration, but rather the specific sugars available.

4. Non-utilization of Pentose sugars:

This is the major drawback when using wild-type S. cerevisiae for ethanol production from biomass hydrolysate. Pentose sugars (such as xylose and arabinose) are common in plant material, but wild-type S. cerevisiae cannot efficiently ferment these sugars. Since biomass hydrolysate contains a significant proportion of pentose sugars, this limits the overall ethanol yield. This is a major bottleneck for using S. cerevisiae in bioethanol production from lignocellulosic materials.

Conclusion:

The major limitation of using wild type S. cerevisiae in producing ethanol from biomass hydrolysate is its inability to utilize pentose sugars effectively. Genetic engineering or metabolic engineering of S. cerevisiae strains to enable the fermentation of pentose sugars can significantly enhance the efficiency of bioethanol production from lignocellulosic biomass. Therefore, the correct answer is (4) Non-utilization of Pentose sugars.