Molecular Biotechnology. Principles and Applications - Glick B., Pasternak J. 2002

Molecular Biotechnology of Microbial Systems
Biodegradation of Toxic Compounds and Biomass Utilization
Conclusion

Biodegradation is the process by which microorganisms break down environmental pollutants. Many Bacteria of the genus Pseudomonas harbor Plasmids encoding Enzymes that catalyze the degradation of aromatic and halogenated Organic compounds. In most cases, a single plasmid contains the genes for enzymes of a single, specific catabolic pathway. By combining plasmids from different Pseudomonas strains within a single host, an Organism capable of degrading multiple compounds can be engineered. Furthermore, genetic manipulation can expand the range of substrates degraded by a specific enzymatic pathway.

Here, biomass refers to the entire range of substances, Materials, and by-products from the food and Processing industries that can serve as raw materials for producing valuable products. The production of ethanol or fructose from ground grain occurs in several enzymatic steps. The enzymes involved in these processes are often used only once. To increase the efficiency of enzymatic reactions and reduce process costs, researchers are cloning and characterizing bacterial genes that encode thermostable, highly active, and alcohol-tolerant enzymes.

To improve the efficiency of industrial ethanol production, genes were introduced into the bacterium Zymomonas mobilis, allowing it to utilize a wide range of compounds as a carbon source through their expression. The first steps have also been taken toward developing Lactobacillus plantarum strains capable of efficiently degrading starch, which is highly abundant in alfalfa, an important agricultural crop.

The processing of plant material often generates large amounts of lignocellulosic waste, which previously found no application. Today, lignocellulose serves as a raw material for producing carbon-containing compounds, primarily glucose, which can be used in other processes. Lignocellulose is a complex of Lignin, hemicellulose, and Cellulose that is resistant to enzymatic action without pretreatment. Recent research has focused primarily on studying The Mechanism of cellulose degradation to produce glucose. Genes for endoglucanases, exoglucanases, and ß-glucosidases from many microorganisms have been cloned and characterized, but the specific set of enzymes required for large-scale, efficient cellulose degradation in vitro has not yet been established.

Certain types of biomass (such as whey and cellulose waste) and petroleum products can serve as substrates for culturing microorganisms. It was envisioned that these pure cultures, as well as their products (so-called Single-Cell Protein, SCP), could be used as food additives or animal feed. Unfortunately, due to high production costs, poor palatability, and occasional toxicity, the commercial production of SCP proved economically unviable. However, there is hope that genetic manipulation will eventually enable The Development of systems for producing inexpensive SCP-based biological supplements.

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Review Questions

1. How should P. putida be modified to obtain a strain that efficiently degrades trichloroethylene?

2. Describe the Procedure for cloning fungal cellulase genes.

3. How are alpha-amylase and glucoamylase used in industrial ethanol production? What manipulations should be performed on the genes encoding these enzymes to increase the efficiency of the process?

4. What is the enzyme glucose isomerase? What is its value? How and why can the gene encoding it be modified?

5. Describe the Advantages and disadvantages of using Zymomonas mobilis instead of Saccharomyces cerevisiae in ethanol production. How can the efficiency of the industrial use of Z. mobilis be improved?

6. How can Genetic engineering Methods be used to modify Z. mobilis so that this microorganism can be used for ethanol production from xylose?

7. Given three Pseudomonas strains—one that uses phenol as its sole carbon source at 0 °C, a second that degrades anthracene to catechol at 35 °C, and a third that degrades p-toluene to protocatechuate at 35 °C—propose a strategy for constructing a strain that can utilize phenol, anthracene, or p-toluene as its sole carbon source at 0 °C.

8. How would you modify a Pseudomonas strain carrying the pWWO plasmid that is unable to degrade 4-ethylbenzoate so that it can utilize this compound?

9. Propose strategies for isolating prokaryotic endoglucanase and ß-glucosidase genes.

10. WHAT IS A "superbacillus"?

11. How can the efficiency of silage production be improved by manipulating Lactobacillus plantarum?

12. How should rumen bacteria be modified to provide cattle with essential amino acids?