Genetic Improvement of microbial strains

By,Abhinava J VUniversity of Agricultural Sciences, Dharwad

Need of Genetic Improvement

For increase in yield of the desired product, medium and growth conditions should be optimized.

Medium and growth optimization is having limited effect on increase in the product due to organism’s maximum ability to synthesize the product which is controlled by its genome.

Thus if one want to increase the product then one should modify the genome.

This is called as genetic improvement of that organisms.

Genetic Improvement can be achieved by:

1 •Mutation and Selection

2 •Natural Gene Transfer Methods

3 •Genetic Engineering

Mutation and Selection

In nature, mutations (changes in the chromosome of an organism) occur spontaneously at very low rates (one mutational event in every 106 to 107 cells per generation.

The mutation rate can be dramatically increased by exposure of microorganisms to mutagenic agents, such as ultraviolet light or various chemicals, which induce changes in the deoxyribonucleic acid (DNA) of host cells.

Types of mutagens

•Physical1

•Chemical2

•Biological3

Physical Mutagens

• X-rays, gamma rays and alpha particles.

Ionizing radiations

• Above 260 nm creates pyrimidine dimers.

Ultraviolet radiations

• 14C decays the DNA into nitrogen.

Radioactive decay

Chemical Mutagens

•5-Bromo Uracil: Thymine analog

•2-amino-purine: Adenine analog

Base analogs •Alkylating agents (eg

nitrosoguanidine) Base-Modifying

Agents

•Cause single base insertions and deletions. Examples: proflavin, acridine orange, ethidium bromide.

Intercalating agents

Biological Mutagens

Transposon

• It insert into chromosomal DNA and disrupt functional elements of the gene.

Virus

• Virus DNA may be inserted into the genome and disrupts genetic function.

Bacteria

• Some bacteria such as Helicobacter pylori causing DNA damage & reducing the efficiency of DNA repair systems, thereby increasing mutation.

Natural Gene Transfer Methods

1 •Transduction

2 •Conjugation

3 •Transformation

Transduction

Transduction involves genetic exchange mediated by a bacterial virus (bacteriophage).

Conjugation

Conjugation, or bacterial mating, is a natural gene transfer system that requires close physical contact between donors and recipients and is responsible for the dissemination of plasmids in nature.

Transformation

Certain microorganisms are able to take up naked DNA present in the surrounding medium.

This process is called transformation and this gene transfer process is limited to strains that are naturally competent.

Electroporation

This technique involving the application of high-voltage electric pulses of short duration to induce the formation of transient pores in cell walls and membranes.

Under appropriate conditions, DNA present in the surrounding medium may enter through the pores.

This is the physical method to make the cell competent.

Genetic Engineering

Genetic engineering is revolutionizing the science of strain improvement and is destined to have a major impact on the food fermentation industry.

Genes code for desirable traits can be used from any living organism (plant, animal, microbe or virus).

Engineered bacteria, yeast, and molds could also be used for the production of other products, including food additives and ingredients, processing aids such as enzymes, and pharmaceuticals.

Metabolic engineering

Metabolic engineering is generally defined as the redirection of one or more enzymatic reactions to produce new compounds in an organism, improve the production of existing compounds, or mediate the degradation of compounds.

Metabolic engineering is the use of genetic engineering to modify the metabolism of an organism.

Metabolic engineering requires the basic molecular biological technologies such as cloning, promoter analysis, protein targeting, plant transformation, biochemical genetics, and other areas of plant biology.

The most successful metabolic engineering approach is Golden rice, production of Vitamin A in rice by introducing new pathways.

Mode

Block a metabolic

fluxChannel a metabolic

flux into new cell

compartmentInduce a metabolic

fluxIntroduce a new

metabolic pathway into

organism

Process

Identification of target metabolite

Analyzing a metabolic pathway

Determining the optimal genetic manipulations

Cloning & Expression of the gene

Application