griffith experiment microbe notes

Biotechnology
Biochemistry
Microbiology
Cell Biology
Cell Signaling
Diversity in Life Form
Molecular Biology

Griffith Experiment - Transformation in Bacteria, DNA as Genetic Material

Griffith's Experiment in 1928 demonstrated bacterial transformation, where non-virulent bacteria turned virulent upon exposure to heat-killed virulent strains. Avery, MacLeod, and McCarty experiment later confirmed in 1944 that DNA, not proteins, was the genetic material responsible for this transformation. Griffith Experiment in conclusion recognized DNA's significant role in heredity. In this article, we will study the Frederick Griffith Experiment - steps, strain of bacteria, and Griffith Experiment summary.

Table of Content

Griffith Experiment & Transforming Principle

Griffith experiment diagram, r strain and s strain bacteria.

Griffith’s Experiment - Transformation in Bacteria

Impact of the Griffith Experiment

Dna as genetic material.

Frederick Griffith conducted an experiment that demonstrated the transfer of genetic information between bacteria. The experiment showed that a heat-killed virulent strain could transform a non-lethal strain of bacteria . Griffith called the material that was transferred the "transforming principle". Griffith's experiment involved mixing living non-virulent bacteria with a heat-inactivated virulent form. The bacteria used in the experiment were Streptococcus pneumoniae, which showed two growth patterns. One culture plate had s mooth, shiny colonies (S), while the other had rough colonies (R) .

Griffith's experiment proved that some organisms can acquire new properties from their environment and from one another. However, it took almost 20 years for Avery, McLeod, and McCarty to confirm that nucleic acids, not proteins , are the molecules of heredity

Also Read : Mendel's Laws of Inheritance

The diagram of griffith experiment is shown below:

The R strain and S strain bacteria are two variants of the bacterium Streptococcus pneumonia, used by Frederick Griffith in his experiment. S strains are pathogenic, meaning they can cause disease. R strains are non-pathogenic, meaning they do not cause disease. Some other differences between R and S strains are:

Appearance: S strains have a smooth capsule , or outer coat, made of polysaccharides. R strains lack a capsule and have a rough appearance.
Colonies: S strains produce rough colonies, while R strains produce smooth colonies.
Virulence: S strains are virulent, while R strains are non-virulent.
Immune responses: The capsule of S strains allows the cell to escape the immune responses of the host mouse.
Mice: Mice injected with S strains die within a few days, while mice injected with R strains do not die.

In Griffith's experiment, when he injected mice with the heat-killed S strain and live R strain , the mice unexpectedly died. This revealed a transformation process where the R strain had taken up genetic material from the heat-killed S strain and become virulent. This observation helped in understanding bacterial transformation and the role of DNA as genetic material.

Also Read: Genetic Code - Molecular Basis of Inheritance

Griffith Experiment of Transformation in Bacteria

In 1928, English bacteriologist Frederick Griffith conducted an experiment that demonstrated how bacteria can change their function and form through transformation. The experiment was the first to suggest that bacteria can transfer genetic information through transformation. The experiment involved two strains of the bacterium Streptococcus pneumoniae: a virulent (disease-causing) strain (S) and a non-virulent (non-disease-causing) strain (R).

Transformation is the process of one thing changing into another. In molecular biology and genetics, transformation is the genetic alteration of a cell. It's one of three processes that lead to horizontal gene transfer , along with conjugation and transduction. The detail description of the Griffith’s Experiment - Transformation in Bacteria is as follows:

Griffith Experiment Steps

In the experiment, Griffith injected two types of Streptococcus pneumoniae into mice.

Griffith then subjected the virulent, smooth strain (S) to heat that killed the bacteria. This heat-killed strain (S) was no longer capable of causing disease.
Griffith injected mice with the heat-killed virulent strain (S). Surprisingly, the mice survived, indicating that the heat-killed bacteria alone were not harmful.
Griffith mixed the heat-killed virulent strain (S) with the live non-virulent, rough strain (R) and injected this mixture into mice.
The mice developed pneumonia and died, even though the strain injected was previously non-virulent.

Observations and Conclusion

Griffith concluded that some factor or biomolecule in the heat-killed virulent bacteria (S) had transformed the live non-virulent bacteria (R) into a virulent form. This phenomenon was termed "transformation," though Griffith could not identify the nature of the transforming substance.

Significance

Griffith's experiment laid the groundwork for understanding genetic transformation and proved that DNA , rather than proteins, carried genetic information. This discovery was fundamental to the development of molecular genetics and is also used in a variety of genetic engineering applications.

Conclusion - Griffith Experiment

Frederick Griffith's 1928 experiment on Streptococcus pneumoniae demonstrated bacterial transformation through a transfer of hereditary traits between strains. In Griffith experiment conclusion, the result showed that the harmless R strain could be transformed into a virulent form when exposed to the heat-killed S strain. Subsequent work by Avery, MacLeod, and McCarty in 1944 identified DNA as the transforming substance, establishing it as the genetic material. The discovery laid the foundation for molecular genetics, confirming the role of DNA in transmitting hereditary information.

Also Read: Inherited Traits Lethal Allele - Examples, & its Types Difference Between Phenotype and Genotype Ratio Importance of Variation

FAQs on Frederick Griffith Experiment

What was griffith’s experiment and why was it important.

Frederick Griffith conducted an experiment that suggested bacteria can transfer genetic information through transformation. The experiment was important because it showed that bacteria can change their function and form through transformation.

What is the Griffith Experiment Conclusion?

Frederick Griffith experiment concluded that bacteria can transfer genetic information through a process called transformation.

What was the Most Significant Conclusion of Griffith’s Experiments with Pneumonia in Mice?

Griffith conducted experiments with mice and Streptococcus pneumonia bacteria. He concluded that heat-killed bacteria can convert live avirulent cells to virulent cells. Griffith called this phenomenon transformation.

What did Frederick Griffith Want to Learn about Bacteria?

Frederick Griffith, a British bacteriologist, wanted to learn how bacteria could acquire new traits and how certain types of bacteria produce pneumonia.

How did the Two Types of Bacteria Used by Griffith Differ?

The two types of bacteria used by Griffith were the R strain, lacking a virulent capsule and non-pathogenic, and the S strain, possessing a smooth capsule and causing pneumonia in mice, making it pathogenic.

What was Oswald Avery's Experiment?

The experiment demonstrated that DNA was the only molecule that transformed from one bacterial strain to another.

What is Griffith's Transforming Principle?

Griffith performed an experiment with bacteria and mice and discovered that bacteria can incorporate foreign genetic material from their environment, which he called the transforming principle.

Why is Chapter Griffith Experiment Class 12 Important?

The Griffith Experiment in Class 12 biology is important as it describes bacterial transformation, highlighting the role of genetic material in heredity and laying the foundation for modern molecular biology and genetics research.

Improve your Coding Skills with Practice

What kind of Experience do you want to share?

Talk to our experts

1800-120-456-456

Griffith Experiment

Griffith Experiment: An Introduction

It may come as a surprise that less than a century ago, even the most educated members of the scientific community were unaware that DNA was a hereditary material. Frederick Griffith conducted a series of experiments with Streptococcus pneumonia bacteria and mice in 1928 and concluded that the R-strain bacteria must have picked up a "transforming principle" from the heat-killed S bacteria, allowing them to "transform" into smooth-coated bacteria and become virulent.

In this article, we'll look at one of the classic experiments that led to the discovery of DNA as a genetic information carrier.

Who was Frederick Griffith?

The "Griffith's Experiment," carried out by English bacteriologist Frederick Griffith in 1928, described the transformation of a non-pathogenic pneumococcal bacteria into a virulent strain.

Griffith combined living non-virulent bacteria with a heat-inactivated virulent form in this experiment.

He was the first to discover the "transforming principle," which led to the discovery of DNA as a carrier of genetic information.

He suggested that bacteria can transfer genetic information via a process known as transformation.

Griffith's goal was not to identify the genetic material but to create a vaccine against pneumonia. In his experiments, Griffith used two related strains of bacteria known as R and S.

Griffith's work was expanded by Avery, MacLeod, and McCarty.

R Strain And S Strain Bacteria

Streptococcus pneumonia comes in several types or strains. Griffith chose two different strains for his experiment.

One strain of bacteria has smooth surfaces and is known as the smooth strain (S strain), while the other has rough surfaces and is known as the rough strain (R strain).

Bacteria of the S strain have smooth surfaces because they produce a polysaccharide protective coating that forms the outermost layer.

Apart from the morphological differences, Griffith discovered another significant difference between the S and R strains of bacteria, i.e., the S strain is the "virulent" strain capable of causing death in mice, whereas the R strain is the "nonvirulent" strain that will not cause death in mice.

Griffith observed that when he injected these bacteria into mice, the mice infected with the virulent S strain died from pneumonia, whereas the mice infected with the nonvirulent R strain survived.

R Strain and S Strain of Streptococcus Pneumonia

Griffith’s Transformation Experiment

Griffith was researching the possibility of developing a pneumonia vaccine.

He used two strains of pneumococcus (Streptococcus pneumonia) bacteria that infect mice – a virulent (causing disease) S (smooth) strain and a non-virulent type R (rough) strain.

The S strain produced a polysaccharide capsule that protected itself from the host's immune system, resulting in the host's death, whereas the R strain lacked that protective capsule and was defeated by the host's immune system.

Griffith attempted to inject mice with heat-killed S bacteria as a part of his research (i.e., S bacteria that had been heated to high temperatures, causing the cells to die). The heat-killed S bacteria, but unsurprisingly, did not cause disease in the mouse.

When harmless R bacteria were combined with harmless heat-killed S bacteria and injected into a mouse, the experiments took an unexpected turn.

Not only did the mouse develop pneumonia and die, but Griffith discovered living S bacteria in a blood sample taken from the dead mouse.

He concluded that some factor or biomolecule from the heat-killed S bacteria had entered the living R bacteria, allowing them to synthesise a polysaccharide coating and become virulent. As a result, this factor "transformed" the R bacteria into S bacteria.

Griffith called this factor the "transforming principle," concluding that it carried some genetic material from the S bacteria to the R bacteria.

This process is now known as bacterial transformation and is used in a variety of significant genetic engineering applications.

Griffith Experiment Diagram

Impact of The Griffith Experiment

One of the characteristics of hereditary material is a changing phenotype . Griffith referred to the phenotypic-changing factor as the transforming principle.

His work on the transforming principle received the most attention, but only after a group of Canadian and American scientists set out to investigate the chemical nature of the transforming principle in Oswald Avery's laboratory.

Avery's group concluded in their studies that deoxyribonucleic acid was the molecule identified by Griffith as the transforming principle after conducting numerous experiments.

The implications of this discovery are farfetched because it was made at a time when scientists considered protein molecules to be genetic material.

DNA, or deoxyribonucleic acid, is now recognised as the molecule that encodes all cell functions and transmits genetic information from parent to offspring in almost every living species .

In the 1940s, however, DNA was thought to be a less qualified candidate for genetic material. Avery and colleagues' research on Griffith's experiment provided the first solid evidence that DNA could be the genetic material.

Griffith's ultimate goal was to find a way to cure pneumonia. Griffith inoculated mice with various strains of pneumococci to see if they would infect and eventually kill the mice. Griffith concluded that heat-killed virulent bacteria transformed living, non-virulent bacteria into virulent bacteria. He performed his experiment on the two strains of Streptococcus pneumonia, which differ from each other due to the presence of a polysaccharide coat.

Griffith's findings were published in the Journal of Hygiene. In 1928, his experiments with mice led to his major discovery of bacterial transformation. Griffith's experiment discovered that bacteria can transfer genetic information through transformation.

FAQs on Griffith Experiment

1. Explain the Oswald Avery Experiment.

Avery and his colleagues conducted additional research on the virulent S strain of Streptococcus pneumonia. They were aware that the potential carriers of genetic material were proteins, RNA, or DNA. When the mixtures were treated with protein-digesting or RNA-digesting enzymes, the DNA remained intact and was capable of transforming R bacteria into S bacteria. However, when the DNA in these mixtures was broken down with DNase, the genetic material could not be passed from the heat-killed S bacteria to the live R bacteria, preventing transformation. As a result, Avery and his colleagues concluded that the transforming principle described by Griffith had to be DNA.

2. What are the characteristics of genetic material?

Any substance that forms the genetic material must fulfil some essential requirements:

It must be stable.

It should be able to carry and transcribe information which is required to control the processes.

It should be able to replicate itself and remain unchanged while passing down from one generation to another.

It must be able to mutate itself to provide variations.

A genetic material must be able to store the information, transmit it, replicate it and provide variation.

DNA fulfils all the above-mentioned requirements and hence acts as genetic material.

3. Define Horizontal Gene Transfer.

Horizontal gene transfer (HGT) is the exchange of genetic information between organisms, which includes the spread of antibiotic resistance genes among bacteria (except those passed down from parent to offspring), thereby, fueling pathogen evolution.

Bacterial horizontal gene transfer occurs via three mechanisms: transformation, transduction, and conjugation. Conjugation is the primary mechanism for the spread of antibiotic resistance in bacteria, and it is critical in the evolution of the bacteria that degrade novel compounds such as pesticides created by humans, as well as in the evolution, maintenance, and transmission of virulence.