Answer:

The correct answer is option D, which states that Escherichia coli and Agrobacterium tumefaciens are two microbes found to be very useful in genetic engineering. Let us understand why these microbes are important in this field.

Escherichia coli (E. coli):
- E. coli is a Gram-negative, rod-shaped bacterium commonly found in the lower intestine of warm-blooded organisms.
- It has been extensively studied and is well understood at the genetic level.
- E. coli has a fast growth rate and is easy to culture in the laboratory, making it a convenient organism for genetic manipulation.
- It has a relatively simple genome, and its genes can be easily modified or replaced, making it an ideal host for recombinant DNA technology.
- E. coli is used as a host organism for the production of many important proteins, including insulin, growth factors, and enzymes, through the process of genetic engineering.

Agrobacterium tumefaciens:
- Agrobacterium tumefaciens is a soil bacterium that causes crown gall disease in plants.
- It has the ability to transfer a piece of its DNA, known as the Ti (tumor-inducing) plasmid, into the plant host's genome.
- Researchers have harnessed this natural capability of Agrobacterium to introduce foreign genes into plant cells for genetic engineering purposes.
- The Ti plasmid contains genes that can induce the formation of a tumor-like growth, which provides a unique environment for the bacterium to grow and reproduce.
- By replacing the tumor-inducing genes with desired genes of interest, scientists can use Agrobacterium to deliver these genes into plants, allowing for the production of genetically modified plants.

Significance in Genetic Engineering:
- E. coli and Agrobacterium tumefaciens are both extensively used in genetic engineering due to their ability to efficiently take up foreign DNA and incorporate it into their genomes.
- E. coli is commonly used as a host organism for cloning and expressing genes of interest, while Agrobacterium is used for the genetic modification of plants.
- These microbes serve as valuable tools in the development of recombinant DNA technology, allowing researchers to manipulate and modify the genetic material of different organisms for various applications.
- Their use in genetic engineering has contributed significantly to advancements in medicine, agriculture, and biotechnology.

In conclusion, E. coli and Agrobacterium tumefaciens are two important microbes in genetic engineering due to their ease of genetic manipulation and their ability to introduce foreign DNA into host organisms. These organisms have played a crucial role in the development of recombinant DNA technology and have contributed to various fields of research and application.