The organism used in construction of the first artificial recombinant DNA by Cohen and Boyer in 1972 was :

The correct option is Salmonella typhimurium.

Here is a step-by-step explanation of why this option is correct:

1. Historical Context of Recombinant DNA Technology:
In 1972, Stanley Cohen and Herbert Boyer accomplished a groundbreaking feat in biotechnology by constructing the first artificial recombinant DNA molecule. This marked the birth of modern genetic engineering.

2. Identifying the Source Organism:
To create the recombinant DNA, Cohen and Boyer isolated an antibiotic resistance gene (specifically, a gene providing resistance to tetracycline) from a plasmid naturally occurring in the bacterium Salmonella typhimurium.

3. Construction of the Recombinant DNA:
The isolated gene from Salmonella typhimurium was linked to a plasmid vector (pSC101) of another bacterium, Escherichia coli (commonly known as E. coli), using restriction enzymes (to cut the DNA) and DNA ligase (to paste/join the DNA segments).

4. Conclusion:
Although the recombinant plasmid was subsequently introduced and cloned into E. coli to replicate, the actual host organism from which the target gene (antibiotic resistance gene) was originally sourced for the construction of the first recombinant DNA was Salmonella typhimurium.