Natural genetic engineer is

The correct option is B Agrobacterium tumefaciens

Pseudomonas putida
Pseudomonas putida is a gram negative bacterium. It is used for bioremediation. Bioremediation is the process of using microorganisms to degrade organic contaminants in soil, groundwater, sludge, etc.

Agrobacterium tumefaciens
The Ti plasmid or tumour inducing plasmid (extrachromosomal DNA) is carried by Agrobacterium tumefaciens. The T-DNA segment of the Ti plasmid integrates itself into the plant cell’s genome to induce tumor formation in plants. This property of the plasmid makes it an effective vector for transferring foreign genes into plant cells. This bacterium is a natural genetic engineer of plants.

Escherichia coli
Escherichia coli is a bacterium used extensively in biotechnology as a host for cloning and recombinant DNA expression. It is not a natural genetic engineer for introducing foreign genes into plants.

Bacillus subtilis
Bacillus subtilis is commonly used as a host, for the production of vitamins, inositol, acetoin, hyaluronan, etc., in genetic engineering. It is not a natural genetic engineer and it does not infect plants.

Final answer
b. Agrobacterium tumefaciens