The correct answer is (b) Escherichia coli and Agrobacterium.
E. coli is a rod-shaped bacterium that is commonly found in the lower intestines of warm-blooded organisms. It is a facultative anaerobe, meaning that it can grow in the presence or absence of oxygen. E. coli is a model organism for molecular biology research, and it is also used in the production of recombinant proteins.
Agrobacterium is a genus of Gram-negative, rod-shaped bacteria that are able to transfer DNA to plants. This ability has been exploited in genetic engineering to introduce genes into plants. Agrobacterium is used in the production of genetically modified crops.
Nitrosomonas and Nitrobacter are both chemoautotrophic bacteria that oxidize ammonia to nitrite and nitrate, respectively. They are important in the nitrogen cycle, and they are also used in the production of nitric acid.
Azotobacter and Rhizobium are both nitrogen-fixing bacteria. They are able to convert atmospheric nitrogen into ammonia, which can be used by plants. Azotobacter is a free-living bacterium, while Rhizobium is a symbiotic bacterium that lives in the roots of legumes.
Diplococcus is a genus of Gram-positive, cocci bacteria that are often found in pairs. They are not typically used in genetic engineering.