Bacteria involved in the given reaction of nitrogen cycle are...

The given reaction represents the oxidation of nitrite to nitrate in the nitrogen cycle.

Ammonia is first oxidized to nitrite by the bacteria Nitrosomonas and Nitrosococcus.

The nitrite is further oxidized to nitrate with the help of the bacterium Nitrobacter.

The reaction is: $2\,\text{HNO}_2 + \text{O}_2 \rightarrow 2\,\text{HNO}_3$

Pseudomonas denitrificans is involved in denitrification, converting nitrate to nitrogen gas.

Answer: Nitrobacter