Final answer:
The correct answer is option 3) Sphingomonas, as it is a genus of purple nonsulfur bacteria that produce protective pigments against UV radiation.
Step-by-step explanation:
The bacterial genera that produce pigments which protect plant leaves from UV irradiation are known as purple nonsulfur bacteria, which include the genus Rhodospirillum. These microorganisms are facultative anaerobes, pink in color due to the pigmentation, and are capable of nitrogen fixation. They also have a potential use in biotechnology for producing biological plastic and hydrogen fuel. Thus, the correct answer to the question is option 3) Sphingomonas