Photosynthetic bacteria include
A. Nitrobacter and Nitrosomonas
B. Chlorobium and Rhodospirillum
C. Streptococcus and Staphylococcus
D. Chlorobium and Clostridium

Hint: Photosynthetic bacteria are those bacteria which are capable of producing energy from the sunlight in a similar way as plants do. However, instead of chlorophyll, they have bacteriochlorophyll to capture sunlight.

Complete Answer:
Let us analyse the options for finding the correct answer.
Option A: Nitrobacter and Nitrosomonas are the chemoautotrophs i.e they get energy by oxidizing chemical compounds such as ammonia nitrite and nitrate by a process known as nitrification. Therefore this is the incorrect option.

Option B: Chlorobium and Rhodospirillum are gram negative bacteria that contain bacteriochlorophyll, which is the light harvesting complex. The former bacteria converts Sulphide to sulphur whereas the latter uses hydrogen as electron donors and hence gaining energy by oxidizing hydrogen. Therefore this is the correct option.

Option C: Streptococcus and Staphylococcus are both gram positive spherical or cocci shaped bacteria. They are facultative anaerobes and are best known for their pathogenicity, like pneumonia, Endocarditis, Osteomyelitis. Therefore this is the incorrect option.

 Option D: Chlorobium and Clostridium are gram negative and gram positive bacteria respectively. As mentioned earlier Chlorobium consists of bacteriochlorophylls and oxidize sulfide to sulphur and hence it is a photosynthetic bacteria. Whereas Clostridium is an obligate anaerobic bacteria which lacks bacteriochlorophyll and it is a pathogen to humans. Therefore this is the incorrect option.

Thus the correct option is B: Chlorobium and Rhodospirillum.

Additional information:
Applications of Photosynthetic bacteria:
- They are used in water purification , bio-fertilizers and animal feed.
- They are used in the treatment of polluted water since they can utilize toxic substances.
- They can be engineered to produce simple sugars and lactic acid.

Note: Bacteriochlorophylls, which are the photosynthetic pigments in bacteria conduct photosynthesis to sustain the energy requirements of bacteria, but do not produce oxygen as a byproduct. They absorb infrared radiation (range from 800-1040nm) in purple bacteria such as Chromatium tepidum and far red light (range from 700 -755nm) as seen in Chlorobium aggregatum.