Question: What is found in Prochlorococcus and essential for photosynthesis?

full_context: Document 1: Plant: Plants are mainly multicellular, predominantly photosynthetic eukaryotes of the kingdom Plantae. The term is today generally limited to the green plants, which form an unranked clade Viridiplantae (Latin for "green plants"). This includes the flowering plants, conifers and other gymnosperms, ferns, clubmosses, hornworts, liverworts, mosses and the green algae, and excludes the red and brown algae. Historically, plants formed one of two kingdoms covering all living things that were not animals, and both algae and fungi were treated as plants; however all current definitions of "plant" exclude the fungi and some algae, as well as the prokaryotes (the archaea and bacteria).
Document 2: Action spectrum: An action spectrum is the rate of a physiological activity plotted against wavelength of light. It shows which wavelength of light is most effectively used in a specific chemical reaction. Some reactants are able to use specific wavelengths of light more effectively to complete their reactions. For example, chlorophyll is much more efficient at using the red and blue spectrums of light to carry out photosynthesis. Therefore, the action spectrum graph would show spikes above the wavelengths representing the colours red and blue. Engelmann split light into its components by the prism and then illuminated Cladophora placed in a suspension of aerobic bacteria. He found that bacteria accumulated in the region of blue and red light of the split spectrum. He thus discovered the effect of the different wavelengths of light on photosynthesis and plotted the first action spectrum of photosynthesis.
Document 3: Cylindrospermum: Cylindrospermum is a genus of filamentous cyanobacteria found in terrestrial and aquatic environments. In terrestrial ecosystems, "Cylindrospermum" is found in soils, and in aquatic ones, it commonly grows as part of the periphyton on aquatic plants. The genus is heterocystous (nitrogen-fixing) cyanobacteria.
Document 4: Chlorophyll a: Chlorophyll "a" is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light. It also reflects green/yellow light, and as such contributes to the observed green color of most plants. This photosynthetic pigment is essential for photosynthesis in eukaryotes, cyanobacteria and prochlorophytes because of its role as primary electron donor in the electron transport chain. Chlorophyll "a" also transfers resonance energy in the antenna complex, ending in the reaction center where specific chlorophylls P680 and P700 are located.
Document 5: Chlorophyll: Chlorophyll (also chlorophyl) is any of several closely related green pigments found in cyanobacteria and the chloroplasts of algae and plants. Its name is derived from the Greek words χλωρός, "chloros" ("green") and φύλλον, "phyllon" ("leaf"). Chlorophyll is essential in photosynthesis, allowing plants to absorb energy from light.
Document 6: Eobacterium: Eobacterium is an extinct genus of bacteria from the Fig Tree Formation in Africa. It is about 3 billion years old, one of the oldest known living organisms. The discovery of "Eobacterium" and other Fig Tree organisms in the 1960s helped prove that life existed over three billion years ago.
Document 7: Prochlorococcus: Prochlorococcus is a genus of very small (0.6 µm) marine cyanobacteria with an unusual pigmentation (chlorophyll "a2" and "b2"). These bacteria belong to the photosynthetic picoplankton and are probably the most abundant photosynthetic organism on Earth. "Prochlorococcus" microbes are among the major primary producers in the ocean, responsible for a large percentage of the photosynthetic production of oxygen. Analysis of the genome sequences of 12 "Prochlorococcus" strains show that 1,100 genes are common to all strains, and the average genome size is about 2,000 genes. In contrast, eukaryotic algae have over 10,000 genes.
Document 8: Chromatium okenii: Chromatium okenii is a Gram-negative bacterium found in water. It belongs to the Purple sulfur bacteria. These bacteria are capable of photosynthesis and use Hydrogen sulfide (HS) as an electron donor for CO reduction and so do not produce oxygen. This type of photosynthesis is called anoxygenic photosynthesis.
Document 9: Auxiliary metabolic genes: Auxiliary metabolic genes (AMGs) are found in many bacteriophages but originated in bacterial cells. AMGs modulate host cell metabolism during infection so that the phage can replicate more efficiently. For instance, bacteriophages that infect the abundant marine cyanobacteria "Synechococcus" and "Prochlorococcus" (cyanophages) carry AMGs that have been acquired from their immediate host as well as more distantly-related bacteria. Cyanophage AMGs support a variety of functions including photosynthesis, carbon metabolism, nucleic acid synthesis and metabolism.
Document 10: Genomic evolution of birds: Birds are the group of amniotes with the smallest genomes. Whereas mammal and reptilian genomes range between 1.0 and 8.2 giga base pairs (Gb), bird genomes have sizes between 0.91 Gb (black-chinned hummingbird, "Archilochus alexandri") and 1.3 Gb (common ostrich, "Struthio camelus"). Just as happens to any other living being, bird genomes’ reflect the action of natural selection upon these animals. Their genomes are the basis of their morphology and behaviour.
Document 11: Volvox: Volvox is a polyphyletic genus of chlorophyte green algae in the family Volvocaceae. It forms spherical colonies of up to 50,000 cells. They live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 1700. "Volvox" diverged from unicellular ancestors approximately   million years ago .
Document 12: Carotenoid: Carotenoids ( ), also called tetraterpenoids, are organic pigments that are produced by plants and algae, as well as several bacteria and fungi. Carotenoids can be produced from fats and other basic organic metabolic building blocks by all these organisms. The only animals known to produce carotenoids are aphids and spider mites, which acquired the ability and genes from fungi or it is produced by endosymbiotic bacteria in whiteflies . Carotenoids from the diet are stored in the fatty tissues of animals, and exclusively carnivorous animals obtain the compounds from animal fat.
Document 13: Atelocyanobacterium thalassa: "Candidatus" Atelocyanobacterium thalassa (previously cyanobacterium UCYN-A,) is a species of cyanobacteria commonly found throughout the world's oceans. Unlike many other cyanobacteria, "A. thalassa" lacks the ability to perform photosynthesis. Instead, it is found in a symbiotic relationship with photosynthetic algae. "A. thalassa" fixes nitrogen for the algae, while the algae provides carbon for "A. thalassa" through photosynthesis.
Document 14: Aerobic anoxygenic phototrophic bacteria: Aerobic anoxygenic phototrophic bacteria (AAPBs) are alphaproteobacteria and gammaproteobacteriathat are obligate aerobes that capture energy from light by anoxygenic photosynthesis. Anoxygenic photosynthesis is the phototrophic process where light energy is captured and stored as ATP. The production of oxygen is non-existent and, therefore, water is not used as an electron donor. They are widely distributed marine plankton that may constitute over 10% of the open ocean microbial community. They can be particularly abundant in oligotrophic conditions where they were found to be 24% of the community. Aerobic anoxygenic phototrophic bacteria are photoheterotrophic (phototroph)microbes that exist in a variety of aquatic environments. Photoheterotrophs(Gk: photo = light, hetero = (an)other, troph = nourishment), are heterotrophic organisms that use light to produce energy, but are unable to utilize carbon dioxide as their primary carbon source. Most are obligately aerobic, meaning they require oxygen to grow. One remarkable aspect of these novel bacteria is that they, unlike other similar bacteria, are unable to utilize BChl (bacteriochlorophyll) for anaerobic growth.The only photosynthetic pigment that exists in AAPB is BChl a. Anaerobic phototrophic bacteria, on the contrary, can contain numerous species of photosynthetic pigments like bacteriochlorophyll a, b, c, d, e, f, etc. There is still a large void in the areas regarding the abundance and genetic diversity of the AAPB, as well as the environmental variables that regulate these properties.
Document 15: Wigglesworthia glossinidia: Wigglesworthia glossinidia is a species of gram-negative bacteria which was isolated from the gut of the tsetse fly. "W. glossinidia" is a bacterial endosymbiont of the tsetse fly. Because of this relationship, "Wigglesworthia" has lost a large part of its genome and has one of the smallest known genomes of any living organism, consisting of a single chromosome of 700,000 bp and a plasmid of 5,200. Together with "Buchnera aphidicola", "Wigglesworthia" has been the subject of genetic research into the minimal genome necessary for any living organism. "Wigglesworthia" also synthesizes key B-complex vitamins which the tsetse fly does not get from its diet of blood. Without the vitamins "Wigglesworthia" produces, the tsetse fly has greatly reduced growth and reproduction. Since the tsetse fly is the primary vector of "Trypanosoma brucei", the pathogen that causes African trypanosomiasis, it has been suggested that "W. glossinidia" may one day be used to help control the spread of this disease.
ground_truth: Chlorophyll