Prochlorococcus and Other Photosynthetic Picoplankton

Abstract

The smallest yet most abundant photosynthetic organism on earth is the marine cyanobacterium, Prochlorococcus, which represent a key component in marine ecology and global biogeochemical cycles. This tiny cell is extremely successful, dominating throughout the surface photic zone of the subtropical and tropical low nutrient, oligotrophic regions of the world's oceans from ∼45 °N to 40 °S. It has evolved to be an oligotrophic specialist, through a reduction in cell size, a streamlined genome and a reduced cellular requirement for the limited resources available in this environment. The ability to examine the abundance and distribution of Prochlorococcus in the wild, and measure its genomic and metabolic properties in the lab and field, has made Prochlorococcus a model system for advancing our understanding of the ecology of marine microbes.

Key Concepts:

  • The smallest photosynthetic cells in the oceans (picophytoplankton) dominate numerically and contribute significantly to primary production on a global scale.

  • Prochlorococcus is a cyanobacterium with a reduced cell size and streamlined genome providing it with advantages over other phytoplankton in oligotrophic oceans around the world.

  • The ability to measure genomic and metabolic properties in natural populations and isolates, and the ability to follow population dynamics, makes Prochlorococcus an excellent model system for studying microbial ecology on all scales.

Keywords: marine cyanobacteria; phytoplankton; biological oceanography; ecophysiology; microbial genomics

Figure 1.

(a) Epifluorescence micrograph of cultured Prochlorococcus and Synechococcus cells. The red is the chlorophyll fluorescence that occurs when the cells are exposed to blue light (excitation wavelength is 488 nm, and emission wavelength is 670 nm long pass). Contrast was adjusted after photo was taken to better visualise cells. Figure courtesy of Abraham Lorrain, University of Southern Maine. (b) Transmission electron micrograph of ProchlorococcusMED4. Figure courtesy of SW Chisholm Lab, Massachusetts Institute of Technology.

Figure 2.

Flow cytometric dot plots (‘signatures’) of scatter and fluorescence obtained for a marine sample collected in the Pacific Ocean at a depth of 65 m (OLIPAC cruise, Cast 94, 5°S to 150°W). (a) Red (chlorophyll) fluorescence versus forward scattered light; (b) Red fluorescence versus side scatter; (c) Red versus orange (phycoerythrin) fluorescence; (d) Orange fluorescence versus side scatter. Prochlorococcus (Proc), Synechoccccus (Syn) and picoeukaryotes (Euk) are discriminated on the basis of the autofluorescence of their natural pigments, chlorophyll or phycoerythrin. 0.95‐μm fluorescent beads were added as internal reference. Reproduced with permission from Marie et al. .

Figure 3.

Neighbour‐joining phylogenetic tree of ITS sequences (not including sequences from the tRNAs). Numbers at nodes are support values (bootstrap values) of MegaNJ and MegaME respectively. Black dots indicate culture isolates that have their complete genome sequenced, black triangles indicate novel cultured isolates and undesignated sequences are from environmental DNA samples. Novel culture isolates have their isolation location preceding their isolate name (HOT‐Hawaii Ocean Time‐series, BATS‐Bermuda Atlantic Time‐Series, UH‐University of Hawaii and SA‐South Atlantic). Clade designations have been determined from Lavin et al. . Environmental DNA samples are from Lavin et al. (LLI‐VI), Martiny et al. (NC1) and Rocap et al. (HL). Grey box indicates novel isolates that have been isolated and maintained in nitrate containing media. Statistical evaluation of tree topologies was performed by bootstrap analysis with 100 resamplings. Environmental DNA samples and culture isolate names are denoted by their GenBank accession numbers. Figure courtesy of Kathryn H. Roache‐Johnson, University of Southern Maine.

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Further Reading

Bang M and Chisholm P (2009) Living Sunlight: How Plants Bring Life to the Earth. New York: Blue Sky Press/Scholastic. 43pp. (a children's book on Photosynthesis).

Chen M and Bibby TS (2005) Photosynthetic apparatus of antenna‐reaction centres supercomplexes in oxyphotobacteria: Insight through significance of Pcb/IsiA proteins. Photosynthesis Research 86: 165–173.

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Van Mooy BAS, Fredricks HF, Pedler BE et al. (2009) Phytoplankton in the ocean use non‐phosphorus lipids in response to phosphorus scarcity. Nature 458: 69–72.

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Moore, Lisa R(Dec 2010) Prochlorococcus and Other Photosynthetic Picoplankton. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0022840]