Phycobiliprotein genes of the marine photosynthetic prokaryote Prochlorococcus: evidence for rapid evolution of genetic heterogeneity.

TitlePhycobiliprotein genes of the marine photosynthetic prokaryote Prochlorococcus: evidence for rapid evolution of genetic heterogeneity.
Publication TypeJournal Article
Year of Publication2001
AuthorsTing, CS, Rocap, G, King, J, Chisholm, SW
JournalMicrobiology
Volume147
IssuePt 11
Pagination3171-82
Date Published2001 Nov
ISSN1350-0872
KeywordsAmino Acid Sequence, Bacterial Proteins, Base Composition, chlorophyll, Cyanobacteria, Cytochrome b Group, Evolution, Molecular, Light-Harvesting Protein Complexes, Molecular Sequence Data, Phycobilisomes, Phycoerythrin, Phylogeny, Phytoplankton, Polymerase Chain Reaction, Proteins, RNA, Ribosomal, 16S, Sequence Analysis, DNA
Abstract

Prochlorococcus is a major photosynthetic prokaryote in nutrient-limited, open ocean environments and an important participant in the global carbon cycle. This phototroph is distinct from other members of the cyanobacterial lineage to which it belongs because it utilizes a chlorophyll a2/b(2) light-harvesting complex as its major antenna, instead of phycobilisomes. Recently, genes encoding the phycobiliprotein phycoerythrin were identified in several Prochlorococcus isolates, thus making it the only extant photosynthetic prokaryote to possess a chlorophyll a/b antenna as well as phycobiliprotein genes. In order to understand the evolution of phycobiliproteins in this genus, the authors have sequenced the phycoerythrin genes of two isolates that are the most deeply branching in the Prochlorococcus lineage and share the highest degree of 16S rDNA sequence similarity to phycobilisome-containing marine SYNECHOCOCCUS: Sequence analyses suggest that within the Prochlorococcus lineage, the selective forces shaping the evolution of the phycoerythrin gene set have not been uniform. Although strains that are most closely related to marine Synechococcus possess genes (cpeB, cpeA) encoding both subunits of phycoerythrin, a more recently evolved strain is shown to lack cpeA and to possess a degenerate form of cpeB. Differences in phycoerythrin gene sequences between Prochlorococcus and Synechococcus appear to be consistent with a model of elevated mutation rates rather than relaxed selection. This suggests that although phycoerythrin is not a major constituent of the light-harvesting apparatus in Prochlorococcus, as it is in Synechococcus, the cpeB and cpeA genes are still under selection, albeit a different type of selection than in Synechococcus. The evolution of the Prochlorococcus light-harvesting antenna complex provides an important system for understanding the origins and scope of phylogenetic diversity in ocean ecosystems.

Alternate JournalMicrobiology (Reading, Engl.)
PubMed ID11700369