Biology

Genome divergence in two Prochlorococcus ecotypes reflects oceanic niche differentiation

Document Type

Article

Abstract

The marine unicellular cyanobacterium Prochlorococcus is the smallest-known oxygen-evolving autotroph. It numerically dominates the phytoplankton in the tropical and subtropical oceans, and is responsible for a significant fraction of global photosynthesis. Here we compare the genomes of two Prochlorococcus strains that span the largest evolutionary distance within the Prochlorococcus lineage and that have different minimum, maximum and optimal light intensities for growth. The high-light-adapted ecotype has the smallest genome (1,657,990 base pairs, 1,716 genes) of any known oxygenic phototroph, whereas the genome of its low-light-adapted counterpart is significantly larger, at 2,410,873 base pairs (2,275 genes). The comparative architectures of these two strains reveal dynamic genomes that are constantly changing in response to myriad selection pressures. Although the two strains have 1,350 genes in common, a significant number are not shared, and these have been differentially retained from the common ancestor, or acquired through duplication or lateral transfer. Some of these genes have obvious roles in determining the relative fitness of the ecotypes in response to key environmental variables, and hence in regulating their distribution and abundance in the oceans.

Publication Title

Nature

Publication Date

8-28-2003

Volume

424

Issue

6952

First Page

1042

Last Page

1047

ISSN

0028-0836

DOI

10.1038/nature01947

Keywords

bacterial genome, bacterioplankton, Cyanobacterium, evolution, gene transfer, genetic variability, genome, marine environment, nucleotide sequence, oceanic regions, photosynthesis, phylogeny, polymerase chain reaction, Prochlorococcus, strain difference

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