Rapid Diversification of Marine Picophytoplankton with Dissimilar Light-Harvesting Structures Inferred from Sequences of Prochlorococcus and Synechococcus (Cyanobacteria)

Abstract

Cultured isolates of the unicellular planktonic cyanobacteria Prochlorococcus and marine Synechococcus belong to a single marine picophytoplankton clade. Within this clade, two deeply branching lineages of Prochlorococcus, two lineages of marine A Synechococcus and one lineage of marine B Synechococcus exhibit closely spaced divergence points with low bootstrap support. This pattern is consistent with a near-simultaneous diversification of marine lineages with divinyl chlorophyll b and phycobilisomes as photosynthetic antennae. Inferences from 16S ribosomal RNA sequences including data for 18 marine picophytoplankton clade members were congruent with results of psbB and petB and D sequence analyses focusing on five strains of Prochlorococcus and one strain of marine A Synechococcus. Third codon position and intergenic region nucleotide frequencies vary widely among members of the marine picophytoplankton group, suggesting that substitution biases differ among the lineages. Nonetheless, standard phylogenetic methods and newer algorithms insensitive to such biases did not recover different branching patterns within the group, and failed to cluster Prochlorococcus with chloroplasts or other chlorophyll b-containing prokaryotes. Prochlorococcus isolated from surface waters of stratified, oligotrophic ocean provinces predominate in a lineage exhibiting low G + C nucleotide frequencies at highly variable positions.

Periodic picophytoplankton predominance in a large, shallow alkaline lake (Lake Fertő, Neusiedlersee)

“…The majority of our 16S rDNA clones clustered within the nonmarine members of the picophytoplankton clade sensu Urbach et al (1998) (Fig. 3).…”

A novel clade of Prochlorococcus found in high nutrient low chlorophyll waters in the South and Equatorial Pacific Ocean

“…For the eMIT9312 ecotype, 16S-ITS-23S rRNA gene fragments were PCR amplified from Prochlorococcus sp. GP2 (Urbach et al, 1998) DNA and cloned as described above. Plasmid DNA was prepared from overnight Escherichia.…”

“…The HL-adapted clade can be divided into two subclades (Urbach et al, 1998;West and Scanlan, 1999) known as HLI and HLII, or alternatively eMED4 and eMIT9312 (Ahlgren et al, 2006). These HL ecotypes exhibit markedly different global distributions; whereas eMIT9312 is the most abundant and widespread ecotype, occurring in warmer, stratified, tropical and sub-tropical waters, eMED4 is usually found in colder and moderately stratified higher latitude waters (Bouman et al, 2006;Johnson et al, 2006;Zwirglmaier et al, 2007Zwirglmaier et al, , 2008.…”

Effects of low temperature on tropical and temperate isolates of marine Synechococcus

“…Phylogenies based on ribosomal RNA genes display three main subclusters, 5.1, 5.2 and 5.3, which are further classified into over 20 phylogenetically-distinct clades. The largest, sub-cluster 5.1, is the dominant cluster in the marine environment (Urbach et al, 1998;Herdman et al, 2001;Fuller et al, 2003;Dufresne et al, 2008;Ahlgren and Rocap, 2012). Oceanic surveys indicate that these clades exhibit broad distribution from the equator to the polar regions having colonized habitats defined by a broad range of light, temperature and nutrient regimes (Fuller et al, 2003;Ahlgren and Rocap, 2006;Penno et al, 2006;Paerl et al, 2008;Zwirglmaier et al, 2008;Scanlan et al, 2009;Post et al, 2011;Huang et al, 2012;Mazard et al, 2012).…”