Genome sequence of the cyanobacterium Prochlorococcus marinus SS120, a nearly minimal oxyphototrophic genome

Abstract

Prochlorococcus marinus, the dominant photosynthetic organism in the ocean, is found in two main ecological forms: high-light-adapted genotypes in the upper part of the water column and low-lightadapted genotypes at the bottom of the illuminated layer. P. marinus SS120, the complete genome sequence reported here, is an extremely low-light-adapted form. The genome of P. marinus SS120 is composed of a single circular chromosome of 1,751,080 bp with an average G؉C content of 36.4%. It contains 1,884 predicted protein-coding genes with an average size of 825 bp, a single rRNA operon, and 40 tRNA genes. Together with the 1.66-Mbp genome of P. marinus MED4, the genome of P. marinus SS120 is one of the two smallest genomes of a photosynthetic organism known to date. It lacks many genes that are involved in photosynthesis, DNA repair, solute uptake, intermediary metabolism, motility, phototaxis, and other functions that are conserved among other cyanobacteria. Systems of signal transduction and environmental stress response show a particularly drastic reduction in the number of components, even taking into account the small size of the SS120 genome. In contrast, housekeeping genes, which encode enzymes of amino acid, nucleotide, cofactor, and cell wall biosynthesis, are all present. Because of its remarkable compactness, the genome of P. marinus SS120 might approximate the minimal gene complement of a photosynthetic organism.

Evolutionary origin of a streamlined marine bacterioplankton lineage

“…Prominent examples are alphaproteobacterial SAR11 (Giovannoni et al, 2005), gammaproteobacterial SAR86 (Dupont et al, 2012), cyanobacterial Prochlorococcus (Dufresne et al, 2003;Rocap et al, 2003) and betaproteobacterial OM43 (Giovannoni et al, 2008). Members of these lineages are either uncultivated or difficult to propagate when cultures are available.…”

Advances in genetic engineering of marine algae

“…The emerging field of marine algal genomics first began with publications of the three genomes of the smallest known oxygenevolving autotroph Prochlorococcus (Dufresne et al, 2003, Rocap et al, 2003. To date, over 20 cyanobacterial genomes have been released.…”

“…However, several Prochlorococcus genomes do not contain genes for the transport systems of nitrate, nitrite, cyanate, and urea, which are present in freshwater cyanobacteria. They also do not contain the coding for a nitrate/nitrite permease that was recently discovered in a marine Synechococcus (Dufresne et al, 2003;El Alaoui et al, 2001), which may be the most surprising discovery regarding substrate utilization (Scanlan et al, 2009). …”

Proteomics of marine bacteria

“…[9]. Recently, the genomes of three different members of the cyanobacterium species Prochlorococcus marinus have been sequenced [10,11]. These members of the genus Prochlorococcus dominate phytoplankton communities in most tropical and temperate open ocean ecosystems [12].…”

“…These members of the genus Prochlorococcus dominate phytoplankton communities in most tropical and temperate open ocean ecosystems [12]. P. marinus is found in two main ecological forms: high-light-adapted genotypes in the upper part of the water column and low-light-adapted genotypes at the bottom of the illuminated layer [10]. The analysis of the genome sequences of the different P. marinus strains led to the identification of genes, which play a role in determining the relative fitness of the ecotypes in response to key environmental variables [11].…”