Ecological Genomics of Marine Picocyanobacteria

Abstract

SUMMARY Marine picocyanobacteria of the genera Prochlorococcus and Synechococcus numerically dominate the picophytoplankton of the world ocean, making a key contribution to global primary production. Prochlorococcus was isolated around 20 years ago and is probably the most abundant photosynthetic organism on Earth. The genus comprises specific ecotypes which are phylogenetically distinct and differ markedly in their photophysiology, allowing growth over a broad range of light and nutrient conditions within the 45°N to 40°S latitudinal belt that they occupy. Synechococcus and Prochlorococcus are closely related, together forming a discrete picophytoplankton clade, but are distinguishable by their possession of dissimilar light-harvesting apparatuses and differences in cell size and elemental composition. Synechococcus strains have a ubiquitous oceanic distribution compared to that of Prochlorococcus strains and are characterized by phylogenetically discrete lineages with a wide range of pigmentation. In this review, we put our current knowledge of marine picocyanobacterial genomics into an environmental context and present previously unpublished genomic information arising from extensive genomic comparisons in order to provide insights into the adaptations of these marine microbes to their environment and how they are reflected at the genomic level.

Functional distinctness in the exoproteomes of marine Synechococcus

“…different binding affinities for phosphate. A potential component of a phosphonate ABC transport protein was detected (Table S4) in strains RS9917, WH5701 and WH7805 (the corresponding gene is conserved across picocyanobacterial genomes, see Scanlan et al ., 2009) despite the fact that C‐P lyase, the enzyme required to cleave the recalcitrant C‐P bond of these compounds, has not been identified in any Synechococcus genome. Transporters for nitrogen were less abundant possibly because of the high N : P ratio (50:1) in ASW medium repressing their expression.…”

“…RS9916) were classified as interaction proteins because of the adhesion and haemolysin‐like domains they contain. This diverse set of peculiar large proteins, that rarely share similarities among strains, are thought to play a role in shielding cells from potential threats (Scanlan et al ., 2009). …”

The Yfr2 ncRNA family, a group of abundant RNA molecules widely conserved in cyanobacteria

“…However, assuming a regulatory function for Yfr2-type ncRNAs, this observation is consistent with the fact that this strain has the highest number of sigma factors (ten) and the second highest number of other protein-based regulators among all picocyanobacteria studied to date. 9 In all other cases, the phylogenetic tree shows a clear separation between Synechococcus and Prochlorococcus Yfr2 sequences (Fig. 3A).…”

Advances in genetic engineering of marine algae

“…Most genomes of the marine cyanobacteria that are currently available harbor a very limited repertoire of hik and rer genes, including only five to six potential hik genes and seven to 11 potential Rer genes, as compared to the 13 to 95 potential hiks and 23 to 94 potential Rers of freshwater and terrestrial strains (Ashby and Houmard, 2006;Mary and Vaulot, 2003). In the N metabolism of the assimilation of ammonium into organic N compounds, as in other cyanobacteria, marine Synechococcus and Prochlorococcus strains use the glutamine synthetase glutamate synthase pathway to assimilate ammonium (Scanlan et al, 2009). However, several Prochlorococcus genomes do not contain genes for the transport systems of nitrate, nitrite, cyanate, and urea, which are present in freshwater cyanobacteria.…”

“…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). …”