Light color acclimation is a key process in the global ocean distribution of Synechococcus cyanobacteria

Understanding the functional diversity of specific microbial groups at the global scale is critical yet poorly developed. By combining the considerable knowledge accumulated through recent years on the molecular bases of photosynthetic pigment diversity in marine Synechococcus, a major phytoplanktonic organism, with the wealth of metagenomic data provided by the Tara Oceans expedition, we have been able to reliably quantify all known pigment types along its transect and provide a global distribution map. Unexpectedly, cells able to dynamically change their pigment content to match the ambient light color were ubiquitous and predominated in many environments. Altogether, our results unveiled the role of adaptation to light quality on niche partitioning in a key primary producer

Light color acclimation is a key process in the global ocean distribution of Synechococcus cyanobacteria

Grébert, Théophile ... et al.-- This article is contribution number 69 of Tara Oceans.-- 10 pages, 4 figures, supporting information http://www.pnas.org/content/suppl/2018/02/09/1717069115.DCSupplementalMarine Synechococcus cyanobacteria are major contributors to global oceanic primary production and exhibit a unique diversity of photosynthetic pigments, allowing them to exploit a wide range of light niches. However, the relationship between pigment content and niche partitioning has remained largely undetermined due to the lack of a single-genetic marker resolving all pigment types (PTs). Here, we developed and employed a robust method based on three distinct marker genes (cpcBA, mpeBA, and mpeW) to estimate the relative abundance of all known Synechococcus PTs from metagenomes. Analysis of the Tara Oceans dataset allowed us to reveal the global distribution of Synechococcus PTs and to define their environmental niches. Green-light specialists (PT 3a) dominated in warm, green equatorial waters, whereas blue-light specialists (PT 3c) were particularly abundant in oligotrophic areas. Type IV chromatic acclimaters (CA4-A/B), which are able to dynamically modify their light absorption properties to maximally absorb green or blue light, were unexpectedly the most abundant PT in our dataset and predominated at depth and high latitudes. We also identified populations in which CA4 might be nonfunctional due to the lack of specific CA4 genes, notably in warm high-nutrient low-chlorophyll areas. Major ecotypes within clades I–IV and CRD1 were preferentially associated with a particular PT, while others exhibited a wide range of PTs. Altogether, this study provides important insights into the ecology of Synechococcus and highlights the complex interactions between vertical phylogeny, pigmentation, and environmental parameters that shape Synechococcus community structure and evolutionThis work was supported by the French “Agence Nationale de la Recherche” Programs SAMOSA (Synechococcus as a model genus for studying adaptation of marine phytoplankton to environmental changes) (Grant ANR-13-ADAP-0010) and France Génomique (Grant ANR-10-INBS-09), the French Government “Investissements d’Avenir” programs World Ocean Bioressources, Biotechnologies and Earth-System Services (OCEANOMICS) (Grant ANR-11-BTBR-0008), the European Union’s Seventh Framework Programs FP7 MicroB3 (Grant Agreement 287589), and Marine Microorganisms: Cultivation Methods for Improving Their Biotechnological Applications (Macumba; Grant Agreement 311975), UK Natural Environment Research Council Grant NE/I00985X/1, and the Spanish Ministry of Science and Innovation Grant MicroOcean PANGENOMICS (GL2011-26848/BOS)Peer Reviewe