The ISME Journal (2014) 8, 1221–1236 & 2014 International Society for Microbial Ecology All rights reserved 1751-7362/14 www.nature.com/ismej ORIGINAL ARTICLE Connecting thermal physiology and latitudinal niche partitioning in marine Synechococcus Justine Pittera1,2, Florian Humily1,2, Maxine Thorel3, Daphne´ Grulois1,2, Laurence Garczarek1,2 and Christophe Six1,2 1University Pierre and Marie Curie (Paris 06), UMR 7144 Adaptation and Diversity in Marine Environments, Marine Phototrophic Procaryotes (MaPP) Team, Station Biologique de Roscoff, Place Georges Teissier, CS 90074, Roscoff cedex, France; 2Centre National de la Recherche Scientifique, UMR 7144 Adaptation and Diversity in Marine Environments, Oceanic Plankton Group, Station Biologique de Roscoff, Place Georges Teissier, CS 90074, Roscoff cedex, France and 3University of Caen-Basse Normandie et Centre National de la Recherche Scientifique, Institut d’Ecologie et d’Environnement, FRE 3484 Biologie des Mollusques Marins et des Ecosyste`mes associe´s, Caen, France Marine Synechococcus cyanobacteria constitute a monophyletic group that displays a wide latitudinal distribution, ranging from the equator to the polar fronts. Whether these organisms are all physiologically adapted to stand a large temperature gradient or stenotherms with narrow growth temperature ranges has so far remained unexplored. We submitted a panel of six strains, isolated along a gradient of latitude in the North Atlantic Ocean, to long- and short-term variations of temperature. Upon a downward shift of temperature, the strains showed strikingly distinct resistance, seemingly related to their latitude of isolation, with tropical strains collapsing while northern strains were capable of growing. This behaviour was associated to differential photosynthetic performances. In the tropical strains, the rapid photosystem II inactivation and the decrease of the antioxydant b-carotene relative to chl a suggested a strong induction of oxidative stress. These different responses were related to the thermal preferenda of the strains. The northern strains could grow at 10 1C while the other strains preferred higher temperatures. In addition, we pointed out a correspondence between strain isolation temperature and phylogeny. In particular, clades I and IV laboratory strains were all collected in the coldest waters of the distribution area of marine Synechococus. We, however, show that clade I Synechococcus exhibit different levels of adaptation, which apparently reflect their location on the latitudinal temperature gradient. This study reveals the existence of lineages of marine Synechococcus physiologically specialised in different thermal niches, therefore suggesting the existence of temperature ecotypes within the marine Synechococcus radiation. The ISME Journal (2014) 8, 1221–1236; doi:10.1038/ismej.2013.228; published online 9 January 2014 Subject Category: Microbial ecology and functional diversity of natural habitats Keywords: adaptation; ecotype; marine cyanobacteria; Synechococcus; temperature Introduction Garczarek, 2010). Prochlorococcus thrives in warm waters of the latitudinal 451N–401S band, whereas Marine picocyanobacteria belonging to the Pro- Synechococcus cells prefer coastal and mesotrophic chlorococcus and Synechococcus genera are major open ocean waters, with a much wider latitudinal contributors to carbon biomass and global oceanic distribution ranging from the equator to the polar primary production and may contribute up to half of fronts (Not et al., 2005; Zwirglmaier et al., 2008; the fixed carbon in some oceanic regions (Li, 1994; Huang et al., 2011). In addition, Synechococcus Liu et al., 1997; Buitenhuis et al., 2012). Although has no obvious depth preference, the highest cell phylogenetically closely related, these two cyano- densities being often observed in the upper mixed bacteria exhibit distinct traits of ecology, physiology layer, whereas Prochlorococcus shows strong depth and evolution (Partensky et al., 1999; Partensky and partitioning, with two main ecotypes that are both physiologically and genetically distinct: a high light (HL)-adapted ecotype, occupying the upper part of Correspondence: C Six, UMR 7144 UPMC-CNRS, University Paris the euphotic zone and a low light(LL)-adapted 06 (Pierre and Marie Curie), Station Biologique de Roscoff, Place ecotype, dominating the bottom of the euphotic Georges Teissier, CS90074, 29688, Roscoff, France. E-mail: [email protected] layer (Moore et al., 1998). The HL ecotype has been Received 30 July 2013; revised 15 November 2013; accepted 16 further subdivided into HLI and HLII, which exhibit November 2013; published online 9 January 2014 distinct latitudinal distributions, HLII dominating Temperature adaptation in marine Synechococcus J Pittera et al 1222 between 281S and 331N and HLI above 321Sor381N, Synechococcus lineages (Palenik 2001; Six et al., a difference seemingly linked to the different 2007c), and therefore do not constitute ecotypes sensu temperature growth optima of their cultured repre- stricto. Similarly, although nutrient availability con- sentatives (Johnson et al., 2006; Zinser et al., 2007). tribute to some of the variability of the Synechococcus Using the 16S ribosomal RNA and Internal community structure (Zwirglmaier et al., 2008; Transcribed Spacer genetic markers, respectively, Mazard et al., 2012a), a clear delineation of nutrient 10 and 15 different clades (Rocap et al., 2002; ecotypes (equivalent to Prochlorococcus light eco- Fuller et al., 2003) have been delineated within the types) within the Synechococcus radiation remains main group of the marine Synechococcus radiation globally elusive (Palenik et al., 2006; Scanlan et al., (cluster 5.1; sensu Herdman et al., 2001). However, a 2009; Stuart et al., 2009). A notable exception recent study by Mazard et al. (2012a) has highlighted concerns the response to phosphorus limitation a greater genetic microdiversity than previously (including cell size change and the ability to thought in this subcluster. Indeed, using the cyto- accumulate polyphosphate) that appears somewhat chrome b6 gene petB, they could define 430 consistent with Synechococcus phylogeny and their different subclades of marine Synechococcus. As a inferred ecology of the different clades (Mazard et al., result of this large number of lineages, the environ- 2012a). However, a large part of the variation observed mental factors that have directed the diversification in the Synechococcus community structure and the of marine Synechococcus appear much more hierarchy of environmental factors shaping ecotype complicated to understand than in the case of genomes remains largely unexplained. Prochlorococcus. Through a vast phylogeographic Adaptation to temperature variations among marine study, Zwirglmaier et al. (2007, 2008) have, Synechococcus has been so far poorly explored. This however, shown that, out of the dozen of marine environmental factor can significantly constrain Synechococcus 16S ribosomal RNA clades, only four growth, as the activity of most enzymes and biomem- (I–IV) predominate in the oceans. Clades I and IV branes directly depends on it, thus impacting major generally co-occur at latitudes above 301N/S and at metabolic processes. Among them, photosynthesis is depth, whereas clade II seems to prevail in warm, known to be particularly affected by temperature coastal or shelf areas (Zwirglmaier et al., 2007, 2008; variations, notably because of the resulting changes Huang et al., 2011; Mella-Flores et al., 2011; Ahlgren in thylakoidal fluidity that eventually lead to photo- and Rocap, 2012). The latitudinal distribution of system (PS) II inactivation (Murata and Los, 1997; clade III appears to be broader, but with an apparent Takahashi and Murata, 2008). Like for Prochlorococcus predominance in oligotrophic, offshore waters (Johnson et al., 2006; Zinser et al., 2007), temperature (Fuller et al., 2005; Zwirglmaier et al., 2008; Mella- might have thus played an important role in the Flores et al., 2011; Post et al., 2011). The other clades differentiation of the Synechococcus lineages, possibly are usually detected at low concentrations and their influencing significantly their genome shaping. How- distribution patterns are less clearly defined ever, given the scarcity of physiological studies of the (Zwirglmaier et al., 2008; Huang et al., 2011). response of open ocean Synechococcus isolates to To understand whether some Synechococcus temperature (Moore et al.,1995;Fuet al.,2007),itis lineages are adapted to specific ecological niches, difficult to assert whether the large latitudinal dis- both phylogeography and comparative physiology tribution of these picocyanobacteria is rather the result studies are necessary. These two approaches indeed of broad acclimation capacities to temperature, or of allow pointing out possible correspondences between adaptation processes underlying the existence of cell performances, phylogeny and ecological niches. different ‘thermotypes’ that would display distinct So far, most of the comparative studies of marine temperature optima for growth. Synechococcus physiology have dealt with adapta- To explore these questions, we describe in this tion and acclimation capacities to light (Six et al., paper the short- and long-term responses to tem- 2004, 2007b,c) and nutrients variations (for example, perature of a panel of six Synechococcus strains, Liu et al., 2012; Mazard et al., 2012b). These works isolated at various latitudes, in mesotrophic waters