Co-occurringSynechococcusecotypes occupy four major oceanic regimes defined by temperature, macronutrients and iron

Abstract

Marine picocyanobacteria, comprised of the genera Synechococcus and Prochlorococcus, are the most abundant and widespread primary producers in the ocean. More than 20 genetically distinct clades of marine Synechococcus have been identified, but their physiology and biogeography are not as thoroughly characterized as those of Prochlorococcus. Using clade-specific qPCR primers, we measured the abundance of 10 Synechococcus clades at 92 locations in surface waters of the Atlantic and Pacific Oceans. We found that Synechococcus partition the ocean into four distinct regimes distinguished by temperature, macronutrients and iron availability. Clades I and IV were prevalent in colder, mesotrophic waters; clades II, III and X dominated in the warm, oligotrophic open ocean; clades CRD1 and CRD2 were restricted to sites with low iron availability; and clades XV and XVI were only found in transitional waters at the edges of the other biomes. Overall, clade II was the most ubiquitous clade investigated and was the dominant clade in the largest biome, the oligotrophic open ocean. Co-occurring clades that occupy the same regime belong to distinct evolutionary lineages within Synechococcus, indicating that multiple ecotypes have evolved independently to occupy similar niches and represent examples of parallel evolution. We speculate that parallel evolution of ecotypes may be a common feature of diverse marine microbial communities that contributes to functional redundancy and the potential for resiliency.

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

“…Their growth physiology is consistent with the environmental distribution of these clades reported in the previous studies (Zwirglmaier et al, 2007(Zwirglmaier et al, , 2008Ahlgren and Rocap, 2012;Huang et al, 2012;Sohm et al, 2016). Growth rates were marginally lower at low temperature in strains of clade I (CC9311) and IV (BL107, CC9902), which are dominant in temperate regions.…”

“…These general responses in growth rate and photophysiology at different temperatures demonstrate the adaptability of Synechococcus isolates across a broad range of optimal growth temperatures. However, they do not explain the fundamental differences in each clade that result in the vastly different observed environmental distributions (Zwirglmaier et al, 2008;Sohm et al, 2016).…”

“…Clades I and IV are predominant in oceanic latitudes above 30°N and below 30°S. Clades II and III are found mostly within tropical and sub-tropical oceanic latitudes (Zwirglmaier et al, 2007(Zwirglmaier et al, , 2008Scanlan et al, 2009;Mella-Flores et al, 2011;Post et al, 2011;Ahlgren and Rocap, 2012;Mazard et al, 2012;Huang et al, 2012;Sohm et al, 2016). In relation to temperature, clades I and IV occur at higher abundances at 10 -20°C whereas clades II and III occur in the range of 20-28°C (Zwirglmaier et al, 2008) suggesting that temperature, among other environmental factors, may have a key role in their partitioning.…”

Global genetic capacity for mixotrophy in marine picocyanobacteria

“…Prochlorococcus and marine Synechococcus (hereafter designated marine picocyanobacteria) can be divided into phylogenetic clusters that generally correspond to physiologically distinct ecotypes (West and Scanlan, 1999;West et al, 2001;Ahlgren et al, 2006;Johnson et al, 2006;Zinser et al, 2006Zinser et al, , 2007Malmstrom et al, 2010;Sohm et al, 2015). In Prochlorococcus these ecotypes have different light and temperature optima, which results in a partitioning of the water column with depth, and different relative abundances along latitudinal gradients (Moore et al, 1998;Moore and Chisholm, 1999;Rocap et al, 2003;Johnson et al, 2006;Zinser et al, 2007).…”

“…In Prochlorococcus these ecotypes have different light and temperature optima, which results in a partitioning of the water column with depth, and different relative abundances along latitudinal gradients (Moore et al, 1998;Moore and Chisholm, 1999;Rocap et al, 2003;Johnson et al, 2006;Zinser et al, 2007). Synechococcus ecotypes can be defined by open ocean and coastal phylogenetic clusters (Dufresne et al, 2008;Ahlgren and Rocap, 2012) as well as by temperature-and nutrient concentration-related groups (Sohm et al, 2015). Because of this ecotype partitioning along phylogenetic lines, if picocyanobacterial mixotrophic capacity is partitioned by phylogenetic group it suggests a role for mixotrophy in niche adaptation.…”