Prochloroccus ecotypes are therefore designated on the basis of their physiology and are classically designated as high light clades (HL) I–IV and low light (LL) clades I–IV. HL clades predominate in the upper water column to ~ 50 m depth RG7420 in vivo in highly stratified tropical waters ( West et al., 2011 and Johnson et al., 2006) while LL clades will persist down to between 150 and 200 m where they become light limited at ~ 0.1% of surface irradiance. Occasionally the LLI clade has been shown to be relatively abundant in near surface waters, or throughout the photic zone ( Johnson et al., 2006) and may

represent an intermediate ecotype ( Partensky and Garczarek, 2010). Distinct HL clades display temperature related optima in abundance. The HL I clade is adapted to cold temperate waters, while the HL II is dominant in both moderate and warm (sub)tropical waters ( Johnson et al., 2006 and Zinser et al., 2007). Clades HL III and HL IV are generally less abundant, accounting for between 5% and 20% when present, but are confined to warm equatorial waters > 26 °C ( Malmstrom et al., 2013, Rusch et al., 2010 and West et al., 2011). Marine Synechococcus classifications are more complicated than those of the Prochlorococcus, and the ecological strategies this website of the different types are less well characterized. The current status is well documented by recent multi-locus phylogenetic studies by Mazard et al. (2012) and Ahlgren and Rocap (2012). Marine

Synechococcus belong to three “sub clusters” 5.1, 5.2 and 5.3, with 5.1 the dominant sub-cluster in

most systems including coastal and open ocean regions. These sub-clusters are further divided in numerous clades and sub-clades. For example, the dominant marine sub-cluster 5.1 is sub-divided into at least 16 ( Ahlgren and Rocap, 2012) and potentially more than 30 ( Mazard et al., 2012) distinct clades. Synechococcus clades also appear to represent ecotypes specifically adapted to a variety of environmental conditions ( Mazard et al., 2012). For example, clades I and IV predominate in both coastal and open ocean temperate and cold environments ( Zwirglmaier et al., 2008) and may vary seasonally in their relative abundances ( Tai and Palenik, 2009), Clade III is the dominant lineage in tropical C59 clinical trial and subtropical oceanic gyres ( Zwirglmaier et al., 2008) and Clade II is found predominantly in tropical open ocean environments ( Ferris and Palenik, 1998, Toledo and Palenik, 2003 and Ahlgren and Rocap, 2006). While there is gathering evidence for the ecological partitioning of Synechcococcus lineages, the physiological bases for potential ‘ecotypes’ is not as clearly defined as for Prochlorococcus. However, distinct growth temperature optima ( Pittera et al., 2014), substrate utilization profiles ( Moore et al., 2005), and spectral tuning of light harvesting antennae ( Six et al., 2007) are some adaptations that may contribute to niche partitioning of clades and sub-groups.