Defining the molecular basis of phylogenetic diversity in marine Synechococcus / a genomic approach

Photosynthesis in the oceans leads to the production of just under half of the oxygen in the atmosphere. In the nutrient-poor central regions of the oceans this production of oxygen is dominated by very small, single celled organisms, which are referred to as the photosynthetic picoplankton. Phycobilisome-containing unicellular cyanobacteria of the genus Synechococcus are a major component of this picoplankton fraction and have a ubiquitous distribution in oceanic waters responsible for around a quarter of the primary production in some regions. The genus is genetically diverse, demonstrating heterogeneity at the level of the 16S rDNA gene, which thus far has phylogenetically defined at least ten distinct lineages or clades. We have previously proposed that this phylogenetic heterogeneity underlies subtle differences in physiology that allow specific lineages to occupy distinct niches in the water column. This idea is consistent with recent molecular ecological work from my lab which has demonstrated distinct spatial distributions of these lineages in situ, which we suggest is akin to occupying specific niches. To more completely understand the molecular basis of this niche adaptation we propose here to undertake a genomic approach to identify what we hypothesise are the sets of genes that define the ecological 'distinctness' of these lineages. By coupling this work to extensive bioinformatic analysis of the sequenced genomes we aim to obtain a comprehensive picture of the mechanisms of genome evolution in this genus.