Unicellular marine picocyanobacteria are key photosynthetic microorganisms that are responsible for a significant fraction of global primary production and which underpin the entire marine food web. The genus Synechococcus, ubiquitous to the marine environment, exhibits a great deal of genetic diversity and harbors the largest pigment array of all marine cyanobacteria. Their habitat ranges across all latitudes and all depths in the euphotic zone, but the molecular adaptations that allow this broad distribution remain unclear.
In this work, we aim to unravel the genetic basis for adaptation of Synechococcus sp. to distinct environments. This encompasses functional characterization of periplasmic binding proteins (PBPs), which facilitate a wide variety of fundamental processes (e.g. transport, chemotaxis, quorum sensing). PBPs bind to the specific ligands/substrates and bring them to the interface of the cell membrane. Subsequently, membrane proteins pump the substrates across the membrane into the cytoplasm.
We systematically identified PBPs across eight fully sequenced Synechococcus genomes and grouped them according to putative specificity for inorganic nutrient transport (e.g. CO3-, PO4-, Fe3+) and organic compounds (amino acids, oligopeptides). The ecological importance of utilizing organic compounds as substrates could have important implications for global carbon and nitrogen cycling in the oceans, yet remains ill defined.
In order to characterize substrate specificity of the identified PBPs, we have initiated high-throughput production to sample the functional range of this protein family. Progress of selected panels of these genes will be outlined.