During my Masters (MSc) and PhD training I was studying the influence of environmental changes (CO2, light, and nutrients) on an ecologically important marine diazotrophic (nitrogen fixing) cyanobacteria Trichodesmium erythraeum and in natural oceanic environments (the Atlantic Ocean and the Red Sea). My work was the first to demonstrate that elevated atmospheric CO2 concentrations can increase new nitrogen fixation and subsequently new carbon inputs to the ocean. I also described the cellular and metabolic mechanisms for how nitrogen fixation might be regulated by environmental factors. I then moved on to my Post-Doctoral research where I climbed up in the evolutionary tree from prokaryotes to eukaryotes and started asking questions on how another important oceanic phytoplankton taxon, diatom, sense their environment and what controls their intermediate metabolism. I examined the model pennate diatom Phaeodactylum tricornutum to explore the possibility of genetically manipulating the diatom for biofuel production. By studying the molecular and metabolic interactions between the central carbon and nitrogen pathways, I pin-pointed two enzymes to be targeted by genetic modifications. Indeed, the phenotypes of my nitrate reductase (NR) knockdown and a type II diacylglycerol acyltransferase (DGAT) over-expression strains clearly indicate that lipid biosynthesis can be uncoupled from protein shuffling. My work significantly advances the community’s basic understanding of carbon allocation, nitrogen metabolism and lipid dynamics in diatoms, and has applications towards development of biofuels.