The sequencing of the complete genomes of environmentally important organisms enables powerful new approaches to study the physiological ecology of microorganisms and their interactions with their of environment. In collaboration with Bess Ward's group, we have assembled a DNA microarray with the complete genome of the marine cyanobacterium Synechococcus WH8102. Ongoing laboratory experiments are designed to test the physiological response of the organism to changes in the metal concentrations of their external medium. Extension of this work will capitalize on the soon-to-be-published genome of the diatom Thalassiosira pseudonana and will involve field applications of gene chips.