Responses of the marine diatom Thalassiosira pseudonana to changes in CO concentration: a proteomic approach.

The concentration of CO in many aquatic systems is variable, often lower than the K of the primary carboxylating enzyme Rubisco, and in order to photosynthesize efficiently, many algae operate a facultative CO concentrating mechanism (CCM). Here we measured the responses of a marine diatom, Thalassiosira pseudonana, to high and low concentrations of CO at the level of transcripts, proteins and enzyme activity. Low CO caused many metabolic pathways to be remodeled. Carbon acquisition enzymes, primarily carbonic anhydrase, stress, degradation and signaling proteins were more abundant while proteins associated with nitrogen metabolism, energy production and chaperones were less abundant. A protein with similarities to the Ca/ calmodulin dependent protein kinase II_association domain, having a chloroplast targeting sequence, was only present at low CO. This protein might be a specific response to CO limitation since a previous study showed that other stresses caused its reduction. The protein sequence was found in other marine diatoms and may play an important role in their response to low CO concentration.