Expression of cadmium carbonic anhydrase of diatoms in seawater

Abstract

The enzyme carbonic anhydrase (CA) plays a key role in the acquisition of inorganic carbon for photosynthesis in phytoplankton. Genes coding for the carbonic anhydrase CDCA, which can use either Cd or Zn as a metal center, are found in many diatom species and in natural seawater samples. The use of Cd in CDCA is the only known biological function of Cd and is thought to explain the nutrient-like concentration profile of Cd in the oceans. Here we report on the expression of CDCA in cultures of Thalassiosira weissflogii and in samples from the Equatorial Pacific and coastal New Jersey. CDCA1 is one of 2 types of CA found in T. weissflogii; its expression is highly modulated by pH changes and is induced by the addition of Cd. Attempts to amplify cdca mRNA from samples of the Equatorial Pacific were not successful. However, protein bands from a sample incubated with Cd and analyzed by polyacrylamide gel electrophoresis (PAGE) reacted with CDCA antiserum, and a sample concentrated by immunoprecipitation yielded peptide sequences matching CDCA1. In samples from New Jersey coastal water, we found a high level of CDCA expression, which was inversely correlated with pCO2. CDCA is indeed expressed in ocean waters and is regulated in a manner consistent with its putative role in CO2 acquisition. © Inter-Research 2008.