A biological function for cadmium in marine diatoms

Abstract

The oceanic distribution of cadmium follows closely that of major algal nutrients such as phosphate. The reasons for this ''nutrientlike'' distribution are unclear, however, because cadmium is not generally believed to have a biological function. Herein, we provide evidence of a biological role for Cd in the marine diatom Thalassiosira weissflogii under conditions of low zinc, typical of the marine environment. Addition of Cd to Zn-limited cultures enhances the growth rate of T. weissflogii, particularly at low pCO2. This increase in growth rate is reflected in increased levels of cellular carbonic anhydrase (CA) activity, although the levels of TWCA1, the major intracellular Zn-requiring isoform of CA in T. weissflogii, remain low. 109 Cd label comigrates with a protein band that shows CA activity and is distinct from TWCA1 on native PAGE of radiolabeled T. weissflogii cell lysates. The levels of the Cd protein are modulated by CO2 in a manner that is consistent with a role for this enzyme in carbon acquisition. Purification of the CA-active fraction leads to the isolation of a Cd-containing protein of 43 kDa. It is now clear that T. weissflogii expresses a Cd-specific CA, which, particularly under conditions of Zn limitation, can replace the Zn enzyme TWCA1 in its carbon-concentrating mechanism.

Carbonic anhydrases in plants and algae

“…The putative CA cDNA obtained in this fashion was sequenced and the sequence does not match a known CA from any of the (Lane & Morel, 2000). Recent work with T. weissflogii indicates that this diatom might be able to substitute Cd for Zn under Znlimiting environmental conditions (Lane & Morel, 2000). They demonstrated that the Cd-CA was different than the other CA they had previously found in T. weissflogii (Roberts et al 1997).…”

“…Using this sequence information, a fragment of DNA was amplified by polymerase chain reaction (PCR) and this was used to screen a T. weissflogii cDNA library. The putative CA cDNA obtained in this fashion was sequenced and the sequence does not match a known CA from any of the (Lane & Morel, 2000). Recent work with T. weissflogii indicates that this diatom might be able to substitute Cd for Zn under Znlimiting environmental conditions (Lane & Morel, 2000).…”

Effects of cadmium and nitrogen on lipid composition of Chlorella vulgaris (Trebouxiophyceae, Chlorophyta)

“…Lane & Morel (2000) showed that a positive effect of Cd on the growth rate of Zn-limited diatoms is mediated through an increase in cellular carbonic anhydrase (CA) activity, and that the increase is due to the expression of a Cd-specific CA. Based on previous results (Lane & Morel, 2000;Lane et al, 2005), Park et al (2007) explored the distribution and diversity of Cd-CA in 21 marine phytoplankton species under pure culture conditions and showed that 12 of them (all diatoms) expressed the Cd-specific CA. The existence of a Cd enzyme in marine phytoplankton may indicate that there is a unique selection pressure for metallo-enzymes in the marine environment by diatoms (Lane et al, 2005).…”

Inhibition of Carbonic Anhydrase II by Thioxolone: A Mechanistic and Structural Study

“…CAs use a two-step "ping-pong" mechanism (2-5) that typically involves a zinc ion cofactor functioning as a Lewis acid to ionize a water molecule, although other metal ion cofactors are known (6)(7)(8). CAs are found in most eukaryotic and many microbial organisms (9,10).…”