Abstract
Abstract
Alexandrium catenella (Group I) causes paralytic shellfish poisoning. Nitrogen is a critical component for both growth and toxin production in A. catenella, and recent studies have indicated that A. catenella uses both inorganic nitrogen and ammonium as nitrogen sources. However, the molecular mechanism underlying the transportation of ammonium in A. catenella has not been identified. In this study, we attempted to isolate and characterize the ammonium transporter (AMT) in A. catenella. cDNA cloning produced a number of AMT clones. To investigate the ammonium transport capability of A. catenella AMT (AlcAMT), we selected three representative cDNAs and the clones were inserted into expression vectors. These vectors were then transferred into an amt-deficient Schizosaccharomyces pombe transgenic yeast strain and grown on a medium containing NH4Cl as the only nitrogen source. Following transformation, yeast transformants carrying only one of the three AMTs were able to grow on the medium, confirming its ability to transport ammonium. Sequence analysis of the three AMT variants revealed that the successful variant included a K residue at sequence position 450, while the other variants contained a T residue at the same position. Mutation analysis confirmed that K450 is important for the function of AlcAMT.