Lack of a Zn/Co substitution ability in the polar diatom Chaetoceros RS19

Functional substitution of the essential trace metals zinc (Zn) and cobalt (Co) within metalloenzymes has been well documented in marine diatoms and is known to be prevalent among varying genera and species. In contrast to the majority of species studied to date, we find that the polar diatom Chaetoceros RS19, originally isolated from the Ross Sea, Antarctica, has a Zn requirement that cannot be met by Co and thus does not demonstrate a Zn/Co substitution ability as assessed by growth rate. We investigate the underlying metabolic basis of Zn/Co substitution at the transporter, sensor/chaperone, and metalloenzyme level by employing metal quota, metal uptake rate, and proteomic analyses of this substitution-incapable diatom. Co appears to be transported into the cell, but not efficiently utilized by Zn metalloenzymes.