Use of Organic Phosphorus Sources by Coccolithophores
Coccolithophores are calcite precipitating phytoplankton that are dominant in many oligotrophic gyres of the oceans and they can form massive blooms visible from space. They owe part of their ecological success to their ability to obtain phosphorus from organic compounds when inorganic P concentrations are vanishingly low. This is achieved through the activity of the zinc enzyme alkaline phosphatase, AP, which cleaves phosphate from various organic substrates. We have studied the activity of this enzyme in the ubiquitous species Emiliana huxleyi and demonstrated that very small enzyme (and thus zinc) concentrations are necessary to provide the phosphate necessary for growth (Shaked et al. 2006). We have also isolated and partially characterized this enzyme which has no homology to other known alkaline phosphatases (Xu et al. 2006). More recently we have studied the regulation of this enzyme under various environmental conditions and are in the process of identufying its metal cofactors in vivo. This work provides the basis for studying the expression of alkaline phosphatase, and, hence, the extent of P limitation, in the field.
