Abstract
Alkaline phosphatases (APases) are important enzymes in organophosphate utilization. A recent study showed that PhoD is more abundant in the marine bacteria than PhoA or PhoX. However, functional characterization of cyanobacterial PhoD remains to be clarified. Here, we cloned the phoD gene (ApphoD) from a halotolerant cyanobacterium Aphanothece halophytica. The deduced protein ApPhoD contains the Tat consensus motifs and peptidase cleavage site in N-terminal tail. The enzyme was activated by Ca2+ and exhibited the alkaline phosphatase (APase) and phosphodiesterase (APDase) activities. Subcellular localization experiments showed the secretion and processing of ApPhoD in transformed cyanobacterium. Expression of ApphoD gene in A. halophytica cells was upregulated not only by phosphorus starvation but also under salt stress conditions. These facts will be discussed.
