A comparative study of acid and alkaline phosphatase activities in several strains ofNannochloris(Chlorophyceae) andNannochloropsis(Eustigmatophyceae)

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Abstract
Acid and alkaline phosphatase activities in whole cells as well as in the particulate and soluble fractions, obtained from late exponential phase cultures of several marine strains of Nannochloris (Chlorophyceae) and Nannochloropsis (Eustigmatophyceae), have been studied. These enzymes exist in whole cells of all Nannochloris strains but only acid phosphatase was detected in particulate and soluble fractions. Nevertheless, at least in N. maculata, the existence of alkaline phosphatase in the soluble fraction has been revealed when the reaction mixture contains sea-water, but not in the presence of Mg2+, Zn2+, Co2+, Mn2+, Mo6+, or Fe3+. In addition to their different Km values, acid phosphatases from the particulate and soluble fractions are also differentiated by their optimum pH or their response to temperature. Of the three Nannochloropsis species studied, N. salina and N. gaditana possessed only acid phosphatase, both in whole cells, and in particulate and soluble fractions, but no phosphatase activity was ever detected in N. oculata. Inorganic phosphate in the culture medium affected phosphatase synthesis in all cases, since the activity per cell was lower in cultures to which phosphate was added.