Factors modulating alkaline phosphatase activity in the diazotrophic rice-field cyanobacterium, Anabaena oryzae

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Alkaline phosphatases (APase), both phosphomonoesterase (PMEase) and phosphodiesterase (PDEase) were studied in the cyanobacterium Anabaena oryzae for their specific requirements of temperature, pH, micro- and macronutrients and their activities in the presence of salinity and heavy metal stress. The alkaline phosphatases (PMEase and PDEase) are quite stable enzymes and require a narrow range of pH (pH 10–10.2) and temperature (35–40 °C) for their optimal activity.

A pH of 10, 10.2 and 10.2 supported optimal activity of cellular PMEase, cellular PDEase and extracellular PMEase, respectively, whereas temperatures of 35, 38 and 40 °C were required for their optimal activity. The requirement for Ca2+ and Mg2+ as macronutrients and the significance of the micronutrients Zn2+, Co2+, Fe2+, Mn2+ and Cu2+ in APase activity in the cyanobacterium suggests nutritional regulation of enzyme activity in A. oryzae. The metals Pb2+, Cr6+ and Ni2+ severely inhibited APase activity, whereas the NaCl stress had a dual role, which was concentration dependent. NaCl stress at lower concentrations (>20 mM) caused an increase in cellular PMEase activity while its higher concentration (>20 mM) favoured release of the extracellular PMEase. The decrease in cellular activity and an increase in extracellular activity suggest that the higher concentrations of salt stimulate the release of the enzyme.

The data suggest that the cyanobacterium A. oryzae possess a potential application as biofertilizer in high salinity and alkaline (Ca2+-rich) soils because of its ability to release PO 43− enzymatically under these conditions.

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