Low cellular P-quota and poor metabolic adaptations of the freshwater cyanobacterium Anabaena fertilissima Rao during Pi-limitation.

Anabaena fertilissima is a filamentous freshwater N(2)-fixing cyanobacterium, isolated from a paddy field. Growth of the cyanobacterium was limited by the non-availability of inorganic phosphate (Pi) in the growth medium and was found to be directly related to the cellular P quota, which declined rapidly in Pi-deficient cells. To overcome Pi-deficiency, cells induced both cell-bound and cell-free alkaline phosphatase activities (APase). The activity of cell-bound APase was rapid and 5-6 times higher than that of the cell-free APase activity. Native gel electrophoresis revealed the presence of two APase activity bands for both the cell bound and cell-free APase (Mr ≈42 and 34 kDa). For Pi-deficient cells, APase activity was inversely related to cellular P-quota. In A. fertilissima phosphate uptake was facilitated by single high-affinity phosphate transporter (K ( s ), 4.54 μM; V(max), 4.84 μmol mg protein(-1) min(-1)). Pi-deficiency severely reduced the photosynthetic rate, respiration rate and nitrate uptake, as well as the activities of nitrate reductase, nitrite reductase and nitrogenase enzymes. In photosynthesis, PSII activity was maximally inhibited, followed by PSI and whole chain activities. Transcript levels of five key glycolytic enzymes showed the poor adaptability of the cyanobacterium to switch its metabolic activity to PPi-dependent enzyme variants, which has rather constant cellular concentrations.