The Complex Regulation of the Phosphate Uptake System of Cyanobacteria

Phosphorus Feast and Famine in Cyanobacteria: Is Luxury Uptake of the Nutrient Just a Consequence of Acclimation to Its Shortage?

“…The observed kinetics of P i uptake is well-described in terms of the model developed by Falkner and Falkner [ 13 ], presuming a biphasic kinetics of uptake when the concentration of the external P i was much higher than the thermodynamic threshold for P i transport into the cells (which was deliberately made the case in our refeeding experiments).…”

“…After the refeeding of the P-starved cells with P i , the nutrient was rapidly absorbed, showing a typical biphasic kinetic of uptake [ 13 ] ( Figure 1 , Figure 2 , Figure 3 and Figure 4 ). We studied the P i uptake kinetics as a function of the concentration of P i added, light, and temperature.…”

“…Still, this study did not reveal specific mechanisms induced in response to the elevated P availability; the observed manifestations of LPU are obviously the “extensions” of the known acclimations to P shortage (see, e.g., [ 82 ]). One can conclude that the observed global reprogramming of gene transcription and, hence, cell metabolic rearrangement is what constitutes the “adaptive responses of phosphate-deficient cells to an abrupt rise of the external phosphate concentration [comprising the] intracellular self-organization process, in which the kinetic and energetic properties of the phosphate uptake system are altered in a complex manner that reflects intracellular information processing about alterations of [the] phosphate supply” described in the seminal works of Falkner et al [ 13 , 14 ]. On the other hand, the key to the specific acclimations to ample P conditions still might remain hidden in the genome of cyanobacteria; the functional role of most genes differentially expressed under a fluctuating P availability have not been characterized yet.…”

“…Most of the inorganic phosphate (P i ) taken up via LPU is stored in the cell in the form of osmotically inert polyphosphate (PolyP) granules [ 13 ], accommodating P sufficient for up to 20 cell divisions [ 14 ] and playing a plethora of other biological roles [ 1 , 4 , 15 ], including a potential role of energy storage [ 16 ]. In general, PolyP is accumulated when the P i influx into the cell is larger than its current metabolic demand and there is enough surplus energy (ATP).…”

“…Overaccumulation of PolyP after refeeding of the P-deprived cells was documented in Plectonema boryanum [ 17 , 18 ], Anacystis nidulans [ 9 ], Microcystis aeruginosa [ 19 ], and Calothrix parietina [ 20 ]. The ATP is needed for pumping of the P i into the cell, unless the external P i concentration is high [ 21 , 22 ], and for the conversion of P i into PolyP [ 6 , 13 ]. The amplest source of energy for LPU is photosynthesis; dark respiration, or even fermentation, can also drive LPU and PolyP formation but with a lower efficiency [ 7 ].…”