Page 143 - The Biochemistry of Inorganic Polyphosphates

Char Count= 0
20:32
March 9, 2004
WU095/Kulaev
WU095-08
Escherichia coli 127
(a) (b)
1
45
2.1 3
Biomass ( µg ml −1 ) 1.7 µg P i /mg biomass 2 2 35 µg P i /ml medium

25
1
1.3
3
4
1 15
0.9 2
3

60 180 300 60 180 300
Time (min) Time (min)
Figure 8.2 Effects of exogenous P i on the levels of intracellular P i and PolyP in E. coli: (a) deficiency
of exogenous P i ; (b) excess of exogenous P i : (1) biomass; (2) PolyP; (3) intracellular P i ; (4) exogenous
P i (Nesmeyanova et al., 1974a).

observed, for instance, during the stationary culture growth, when the content of PolyP
in the cells significantly decreased. On the contrary, the activity of an enzyme of PolyP
degradation, exopolyphosphatase, directly correlated with PolyP accumulation and with
the activity of the alkaline phosphatase (non-specific phosphohydrolase) of E. coli.

8.1.2 The Effects of P i Limitation and Excess

Similar dynamics of the PolyP content in E. coli cells was observed under external P i
limitation and excess (Figure 8.2). The culture growth continues during P i deprivation, but
less rapidly than in a P i -containing medium. In a medium without P i , there was a greater
consumption of PolyP. The level of intracellular orthophosphate actually remained the same,
supporting the regulatory role of PolyP in the maintenance of the phosphate level in the cell
(Figure 8.2(a)). Rapid growth of the culture on a complete PolyP-containing medium was
also accompanied by a fall in the level of both phosphorus compounds in the cells. In the
final analysis, however, the level of P i and PolyP remained higher than in a deprived culture
(Nesmeyanova et al., 1974a; Nesmeyanova, 2000).
In many organisms, the addition of P i to a culture previously deprived of phosphorus
results in a rapid accumulation of PolyP to an extent many times exceeding the level which
is characteristic of normal growth on a complete medium. This phenomenon is called
‘hypercompensation’ or ‘phosphate overplus’. In E. coli, this effect was not found. The
addition of P i to a starved culture resulted in a rapid restoration of biomass accumulation.