Page 152 - The Biochemistry of Inorganic Polyphosphates

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Peculiarities of polyphosphate metabolism
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Figure 8.9 Accumulation of PolyPs in Aerobacter aerogenes (Harold, 1966): (a) sulfur deprivation,
cells placed at 0 h in a P i - free medium; (b) phosphate overplus, cells placed at0hinaP i -free medium,
with P i was added after 4 h: (1) PolyP; (2) polyphosphate kinase activity; (3) exopolyphosphatase
activity.

of the latter the growth was restored and PolyP was utilized for biosynthetic processes. It
is probable that such mechanisms are realized by the same way as in other bacteria by the
ppGpp and rpoS controlling genes (see earlier in Chapter 7).
In contrast to E. coli, K. aerogenes exhibits rapid and extensive PolyP accumulation
(known as ‘PolyP overplus’) when P i is added to cells previously subjected to P i starvation
(Harold, 1966). The changes in PolyP content, polyphosphate kinase and exopolyphos-
phatase activities under phosphate overplus are presented in Figure 8.9(b). It was shown
that the absence of P i in the medium de-repressed the polyphosphate kinase (Harold, 1964;
Harold and Harold, 1963, 1965).
The mutant, which was devoid of polyphosphate kinase, had no PolyP accumulation in-
dependent of the growth conditions (Harold, 1964). Later, using specific gene constructions
with a cloned ppk gene, it was confirmed that in K. aerogenes,asin E. coli, polyphosphate
kinase is responsible for the synthesis of the most part of PolyP and for PolyP overplus
(Kato et al., 1993b; Ohtake et al., 1999; Kuroda and Ohtake, 2000). A ppk mutant of
K. aerogenes showed no PolyP overplus. Like the E. coli ppk-ppx operon, the ppx gene is
located immediately ‘downstream’ of the ppk gene (Kato et al., 1993b). As expected, the
polyphosphate kinase activity increased in response to P i starvation and decreased upon
addition of P i . However, unlike polyphosphate kinase, the exopolyphosphatase activity did
not increase but rather slightly decreased under conditions of P i starvation, although the
ppx mRNA was induced (Kuroda and Ohtake, 2000). Earlier, it had been shown that PolyP
degradation was completely inhibited in the mutant without exopolyphosphatase (Harold,
1966).