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Peculiarities of polyphosphate metabolism
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restores alginate, GTP, ppGpp and PolyP synthesis (see Figure 8.8) in AlgR2 mutants (Kim
et al., 1998).
The ppk (Ishige et al., 1998; Zago et al., 1999) and ppx (Miyake et al., 1999; Zago et al.,
1999) genes of P. aeruginosa were cloned. In contrast to E. coli, where the ppx and ppk1
genes are organized in an operon, in P. aeruginosa ppx is located in the opposite direction
from the ppk gene and therefore they do not constitute an operon (Miyake et al., 1999;
Zago et al., 1999). Thus, the independent regulation of ppk1 and ppx in this bacterium may
explain the high level of PolyP, since it is possible to regulate the exopolyphosphatase level
independently of the polyphosphate kinase level. No coregulation between the ppk and ppx
promoters has been demonstrated in response to osmotic shock and oxidative stress (Zago
et al., 1999). It was proposed that PolyP accumulation in P. aeruginosa is regulated at the
enzymatic level through ppx activity inhibition by the stress response molecules of ppGpp
without any modulation of the transcription rate of these two genes (Kim et al., 1998; Zago
et al., 1999).
After ppk1 inactivation, the knockout mutants show no growth defects when compared
with the parent strain. One of the remarkable defects in these mutants was the loss of motility
(Rashid and Kornberg, 2000; Rashid et al., 2000a,b). A low-residual polyphosphate kinase
activity was detected in these mutants (Zago et al., 1999) and attributed to the activity of
the ppk2 gene (Zhang et al., 2002). However, one cannot exclude the existence of other
pathways of PolyP synthesis in this bacterium.

8.3 Acinetobacter

PolyP metabolism has been intensively studied in Acinetobacter, because this organism may
be responsible for enhanced biological phosphorus removal (EBPR) at many wastewater
treatment plants and serves as a good model organism for developing molecular techniques
to characterize metabolism and genetic control in potential EBPR organisms. The ability of
this organism to accumulate PolyP and the peculiarities of this process have been effectively
studied (Deinema et al., 1980, 1985; Van Groenestijn et al., 1989; Bonting et al., 1991,
1993a,b; Van Veen et al., 1994; Geissdorfer et al., 1998). The PolyP metabolism of these
bacteria has been described in detail in many reviews, for example, Kortstee and Van Veen
(1999) and Kortstee et al. (2000). A number of Acinetobacter species have been isolated,
and many of them accumulate large amounts of PolyP under certain conditions (Vasiliadis
et al., 1990; Kim et al., 1997; Gavigan et al., 1999).
Polyphosphate kinase is important for PolyP metabolism in Acinetobacter (Van Groen-
estijn et al., 1989). The ppk gene from the Acinetobacter sp. strain ADP1 was cloned
(Geissd¨orfer et al., 1998) and the polyphosphate kinase was purified and characterized
(Trelstad et al., 1999). The induction of ppk transcription by P i starvation was revealed
(Gavigan et al., 1999). The polyphosphate kinase showed an interesting behaviour when
the Acinetobacter cultures were subjected to a cycle of P i starvation and surplus (Kort-
stee and Van Veen, 1999). Although the ppk gene was strongly induced under P i -limited
conditions, the net PolyP-synthesis activity declined and the PolyP levels became almost
negligible. In addition, a strong PolyP-degrading activity, which seemed to be due to the
presence of exopolyphosphatase but not the reverse work of polyphosphate kinase, was de-
tected in cultures grown under low-P i conditions. The exopolyphosphatase and AMP–PolyP