Page 128 - The Biochemistry of Inorganic Polyphosphates

WU095/Kulaev
WU095-07
Functions of polyphosphate and polyphosphate-dependent enzymes
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1996). Therefore, the interrelation of PolyP, polyphosphate kinase and the σ 38 sub-unit of
RNA polymerase was confirmed.
The interrelation of PolyP and induction of rpoS expression were studied when the PolyP
level in E. coli was down-shifted by expression of the yeast PPX1 (Shiba et al., 1997). As
a consequence, a 10-fold increase of H 2 O 2 sensitivity was observed. The sensitivity in-
creased 1000-fold in a mutant lacking HPI catalase. Thus, the catalase most dependent on
PolyP was stationary-phase rpoS-dependent catalase HPII (Shiba et al., 1997). Induction
of the expression of both catalase HPII and the stationary-phase σ factor was prevented
in cells with low PolyP levels. The resistance was restored to the parent-strain level by
complementation with plasmids expressing ppk1. The levels of ppGpp and pppGpp were
not changed in mutants possessing yeast exopolyphosphatase PPX1 with enhanced PolyP
hydrolysis. In view of the capacity of additional rpoS expression to suppress the sensi-
tivity to H 2 O 2 , the PolyP action was attributed to the induction of rpoS (Shiba et al.,
1997).
E. coli mutants lacking cytoplasmic superoxide dismutases (SODs) show an inability
to survive in the stationary phase and a high sensitivity to redox-cycling reagents and
H 2 O 2 (Carlioz and Touati, 1986) similar to the ppk1 mutants. E. coli mutants lacking SODs
accumulate as much PolyP as the parent strain (Al-Maghrebi and Benov, 2001), when grown
in the PolyP-accumulating conditions described by Rao et al. (1998). The increase of PolyP
content makes the SODs mutants more resistant to H 2 O 2 , and the cells show the higher rate
of H 2 O 2 consumption (Al-Maghrebi and Benov, 2001). No direct protective effect of PolyP
on oxidative DNA damage was observed. Indeed, rpoS dependent-HPII catalase was much
higher in those cells with high levels of PolyP (Al-Maghrebi and Benov, 2001). Thus, the
results of Shiba et al. (1997) were confirmed. The reason for the protective effect of PolyP
is the induction of catalase and probably some DNA repair enzymes as members of the
rpoS regulon (Shiba et al., 1997, 2000; Al-Maghrebi and Benov, 2001).
Many other bacteria show similar phenotypic defects, when the ppk1 gene is knocked out.
The ppk1 mutants of Neisseria gonorrhoeae and N. meningitidis grew less vigorously than
the wild-type cells and showed a striking increase in sensitivity to human serum (Tinsley
and Gotschlich, 1995). The Vibrio cholerae ppk mutant was similar to that of E. coli in
response to heat and oxidants and in a long-term survival on synthetic medium (Ogawa
et al., 2000b). The P. aeruginosa PAO1 ppk mutant shows no defects in adaptive responses
but is severely impaired in motility and surface attachment (Rashid and Kornberg, 2000;
Rashid et al., 2000a,b). The ppk mutants of Porfiromonas gingivalis (Chen et al., 2002)
failed to survive in the stationary phase, while those of Shigella and Salmonella (Kim et al.,
2002) have defects in growth on minimal media. It appears that the ppk gene is essential
for stationary-phase long-term survival of P. gingivalis (Chen et al., 2002), although this
gene may be not the only enzyme responsible for PolyP production in this organism. Unlike
the ppk1 mutant of E. coli, the sensitivity of the ppk1 mutant of P. gingivalis to heat and
oxidants remains the same as in the parent strain.
Biofilms are sessile microbial communities, the formation of which is initiated by sur-
face attachment of individual bacteria, followed by cell–cell interactions and development
in a three-dimensional structure of the colonies (O’Toole et al., 2000). Biofilm forma-
tion is a multi-step development process over a period of several hours (Costerton et al.,
1995). The initial surface interaction is mediated by flagella and pili functioning, then the
exopolysaccharides stabilize the biofilm and, finally, intercellular communication occurs
through signaling molecules (Watnic and Kolter, 1999).