Page 71 - The Biochemistry of Inorganic Polyphosphates

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Eukaryotes 55
granules contained magnesium and potassium, but if Agrobacterium tumefaciens was culti-
vated in the presence of CaCl 2 , no magnesium and potassium was detected, but a dramatic
increase in calcium content was revealed (Seufferheld et al., 2003). Transmission electron
microscopy revealed that each granule was surrounded by a membrane (Seufferheld et al.,
2003), similar to the poly-β-hydroxybutyric granules of some Bacillus (Williamson and
Wilkinson, 1958). This supported the earlier data that under certain cultivation conditions,
e.g. when grown on a medium containing oleic acid, the PolyP granules of mycobacteria
were surrounded by lipid layers (Schaefer and Lewis, 1965).
Voelz et al. (1966) described a detailed investigation into the formation of PolyP gran-
ules in Myxococcus xanthus under various growth conditions. It was found that the PolyP
granules in this organism are closely associated with glycogen inclusions, and are either dis-
tributed throughout the cytoplasm or localized within the nucleoids. A similar localization
of PolyP granules was found in Micrococcus lysodeikticus (Friedberg and Avigad, 1968).
Some part of the PolyP may be located in the periplasmic region or in the cell capsule, i.e.
outside the cytoplasmic membrane of bacterial cells. Ostrovsky et al. (1980), for example,
believed that a marked increase in the intensity of the PolyP signals was observed when
cells of Mycobacterium smegmatis were treated with EDTA, which points to localization
of a certain amount of mobile PolyP in the periplasmic region. In the bacterial parasite
Bdellovibrio bacteriovorus, most of the PolyP occur in the form of acid-insoluble highly
polymerized fractions predominantly localized outward (Bobyk et al., 1980; Egorova et al.,
1981). Similar observations were made with the oligotrophic bacteria Tuberoidobacter and
Renobacter (Nikitin et al.,1979).
PolyP is a component of the cell capsule, which is loosely attached to the surface mem-
brane of the Neisseria species. This capsular PolyP represents about a half of the PolyP
content in Neisseria cells (Tinsley et al., 1993).
Bacterial membranes possess PolyPs as complexes with Ca 2+ and poly-β-hydro-
xybutyrate (Reusch and Sadoff, 1988). The finding of these unusual structures is one of
the most remarkable recent discoveries in PolyP biochemistry (see the reviews of Reusch,
1992; Reusch, 1999a; Reusch, 2000).
As a whole, it might be affirmed that PolyP is localized in prokaryotic cells in many
cell compartments. For example, in the Helicobacter pylori bacteria colonizing gastric
antrum, PolyP was found in at least three different locations: the cytoplasm, the flagellar
pole and in association with the cell membrane (Bode et al., 1993). In PolyP-accumulating
microorganisms of activated sludge, PolyP was observed by electron microscopy in the
periplasm, cytoplasm and on the cell surface (Bond and Rees, 1999). One example of the
cytochemical picture of PolyP localization in the bacterial cell is shown in Figure 5.1.

5.2 Eukaryotes

The basic difference between eukaryotes and prokaryotes is a much better developed com-
partmentalization of biochemical processes in eukaryotes, wherein some of the processes
take place in specialized cell organelles. However, eukaryotic cells possess PolyP pools in
all cell compartments studied in this respect.
The study of PolyP content in different cell compartments of eukaryotic cells is still a dif-
ficult task. Quantitative estimation of the PolyP content in the compartments of eukaryotic