Page 154 - The Biochemistry of Inorganic Polyphosphates

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Peculiarities of polyphosphate metabolism
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8.6 Cyanobacteria (Blue–Green Algae) and other
Photosynthetic Bacteria
The great interest in PolyP metabolism in Cyanobacteria is connected with the ability of
PolyPs to grow rapidly under P i and heavy metal excesses in the water. In many studies,
special attention was paid to a possible use of cyanobacteria as assimilators of substantial
amounts of phosphate in the form of PolyP. This problem arose from severe pollution of
inland waters with various detergents, among which PolyP 3 is the most abundant pollutant.
It should be noted that an important contribution to the study of PolyP metabolism
in cyanobacteria was made by Jensen and co-workers (Jensen, 1968, 1969; Jensen and
Sicko, 1974; Sicko-Goad et al., 1975; Sicko-Goad and Jensen, 1976; Lawry and Jensen,
1979; Baxter and Jensen, 1980a,b). In these experiments, a special emphasis was laid on
the accumulation of PolyP granules by cyanobacteria under conditions similar to those of
inland waters. Normally, the conditions of phosphorus and sulfur starvation occur in these
waters. When large amounts of industrial and domestic detergents enter inland waters, an
intensive bloom of cyanobacteria occurs, leading to contamination of vast water reservoirs.
Using electron microscopy with the cyanobacteria Nostoc puriforme (Jensen, 1968),
Plectonema boryanum (Jensen, 1969; Jensen and Sicko, 1974; Sicko-Goad et al., 1975)
and Anacystis nidulans (Lawry and Jensen, 1979), Jensen and his colleagues investigated
the accumulation of PolyP granules under various cultivation conditions. From these stud-
ies, in particular with Plectonema boryanum cultured under phosphate starvation followed
by phosphate overplus, Jensen drew the following conclusions (Jensen and Sicko, 1974).
Under normal growth conditions, PolyP granules were found mainly on DNA fibrills and
in a zone enriched in ribosomes. Under conditions of P i starvation, an additional zone was
formed in the region of nucleoplasm. Under phosphate overplus, PolyP granules accumu-
lated in nucleoplasm and appeared in the polyhedral bodies involved in the dark reactions of
photosynthesis in cyanobacteria (Stewart and Codd, 1975). In certain cells, PolyP granules
formed near thylakoids. Similar reports for cyanobacteria have been made by other authors
(Vaillancourt et al., 1978; Barlow et al., 1979).
In Anacystis nidulans, the intacellular PolyP level, which was manipulated by growth in
the presence of various P i concentrations in the medium (0.3–3 mM), increased with the
P i concentration up to 2.1 mM and decreased thereafter (Keyhani et al., 1996). Thus, the
PolyP accumulation in cyanobacteria depended on the phosphorus content in the medium,
as in other bacteria. The growth rate of cyanobacteria under phosphate starvation has been
shown to be a function of the amount of previously accumulated PolyPs in the cells (Rhee,
1973). PolyP storage is a survival strategy under conditions of fluctuating phosphate supply
characteristic of the environmental conditions, in which the cyanobacteria live (Falkner
et al., 1995).
The above studies also give evidence of multiple localization of PolyP in the cells of
cyanobacteria. This conclusion was confirmed by a 31 P NMR spectroscopic study. In the
cyanobacterium Synechocystis sp., two pools of soluble PolyP were identified in vivo by
31
P NMR spectroscopy (Lawrence et al., 1998). One of these (PolyP–cation complexes)
lost their association cations after EDTA treatment, while the other did not.
The increase of PolyP accumulation in cyanobacteria was observed under conditions
of sulfur deficiency, which diminished the growth (Lawry and Jensen, 1979; 1986). This