P008
Ralstonia eutropha has six polyphosphate
granule-bound proteins
Tony Tumlirsch and Dieter Jendrossek
Institute of Microbiology, Stuttgart, Germany
Many functions have been addressed to polyP such as a storage
compound for P and energy, as chaperone, as a universal
stress-resistant factor, as a virulence factor and others. PolyP
is complexed with cations in an acidic, membrane-surrounded
compartment in yeast and in two prokaryotes (A. tumefaciens
and R. rubrum) and has been designated as acidocalcisome.
This study aimed at the identification of polyP-bound proteins in
Ralstonia eutropha, a beta-proteobacterium with well-documented
ability to accumulate inclusion bodies such as PHB granules and
polyP granules. Proteome analysis and GFP labeling revealed
the presence of at least six proteins that co-localized with polyP
granules in vivo. Four of the identified proteins were polyphosphate kinases (PPKs) and harbored PPK1 or PPK2 motifs. Two of
the PPKs were essential for polyP granule formation. No putative
function could be deduced for two remaining polyP-granule bound
proteins from their amino acid sequences. However, over-expression resulted in exclusive positioning of polyP granules near the
cell poles while mid-cell-location of polyP granules was found in a
deletion mutant of one of the genes. These findings suggest that
positioning and presumably also partitioning of polyP granules are
controlled in R. eutropha and that the newly identified protein is
part of the polyP-partitioning system.