Agrobacterium tumefaciens has two
polyphosphate (
polyP)
kinases, one of which (PPK1AT) is responsible for the formation of
polyP granules, while the other (PPK2AT) is used for replenishing the NTP pools by using
polyP as a
phosphate donor to phosphorylate
nucleoside diphosphates. Fusions of eYFP with PPK2AT or of the
polyP granule-associated phosin PptA from Ralstonia eutropha always co-localized with
polyP granules in A. tumefaciens and allowed the tracking of
polyP granules in time-lapse microscopy experiments without the necessity to label the cells with the toxic
dye DAPI. Fusions of PPK1AT with mCherry formed fluorescent signals often attached to, but not completely co-localizing with,
polyP granules in wild-type cells. Time-lapse microscopy revealed that
polyP granules in about one-third of a cell population migrated from the old pole to the new cell pole shortly before or during cell division. Many cells de novo formed a second (nonmigrating)
polyP granule at the opposite cell pole before cell division was completed, resulting in two daughter cells each having a
polyP granule at the old pole after septum formation. Migration of
polyP granules was disordered in
mitomycin C-treated or in PopZ-depleted cells, suggesting that
polyP granules can associate with
DNA or with other molecules that are segregated during the cell cycle.