title: Identification of organelles in bacteria similar to acidocalcisomes of unicellular eukaryotes.
abstract: Acidocalcisomes are acidic calcium storage compartments described in several unicellular eukaryotes, including trypanosomatid and apicomplexan parasites, algae, and slime molds. In this work, we report that the volutin granules of Agrobacterium tumefaciens possess properties similar to the acidocalcisomes. Transmission electron microscopy revealed that each intracellular granule was surrounded by a membrane. X-ray microanalysis of the volutin granules showed large amounts of phosphorus, magnesium, potassium, and calcium. Calcium in the volutin granules increased when the bacteria were incubated at high extracellular calcium concentration. Immunofluorescence and immunoelectron microscopy, using antisera raised against peptide sequences conserved in the A. tumefaciens proton pyrophosphatase, indicated localization in intracellular vacuoles. Purification of the volutin granules using iodixanol density gradients indicated a preferential localization of the pyrophosphatase activity in addition to high concentrations of phosphate, pyrophosphate, short- and long-chain polyphosphate, but lack of markers of the plasma membrane. The pyrophosphatase activity was potassium-insensitive and inhibited by the pyrophosphate analogs, amynomethylenediphosphonate and imidodiphosphate, by dicyclohexylcarbodiimide, and by the thiol reagent N-ethylmaleimide. Polyphosphate was also localized to the volutin granules by 4',6'-diamino-2-phenylindole staining. The organelles were acidic, as demonstrated by staining with LysoSensor blue DND-167, a dye especially used to detect very acidic compartments in cells, and cycloprodigiosin, a compound isolated from a marine bacterium that has been shown to uncouple proton pyrophosphatase activity acting as a chloride/proton symport. The results suggest that acidocalcisomes arose before the prokaryotic and eukaryotic lineages diverged.
authors.affiliation: Laboratory of Molecular Parasitology, Department of Pathobiology and Center for Zoonoses Research, University of Illinois at Urbana-Champaign, Urbana, Illinois 61802, USA.
authors.forename: Manfredo
authors.initials: M
authors.lastname: Seufferheld
authors.forename: Mauricio C F
authors.initials: MC
authors.lastname: Vieira
authors.forename: Felix A
authors.initials: FA
authors.lastname: Ruiz
authors.forename: Claudia O
authors.initials: CO
authors.lastname: Rodrigues
authors.forename: Silvia N J
authors.initials: SN
authors.lastname: Moreno
authors.forename: Roberto
authors.initials: R
authors.lastname: Docampo
mesh_terms: D016960:Agrobacterium tumefaciens / Q000502:physiology* / Q000648:ultrastructure; D000595:Amino Acid Sequence; D000818:Animals; D018407:Bacterial Physiological Phenomena; D015153:Blotting, Western; D002118:Calcium / Q000737:chemistry; D019070:Cell Lineage; D002462:Cell Membrane / Q000378:metabolism; D022162:Cytoplasmic Vesicles / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D004305:Dose-Response Relationship, Drug; D005033:Ethylmaleimide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D007150:Immunohistochemistry; D007211:Indoles / Q000737:chemistry; D008274:Magnesium / Q000737:chemistry; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D010758:Phosphorus / Q000737:chemistry; D011188:Potassium / Q000737:chemistry; D011758:Pyrroles / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D014349:Trypanosoma cruzi
chemical_list: D007211:Indoles; D010455:Peptides; D011758:Pyrroles; D010758:Phosphorus; C108328:cycloprodigiosin; D008274:Magnesium; D005033:Ethylmaleimide; D011188:Potassium; D002118:Calcium