Bacteria possess organelles — acidic calcium storage compartments, known as acidocalcisomes — that are also present in eukaryotes, according to a recent report in the Journal of Biological Chemistry.

For years, students have been taught that bacteria are 'empty sacks'. But now, research by Roberto Docampo and his colleagues from the University of Illinois, Urbana, indicates that bacteria have specialized compartments that are equivalent to eukaryotic organelles.

Bacteria contain subcellular entities, known as volutin granules, which were previously thought to lack an enclosing membrane and enzymatic activity. However, volutin granules (or acidocalcisomes) of unicellular eukaryotes are surrounded by a membrane that contains enzymatic pumps and exchangers.

Choosing Agrobacterium tumefaciens — which contains a proton pyrophosphatase (H+-PPase), a marker for acidocalcisomes — for his studies, Docampo investigated whether the bacterial volutin granules have characteristics similar to the acidocalcisomes.

The researchers found that each bacterial granule was surrounded by a membrane. Then, using antibodies against A. tumefaciens H+-PPase, they showed the presence of a H+-PPase in the membrane.

The origin of the organelles is unknown. Usually, organelles are either components of an intracellular trafficking system, or they evolved from formerly free-living organisms. “Which of these might happen in bacteria is not clear”, says Andrew Roger from Dalhousie University in Nova Scotia (Nature, 26 June 2003).