Wilson da Silva, Sydney
A SECOND bizarre bacterium which packs all its DNA into a central compartment has been discovered by researchers in Australia. Like its predecessor, the cell may also shed light on how animal and plant cells evolved. “It’s a ‘rewrite the textbooks’ finding in some ways,” says microbiologist John Fuerst of the University of Queensland in Brisbane.
Fuerst and his colleagues Margaret Lindsay and Richard Webb were studying the planctomycete bacterium Pirellula, an organism that inhabits both saltwater and freshwater environments, when they discovered that the cell contains a new compartment, bounded by a membrane, that houses the organism’s DNA.
“The DNA is located exclusively within this compartment, whereas in all other bacteria, the DNA strands are free and extend throughout other regions of the cell,” says Fuerst.
Fuerst’s team has named the compartment the “pirellulosome” (Microbiology, vol 143, p 739). They say that the cytoplasm that lies outside the pirellulosome has an extended cap.
Fuerst and Webb discovered a similarly complex planctomycete bacterium, Gemmata obscuriglobus, in 1991 (see New Scientist, 25 January 1992, p 26). In that bacterium, a double membrane surrounded the central compartment. Fuerst says that the new structure found in Pirellula, although different, seems to be closely related and confirms that this type of bacterium may be more widespread than anyone realised.
Both bacterial cells are intriguingly similar to those of animals, with a nucleus bounded by membranes. Fuerst suspects that they could represent an advanced evolutionary form of bacteria: “It may well be an evolutionary model for the ancestral origins of animal, plant, protozoan and fungal cells.”