Bacterial discovery helps University researchers take some evolutionary steps
University of Queensland researchers have discovered a new distinctive form of cell organisation within bacteria with possible implications for cell evolution.
This form of cell organisation was previously believed not to exist within bacteria but is analogous to the type found within the cells of animals, plants, fungi and protozoans.
The discovery has implications for cell evolution because it shows bacteria can package DNA in a separate compartment within the cell - like cells of more complex forms of life, according to PhD student Margaret Lindsay and her supervisor Dr John Fuerst, both of the Microbiology Department, and Richard Webb of the Centre for Microscopy and Microanalysis.
The research was part of work funded by an Australian Research Council (ARC) grant. The findings were recently published by Microbiology, an internationally prestigious journal of the UK's Society for General Microbiology.
In the new form of cell organisation - discovered in both species of the planctomycete bacterial genus Pirellula - the cell contains a membrane-bounded cell compartment, named a pirellulosome by the researchers. This means the cell is divided into two distinct regions separated by a single membrane.
"Testing revealed that DNA is located exclusively within this compartment," Dr Fuerst said, "whereas in all other bacteria, the DNA strands are free and extend throughout other regions of the cell.
The pirellulosome contains an area consisting of DNA fibres as well as dense particles similar to protein-synthesizing bodies of other bacteria. The other area of the cell forms a layer surrounding the pirellulosome and includes a "cap" at one pole.
Dr Fuerst said animal, plant, protozoa and fungus cells all possessed a nucleus bounded by membranes. However, it had been thought bacteria usually had a simple cell structure with DNA not bounded by membranes.
"The planctomycete bacteria include organisms with a distinctive form of structure bearing some similarities to plant and animal cell organisation," he said.
Dr Fuerst said the discovery gave a better understanding of the diversity of bacteria in terms of structure.
"It may well be an evolutionary model for the ancestral origins of animal, plant, protozoan and fungal cells," he said. "It's a 'rewrite the textbooks' finding in some ways."
Dr Fuerst and Mr Webb discovered the first example of unusual cell organisation within planctomycete bacteria in the species Gemmata obscuriglobus in 1991, as a double membrane-bounded nuclear body enclosing the cell DNA. The latest research findings show a second type of cell organisation ? a single membrane-bounded DNA-enclosing compartment.
Dr Fuerst said finding another set of species in the same group of bacteria with membrane-bounded DNA suggested the first finding was not just an isolated result confined to one species.
He said the current research extended the previous discovery to another group of bacteria. It was also a confirmation of that discovery's importance because these organisms were very closely related in terms of their evolutionary relationship.
The organisms are all members of the distinctive planctomycete division, a group related only distantly to other bacteria.
"It might have some real evolutionary significance to find it in several different species sharing a common ancestor," he said.
Dr Fuerst said the search for the evolutionary origins of the ancestor of all cells with nuclei was one of the central problems of biology, and this discovery could give clues to how that may have happened.
He also said the latest discovery could form a model revealing new mechanisms of transport in bacteria analogous to those occurring across the membranes of animal and plant nuclei.
Ms Lindsay said finding this sort of organisation in two different species had prompted a search for more compartmentation within other bacteria.
Dr Fuerst said an ARC large grant would fund further research examining the cell biology of these organisms in much more detail to determine the function of the new structures.
For more information, contact Dr John Fuerst (telephone 3365 4643).
24/04/97
