The procyclic form of african trypanosomes move together as a group when grown on a semisolid surface, according to new research from US scientists published in the journal PLoS Pathogens. This “social motility” is mediated by their flagellum and is a surprising new feature in trypanosome biology.
The African trypanosome, Trypansoma brucei, is a parasite which causes the disease “sleeping sickness” or African trypanosomiasis. The disease is endemic in regions of Sub-Saharan Africa and causes significant mortality, with estimates suggesting that 50,000-70,000 people are currently infected. The disease is transmitted to humans by bites from tsetse flies which are infected with the parasite. Initially, symptoms include fever and joint pains but once the parasite has entered the brain from the bloodstream it causes the neurological symptoms of the infection which gives the disease its name—confusion, fatigue and sleep cycle disturbances. Under certain conditions, bacteria can move by various forms of social motility including gliding, swarming and twitching. They are known to group together in multicellular communities in which the bacteria can communicate together to move and respond to external stimuli. Trypansomes on the otherhand are thought to live as single cell entities.
Michael Oberholzer and colleagues studied the growth of procyclic T. brucei on a semisolid agar surface. The researchers found that the parasites grouped into a large multicellular community that could move across the surface of the agar, and could recruit more cells into the heaving mass (see the supporting video S1). They found that the parasite groups moved in a polarised direction and sent out “scout” parasites which moved in and out of the main group to come into contact with neighbouring cells. These scouts then communicated in some way to the main parasite crowd in order to merge new parasites into the main group or avoid them altogether by changing the direction of movement of the group. The investigators then used knockdown parasites which lacked a normal flagellum (a sort of tail on the parasite which helps them to move) and showed that their co-operative movements were mediated by their flagellum.
This research shows an interesting new facet to trypanosome biology and offers an insight into how the parasites behave. It will be interesting to see whether the trypanosomes act in the same way when they have infected humans or tsetse flies, and more research is needed to determine the physiological role of this trypanosome social motility.
Michael Oberholzer, Miguel A. Lopez, Bryce T. McLelland, & Kent L. Hill (2010). Social motility in African Trypanosomes PLoS Pathogens, 6 (1) : doi:10.1371/journal.ppat.1000739