The newly-discovered algae, Chromera velia, sheds light on the evolution of malaria-causing parasites, and may open the way to new treatments for the disease.
Credit: The University of Sydney
SYDNEY: A new species of algae found living in coral in Sydney Harbour is a missing evolutionary link between algae and malaria-causing parasites, and may hold the key to improved malaria treatments, scientists say.
The algae, Chromera velia, is a missing link between photosynthesising algae and Apicomplexa, a group of parasites that cause a range of diseases including malaria. The algae has a unique stretch of DNA in the psbA gene, which was previously only found in the largest group of Apicomplexa, confirming the relationship between the organisms.
The finding may also provide a new model for developing malaria treatments and other anti-parasitic drugs. Apicomplexa, which are currently used in research for these treatments, are grown in living host cells so can be difficult to work with in the laboratory. Chromera velia, on the other hand, can be grown without its coral host on simple media in the lab.
"Malaria and other diseases caused by organisms belonging to the class of parasites known as the apicomplexans kill and disable millions of people every year," said Dee Carter of the School of Molecular and Microbial Biosciences at the University of Sydney in Australia. Carter's former PhD student, Robert Moore, discovered the algae in Sydney Harbour in 2001, and the pair published their findings this year in the British journal Nature.
Malaria treatments
Geoff McFadden of Melbourne University in Australia, an expert on Apicomplexa who was not involved in the research, called Chromera velia the "most important find in decades". He said the algae "truly related the organisms and provided the missing link that we always suspected was there".
Like other types of algae, Chromera velia uses photosynthesis to convert sunlight into chemical energy, a reaction that takes place in an organelle called the chloroplast. The malaria-causing species of Apicomplexa has an organelle called the apicoplast which – while an evolutionary remnant of the chloroplast – does not photosynthesise. The apicoplast's function is not fully understood, but the organelle is vital to the parasite's survival.
In fact, existing malaria treatments target the apicoplast; since mammal cells don't contain the organelle, the treatment is relatively harmless to the host. According to Carter, new knowledge on the evolution of the apicoplast may prove helpful in finding new ways to combat malaria.
Lacking pigment
Compared with other algae, Chromera velia is missing one photosynthetic pigment, which, according to Carter, may make it vulnerable to light. This missing pigment also reduces its photosynthetic ability, and may explain the algae's relationship with its coral host, Plesiastrea versipora, which provides the algae with some of its energy.
This missing pigment may also represent an evolutionary link to the Apicmoplexa parasites: while Apicmoplexa once obtained energy through photosynthesis – indicated by the presence of the apicolast – they eventually lost this ability, and become entirely dependent on their host cell for energy.
According to Carter, "the apicomplexans are the only organism where we can say this has certainly happened, as they are the only ones yet found that have a relic chloroplast."
Future research will focus on the search for related Chromera species in a variety of corals and other potential hosts around Sydney, as well as on the Great Barrier Reef off the coast of Queensland, Australia.
