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Missing link found in Sydney Harbour

Thanks to Clayton Smith for the link.

Reposted from:

Richard Macey
February 21, 2008 - 5:56AM

ONE of evolution's missing links has been found lurking in Sydney Harbour.

Although only a microscopic, single-celled creature, it has excited scientists around the world because it is the nearest relative yet found of a group of deadly parasites.

Its discovery, said Dee Carter, a University of Sydney microbiologist and member of the international team that found the organism, may provide vital clues for researchers seeking new weapons in the war against diseases such as malaria.

Despite being a type of brown algae, an analysis of the new organism's DNA revealed that its closest relatives include cryptosporidium, the parasite which invaded Sydney's water in 1998, and plasmodium, the cause of malaria.

"Scientists have known for some time that these parasites are related to algae," Associate Professor Carter said yesterday.

That is because parasites contain relics of what were once chloroplasts, the mechanisms that allow plants to turn sunlight into energy through photosynthesis.

However, until now, the closest known parasite relatives were a group of simple algae called dinoflagellates, often found living in coral.

But, said Professor Carter, they were very distant relatives indeed. Comparing dinoflagellates with parasites was "like comparing us with ants".

The new organism was much more closely related and appeared to be the long sought "missing link" between the two forms of life.

It was discovered by one of Professor Carter's former students, Bob Moore, while exploring Sydney Harbour for algae living in coral.

Only when then the organism was studied by the team of Australian, US and Czech scientists was it realised that it bridged the evolutionary gap. Their findings have been published in Nature.

Professor Carter said it was amazing that such an important discovery could be made in Sydney Harbour.

She speculated that the first parasites may have evolved long ago from algae which grew inside marine animals. "At some stage [the algae] said: 'Let's stop making our own food. Let's take it from our host"'.

As the organisms invaded the animal cells and evolved into parasites, they gradually lost their ability to convert sunlight into energy.



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