The discovery of a group of oil-producing microbes on a Canadian salt lake may make it possible to replenish much of the world's dwindling oil supplies, according to a University of Toronto scientist.

New evidence indicates that billions of years ago, many of Earth's oil deposits were created by similar bacteria, Morris Wayman reported at the annual meeting of the American Association for the Advancement of Science.

Although warning that the microbes are not an instant answer to the energy crisis, the Toronto chemist said the organisms could probably produce oil more cheaply than obtaining it from tar sands or using synthetic fuels.

"Once established on a large enough scale, oil-bearing microbes will continue to provide liquid fuel feedstocks forever," he said.

One combination of bacteria, if grown in vats covering a square mile, could produce the equivalent of 12 million barrels of crude oil a year, Wayman said.

"With such rates of oil formation, microbial systems for energy production deserve close attention," he said.

One of the first oil-producing microbes involved a purple photosynthetic bacterium called Chromatium warmingii, which was discovered in Saskatchewan.

This purple bacterium can grow with very weak light, eating up carbon dioxide in its environment to produce organic chemicals.

Living in tandem with the purple microbe is a colorless bacterium called Desulforistella, which eats up the organic chemicals made by the purple bacterium.

The colorless bugs then make oils out of the organic chemicals than can be used for either crude oil or vegetable oil. These types of bacteria probably lived on the primitive Earth, which had an atmosphere rich in carbon dioxide and short of oxygen, Wayman said.

The bacteria prefer to live in conditions where there is little or no oxygen.

The primordial Earth also received little sunlight because of dense clouds, which forced the bacteria to become very efficient at converting weak light into energy, he said.

"They could live comfortably then, and by their symbiotic relationships make oil," he said.

Scientists recently discovered another bacterium called Chlorella, which is capable of producing oil at higher rates. Oil harvests from these green microbes are possible about every two days.

Oil-bearing microbes could provide liquid fuels in space, in space satellite cities, on the moon, or on other planetary bodies, Wayman said.

One of the microbe oil "factories," called Arthrobacter AK19, is able to convert 85 percent of its total weight into oil. It looks like a transparent plastic bag bulging with spherical oil droplets, Wayman said.

Another microbe, a yeast called Candida 107, can accumulate more than 60 percent of its weight in oil and looks like a strong bean but with each bean made of oil.