Microbial gases in the sinkhole sediment shape the cyanobacteria mats into finger-like projections. ROV photo courtesy of UW Milwaukee Great Lakes WATER Institute and the National Undersea Research Center, North Atlantic and Great Lakes
By Sarah Coefield
Coefield@msu.edu
Great Lakes Echo
July 15, 2009
The scientists studying the Lake Huron sinkholes know the colorful bacteria they host have a prehistoric ancestry, but a major question remains: Where did it all come from?
The purple cyanobacteria mats in the Lake Huron sinkholes resemble mats found in ice-covered Antarctic lakes. Bopi Biddanda, a research scientist with the Grand Valley State University Annis Water Resources Institute, suspects they may have a similar ancestry. This suspicion relies on a theory that microbial life is already distributed across the planet, and comes out of hiding when conditions are just right, he said.
The Lake Huron mats provide clues for how ocean and lake currents could have spread the bacteria. Microbial gases in the sinkhole sediment force portions of the cyanobacteria mats to protrude like purple fingers pointing toward the lake’s surface. The protrusions sometimes tear off and float away on the currents.
Bopi Biddanda
“I think it is one of the ways (the bacteria) get distributed to other distant regions where groundwater may be coming out,” Biddanda said. “And if they land there, they can populate with the same kind of microbes.”
If the bacteria spread on currents, it likely happened long ago. “We think they’re survivors of the past, that upon conditions returning to favorable conditions they were able to thrive and reestablish and keep going,” Biddanda said.
For the bacteria in the Lake Huron sinkholes and Antarctic lakes, that would mean waiting for water that has a lot of sulfur but little oxygen – conditions similar to the ancient Earth.
Biddanda’s theory is supported by a surprising source: a fountain in front of the Alpena County public library. The water in the fountain originates 600 feet belowground. It stinks like rotten eggs, an odor caused by bacteria releasing hydrogen sulfide. The same type of bacteria dwell in the sinkholes.
“In that fountain you can see all the kinds of life we have described in these different sinkholes in different depths in Lake Huron,” Biddanda said. “It’s all there. There are white mats, purple mats and some green (algae).
Scott Kendall with the Annis Water Resources Intistute tests water from the fountain at the Alpena County public library. Photo: Scott Kendall
The bacteria couldn’t have traveled to the fountain from the sinkholes. Biddanda suspects it may have been in the 400-million-year-old bedrock all along.
If so, it would be tucked away with salts and minerals 600 feet below the Earth’s surface that were left behind when a sea covering the Great Lakes basin evaporated hundreds of millions of years ago. Such substances are called evaporites.
“I know it’s possible that in the ancient marine evaporites, seeds of this bacteria were still there, in spores or other resting stages,” Biddanda said. “So as the water began to come out and aquifers filled and dissolved some of these ancient evaporites, (the bacteria) might have started to come out.”
But, Biddanda cautions, “We have no real answers.”
“Just in June we collected a lot of samples from right there (the fountain) and we were thinking to ourselves, ‘Here is like a lab model of everything that’s out there in the big lake,'” Biddanda said. “It’s a very, very real part of that part of the Great Lakes, of the ecology.”
“Trying to figure out how all this fits in is going to take some time, for sure.”
Tomorrow: Ancient life triggers new discoveries.