Grand Valley team chronicles microbial migration related to Earth's oxygenation

Grand Valley researchers believe they have discovered one of the mysteries behind how oxygen levels rose to levels necessary to encourage the expansion of life on Earth billions of years ago, and the key lies at the bottom of Lake Huron.

Life as we know it may owe its existence to thin microbial mats, resting along the bottom of a young Earth’s shallow coastlines, similar to the mats in sinkholes in Lake Huron. A team from the Annis Water Resources Institute in Muskegon has been studying the mats and its findings have been published in the February issue of “Journal of Great Lakes Research.”

The sinkholes and microbial mats in Lake Huron give Bopi Biddanda, professor of water resources at AWRI, and his team a glimpse into what life was like in Earth’s oceans 500 million to four billion years ago.

“(The mats) look like a rug or carpet, they would grow where there was still sunlight,” said Biddanda. “Too shallow, and they would burn in the UV-rich environment that was there before the ozone layer. Too deep, and they would be cut off from the light.”

Biddanda was part of an international team that published its research in August 2021, showing how the mats were key to oxygenating the atmosphere as Earth’s daylight increased over geologic time.

The data and images released this month show how the GVSU researchers tracked the microbes’ miniscule migration in that process, said Biddanda.

“It might have been the largest mass movement of life for the first three billion years of life on the planet, which essentially set the stage for today,” he said. “Nobody had ever visually tracked  this migration with such high quality and frequency of imagery.”

As they were studying the Lake Huron mats, Biddanda and his team, including researcher Anthony Weinke and undergraduate students Ian Stone and Janelle Cook, noticed a changing color pattern, he said. 

“We noticed that if we went early in the morning, the mat would be whitish,” Biddanda said. “But later in the day when we dove down, it would be more dark purple. So we had this hypothesis that maybe the different colored microbes that are capable of different functions are switching places.”

Biddanda and his team believe purple-pigmented microbes that harness sunlight for photosynthesis migrate to the top of the mats for better positioning to capture sunlight. 

In the evening, these microbes would switch places with another group of pigment-free microbes within the mat that are chemically sensitive to sulfide for their energy production. The entire migration is merely millimeters, Biddanda said. 

Biddanda and his team described it as a tango between the microbes. 

“By establishing these alternating day and night shifts it’s almost like a factory but with very different rules, very different roles,” Biddanda said. “In the morning the technicians come and set up the body, and at night the other technicians come up and fix the engine to it.” 

To witness the migration in real time, the team attached a time-lapse camera to a makeshift frame and, with the help of divers at the Thunder Bay Marine Sanctuary in Alpena, positioned the camera over the mats.

“The first year of observation in 2018 was stunning,” Biddanda said. “We went and confirmed it for two more years that this is really happening over multiple daily cycles.”

The mats also play a large role in capturing and storing carbon in the lake floor. Organic material like plants that fall onto the mat would be rapidly covered by the migrating microbes and pushed into the sediment, Biddanda said. 

With no oxygen in the sediment, the organic matter gets preserved and sequestered as might have occurred in the mat-covered shallow seas of the early Earth. Biddanda said. The more carbon stored in the sediment, more oxygen can be released into the water and eventually the atmosphere. 

“The very small scale processes by microorganisms we're now seeing macroscopically in refugia like sinkholes today may represent what might have happened globally and over a long length of time leading to the oxygenated and diverse biosphere we have today,” Biddanda said.