How Ancient Red Algae Power Extreme Ecosystems – and Offer Clues to Life’s Evolution

Rutgers researchers reveal how ancient organisms drive microbial communities and may yield tools for biotechnology

Ancient single-celled red algae that thrive in scalding, acidic waters are emerging as far more than specialized survivors.

Research by Rutgers evolutionary biologist Debashish Bhattacharya and his collaborators show that the organisms, known as Cyanidiophyceae, form the foundation of entire microbial ecosystems, providing new insights into how complex life may have evolved and adapted to some of Earth's harshest environments.

"They are like a work of art," said Bhattacharya, a Distinguished Professor with the Department of Biochemistry and Microbiology in the Rutgers School of Environmental and Biological Sciences. "This is a success story a billion years in the making."

The work is reshaping scientists' understanding of the Cyanidiophyceae, which are an ancient branch of red algae whose ancestors diverged from other red algae about eons years ago.

From left, retired Montana State University professor Timothy McDermott; Julia Van Etten, who earned her doctorate at Rutgers and is now an assistant professor at the University of Maryland; and Gabrielle Panayotakis, a doctoral student in Rutgers' microbial biology program, search for samples at Nymph Creek in Yellowstone National Park.

Bhattacharya is a coauthor of a review published in New Phytologist that brings together findings from his Rutgers research group and scientists around the world. Cyanidiophyceae arose about 1.2 billion years ago, long after the planet's first cells evolved, so they are not direct representatives of life on early Earth. But the way these algae sustain microbial communities in hot springs may resemble how much older ecosystems functioned, when bacteria rather than algae likely served as the primary producers.

Bhattacharya said the algae also may hold practical value. Their enzymes evolved to function under heat, acidity and exposure to toxic metals, conditions that disable many ordinary enzymes. He and other researchers hope those biological tools could eventually be used in pollution cleanup, wastewater treatment and industrial manufacturing.

At the center of Bhattacharya's research is the algae's role as primary producers, organisms that use sunlight to create food and energy supporting an ecosystem. Through photosynthesis, they release organic forms of carbon that sustains surrounding bacteria and archaea, the latter are single-celled organisms that resemble bacteria but belong to a separate branch of life.

"The algae are the primary producers in these ecosystems," Bhattacharya said. "Through photosynthesis, they release pulses of carbon over the day-night cycle, and the bacteria and archaea around them respond."

Yellowstone National Park is a pivotal site for Rutgers evolutionary biologist Debashish Bhattacharya's research on ancient red algae, which thrive in the park's hot, acidic springs and help sustain diverse microbial communities. From left are Bhattacharya and his collaborators Gabrielle Panayotakis, Timothy McDermott and Julia Van Etten.

Bhattacharya's Rutgers group and its collaborators study the algae at Lemonade Creek and other hot springs in Yellowstone National Park. Water emerging from geothermal springs is initially too hot to support them. As it flows downstream and cools to between about 97 and 122 degrees Fahrenheit, Cyanidiophyceae become the dominant life form.

Despite their name, the algae do not appear red. Their ancestors lost phycoerythrin, the pigment that gives many red algae their color, leaving the green of chlorophyll visible.

The researchers found that two Cyanidiophyceae species divide the habitat by time of day. Cyanidioschyzon merolae is highly active during daylight, using photosynthesis to produce carbon-rich compounds that feed nearby microbes. Galdieria yellowstonensis conducts less photosynthesis during peak daylight and becomes more active at night, consuming carbon already available in the environment.

In ongoing research, Bhattacharya's team tracked microbial gene activity throughout the day and night. Some bacteria followed the rise and fall of the algae's photosynthesis, while others became more active after sunset. "The algae are the true drivers of this ecosystem," Bhattacharya said. "The microbes around them are responding to their photosynthetic activity."

The Yellowstone sites also reveal how quickly life can adapt. Temperature, acidity, moisture, sunlight and metal concentrations can vary across only a few centimeters among stream water, nearby soil and spaces inside volcanic rock. Each habitat may support a distinct community of algae, bacteria and viruses.

"You end up with this hidden biodiversity within centimeters of each other," Bhattacharya said.

Genetic analyses by the team show that even populations of the same algal species can begin to diverge in their DNA sequence when one occupies water and another lives in nearby soil, demonstrating how local conditions can drive adaptation over small distances.

Rutgers researchers also explore the algae's unusual genetic history.

Studies by Bhattacharya and other scientists have shown that the organisms acquired genes from bacteria and archaea through horizontal gene transfer, a process in which genetic material moves between unrelated organisms. Bhattacharya described it as the algae "stealing" useful genes from neighboring microbes.

Those borrowed genes helped the algae tolerate acidity, use new carbon sources and survive exposure to toxic metals, according to the scientists.

In a separate paper published in Trends in Microbiology, Bhattacharya and his colleagues proposed the Integrated Horizontal Gene Transfer Model, which suggests that sharing resources and survival functions within microbial communities may have influenced how the borrowed genes evolved. It could help explain how cells developed new abilities while maintaining small, efficient genomes.

Bhattacharya and his colleagues used arsenic and mercury to illustrate two different survival strategies. Evidence from Yellowstone suggests that different organisms may perform different steps in response to arsenic.

"Arsenic detoxification is a community affair," Bhattacharya said.

Mercury presents a different challenge, the researchers found. Because it is extremely toxic, organisms cannot safely depend on neighboring species. Individual bacteria and algae instead maintain their own genes for converting mercury into a less harmful form.

Other studies summarized in the New Phytologist review have overturned another long-standing belief about the algae: For more than a century, scientists thought Cyanidiophyceae reproduced only by making copies of themselves through a process known as mitosis. Researchers now know the algae also have a sexual life cycle and can switch between forms with different numbers of chromosome sets. Scientists are investigating which environmental conditions trigger that change.

These days, Bhattacharya is exploring whether the algae and their microbial partners contain enzymes capable of working under extreme heat, acidity and metal exposure. Such enzymes could eventually prove useful in environmental cleanup and industrial processes.

For Bhattacharya, those possibilities increase directly from fundamental research. Scientists first need to understand how the algae grow, reproduce and interact with surrounding microbes before they can determine which of their unusual abilities can be put to work, he said.

Explore more of the ways Rutgers research is shaping the future.