Purple bacteria, typically found in aquatic environments, may seem similar to other bacteria. However, researchers recently discovered the bacteria has a special ability to act like microscopic plastic factories.
Named for their purple color, this group of microbes use energy from the sun to turn carbon dioxide into food. However, they do not use green chlorophyll like plants do.
According to Washington University in St. Louis, two studies were published this week on purple bacteria and its ability to create bioplastic. One led by graduate student Eric Conners was published in the Microbial Biotechnology journal and another led by research lab supervisor Tahina Ranaivoarisoa was published in the Applied and Environmental Biology journal.
“We hope these bioplastics will produce real solutions down the road,” Arpita Bose, associate professor of biology and corresponding author of the new studies. She runs the lab where Connors and Ranaivoarisoa work.
Conners’ study found “two relatively obscure species of purple bacteria” that are able to make polyhydroxyalkanoates (PHAs). These are natural polymers that can be used to make plastic.
“It’s worth taking a look at bacteria that we haven’t looked at before,” Conners said. “We haven’t come close to realizing their potential.”
Ranaivoarisoa’s study found that “genetic engineering could coax a well-studied but notoriously stubborn species of purple bacteria,” to increase its production of the polymers. That species is Rhodopseudomonas palustris TIE-1.
“TIE-1 is a great organism to study, but it’s historically not been the best for producing PHA,” Ranaivoarisoa said.
Plastics are typically derived from natural gas processing or crude oil refining feedstocks, according to the U.S. Energy Information Administration. Per a 2018 article from the U.S. Department of Agriculture, these traditional, oil-based plastics made from non-renewable sources are part of nearly everything we touch. Each year, around 300 million metric tons of traditional plastics are produced worldwide.
“Non-biodegradable plastics are continually amassing landfills and oceans worldwide while creating severe environmental issues and hazards to animal and human health,” said a 2022 study published in the Springer Nature journal. “Plastic pollution has resulted in the death of millions of seabirds and aquatic animals.”
Bioplastics – such as the ones derived from purple bacteria – are more biodegradable than traditional plastics and they have a lower carbon footprint. They also have advantages related to energy efficiency, versatility and unique mechanical and thermal characteristics.
These plastics “have huge potential to replace petroleum-based plastics in a wide range of industries from automobiles to biomedical applications,” said the 2022 study. According to Washington University, purple bacteria has the ability to keep producing polymers for bioplastic production “indefinitely” under the right conditions.
“Two little-known species of purple bacteria in the genus Rhodomicrobium showed a remarkable willingness to produce polymers, especially when energized with small amounts of electricity and nourished with nitrogen,” said the university of Conners’ study. He added that it is a “unique bacteria that looks very different from other purple bacteria,” since it forms interconnected networks rather than floating around as individual cells.
As for Rhodopseudomonas palustris TIE-I, researchers worked to improve its PHA-production ability by inserting a gene that increased the natural enzyme RuBisCO. This enzyme is the “catalyst that helps plants and bacteria capture carbon from air and water,” said Washington University in St. Louis.
“With the help of the super-charged enzyme, the usually sluggish bacteria turned into relative PHA powerhouses,” it added. “The researchers are optimistic a similar approach could be possible with other bacteria that might be able to produce even higher levels of bioplastics.”