Biologists Uncover Innovative Methods to Boost Bioplastic Production Using Purple Bacteria

Two groundbreaking studies led by WashU biologists highlight the potential of these microbes. In the first study, graduate student Eric Conners discovered that two relatively unknown species of purple bacteria have a remarkable ability to produce polyhydroxyalkanoates (PHAs)—natural polymers that can be purified to create bioplastics.

Meanwhile, in a second study, research lab supervisor Tahina Ranaivoarisoa demonstrated that genetic engineering could significantly enhance PHA production in a well-known, yet traditionally stubborn, species of purple bacteria. 

Both Conners and Ranaivoarisoa work under the guidance of Arpita Bose, an associate professor of biology in Arts & Sciences at WashU, who is the corresponding author of the studies. “There's a huge global demand for bioplastics,” Bose said. “They can be produced without adding CO2 to the atmosphere and are completely biodegradable. These two studies show the importance of exploring multiple approaches to discovering new ways to produce this valuable material.”

Purple bacteria, a unique group of aquatic microbes, are renowned for their adaptability and ability to create useful compounds from simple ingredients. Like green plants, they can convert carbon dioxide into food using sunlight. However, unlike plants, they use different pigments to capture light, giving them their characteristic purple hue.

These bacteria naturally produce PHAs and other bioplastic precursors as a way to store extra carbon. Under the right conditions, they can continue producing these polymers indefinitely.

In the study published in Microbial Biotechnology, Conners found that two lesser-known species of purple bacteria within the genus Rhodomicrobium displayed a remarkable capacity to produce polymers, especially when supplemented with small amounts of electricity and nitrogen. “Exploring bacteria that have been overlooked could unlock their untapped potential,” Conners said.

Rhodomicrobium bacteria have unique properties that make them intriguing candidates for natural bioplastic production. Unlike other species that float freely as individual cells, Rhodomicrobium forms interconnected networks, which appear to be particularly well-suited for PHA production.

In the second study, published in Applied and Environmental Microbiology, the researchers focused on Rhodopseudomonas palustris TIE-1, a species traditionally known for its reluctance to produce PHAs. Through genetic engineering, the team significantly boosted the bacteria’s PHA output. One particularly successful approach involved the insertion of a gene that enhanced the production of RuBisCO, an enzyme crucial for capturing carbon from air and water. The result? A dramatic increase in PHA production, turning the previously sluggish bacteria into potent bioplastic producers.

The WashU team is optimistic that similar genetic engineering techniques could be applied to other bacteria, potentially yielding even greater levels of bioplastic production.

Looking ahead, Bose and her team plan to closely examine the quality and potential applications of the bioplastics produced in their lab. “We hope these bioplastics will lead to real-world solutions in the near future,” she said.

These discoveries mark a significant step forward in the quest for sustainable materials, offering hope for a future where environmentally friendly bioplastics replace their petroleum-based counterparts.