BioCoder #7

Chapter 7. Allison Pieja and the Minor Miracle of Methanotrophs

Glen Martin

Harnessing Bacteria to Generate Earth-Friendly Bioplastics

Methane is a problematic gas. It is expelled in massive quantities by everything from marshes and muskegs to wastewater treatment plants and landfills. And because it has 21 times the heat-retaining qualities of CO2, it’s pretty much public enemy number one when it comes to global warming.

But for Allison Pieja and her colleagues at Bay Area–based Mango Materials, methane is a valuable —indeed, indispensable —resource. The company uses microbes that consume the gas to produce an essential commodity: polyhydroxybutyrate (PHB). Plastics, in other words.

“Our process involves a kind of octopus arrangement of anaerobic reactors aimed at continuous production,” says Pieja, Mango Materials’ director of technology. “We culture the bacteria in a central tank, and then ‘fatten’ them with methane in a series of satellite tanks.”

The microorganisms, known as methanotrophs, are astoundingly adept at their assigned task. In a methane-rich environment, up to 60% of their mass will manifest as PHB. The polyester-class polymer is harvested as exceedingly small granules from the expired microbes.

But is there any significant value to PHB? For the short answer, simply harken back to the 1967 film The Graduate, specifically to the scene where a certain Mr. McGuire is advising young Ben Braddock on a career path: “I just want to say one word to you. Just one word. ...