Engineered Marine Bacteria Speed Up Rock Weathering to Pull More CO2 From Air

Researchers at the Wyss Institute at Harvard University, Harvard Medical School and the Stanford Doerr School of Sustainability have genetically engineered a marine bacterium to accelerate rock weathering, a natural process that removes carbon dioxide from the atmosphere. The work, led by Pamela Silver and Michael Springer with first author Neil Dalvie, is published in Nature Biotechnology.

Rock weathering, in which silicate minerals like olivine dissolve and trap atmospheric carbon dioxide as bicarbonate, normally takes hundreds of thousands of years, which has driven companies to try enhanced rock weathering by scattering crushed rock on farmland or into water. But iron released from the minerals is not soluble in air and forms rust on the mineral surface, slowing the process. The researchers engineered the marine bacterium Alteromonas macleodii to produce much higher amounts of siderophores, molecules that extract iron from silicate minerals and dissolve the rust layer.

In customized bioreactors with a continuous flow of seawater, the engineered bacterium sped up the weathering of olivine by 2.6-fold, boosting the amount of carbon dioxide removed from the air. Wild bacteria normally stop producing siderophores once they have enough iron to grow, which Dalvie said posed a problem for industrial-scale use. The team decoupled siderophore production from environmental iron levels so the engineered bacteria always produce them.

It took the team about a month to engineer the microbes, but validating the approach required building pilot-scale bioreactors loaded with kilograms of green olivine sand and gallons of raw seawater from Boston Harbor, run in small-scale devices called eVOLVERs before scaling up.