Engineered bacteria accelerate CO2 removal in pilot olivine reactors

Several kilograms of green olivine sand sat beneath raw seawater from Boston Harbor as engineered bacteria flowed continuously through pilot bioreactors. By the end of the steady-state tests, the system was absorbing 0.5 grams of atmospheric CO2 per day—a small output, but a measurable demonstration of a process that usually unfolds over geological timescales.

The team from Harvard University’s Wyss Institute, Harvard Medical School and Stanford’s Doerr School of Sustainability modified Alteromonas macleodii, a widespread marine bacterium. Its target was olivine, a silicate mineral whose dissolution can remove carbon dioxide from the atmosphere: in water, the carbon becomes bicarbonate while the rock releases magnesium, iron and silicate.

The obstacle was rust. Iron released during weathering oxidizes and forms a coating over the mineral, slowing further dissolution. Some bacteria naturally produce siderophores—molecules that bind oxidized iron and keep it soluble—but stop once they have enough iron to grow. The researchers rewired A. macleodii to keep producing those molecules regardless of the surrounding iron level. In the reactors, that change accelerated olivine weathering by 2.6-fold compared with control conditions.

And so, concretely? The result offers a possible way to process seawater and mineral feedstock in larger basins, similar to those used at sewage-treatment facilities. Such a system could pump untreated seawater through the basins before releasing alkaline water containing captured carbon into the ocean. It is not yet an industrial deployment: the researchers still need to identify economically viable silicate sources and other feedstocks, while studying whether metals can be recovered during carbon sequestration.

The team also carried out a life-cycle analysis of the system’s biological, geological and chemical components to identify the conditions needed for net carbon removal at industrial scale. The pilot establishes the operating concept and its measured effect; whether it can deliver net removal economically at larger scale remains an open research question.