Engineered ocean bacterium strips the rust that stalls carbon-capturing olivine

Sooner or later a version of this arrives at a state permit desk as a flow-through basin with an intake and an outfall. What that reviewer evaluates is the outflow description: untreated seawater in, alkaline water carrying the captured carbon out into the ocean, with engineered bacteria growing in the basin in between ^[13]. The published account of the proposed design does not describe a step that keeps the organism out of that outflow ^[14].

The scale numbers are worth doing by hand before anyone argues about them. A reactor absorbing 0.5 grams of atmospheric CO2 per day ^[9] takes up 182.5 grams a year, call it 0.18 kilograms ^[15]. One tonne of annual removal is therefore roughly 5,500 of those reactor-years, or one basin about 5,500 times bigger, pumping raw seawater the entire time ^[16]. The experiment itself was several kilograms of green olivine sand in Boston Harbor seawater run to steady state ^[8], and that arithmetic simply shows which part of the design gets large first.

The mechanism is genuinely clever. Olivine dissolution stalls because the iron it releases oxidizes into a rust coat on the mineral face, which slows the reaction and caps the capture rate ^[4]. Siderophores bind that oxidized iron and dissolve the coat ^[5]. Wild bacteria stop making siderophores once they have the iron they need for growth ^[6], so the group rewired Alteromonas macleodii to make them whatever the surrounding iron level is; first author Neil Dalvie describes it as decoupling siderophore production from environmental iron ^[7]. If uptake tracks the weathering rate, the 2.6-fold acceleration ^[2] implies about 0.19 grams a day of that reactor's 0.5 was going to happen without any biology, and the engineered strain adds roughly 0.31 ^[18].

The thing being pitched is wider than the thing being done. Pamela Silver, a founding core faculty member at the Wyss Institute, calls it an easily applicable, risk-free environmental engineering strategy with real-world decarbonization outcomes ^[17]. The same account says the group still has to find economically viable silicate feedstocks ^[12], and while a life-cycle analysis was completed across the biological, geological and chemical parts of the system ^[10], what is reported is which operating parameters matter, not a net removal figure ^[11]. Whether the approach is risk-free is a determination someone else will have to make once that record exists.

For anyone doing diligence on carbon removal suppliers, the useful grid has two axes. Down one side: is the rate limit chemistry, or is it siting and permitting. Across the top: does the living component stay inside the vessel, or does it leave with the product. Work whose speedup comes from deleting a feedback loop lands in the corner where the chemistry question is answered and the organism exits through the outfall, which means the delivery date is set by a permit clock rather than an engineering one. Suppliers in that corner are worth funding and worth discounting on schedule, and the question to put to them is what stops the strain when the pump stops.