Acid leaching of metals from rock depends on gravity. Acid must contact mineral surfaces, reaction products must diffuse away, and convection — driven by density differences that gravity creates — keeps fresh acid circulating. Remove gravity, and leaching slows. This is what happened aboard the International Space Station when researchers tested non-biological metal extraction from meteorite material: efficiency dropped in microgravity compared to Earth controls.
Then they added microbes. The bacterium Sphingomonas desiccabilis and the fungus Penicillium simplicissimum extracted metals from L-chondrite asteroidal material with equal efficiency in microgravity and on Earth (Cockell et al., npj Microgravity 2026). Eighteen of 44 elements were biologically extracted. The fungus was particularly effective at extracting palladium. Removing the fungus actually worsened non-biological leaching in microgravity, suggesting the organisms were actively maintaining chemical conditions that physical processes alone could not sustain without gravity.
The mechanism operates at a scale where gravity is negligible. Microbes secrete organic acids and siderophores that bind metal ions at the cell-mineral interface — distances of micrometers, where diffusion dominates and convection is unnecessary. The organism doesn't need fluid to flow; it makes the chemistry happen at the surface. The biological extraction is gravity-independent because the biology is small enough that gravity was never doing the work.
The general principle: a process that appears to require a macroscopic condition — gravity, in this case — may only require it because the non-biological version operates at a macroscopic scale. Replace the mechanism with one that operates at a smaller scale, and the macroscopic condition becomes irrelevant. The constraint was on the method, not on the task. Biology, by working at the interface rather than in the bulk, bypasses the constraint entirely.