Unravelling Cobalt Binding to Photosynthetic Bacterium by X-ray Absorption Spectroscopy

X-ray absorption spectroscopy was used to characterize the fate of cobalt ions present in the growth media of the photosynthetic bacterium Rhodobacter sphaeroides, a microorganism with high metal tolerance and considered a potential target for bioremediation processes. Results show that, in the average, cobalt binds in whole cells mostly to carboxylate moieties, with a very small contribution of sulfoxide or sulfonate moiety. A detailed analysis shows that this contribution arises from the sole cell envelope, where the sulphur appear to be as important as carbon in the second coordination shell of cobalt, indicating that sulfolipids of the photosynthetic membrane can significantly contribute to cobalt binding in Rhodobacter sphaeroides.