Istituto di Cristallografia, Consiglio Nazionale delle Ricerche, Via Amendola 122/O, 70126, Bari, Italy.
Biometals. 2013 Oct;26(5):693-703. doi: 10.1007/s10534-013-9641-3. Epub 2013 Jun 9.
Cobalt is an important oligoelement required for bacteria; if present in high concentration, exhibits toxic effects that, depending on the microorganism under investigation, may even result in growth inhibition. The photosynthetic bacterium Rhodobacter (R.) sphaeroides tolerates high cobalt concentration and bioaccumulates Co(2+) ion, mostly on the cellular surface. Very little is known on the chemical fate of the bioaccumulated cobalt, thus an X-ray absorption spectroscopy investigation was conducted on R. sphaeroides cells to gain structural insights into the Co(2+) binding to cellular components. X-ray absorption near-edge spectroscopy and extended X-ray absorption fine structure measurements were performed on R. sphaeroides samples containing whole cells and cell-free fractions obtained from cultures exposed to 5 mM Co(2+). An octahedral coordination geometry was found for the cobalt ion, with six oxygen-ligand atoms in the first shell. In the soluble portion of the cell, cobalt was found bound to carboxylate groups, while a mixed pattern containing equivalent amount of two sulfur and two carbon atoms was found in the cell envelope fraction, suggesting the presence of carboxylate and sulfonate metal-binding functional groups, the latter arising from sulfolipids of the cell envelope.
钴是细菌所需的一种重要微量元素；如果浓度过高，会表现出毒性作用，具体表现取决于所研究的微生物，甚至可能导致生长抑制。光合细菌球形红杆菌（R.）能够耐受高浓度的钴，并在细胞表面大量积累 Co(2+)离子。对于生物积累的钴的化学命运，人们知之甚少，因此对球形红杆菌细胞进行了 X 射线吸收光谱研究，以深入了解 Co(2+)与细胞成分的结合情况。对含有全细胞和无细胞部分的 R. sphaeroides 样品进行了 X 射线吸收近边光谱和扩展 X 射线吸收精细结构测量，这些样品是从暴露于 5 mM Co(2+)的培养物中获得的。研究发现，钴离子具有八面体配位几何形状，第一壳层有六个氧配体原子。在细胞的可溶性部分中，发现钴与羧酸盐基团结合，而在细胞包膜部分则发现了含有等量两个硫原子和两个碳原子的混合模式，表明存在羧酸盐和磺酸盐金属结合功能基团，后者来自细胞包膜的硫脂。
