Puzon Geoffrey J, Huang Yan, Dohnalkova Alice, Xun Luying
School of Molecular Biosciences, Washington State University, Abelson Hall 301, Pullman, WA 99164-4234, USA.
Biodegradation. 2008 Jun;19(3):417-24. doi: 10.1007/s10532-007-9147-1. Epub 2007 Aug 15.
Microorganisms can reduce toxic chromate to less toxic trivalent chromium [Cr(III)]. Besides Cr(OH)(3) precipitates, some soluble organo-Cr(III) complexes are readily formed upon microbial, enzymatic, and chemical reduction of chromate. However, the biotransformation of the organo-Cr(III) complexes has not been characterized. We have previously reported the formation of a nicotinamide adenine dinucleotide (NAD(+))-Cr(III) complex after enzymatic reduction of chromate. Although the NAD(+)-Cr(III) complex was stable under sterile conditions, microbial cells were identified as precipitates in a non-sterile NAD(+)-Cr(III) solution after extended incubation. The most dominant bacterium PTX1 was isolated and assigned to Leifsonia genus by phylogenetic analysis of 16S rRNA gene sequence. PTX1 grew slowly on NAD(+) with a doubling time of 17 h, and even more slowly on the NAD(+)-Cr(III) complex with an estimated doubling time of 35 days. The slow growth suggests that PTX1 passively grew on trace NAD(+) dissociated from the NAD(+)-Cr(III) complex, facilitating further dissociation of the complex and formation of Cr(III) precipitates. Thus, organo-Cr(III) complexes might be an intrinsic link of the chromium biogeochemical cycle; they can be produced during chromate reduction and then further mineralized by microorganisms.
微生物可将有毒的铬酸盐还原为毒性较低的三价铬[Cr(III)]。除了Cr(OH)(3)沉淀外，铬酸盐经微生物、酶和化学还原后，还会很容易形成一些可溶性有机-Cr(III)配合物。然而，有机-Cr(III)配合物的生物转化尚未得到表征。我们之前报道过，铬酸盐经酶还原后会形成烟酰胺腺嘌呤二核苷酸(NAD(+))-Cr(III)配合物。虽然NAD(+)-Cr(III)配合物在无菌条件下是稳定的，但长时间孵育后，微生物细胞在非无菌的NAD(+)-Cr(III)溶液中被鉴定为沉淀物。通过对16S rRNA基因序列进行系统发育分析，分离出了最主要的细菌PTX1，并将其归类为Leifsonia属。PTX1在NAD(+)上生长缓慢，倍增时间为17小时，而在NAD(+)-Cr(III)配合物上生长更慢，估计倍增时间为35天。生长缓慢表明PTX1在从NAD(+)-Cr(III)配合物解离出的微量NAD(+)上被动生长，促进了该配合物的进一步解离和Cr(III)沉淀的形成。因此，有机-Cr(III)配合物可能是铬生物地球化学循环的一个内在环节；它们可以在铬酸盐还原过程中产生，然后被微生物进一步矿化。
