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In nature, microbes use extracellular electron transfer (EET) to recover noble metals. Most attention has been paid to the biorecovery process occurring intracellularly and on the cell surface. In this work, we report that Pd nanorods could be biosynthesized by Enterobacter cloacae SgZ-5T in the extracellular space. This bacterium possesses both a direct EET pathway through membrane redox systems and an indirect EET pathway via the self-secreted electron carrier hydroquinone (HQ). When exposed to Pd(II), the bacteria adjusted their metabolic pathway and membrane-bound proteins to secrete riboflavin (RF). However, no HQ was detected in the supernatant in presence of Pd(II). No significant change was observed through metabolomic analysis regarding the abundance of HQ in presence of Pd(II) compared to Pd(II)-free supernatant. Similar results were also obtained through transcriptomic analysis of YqjG gene encoding glutathionyl-HQ reductase synthase. X-ray photoelectron spectroscopic evidence indicated that HQ may adsorb to the surface of Pd nanorods. Moreover, the gene encoding RF synthase (ribE) was up-regulated in the present of Pd(II), suggesting that this bioreduction process induced RF synthase, which had been shown in previous results. The UV-vis spectroscopy data demonstrated that the Pd(II) reduction rate was enhanced by 5%, 5.5% and 30% by the addition of 3.33 μM HQ, 3.33 μM RF and the both, respectively. All these results revealed that the bi-mediators secreted by bacteria were beneficial for biorecovery of Pd. This work is of significance for understanding metal biorecovery processes and natural biogeochemical processes., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

New cytotoxic, mononuclear Pt and Pd coordination complexes featuring the planar, multi-donor ligand (2,3-f)pyrazino(1,10)phenanthroline-2,3-dicarboxylic acid (H 2 PPDA) have been synthesized under hydrothermal conditions (in water, at high temperature and pressure) and fully characterized. The complexes were proven to be isostructural by applying the single-crystal X-ray diffraction technique. UV-Vis and fluorescence spectroscopy investigations on their interaction with fish sperm DNA revealed a considerable binding capacity while gel electrophoresis provided evidence in favor of cleavage of pBR322 plasmid DNA. The newly synthesized complexes manifested significant in vitro cytotoxic activity against two different human cancer cell lines, the KB and JEKO cells, with cell death mainly caused by apoptosis., (Copyright © 2016 Elsevier Inc. All rights reserved.)