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Many bacterial species modify their DNA with the addition of sulfur to phosphate groups, a modification known as DNA phosphorothioation. DndA is known to act as a cysteine desulfurase, catalyzing a key biochemical step in phosphorothioation. However, bioinformatic analysis revealed that 19 out of the 31 known dnd gene clusters, contain only four genes (dndB-E), lacking a key cysteine desulfurase corresponding gene. There are multiple cysteine desulfurase genes in Escherichia coli, but which one of them participates into DNA phosphorothioation is unknown. Here, by employing heterologous expression of the Salmonella enterica dnd gene cluster named dptBCDE in three E. coli mutants, each of which lacked a different cysteine desulfurase gene, we show that IscS is the only cysteine desulfurase that collaborates with dptB-E, resulting in DNA phosphorothioation. Using a bacterial two-hybrid system, protein interactions between IscS and DptC, and IscS and DptE were identified. Our findings revealed IscS as a key participant in DNA phosphorothioation and lay the basis for in-depth analysis of the DNA phosphorothioation biochemical pathway.

For detoxification of Cr(VI)-contaminated water, a new process concept of using conductive polypyrrole/cellulose fiber composite (prepared by in situ polymerization of pyrrole in the presence of cellulose fibers) for water treatment was proposed and demonstrated. The effects of preparation conditions of the composite, as well as the water treatment conditions, on the detoxification efficiency were studied. Under the optimized conditions, the composite was highly effective in Cr(VI) detoxification. The desorption results and XPS analyses showed that the highly toxic Cr(VI) was reduced to less toxic Cr(III) and then adsorbed onto the composite. At least 3/4 of the Cr adsorbed to the composite was Cr(III). ATR-FTIR spectra and SEM images also proved that redox reaction occurred during the water treatment process. The integrated reductive/adsorptive Cr(VI) detoxification by polypyrrole-engineered cellulose fibers would provide new possibilities for the commercial application of conductive fibers.

Polypyrrole (PPy)-cellulose composites were prepared by in situ polymerization of pyrrole in pulp suspension using ferric chloride as an oxidant. Some sulfonic compounds including p-toluenesulfonic acid and its sodium salt (PTSA and PTSA-Na), benzenesulfonic acid (BSA), dodecylbenzene sulfonic acid and its sodium salt (DBSA and DBSA-Na), 2-naphthalene sulfonic acid (NSA) and 9,10-anthraquinone-2-sulfonic acid sodium salt (AQSA-Na) were used as dopants, and their effect on the conductivity of PPy-cellulose composite was investigated. The results showed that the species and dose of dopants had significant effect on the surface resistivity and environmental stability of PPy-cellulose composite. As the dopant, PTSA and DBSA had a superior doping effect compared to their sodium salts. The doping result of BSA was close to that of PTSA. NSA bearing a naphthalene ring and AQSA-Na bearing an anthraquinone ring gave the best conductivity. Using NSA or AQSA-Na as a dopant, along with suitable polymerization conditions, the PPy-cellulose composite obtained showed a surface resistivity as low as 20 X cm -2 . For most dopants, the lowest surface resistivity could be obtained when the molar ratio of dopant to pyrrole was 1:1. Both ATR-FTIR (attenuated total reflection-Fourier transform infrared spectroscopy) and XPS (X-ray photoelectron spectroscopy) analysis confirmed that the PPy on pulp fibers doped with PTSA, PTSA-Na, NSA and AQSANa had different doping levels. The higher doping level of the PPy in the composites doped with NAS and AQSA-Na might be related to the stronger interaction of cellulose with PPy chains. Both SEM (scanning electron microscopy) and AFM (atomic force microscopy) observation revealed the fine grain microstructure of the PPy on the composites with average grain sizes in the range of 100-200 nm, and the PPy on the samples doped with NSA and AQSANa exhibited quite different morphology as compared to those doped with PTSA and its sodium salt.

A copper-based metal-organic frameworks/cellulose fibers (HKUST-1/CF) composite was prepared by in situ and green method. Scanning electron microscopy with energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction analyses revealed the functionalization of cellulose fibers (CFs) was successfully achieved by in situ deposition of HKUST-1 via a DMF-free green process. The synthetized HKUST-1/ CF composite exhibited excellent antibacterial activity against Escherichia coli and Staphylococcus aureus. The composite was more effective against Gram-positive S. aureus than Gram-negative E. coli. The optimization of process variables indicated that the novel composite could be prepared at room temperature for a short time.

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