High precision silver isotope ratios in environmental s amples were determined by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). Purification of Ag from sample matrices was performed by a two stage tandem column setup with use of anion and cation exchange resin, sequentially. It was found that a 1 % HNO 3 and 3 % HCl was efficient to stabilize Ag in the final purified sample digests prior to MC-ICP-MS determination. Pd at 2 µg g -1 was added to both sample and Ag standard solution as a common doping matrix as well as an internal s tandard for mass bias correction. Mass discrimination and instrument drift were corrected by a combination of internal normalization with Pd and standard-sample-standard bracketing, without assuming identical mass bias for Pd and Ag. NIST SRM 978a (silver isotopic standard reference material) was used for method validation and subjected to column separation and sample preparation processes. A value of -0.003±0.010 ‰ for  107/109 Ag (mean and 2SD, n=4) was obtained, confirming accurate results can be obtained using the proposed method.To the best of o ur knowledge, this is the first report on  107/109 Ag variations in environmental samples. Significant differences in Ag isotope ratios were found among NIST SRM 978a standard, sediment CRM PACS-2, domestic sludge SRM 2781, industrial sludge 2782 and the fish liver CRM DOLT-4. The sediment CRM PACS-2 has very small negative High precision of better than ±0.015 ‰ (2SD, n=4) obtained in real sample matrices makes the present method well suited for monitoring small Ag isotope fractionation in nature.

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Thirty-three endophytic diazotrophs were isolated from surface-sterilized leaves, stem, and roots of wild rice Oryza alta. The SDS-PAGE profile of total protein and insertion sequence-based polymerase chain reaction (IS-PCR) fingerprinting grouped the isolates into four clusters (I-IV). The 16S rRNA gene sequence homology of the representative strains B21, B31, B1, and B23 of clusters I, II, III, and IV were assigned to Pseudomonas oleovorans (99.2% similarity), Burkholderia fungorum (99.4% similarity), Enterobacter cloacae (98.9% similarity), and Acinetobacter johnsonii (98.4% similarity), respectively. The results showed wide genetic diversity of the putative diazotrophic strains of the wild rice, O. alta, and the strains of cluster IV are the first report of nitrogen-fixing Acinetobacter species. The cell size, phenotypic characters, total protein profile, genomic DNA fingerprinting, DNA-DNA hybridization, and antibiotic resistance differentiated strain B23(T) from its closest relatives A. johnsonii LMG999(T) and Acinetobacter haemolyticus LMG996(T). The DNA-DNA hybridization also distinguished the strain B23(T) from the closely related Acinetobacter species. Based on these data, a novel species, Acinetobacter oryzae sp. nov., and strain B23(T) (=LMG25575(T) = CGMCC1.10689(T)) as the type strain were proposed.

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