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Microorganisms facilitate the formation of a wide range of minerals that have unique physical and chemical properties as well as morphologies that are not produced by abiotic processes. Here, we report the production of an extensive extracellular network of filamentous, arsenic-sulfide (As-S) nanotubes (20 -100 nm in diameter by Ϸ30 m in length) by the dissimilatory metal-reducing bacterium Shewanella sp. HN-41. The As-S nanotubes, formed via the reduction of As(V) and S2O3 2؊ , were initially amorphous As2S3 but evolved with increasing incubation time toward polycrystalline phases of the chalcogenide minerals realgar (AsS) and duranusite (As4S). Upon maturation, the As-S nanotubes behaved as metals and semiconductors in terms of their electrical and photoconductive properties, respectively. The As-S nanotubes produced by Shewanella may provide useful materials for novel nano-and opto-electronic devices. N anotubes are considered critically important building blocks for the production of nanodevices because of their high aspect ratios and unique size-dependent properties (1-3). The former property makes them useful for integration into highdensity devices, and the latter, which diverges from the bulk because of quantum confinement effects, helps adjust the electrical and optoelectronic properties by controlling their dimensions for specific applications. Since the first discovery of carbon nanotubes in 1991 (4), there has been growing interest in synthesizing diverse inorganic nanotubes, nanowires, and nanofilms, including metal dichalcogenides, MX 2 (M ϭ Mo, W, Nb, Hf; X ϭ S, Se), which are known to be photoconductive and sensitive to the near-optical-band-gap illumination (5-9). Although chalcogenide As 2 S 3 glasses (bandgap ϭ 2.35 eV) are important infrared (IR) transparent materials that have been used in many applications, including waveguides, photonic crystals, sensors, and photolithography (10), there have been no reports of nanotube structures made of arsenic-sulfide that have useful nano-and optoelectronic properties.Microorganisms play an essential role in the biogeochemical cycling of elements and in the formation of unique minerals (11)(12)(13)(14). Biogenic minerals are often formed in the nanometer scale through diverse microbiologically mediated physiological and metabolic activities and by passive surface reactions on cell walls or extracellular structures. They have unique chemical and physical properties (15, 16) as well as diverse morphologies (17, 18) that are not easily duplicated by means of strictly abiotic or synthetic reactions (16). Bacterial dissimilatory metal reduction, for example, can result in the biogenesis of diverse minerals, such as magnetite (Fe 3 O 4 ) (19,20) and uraninite (UO 2 ) (21, 22), with unique nanometer-size domains. Because of their small size and large specific surface area, biogenic nanoparticles have found wide use in various medical, biotechnological, chemical, and electronic applications (23).It was thought that As 2 S 3 (orpiment) was formed by abiological...

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The overall ecotoxicological effect of pharmaceutically active compounds (PhACs) detected in the effluents of Korean wastewater treatment plants (WWTPs) to Daphnia magna was investigated using biological and chemical analyses. The bioassay results showed median lethal concentrations and no-observed-effect concentrations ranging from a few to tens of ppm levels for nine PhACs in 48-h acute and 21-d chronic tests. The mixture effects of pharmaceuticals also were examined by other acute and chronic tests, which showed no significant toxicity despite a slightly increased combined effect of approximately twofold. The residual concentrations of nine PhACs were analyzed at concentrations ranging from 10 ng/L to 89 microg/L in the influents and from 10 ng/L to 11 microg/L in the effluents from four metropolitan cities in South Korea between January and November of 2004. Through repeated investigations of the influents and the effluents from different WWTPs, relatively higher removal efficiencies (23.9-91.3%) compared with those of previous surveys performed in other countries were observed for most pharmaceuticals, with the exception of acetaminophen (8.7%). The present study showed no significant risk effects of the effluents from WWTPs containing pharmaceuticals (i.e., hazard quotient < 1), even at the 95th percentile contamination range, although a risk assessment factor of 1,000 was applied. Therefore, it can be concluded that the potential risk of pharmaceuticals should be monitored carefully with more bioassay data, because many uncertainties still exist in the determination and toxicity of metabolites in water environments. No significant risk was observed, however, from the selected PhACs in the effluents from WWTPs discharged into surface waters.

While many current microbial source tracking (MST) methods rely on the use of specific molecular marker genes to identify sources of fecal contamination, these methods often fail to determine all point and nonpoint contributors of fecal inputs into waterways. In this study, we developed a new library-dependent MST method that uses pyrosequencing-derived shared operational taxonomy units (OTUs) to define sources of fecal contamination in waterways. A total 56,841 pyrosequencing reads of 16S rDNA obtained from the feces of humans and animals were evaluated and used to compare fecal microbial diversity in three freshwater samples obtained from the Yeongsan river basin in Jeonnam Province, South Korea. Sites included an urbanized agricultural area (Y1) (Escherichia coli counts ≥ 1600 CFU/100 mL), an open area (Y2) with no major industrial activities (940 CFU/100 mL), and a typical agricultural area (Y3) (≥ 1600 CFU/100 mL). Data analyses indicated that the majority of bacteria in the feces of humans and domesticated animals were comprised of members of the phyla Bacteroidetes or Firmicutes, whereas the majority of bacteria in wild goose feces and freshwater samples were classified to the phylum Proteobacteria. Analysis of OTUs shared between the fecal and environmental samples suggested that the potential sources of the fecal contamination at the sites were of human and swine origin. Quantification of fecal contamination was also examined by comparing the density of pyrosequencing reads in each fecal sample within shared OTUs. Taken together, our results indicated that analysis of shared OTUs derived from barcoded pyrosequencing reads provide the necessary resolution and discrimination to be useful as a next generation platform for microbial source tracking studies.

Eubacterium limosum (ATCC 8486), a strict anaerobe from the human intestinal tract that is capable of O-demethylation of several compounds, was tested for the ability to metabolize three methoxylated isoflavonoids, biochanin A, formononetin, and glycitein. High-performance liquid chromatography elution profiles of metabolites produced from biochanin A, formononetin, and glycitein showed peaks that had identical retention times to authentic genistein, daidzein, and 6,7,4'-trihydroxyisoflavone, respectively. The metabolites were identified, using an on line liquid chromatography-electrospray mass spectrometer. E. limosum produced 61.4 microM of genistein and 13.2 microM of daidzein from 100 microM of biochanin A and formononetin, after 26 days incubation. O-demethylase activity is cell-associated and was not detected in the extracellular fraction of bacterial culture. This is the first study in which conversion of biochanin A, and formononetin to more potent phytoestrogens by a bacterium has been shown.

Production and emission of methane have been increasing concerns due to its significant effect on global climate change and the carbon cycle. Here we report facilitated methane production from acetate by a novel community of methanogens and acetate oxidizing bacteria in the presence of poorly crystalline akaganeite slurry. Comparative analyses showed that methanogenesis was significantly enhanced by added akaganeite and acetate was mostly stoichiometrically converted to methane. Electrons produced from anaerobic acetate oxidation are transferred to akaganeite nanorods that likely prompt the transformation into goethite nanofibers through a series of biogeochemical processes of soluble Fe(II) readsorption and Fe(III) reprecipitation. The methanogenic archaea likely harness the biotransformation of akaganeite to goethite by the Fe(III)-Fe(II) cycle to facilitate production of methane. These results provide new insights into biogeochemistry of iron minerals and methanogenesis in the environment, as well as the development of sustainable methods for microbial methane production.

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