Phototrophic iron(II) [Fe(II)]-oxidizing bacteria are present in modern environments and evidence suggests that this metabolism was present already on early earth. We determined Fe(II) oxidation rates depending on pH, temperature, light intensity, and Fe(II) concentration for three phylogenetically different phototrophic Fe(II)-oxidizing strains (purple nonsulfur bacterium Rhodobacter ferrooxidans sp. strain SW2, purple sulfur bacterium Thiodictyon sp. strain F4, and green sulfur bacterium Chlorobium ferrooxidans strain KoFox). While we found the overall highest Fe(II) oxidation rates with strain F4 (4.5 mmol L(-1) day(-1), 800 lux, 20 degrees C), the lowest light saturation values [at which maximum Fe(II) oxidation occurred] were determined for strain KoFox with light saturation already below 50 lux. The oxidation rate per cell was determined for R. ferrooxidans strain SW2 to be 32 pmol Fe(II) h(-1) per cell. No significant toxic effect of Fe(II) was observed at Fe(II) concentrations of up to 30 mM. All three strains are mesophiles with upper temperature limits of c. 30 degrees C. The main pigments were identified to be spheroidene, spheroidenone, OH-spheroidenone (SW2), rhodopinal (F4), and chlorobactene (KoFox). This study will improve our ecophysiological understanding of iron cycling in modern environments and will help to evaluate whether phototrophic iron oxidizers may have contributed to the formation of Fe(III) on early earth.

Microbial anaerobic Fe(II) oxidation at neutral pH produces poorly soluble Fe(III) which is expected to bind to cell surfaces causing cell encrustation and potentially impeding cell metabolism. The challenge for Fe(II)-oxidizing prokaryotes therefore is to avoid encrustation with Fe(III). Using different microscopic techniques we tracked Fe(III) minerals at the cell surface and within cells of phylogenetically distinct phototrophic and nitrate-reducing Fe(II)-oxidizing bacteria. While some strains successfully prevented encrustation others precipitated Fe(III) minerals at the cell surface and in the periplasm. Our results indicate differences in the cellular mechanisms of Fe(II) oxidation, transport of Fe(II)/Fe(III) ions, and Fe(III) mineral precipitation.

volV) (0123456789().,-volV) can move into the groundwater specified in the exposure assessment option as well as the magnitude of residues in groundwater. The objective may also include determining degradation rates in soil as a function of depth, persistence and movement of residues in groundwater, efficacy of mitigation measures, or confirmation of more detailed studies on a wider range of sites. Sampling schedules should consider the expected time required for an active substance to move through the soil into groundwater, as well as expected persistence in both soil and groundwater. Movement and persistence can be affected by both site characteristics and properties of the active substance and its metabolites. The need to tailor study designs to objectives, exposure assessment options, compound properties and site characteristics complicates the development of standardised study designs. Therefore, this report includes a number of example designs.Other key points that must be addressed by study designs are the vulnerability of the chosen sites compared to the vulnerability of all use areas supported by the study, the product use before and during the study, and the connectivity of the sampled groundwater to treated fields. Demonstrating connectivity (a quality criterion in the EU assessment of monitoring sites to exclude false negative measurements) is more challenging for catchment or aquifer monitoring compared to shallow wells installed as part of in-field or edge-of-field studies. This report includes an extensive discussion on assessing vulnerability of monitoring sites. This includes information on different approaches to vulnerability assessment and mapping as well as for setting monitoring sites into context. Lists of available methods and data sources available at the European level are also included. In addition to information on study design and estimating vulnerability, this report includes information on a number of other topics: avoiding contamination during sampling and/or analysis, avoiding influencing residue movement as a result of purging during sampling, and proper study documentation (Good Laboratory Practices and/or quality criteria). Procedures that are discussed include site selection (new or existing wells), installation of monitoring wells, sample collection, and analysis of samples. The report also provides information on causes of outliers (abnormally high concentrations not the result of normal leaching through soil), the use of public monitoring data, information on further hydrological characterisation (such as use of tracers, groundwater age dating, and geophysical methods), and information that should be included in reports providing results of groundwater studies. AbstractGroundwater monitoring is recommended as a higher-tier option in the regulatory groundwater assessment of crop protection products in the European Union. However, to date little guidance has been provided on the study designs. The SETAC EMAG-Pest GW group (a mixture of regulatory, academic, and industry scien...

Iron oxidation at neutral pH by the phototrophic anaerobic iron-oxidizing bacterium Rhodobacter sp. strain SW2 leads to the formation of iron-rich minerals. These minerals consist mainly of nano-goethite (␣-FeOOH), which precipitates exclusively outside cells, mostly on polymer fibers emerging from the cells. Scanning transmission X-ray microscopy analyses performed at the C K-edge suggest that these fibers are composed of a mixture of lipids and polysaccharides or of lipopolysaccharides. The iron and the organic carbon contents of these fibers are linearly correlated at the 25-nm scale, which in addition to their texture suggests that these fibers act as a template for mineral precipitation, followed by limited crystal growth. Moreover, we evidence a gradient of the iron oxidation state along the mineralized fibers at the submicrometer scale. Fe minerals on these fibers contain a higher proportion of Fe(III) at cell contact, and the proportion of Fe(II) increases at a distance from the cells. All together, these results demonstrate the primordial role of organic polymers in iron biomineralization and provide first evidence for the existence of a redox gradient around these nonencrusting, Fe-oxidizing bacteria.

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