|Nordhoff, M; Tominski, C; Halama, M; Byrne, J; Obst, M; Kleindienst, S; Behrens, S; Kappler, A: Insights into nitrate-reducing Fe(II) oxidation mechanisms by analyzing cell-mineral associations, cell encrustation and mineralogy in the chemolithoautotrophic enrichment culture KS, Applied and Environmental Microbiology, 83(13), e00752-17 1-19 (2017), online: 28.04.2017|
Most described nitrate-reducing Fe(II)-oxidizing bacteria (NRFeOB) are mixotrophic and depend on organic cosubstrates for growth. Encrustation of cells in Fe(III) minerals has been observed for mixotrophic NRFeOB but not for autotrophic phototrophic and microaerophilic Fe(II) oxidizers. So far, little is known about cell-mineral associations in the few existing autotrophic NRFeOB. Here, we investigate whether the designated autotrophic Fe(II)-oxidizing strain (closely related to Gallionella and Sideroxydans) or the heterotrophic nitrate reducers that are present in the autotrophic nitrate-reducing Fe(II)-oxidizing enrichment culture KS form mineral crusts during Fe(II) oxidation under autotrophic and mixotrophic conditions. In the mixed culture, we found no significant encrustation of any of the cells both during autotrophic oxidation of 8 to 10 mM Fe(II) coupled to nitrate reduction and during cultivation under mixotrophic conditions with 8 to 10 mM Fe(II), 5 mM acetate, and 4 mM nitrate, where higher numbers of heterotrophic nitrate reducers were present. Two pure cultures of heterotrophic nitrate reducers (Nocardioides and Rhodanobacter) isolated from culture KS were analyzed under mixotrophic growth conditions. We found green rust formation, no cell encrustation, and only a few mineral particles on some cell surfaces with 5 mM Fe(II) and some encrustation with 10 mM Fe(II). Our findings suggest that enzymatic, autotrophic Fe(II) oxidation coupled to nitrate reduction forms poorly crystalline Fe(III) oxyhydroxides and proceeds without cellular encrustation while indirect Fe(II) oxidation via heterotrophic nitrate-reduction-derived nitrite can lead to green rust as an intermediate mineral and significant cell encrustation. The extent of encrustation caused by indirect Fe(II) oxidation by reactive nitrogen species depends on Fe(II) concentrations and is probably negligible under environmental conditions in most habitats.
Iron, sulfur and a pinch of antimony - new perspectives on secondary mineral pathways and metalloid mobility
Intensify or diversify? How agriculture affects biodiversity and ecosystem processes in European farmland
The meat of the Anthropocene: Food, capital and the globalisation of industrialised animal killing
Auf ins Neue! Winterspaziergang im ÖBG
Konzert: Musikalischer Jahresbeginn mit den Rockin`Dinos
Stoichiometric controls of C and N cycling
Flying halfway across the globe to dig in the dirt – a research stay in Bloomington, USA
EGU – interesting research and free coffee
Picky carnivorous plants?