NO formation by nitrite-induced (chemo)denitrification in coastal marine sediment.

Nitrous oxide (NO) is a potent greenhouse gas that also contributes to stratospheric ozone depletion. Besides microbial denitrification, abiotic nitrite reduction by Fe(II) (chemodenitrification) has the potential to be an important source of NO. Here, using microcosms, we quantified NO formation in coastal marine sediments under typical summer temperatures.

Sterilization impacts on marine sediment---Are we able to inactivate microorganisms in environmental samples?

To distinguish between biotic and abiotic processes in laboratory experiments with environmental samples, an effective sterilization method is required that prevents biological activity but does not change physico-geochemical properties of samples. We compared standard sterilization methods with respect to their impact on microbial abundance and activity. We exposed marine sediment to (i) autoclaving, (ii) gamma-radiation or (iii) sodium azide (NaN3) and determined how nucleic acids, microbial productivity, colony forming units (CFUs) and community composition of microorganisms, fungi, unicellular protists and protozoa were affected.

Microbial anaerobic Fe(II) oxidation - Ecology, mechanisms and environmental implications.

Iron is the most abundant redox-active metal in the Earth's crust. The one electron transfer between the two most common redox states, Fe(II) and Fe(III), plays a role in a huge range of environmental processes from mineral formation and dissolution to contaminant remediation and global biogeochemical cycling. It has been appreciated for more than a century that microorganisms can harness the energy of this Fe redox transformation for their metabolic benefit.

The distribution of active iron-cycling bacteria in marine and freshwater sediments is decoupled from geochemical gradients.

Microaerophilic, phototrophic and nitrate-reducing Fe(II)-oxidizers co-exist in coastal marine and littoral freshwater sediments. However, the in situ abundance, distribution and diversity of metabolically active Fe(II)-oxidizers remained largely unexplored. Here, we characterized the microbial community composition at the oxic-anoxic interface of littoral freshwater (Lake Constance, Germany) and coastal marine sediments (Kalø Vig and Norsminde Fjord, Denmark) using DNA-/RNA-based next-generation 16S rRNA (gene) amplicon sequencing.

Malonic semialdehyde reductase from the archaeon Nitrosopumilus maritimus is involved in the autotrophic 3-hydroxypropionate/4-hydroxybutyrate cycle.

The recently described ammonia-oxidizing archaea of the phylum Thaumarchaeota are highly abundant in marine, geothermal, and terrestrial environments. All characterized representatives of this phylum are aerobic chemolithoautotrophic ammonia oxidizers assimilating inorganic carbon via a recently described thaumarchaeal version of the 3-hydroxypropionate/4-hydroxybutyrate cycle. Although some genes coding for the enzymes of this cycle have been identified in the genomes of Thaumarchaeota, many other genes of the cycle are not homologous to the characterized enzymes from other species and can therefore not be identified bioinformatically.