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Importance of Cyanate as Substrate for Nitrifiers

 

Supervisor: Michael Wagner

PhD student: Johanna Wiesinger

Group: Division of Microbial Ecology, Centre for Microbiology and Environmental Systems Science

 

 

For decades nitrifiers were considered to be highly specialized organisms that exclusively obtain energy for aerobic growth from ammonia and urea (ammonia oxidizers) as well as nitrite (nitrite oxidizers). During the last year our lab challenged this view by demonstrating that some nitrite oxidizers can grow by aerobic oxidation of hydrogen (Koch et al. 2014) or by reciprocal feeding with ammonia oxidizers by using urea as substrate (Koch et al., in press). Furthermore, some ammonia-oxidizers and likely all known nitrite oxidizers are capable to use cyanate as source of energy and reductant (Palatinszky et al. 2015). Again, growth of nitrite-oxidizers on cyanate is achieved by reciprocal feeding with ammonia oxidizers, a new mode of interaction among nitrifiers.

Cyanate is formed in the environment among others from spontaneous urea decomposition as well as from photooxidation and enzymatic degradation of cyanide, which is produced by many plants as defense against herbivores. Thus, likely significant amounts of cyanate are produced in the environment, but only very recently analytical tools were developed that allow measuring this compound in environmental samples in the nM range. We hypothesize that cyanate is a quantitatively important substrate for nitrifiers in terrestrial and marine systems. In order to test this hypothesis, a pool dilution assay for measuring cyanate formation and consumption in environmental samples will be established. In addition, single cell stable isotope labeling experiments with labeled cyanate will be performed in order to identify cyanate-degrading nitrifiers using Raman microspectroscopy (Berry et al. 2015) or NanoSIMS. In parallel, cyanate degrading nitrifiers will be enriched and isolated by innovative flow-through cultivation assays. In particular, we will focus on the importance of cyanate in urea-fertilized rice fields, in arctic soils, and in marine oxygen minimum zones.

The project will primarily be based at the University of Vienna, and transcriptomic as well as proteomic experiments will be conducted during an extended research stay in the lab of Prof. Per Nielsen, University of Aalborg, Denmark.

 

 

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