Project description:Nitrification, the oxidation of ammonia via nitrite to nitrate, has always been considered to be a two-step process catalysed by chemolithoautotrophic microorganisms oxidizing either ammonia or nitrite. No known nitrifier carries out both steps, although complete nitrification should be energetically advantageous. This functional separation has puzzled microbiologists for a century. Here we report on the discovery and cultivation of a completely nitrifying bacterium from the genus Nitrospira, a globally distributed group of nitrite oxidizers. The genome of this chemolithoautotrophic organism encodes the pathways both for ammonia and nitrite oxidation, which are concomitantly activated during growth by ammonia oxidation to nitrate. Genes affiliated with the phylogenetically distinct ammonia monooxygenase and hydroxylamine dehydrogenase genes of Nitrospira are present in many environments and were retrieved on Nitrospira contigs in new metagenomes from engineered systems. These findings fundamentally change our picture of nitrification and point to completely nitrifying Nitrospira as key components of nitrogen-cycling microbial communities.
Project description:In this experiment, we used advanced proteomics techniques to discern differences in energy allocation between three strains of ammonia oxidizing bacteria: Nitrosomonas europaea, Nitrosomonas ureae, and Nitrosospira multiformis, during ammonia starved and ammonia replete conditions. Replicate cultures in late log phase from the three strains were starved of ammonia for 24 hours and compared to replicate control cultures grown for the same period. All three species were grown with three biological replicates for each condition and species with the exception of two replicates from the N. ureae starved cultures due to sample processing loss. This study has, to our knowledge, produced the first complete proteomes of Nitrosospira multiformis and Nitrosomonas ureae.
