Nitrogen Kinetic Isotope Effects of Nitrification by the Complete Ammonia Oxidizer Nitrospira inopinata

Abstract

Nitrification is an important nitrogen cycle process in terrestrial and aquatic environments. The discovery of comammox has changed the view that canonical AOA, AOB, and NOB are the only chemolithoautotrophic organisms catalyzing nitrification.

Physiological Influence of Fe and Cu Availability on Nitrogen Isotope Fractionation during Ammonia Oxidation

“…This has been demonstrated in numerous studies of elemental cycling in biological systems − with results helping provide a more mechanistic understanding of the behavior of isotope fractionation and strengthening conclusions made from environmental observations. Ammonia oxidation imparts a kinetic isotope effect on N ( 15 ε AO ), with reported 15 ε AO values from culture studies varying considerably (e.g., −14 to −46‰, wherein product NO 2 – is less enriched in 15 N than reactant NH 3 ) across a range of potentially relevant and interrelated factors, including phylogeny, substrate availability (NH 3 , O 2 ), temperature, and pH. ,− More broadly, the relationships between microbial growth and the expression of isotope effects can vary widely among different organisms and elemental systems. For example, sulfur and carbon isotopes in sulfate-reducing bacteria and marine phytoplankton, respectively, both exhibit growth rate dependence of their respective fractionation factors but with opposing directionality. ,, Conversely, coccolithophores show no link between growth or the calcification rate and Ca isotope fractionation .…”