The removal of excess nutrients
from water ecosystems requires oxidation of toxic
ammonium by two types of bacteria; one oxidizes
ammonium to nitrite and the other oxidizes nitrite
to nitrate. The oxidation of ammonium is often
incomplete and nitrite accumulates. Nitrite is also
toxic, and is converted by the ammoniumoxidizing
bacteria to nitrous oxide, a powerful
greenhouse gas. Here we use mathematical
modeling to analyze a potential solution to the
problems related to incomplete oxidation of
ammonium. We propose that a single engineered
nitrifying bacterium should be capable of
complete oxidation of high concentrations of
ammonium to nitrate. Our model is based on
available data on ammonium- and nitrite-oxidizing
bacteria. The model predicts that insertion of
highly expressed genes of a nitrite oxidation
system into the genome of an ammonia-oxidation
bacterium should result in complete oxidation of
ammonium to nitrate in nutrient-overloaded
conditions. Due to its increased capacity to fully
oxidize ammonium to nitrate, the proposed
bacterium would display dramatically reduced
production of nitrous oxide, and therefore might
have great potential to reduce the greenhouse
effect of nutrient-overloaded water system
