A Mathematical Model Of Bacteria Capable Of Complete Oxidation Of Ammonium Predicts Improved Nitrogen Removal And Reduced Production Of Nitrous Oxide

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 ammoniumand 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 systems Keywords— mathematical model; ammonium oxidation; nitrous oxide