is a heterotrophic organism capable of oxidizing ammonia to nitrite during growth on an organic carbon and energy source. This pathway, termed heterotrophic nitrification, requires the concerted action of an ammonia monooxygenase (AMO) and hydroxylamine oxidase (HAO). The genes required for heterotrophic nitrification have been isolated by introducing a genomic library into and screening for the accumulation of nitrite. In contrast to the situation in chemolithoautotrophic ammonia oxidizers, the genes encoding AMO and HAO are present in single linked copies in the genome of AMO from expressed in is capable of oxidizing ethene (ethylene) to epoxyethane (ethylene oxide), which is indicative of a relaxed substrate specificity. Further, when expressed in the methylotroph AM1, the AMO endows on this organism the ability to grow on ethene and methane. Thus, the AMO is capable of oxidizing methane to methanol, as is the case for the AMO from The heterotrophic nitrification genes are moderately toxic in more toxic in and non-toxic in Toxicity is due to the activity of the gene products in and both expression and activity in This is the first time that the genes encoding an active AMO have been expressed in a heterologous host.


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