Physical Map Location of the Multicopy Genes Coding for Ammonia Monooxygenase and Hydroxylamine Oxidoreductase in the Ammonia-Oxidizing Bacterium Nitrosomonas sp. Strain ENI-11

Pulsed-field gel electrophoresis ofPme I digests of theNitrosomonas sp. strain ENI-11 chromosome produced four bands ranging from 1,200 to 480 kb in size. Southern hybridizations suggested that a 487-kbPme I fragment contained two copies of theamoCAB genes, coding for ammonia monooxygenase (designatedamoCAB1 andamoCAB2 ), and three copies of thehao gene, coding for hydroxylamine oxidoreductase (hao1 ,hao2 , andhao3 ). In this DNA fragment,amoCAB1 andamoCAB2 were about 390 kb apart, whilehao1 ,hao2 , andhao3 were separated by at least about 100 kb from each other. Interestingly,hao1 andhao2 were located relatively close toamoCAB1 andamoCAB2 , respectively. DNA sequence analysis revealed thathao1 andhao2 shared 160 identical nucleotides immediately upstream of each translation initiation codon. However,hao3 showed only 30% nucleotide identity in the 160-bp corresponding region.