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 of PmeI digests of the Nitrosomonas sp. st rain ENI-11 chromosome produced four bands ranging from 1,200 to 480 kb in size. Southern hybridizations suggested that a 487-kb PmeI fragment contain ed two copies of the amoCAB genes, coding for ammonia monooxygenase (design ated amoCAB(1) and amoCAB(2)), and three copies of the hao gene, coding for hydroxylamine oxidoreductase (hao(1), hao(2), and hao(3)). In this DNA fra gment, amoCAB(1) and amoCAB(2) were about 390 kb apart, while hao(1), hao(2 ), and hao(3) were separated by at least about 100 kb from each other. Inte restingly, hao, and hao, were located relatively close to amoCAB(1) and amo CAB(2), respectively. DNA sequence analysis revealed that hao(1) and hao(2) shared 160 identical nucleotides immediately upstream of each translation initiation codon. However, hao(3) showed only 30% nucleotide identity in th e 160-bp corresponding region.