抄録
The nitrifying bacterium Nitrosomonas sp. strain ENI-11 has three copies of the gene encoding hydroxylamine oxidoreductase (hao1, hao2, and hao3) on its genome. Broad-host-range reporter plasmids containing transcriptional fusion genes between hao copies and lacZ were constructed to analyze the expression of each hydroxylamine oxidoreductase gene (hao) copy individually and quantitatively. β-Galactosidase assays of ENI-11 harboring reporter plasmids revealed that all hao copies were transcribed in the wild-type strain. Promoter analysis of hao copies revealed that transcription of hao3 was highest among the hao copies. Expression levels of hao1 and hao2 were 40% and 62% of that of hao3 respectively. Transcription of hao1 was negatively regulated, whereas a portion of hao3 transcription was read through transcription from the rpsT promoter. When energy-depleted cells were incubated in the growth medium, only hao3 expression increased. This result suggests that it is hao3 that is responsible for recovery from energy-depleted conditions in Nitrosomonas sp. strain ENI-11.
