| Abstract: | The nitrifying bacterium Nitrosomonas sp. strain ENI-11 has three copies of the gene encoding hydroxylamine oxidoreductase (hao 1, hao 2, and hao 3) 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 hao 3 was highest among the hao copies. Expression levels of hao 1 and hao 2 were 40% and 62% of that of hao 3 respectively. Transcription of hao 1 was negatively regulated, whereas a portion of hao 3 transcription was read through transcription from the rpsT promoter. When energy-depleted cells were incubated in the growth medium, only hao 3 expression increased. This result suggests that it is hao 3 that is responsible for recovery from energy-depleted conditions in Nitrosomonas sp. strain ENI-11. |
