COPPER-DEPENDENT RECIPROCAL TRANSCRIPTIONAL REGULATION OF METHANE MONOOXYGENASE GENES IN METHYLOCOCCUS-CAPSULATUS AND METHYLOSINUS-TRICHOSPORIUM

The methanotrophic bacteria Methylococcus capsulatus (Bath) and Methyl osinus trichosporium OB3b convert methane to methanol using the enzyme , methane monooxygenase (MMO). These bacteria are able to express two distinct MMOs: a cytoplasmic or soluble form (sMMO) and a membrane-bou nd or particulate form (pMMO). Differential expression of sMMO and pMM O is regulated by the amount of copper ions available to the cells; sM MO is expressed at low copper-biomass ratios, whereas pMMO is expresse d at high copper-biomass ratios. In both methanotrophs, transcription of the sMMO gene cluster is negatively regulated by copper ions. Data suggest that transcription of the M. trichosporium OB3b sMMO gene clus ter is directed from a sigma(54)-like and a sigma(70)-like promoter. T he pMMO (pmo) genes of M. capsulatus (Bath) are transcribed into a pol ycistronic mRNA of 3.3 kb. The synthesis of this mRNA was activated by copper ions. Activation of pmo transcription by copper ions was conco mitant with repression of sMMO gene transcription in both methanotroph s. This suggests that a common regulatory pathway may be involved in t he transcriptional switch between sMMO and pMMO gene expression.