Heterologous expression of soluble methane monooxygenase genes in methanotrophs containing only particulate methane monooxygenase

The methanotrophs Methylococcus capsulatus (Bath) and Methylosinus trichosp orium OB3b contain particulate methane monooxygenase (pMMO) and soluble met hane monooxygenase (sMMO) genes. Other methanotrophs such as Methylomicrobi um album BG8 and Methylocystis parvus OBBP contain only pMMO genes. Althoug h molecular genetic techniques are poorly developed in methanotrophs, sMMO genes were expressed in methanotrophs normally containing only pMMO genes. This was achieved by conjugation using broad-host-range plasmids containing the native promoter and sMMO genes from Me, capsulatus (Bath) and Ms. tric hosporium OB3b, sMMO genes derived from Ms. trichosporium OB3b were express ed in an active form in Mcy. parvus OBBP and in Mm. album BG8. Therefore, a ll of the genes required for active sMMO synthesis were contained on the br oad-host-range plasmids and were expressed in the heterologous hosts. Const itutive synthesis of pMMO was observed in Mm. album BG8 when grown at high and low copper-to-biomass ratios, while transcription of the recombinant sM MO genes was only observed under growth conditions of low copper-to-biomass ratios. Therefore, the regulatory protein(s) for sMMO synthesis was also p resent on the plasmid used, or the heterologous host contained a regulatory system for sMMO. Expression of sMMO genes in methanotrophs containing only pMMO will assist further investigations on the expression and regulation o f MMO genes in methanotrophs.