THE PLASMID-ENCODED HYDROGENASE GENE-CLUSTER IN ALCALIGENES-EUTROPHUS

Alcaligenes eutrophus strain H16 harbors a 450 kilobase pairs (kb) conjugative plasmid which codes for the ability of the organism to grow lithoautotrophically on hydrogen and carbon dioxide (reviewed in [1]). The genes for hydrogen oxidation, designated hox, are clustered on plasmid pHG1 in DNA region of approximately 100-kb in size ([2]. Fig. 1). The hox genes and their organization have been analyzed by isolation of Hox-deficient mutants, by complementation analysis, by cloning of hox genes, identification of hox-encoded polypeptides and most recently, by DNA sequencing. The hox cluster is flanked by the two structural gene regions, hoxS and hoxP; it contains a regulatory locus, hoxC, and additional genes like hoxN and hoxM whose products play a role in the formation of catalytically active hydrogenase proteins. Of four indigenous 1.3-kb insertion elements, two copies of IS491 map in the hox gene cluster. These elements may be involved in rearrangements and deletions which occur particularly frequently in this region of the megaplasmid (Schwartz, Kortluke and Friedrich, unpublished).