Acinetobacter baumannii has two genes encoding glutathione-dependent formaldehyde dehydrogenase: evidence for differential regulation in response to iron

• Published in: Microbiology (Society for General Microbiology) 2001-10, Vol.147 (10), p.2805-2815
• Main Authors: Echenique, Jose R, Dorsey, Caleb W, Patrito, Luis C, Petroni, Alejandro, Tolmasky, Marcelo E, Actis, Luis A
• Format: Article
• Language: English
• Subjects: Acinetobacter - enzymology; Acinetobacter - genetics; Acinetobacter baumannii; Acinetobacter Infections - microbiology; adhC2 gene; Aldehyde Oxidoreductases - genetics; ashC1 gene; Bacteriology; Base Sequence; Biological and medical sciences; Cloning, Molecular; Culture Media; Fundamental and applied biological sciences. Psychology; Gene Duplication; Gene Expression Regulation, Bacterial; Genetics; Glutathione - metabolism; Humans; Iron - metabolism; Microbiology; Molecular Sequence Data; Mutation; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Promoter Regions, Genetic; Sequence Analysis, DNA
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/00221287-147-10-2805

Departamento de Bioquímica Clínica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina 1 Department of Microbiology, Miami University, Oxford, OH 45056, USA 2 Instituto de Investigaciones Bioquímicas "Fundación Campomar", Buenos Aires, Argentina 3 Institute of Molecular Biology and Nutrition, Department of Biological Science, California State University Fullerton, Fullerton, CA 92834-6850, USA 4 Author for correspondence: Luis A. Actis. Tel: [phone]. Fax: [phone]. e-mail: actisla{at}muohio.edu The adhC1 gene from Acinetobacter baumannii 8399, which encodes a glutathione-dependent formaldehyde dehydrogenase (GSH-FDH), was identified and cloned after mapping the insertion site of Tn 3 -HoHo1 in a recombinant cosmid isolated from a gene library. Sequence analysis showed that this gene encodes a protein exhibiting significant similarity to alcohol dehydrogenases in bacterial, yeast, plant and animal cells. The expression of the adhC1 gene was confirmed by the detection of GSH-FDH enzyme activity in A. baumannii and Escherichia coli cells that expressed the cloned gene. However, the construction and analysis of an A. baumannii 8399 adhC1 ::Tn 3 -HoHo1 isogenic derivative revealed the presence of adhC2 , a second copy of the gene encoding GSH-FDH activity. Enzyme assays and immunoblot analysis showed that adhC2 encodes a 46·5 kDa protein that is produced in similar amounts under iron-rich and iron-limited conditions. In contrast, the expression of adhC1 , which encodes a 45 kDa protein with GSH-FDH activity, is induced under iron limitation and repressed when the cells are cultured in the presence of free inorganic iron. The differential expression of adhC1 is controlled at the transcriptional level and mediated through the Fur iron-repressor protein, which has potential binding sites within the promoter region of this adhC copy. The expression of both adhC copies is significantly enhanced by the presence of sub-inhibitory concentrations of formaldehyde in the culture media. Examination of different A. baumannii isolates indicates that they can be divided into two groups based on the type of GSH-FDH they produce. One group contains only the constitutively expressed 46·5 kDa protein, whilst the other produces this GSH-FDH type in addition to the iron-regulated isoenzyme. Further analysis showed that the presence and expression of the two adhC genes does not confer resistance to exogenous formaldehyde, nor does it enable it t