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Characterization of a two-component regulatory system from Acinetobacter baumannii that controls biofilm formation and cellular morphology

Andrew P. Tomaras

Michael J. Flagler

Caleb W. Dorsey

Department of Microbiology, Miami University, Oxford, OH 45056, USA

Correspondence
Luis A. Actis
actisla{at}muohio.edu

Acinetobacter baumannii forms biofilms on abiotic surfaces, a phenotype that may explain its ability to survive in nosocomial environments and to cause device-related infections in compromised patients. The biofilm proficiency of the 19606 type strain depends on the production of pili, cell-surface appendages assembled via the CsuAB-A-B-C-D-E chaperone–usher secretion system. The screening of a bank of isogenic insertion derivatives led to the identification of a biofilm-deficient derivative in which a transposon insertion disrupted a gene predicted to encode the response regulator of a two-component regulatory system. This gene, which was named bfmR, is required for the expression of the Csu pili chaperone–usher assembly system. This coding region is followed by an ORF encoding a putative sensor kinase that was named bfmS, which plays a less relevant role in biofilm formation when cells are cultured in rich medium. Further examination showed that the bfmR mutant was capable of attaching to abiotic surfaces, although to levels significantly lower than those of the parental strain, when it was cultured in a chemically defined minimal medium. Additionally, the morphology of planktonic cells of this mutant, when grown in minimal medium, was drastically affected, while adherent mutant cells were indistinguishable in shape and size from the parental strain. Together, these results indicate that BfmR is part of a two-component regulatory system that plays an important role in the morphology of A. baumannii 19606 cells and their ability to form biofilms on abiotic surfaces.

Present address: Department of Microbiology, University of Colorado Health Sciences Center, Aurora, CO 80045, USA.

Present address: Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, Cincinnati, OH 45267, USA.

Present address: Department of Microbiology and Molecular Genetics, Medical College of Wisconsin, Milwaukee, WI 53226, USA.

The GenBank/EMBL/DDBJ accession number for the 19606 genomic region sequence of Acinetobacter baumannii is AY838282.