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Dielectrophoresis as a Tool to Characterize and Differentiate Isogenic Mutants of Escherichia coli

M. Castellarnau ^* , A. Errachid ^* , C. Madrid ^* , A. Juárez ^*  and J. Samitier ^* 

^* Nanobioengineering Research Laboratory, Institut de BioEnginyeria de Catalunya (IBEC), Barcelona, Spain; and Departament d'Electrònica, and Departament de Microbiologia, Universitat de Barcelona, Barcelona, Spain

Correspondence: Address reprint requests to M. Castellarnau, Tel.: 34-93-403-7179; E-mail: mcastellarnau{at}pcb.ub.es.

In this study we report on an experimental method based on dielectrophoretic analysis to identify changes in four Escherichia coli isogenic strains that differed exclusively in one mutant allele. The dielectrophoretic properties of wild-type cells were compared to those of hns, hha, and hha hns mutant derivatives. The hns and hha genes code respectively for the global regulators Hha and H-NS. The Hha and H-NS proteins modulate gene expression in Escherichia coli and other Gram negative bacteria. Mutations in either hha or hns genes result in a pleiotropic phenotype. A two-shell prolate ellipsoidal model has been used to fit the experimental data, obtained from dielectrophoresis measurements, and to study the differences in the dielectric properties of the bacterial strains. The experimental results show that the mutant genotype can be predicted from the dielectrophoretic analysis of the corresponding cultures, opening the way to the development of microdevices for specific identification. Therefore, this study shows that dielectrophoresis can be a valuable tool to study bacterial populations which, although apparently homogeneous, may present phenotypic variability.