title: Internal Hydration Properties of Single Bacterial Endospores Probed by Electrostatic Force Microscopy.
abstract: We show that the internal hydration properties of single Bacillus cereus endospores in air under different relative humidity (RH) conditions can be determined through the measurement of its electric permittivity by means of quantitative electrostatic force microscopy (EFM). We show that an increase in the RH from 0% to 80% induces a large increase in the equivalent homogeneous relative electric permittivity of the bacterial endospores, from ∼4 up to ∼17, accompanied only by a small increase in the endospore height, of just a few nanometers. These results correlate the increase of the moisture content of the endospore with the corresponding increase of environmental RH. Three-dimensional finite element numerical calculations, which include the internal structure of the endospores, indicate that the moisture is mainly accumulated in the external layers of the endospore, hence preserving the core of the endospore at low hydration levels. This mechanism is different from what we observe for vegetative bacterial cells of the same species, in which the cell wall at high humid atmospheric conditions is not able to preserve the cytoplasmic region at low hydration levels. These results show the potential of quantitative EFM under environmental humidity control to study the hygroscopic properties of small-scale biological (and nonbiological) entities and to determine its internal hydration state. A better understanding of nanohygroscopic properties can be of relevance in the study of essential biological processes and in the design of bionanotechnological applications.
authors.affiliation: Institut de Bioenginyeria de Catalunya (IBEC) , c/Baldiri i Reixac 11-15, Barcelona 08028, Spain.|Departament d'Enginyeries: Electrònica, Universitat de Barcelona , C/Martí i Franqués 1, Barcelona 08028, Spain.
authors.forename: Marc
authors.initials: M
authors.lastname: Van Der Hofstadt
authors.affiliation: Institut de Bioenginyeria de Catalunya (IBEC) , c/Baldiri i Reixac 11-15, Barcelona 08028, Spain.|Departament d'Enginyeries: Electrònica, Universitat de Barcelona , C/Martí i Franqués 1, Barcelona 08028, Spain.
authors.forename: Rene
authors.initials: R
authors.lastname: Fabregas
authors.affiliation: Institut de Bioenginyeria de Catalunya (IBEC) , c/Baldiri i Reixac 11-15, Barcelona 08028, Spain.
authors.forename: Ruben
authors.initials: R
authors.lastname: Millan-Solsona
authors.affiliation: Institut de Bioenginyeria de Catalunya (IBEC) , c/Baldiri i Reixac 11-15, Barcelona 08028, Spain.|Departament de Microbiologia, Universitat de Barcelona , Av. Diagonal 643, Barcelona 08028, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Juarez
authors.affiliation: School of Physics and Astronomy, University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom.
authors.forename: Laura
authors.initials: L
authors.lastname: Fumagalli
authors.affiliation: Institut de Bioenginyeria de Catalunya (IBEC) , c/Baldiri i Reixac 11-15, Barcelona 08028, Spain.|Departament d'Enginyeries: Electrònica, Universitat de Barcelona , C/Martí i Franqués 1, Barcelona 08028, Spain.
authors.forename: Gabriel
authors.identifier: 0000-0002-1949-1757
authors.initials: G
authors.lastname: Gomila
mesh_terms: D001409:Bacillus cereus; D018625:Microscopy, Atomic Force; D013171:Spores, Bacterial; D055672:Static Electricity
keywords: bacterial endospores; electric permittivity; electrostatic force microscopy; nanohygroscopicity; relative humidity