title: Mechanical and cell-to-cell adhesive properties of aggregated Methanosarcina.
abstract: The mechanical and adhesive properties as well as the turgor pressure of microbes play an important role in cell growth and aggregation. By applying AFM together with finite element modelling, one can determine the cell wall structural homogeneity, mechanical and cell-to-cell adhesive properties for aggregated Methanosarcina barkeri cells. This also allows a novel approach to determine in-aggregate turgor pressure determination. Analyzing the AFM force-indentation response of the aggregates under loads less than 10 nN, our study reveals structural inhomogeneity of the polymeric part of the cell wall material and suggests that the cell wall consists of two layers of methanochondroitin (external: with a thickness of 3 ± 1 nm and internal: with a thickness of 169 ± 30 nm). On average, the hyperelastic finite element model showed that the internal layer is more rigid (μ = 14 ± 4 MPa) than the external layer (μ = 2.8 ± 0.9 MPa). To determine the turgor pressure and adhesiveness of the cells, a specific mode of indentation (under a load of 45 nN), aimed towards the centre of the individual aggregate, was performed. By modelling the AFM induced decohesion of the aggregate, the turgor pressure and the cell-to-cell adhesive interface properties could be determined. On average, the turgor pressure is estimated to be 59 ± 22 kPa, the interface strength is 78 ± 12 kPa and the polymer network extensibility is 2.8 ± 0.9 nm. We predict that internal cell wall comprised highly compressed methanochondroitin chains and we are able to identify a conceptual model for stress dependent inner cell wall growth.
authors.affiliation: Department of Engineering, Aarhus University, Hangøvej 2, 8200 Aarhus N, Denmark. Electronic address: vimi@iha.dk.
authors.forename: V
authors.initials: V
authors.lastname: Milkevych
authors.affiliation: Advanced Water Management Centre, The University of Queensland, Saint Lucia, Gehrmann Building (60), QLD 4072, Australia; Centre for Microbial Electrosynthesis, The University of Queensland, Saint Lucia, Gehrmann Building (60), QLD 4072, Australia.
authors.forename: B C
authors.initials: BC
authors.lastname: Donose
authors.affiliation: Advanced Water Management Centre, The University of Queensland, Saint Lucia, Gehrmann Building (60), QLD 4072, Australia.
authors.forename: N
authors.initials: N
authors.lastname: Juste-Poinapen
authors.affiliation: Advanced Water Management Centre, The University of Queensland, Saint Lucia, Gehrmann Building (60), QLD 4072, Australia.
authors.forename: D J
authors.initials: DJ
authors.lastname: Batstone
mesh_terms: D002448:Cell Adhesion; D017020:Methanosarcina / Q000166:cytology* / Q000254:growth & development / Q000648:ultrastructure*; D018625:Microscopy, Atomic Force
keywords: Atomic force microscopy; Cell-to-cell interface; Cohesive force; Methanosarcina; Stress dependent growth; Turgor pressure