The formation of multicellular microbial communities, called biofilms, starts from the adhesion of a few planktonic cells to the surface. The transition from a free-living planktonic lifestyle to a sessile, attached state is a multifactorial process that is determined by biological, chemical and physical properties of the environment, the surface and the bacterial cell. The initial weak, reversible interactions between a bacterium and a surface strengthen to yield irreversible adhesion. In this Review, we summarize our understanding of the mechanisms governing bacterial adhesion at the single-cell level, including the physical forces experienced by a cell before reaching the surface, the first contact with a surface and the transition from reversible to permanent adhesion.

Bacterial adhesion at the single-cell level

The Peculiar Functions of the Bacterial Extracellular Matrix

https://repository.tudelft.nl/islandora/object/uuid%3Ac81e4ead-4320-412b-8c14-0c66a6369ce5/datastream/OBJ/download

Bactericidal effects of nanopatterns: a systematic review

Biofilms are densely populated communities of microbial cells protected and held together by a matrix of extracellular polymeric substances. The structure and rheological properties of the matrix at the microscale influence the retention and transport of molecules and cells in the biofilm, thereby dictating population and community behavior. Despite its importance, quantitative descriptions of the matrix microstructure and microrheology are limited. Here, particle-tracking microrheology in combination with genetic approaches was used to spatially and temporally study the rheological contributions of the major exopolysaccharides Pel and Psl in Pseudomonas aeruginosa biofilms. Psl increased the elasticity and effective cross-linking within the matrix, which strengthened its scaffold and appeared to facilitate the formation of microcolonies. Conversely, Pel reduced effective cross-linking within the matrix. Without Psl, the matrix becomes more viscous, which facilitates biofilm spreading. The wild-type biofilm decreased in effective cross-linking over time, which would be advantageous for the spreading and colonization of new surfaces. This suggests that there are regulatory mechanisms to control production of the exopolysaccharides that serve to remodel the matrix of developing biofilms. The exopolysaccharides were also found to have profound effects on the spatial organization and integration of P. aeruginosa in a mixed-species biofilm model of P. aeruginosa -Staphylococcus aureus. Pel was required for close association of the two species in mixed-species microcolonies. In contrast, Psl was important for P. aeruginosa to form single-species biofilms on top of S. aureus biofilms. Our results demonstrate that Pel and Psl have distinct physical properties and functional roles during biofilm formation. IMPORTANCE Most bacteria grow as biofilms in the environment or in association with eukaryotic hosts. Removal of biofilms that form on surfaces is a challenge in clinical and industrial settings. One of the defining features of a biofilm is its extracellular matrix. The matrix has a heterogeneous structure and is formed from a secretion of various biopolymers, including proteins, extracellular DNA, and polysaccharides. It is generally known to interact with biofilm cells, thus affecting cell physiology and cell-cell communication. Despite the fact that the matrix may comprise up to 90% of the biofilm dry weight, how the matrix properties affect biofilm structure, maturation, and interspecies interactions remain largely unexplored. This study reveals that bacteria can use specific extracellular polymers to modulate the physical properties of their microenvironment. This in turn impacts biofilm structure, differentiation, and interspecies interactions.

/pdf/dynamic-remodeling-of-microbial-biofilms-by-functionally-29up51qvt2.pdf

Dynamic Remodeling of Microbial Biofilms by Functionally Distinct Exopolysaccharides

Bacterial biofilms can cause medical problems and issues in technical systems. While a large body of knowledge exists on the phenotypes of planktonic and of sessile cells in mature biofilms, our understanding of what happens when bacteria change from the planktonic to the sessile state is still very incomplete. Fundamental questions are unanswered: for instance, how do bacteria sense that they are in contact with a surface, and what are the very initial cellular responses to surface contact. Here, we review the current knowledge on the signals that bacteria could perceive once they attach to a surface, the signal transduction systems that could be involved in sensing the surface contact and the cellular responses that are triggered as a consequence to surface contact ultimately leading to biofilm formation. Finally, as the main obstacle in investigating the initial responses to surface contact has been the difficulty to experimentally study the dynamic response of single cells upon surface attachment, we also review recent experimental approaches that could be employed to study bacterial surface sensing, which ultimately could lead to an improved understanding of how biofilm formation could be prevented.

https://pure.rug.nl/ws/files/119237376/fuz029_1_.pdf

How bacteria recognise and respond to surface contact.

Submitted for the MAR12 Meeting of The American Physical Society Roles of Pel and Psl in very early biofilm development B.J. COOLEY, TRAVIS THATCHER, GUILLAUME L’HER, ERIN REED, JAMIE STUART, APRIL KISSINGER, VERNITA GORDON, Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin — Biofilms are dynamic, multicellular communities of unicellular organisms. Biofilms cause many chronic infections; an important case is the opportunistic human pathogen Pseudomonas aeruginosa. Bacteria in biofilms produce an extracellular matrix that binds bacteria to each other and to a surface. The two primary extracellular matrix components produced by P. aeruginosa are the polysaccharides Pel and Psl. Here we examine the roles of Pel and Psl in the very early stages of biofilm development, just after initial surface attachment. We use high-throughput automated tracking and analysis to compare wildtype bacteria with mutants incapable of producing Pel, Psl, or both. We examine motion on a surface as well as inter-bacterial interactions. These results quantify the unique roles played by Pel and Psl and show an unexpected relationship between Pel expression and adhesion to a surface. B. J. Cooley Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin Date submitted: 12 Dec 2011 Electronic form version 1.4

http://absimage.aps.org/image/MAR12/MWS_MAR12-2011-008473.pdf

Roles of Pel and Psl in very early biofilm development

Biofilms are surface-mounted, multicellular communities of microbes. Biofilms are often associated with chronic infections that resist treatment, evade the immune system, and damage host tissue. An essential characteristic of the biofilm state is that constituent organisms are bound in a polymeric matrix. This matrix gives the system spatial structure and clusters bacteria near each other, facilitating intercellular interactions. The Pseudomonas aeruginosa strain PAO1 is widely studied as a model biofilm-forming organism. The polymeric matrix of PAO1 biofilms is dominated by two bacteria-produced extracellular polymers, Pel and Psl. We use a combination of optical and atomic force microscopy to examine the roles of these polymers in very early biofilm development. In agreement with other researchers, we find that Psl mediates strong attachment to a glass surface. We find that Pel alone can mediate some attachment, but not as permanent as that mediated by Psl. Unexpectedly, we find that Pel promotes symmetric attachment, in the form of rod-shaped bacteria lying down flat on the surface, and that the presence of Pel makes attachment forces more short-ranged than they are with Psl alone. We suggest that these effects may result from synergistic interactions of Pel with the Psl polymeric matrix.

The extracellular polysaccharide Pel makes the attachment of P. aeruginosa to surfaces symmetric and short-ranged

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Roles of Pel and Psl in very early biofilm development

The extracellular polysaccharide Pel makes the attachment of P. aeruginosa to surfaces symmetric and short-ranged