Mechanics of biofilms formed of bacteria with fimbriae appendages

Abstract

Gram-negative bacteria, as well as some Gram-positive bacteria, possess hair-like appendages known as fimbriae, which play an important role in adhesion of the bacteria to surfaces or to other bacteria. Unlike the sex pili or flagellum, the fimbriae are quite numerous, with of order 1000 fimbriae appendages per bacterial cell. In this paper, a recently developed hybrid model for bacterial biofilms is used to examine the role of fimbriae tension force on the mechanics of bacterial biofilms. Each bacterial cell is represented in this model by a spherocylindrical particle, which interact with each other through collision, adhesion, lubrication force, and fimbrial force. The bacterial cells absorb water and nutrients and produce extracellular polymeric substance (EPS). The flow of water and EPS, and nutrient diffusion within these substances, is computed using a continuum model that accounts for important effects such as osmotic pressure gradient, drag force on the bacterial cells, and viscous shear. The fimbrial force is modeled using an outer spherocylinder capsule around each cell, which can transmit tensile forces to neighboring cells with which the fimbriae capsule collides. We find that the biofilm structure during the growth process is dominated by a balance between outward drag force on the cells due to the EPS flow away from the bacterial colony and the inward tensile fimbrial force acting on chains of cells connected by adhesive fimbriae appendages. The fimbrial force also introduces a large rotational motion of the cells and disrupts cell alignment caused by viscous torque imposed by the EPS flow. The current paper characterizes the competing effects of EPS drag and fimbrial force using a series of computations with different values of the ratio of EPS to bacterial cell production rate and different numbers of fimbriae per cell.

Permeation Increases Biofilm Development in Nanofiltration Membranes Operated with Varying Feed Water Phosphorous Concentrations

“…Previous studies [ 37 ] found that the dominant bacterial families for biofilms grown under 0 μg P·L −1 were Sphingomonadaceae , which are related to extracellular polymeric substances production [ 57 , 58 , 59 ]. This study’s results agree with Jin and Marshall’s model [ 56 ], where OCT images confirmed that a compact biofilm formed around the spacer ( Figure 5 ) at higher dosed phosphorus concentration (low EPS to bacterial cell ratio). A uniform observation that permeation affects biofilm development can be made, however, with varying extent depending on the nutrient availability.…”

“…Values of EPS to bacteria cells for different types of biofilms reported in the literature range from 0.2–4.5 [ 54 , 55 ]. According to a model proposed by Jin and Marshall (2020) [ 56 ], low EPS to bacterial cell ratios form compact and denser biofilms, compared to higher EPS to bacteria cell ratios where a less dense and disperse biofilm is formed with a tendency to break up. This study shows that permeation accelerated the pressure drop increase for biofilms grown at 0 more than 25 μg P·L −1 .…”

Productive biofilms: from prokaryotic to eukaryotic systems

“…Microrheology, which is used to study materials and the mechanics of fluids at the microscale, gained attention some time ago for the study of biofilms 30 . Modern rheological techniques, such as long amplitude, oscillatory shear (LAOS), and optical tweezing (OT), allow for the rheological signatures of biofilms to be studied to understand the interactions between the components of the matrix 31,32 . A micro‐cantilever can also be used to determine the deflection of the biofilm and, thus, its strength 32 …”

Toward Designing of Anti-infective Hydrogels for Orthopedic Implants: From Lab to Clinic

“…Most therapeutic strategies target this particular stage of biofilm formation, rendering it significant to understand the mechanism of bacterial adhesion . The primary attachment of bacteria to the implant surface is driven by nonspecific and reversible factors, including Lifshitz–van der Waal forces, hydrophobic interactions, and electrostatic interactions. , Filamentous bacterial cell appendages (e.g., pili, the nanofibers) facilitate strong adhesion of bacterial cells with the surface. , When an implant is introduced in the human body, components of the immune system and extracellular matrix (ECM) proteins get rapidly adsorbed on its surface. ECM components, mainly fibronectin (Fn) and collagen, mediate bacterial adhesion by specifically binding to bacterial adhesion molecules known as microbial surface components recognizing adhesive matrix molecules (MSCRAMMs). , For instance, to promote adhesion, MSCRAMMs such as collagen-binding adhesin (CNA) and fibronectin-binding proteins (FnBPs) interact specifically with collagen and Fn, respectively (Figure B). − Another essential species-specific adhesion protein, autolysin, is also involved in bacterial adhesion.…”

“…36,40 Filamentous bacterial cell appendages (e.g., pili, the nanofibers) facilitate strong adhesion of bacterial cells with the surface. 41,42 When an implant is introduced in the human body, components of the immune system and extracellular matrix (ECM) proteins get rapidly adsorbed on its surface. ECM components, mainly fibronectin (Fn) and collagen, mediate bacterial adhesion by specifically binding to bacterial adhesion molecules known as microbial surface components recognizing adhesive matrix molecules (MSCRAMMs).…”