Abstract
Cellulose effects on Vibrio fischeri biofilm morphology were tested for the wild-type and two of its isogenic mutants that either exhibit increased cellulose production or do not produce cellulose at all. Confocal laser scanning microscopy imaging of each biofilm revealed that total sessile volume increases with cellulose expression, but the size of colonies formed with cellulose was smaller, creating a more diffuse biofilm. These morphological differences were not attributed to variations in bacterial deposition, extracellular polymeric substances affinity to the surface or bacterial growth. A positive correlation was found between cellulose expression, Young’s (elastic) modulus of the biofilm analyzed with atomic force microscope and shear modulus of the related extracellular polymeric substances layers analyzed with quartz crystal microbalance with dissipation monitoring. Cellulose production also correlated positively with concentrations of extracellular DNA. A significant negative correlation was observed between cellulose expression and rates of diffusion through the extracellular polymeric substances. The difference observed in biofilm morphology is suggested as a combined result of cellulose and likely extracellular DNA (i) increasing biofilm Young’s modulus, making shear removal more difficult, and (ii) decreased diffusion rate of nutrients and wastes into and out of the biofilm, which effectively limits colony size.
Highlights
Bacteria in aquatic environments exhibit a strong preference toward living in a sessile phase, attaching to a surface and developing a biofilm community.[1,2] Living in a biofilm enables horizontal gene transfer and increases resistance to antibiotics, dehydration, changes in temperature, pH, and other environmental hazards.[1,2] Maximizing these protections and growth opportunities while allowing sufficient exchange of nutrients and waste into and out of the biofilm requires a complex threedimensional structure, which is held together by a matrix of extracellular polymeric substances (EPS)
Though the modeling of The expression of cellulose in V. fischeri biofilms has significant shear viscosity exhibits the same limitations as the modeling of impacts on the mechanical properties, and, in turn, on the shear modulus, the similar viscosities reported for each strain morphological characteristics of the biofilm
Increasing cellulose imply that cellulose expression does not affect the viscous expression elevated the extent of extracellular DNA (eDNA) in the biofilms, increased behavior of these biofilms
Summary
Bacteria in aquatic environments exhibit a strong preference toward living in a sessile phase, attaching to a surface and developing a biofilm community.[1,2] Living in a biofilm enables horizontal gene transfer and increases resistance to antibiotics, dehydration, changes in temperature, pH, and other environmental hazards.[1,2] Maximizing these protections and growth opportunities while allowing sufficient exchange of nutrients and waste into and out of the biofilm requires a complex threedimensional structure, which is held together by a matrix of extracellular polymeric substances (EPS) This EPS governs the physical characteristics of the biofilm, like strength, elasticity, and permeability. Biofilms of each strain have been grown under low-shear, richmedia conditions, stained with live/dead fluorescent markers, and visualized using confocal laser scanning microscopy (CLSM)
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