Abstract:Bacteria inhabit a variety of locations and play important roles in the environment and health. Our understanding of bacterial biomechanics has improved markedly in the last decade and has revealed that biomechanics play a significant role in microbial biology. The obtained knowledge has enabled investigation of complex phenomena, such as biofilm formation and the dynamics of the gut flora. A bottom-up strategy, i.e., from the cellular to the macroscale, facilitates understanding of macroscopic bacterial pheno… Show more
“…The total duration of the DMP is approximately 5 s; it is repeated at intervals of 45 ± 3 s (mean ± standard deviation) in healthy wild-type worms 35 , 36 . Because digestion and nutrient uptake associated with microbiota in C. elegans has been evaluated as a model experiment of pathogenic bacteria on symbiotic microbiota 37 , the mechanical role of DMP might have contributions involving nutrient uptake and host health 38 . Figure 1 Body structures and intestinal functions of C. elegans .…”
Despite its physiological and pathological importance, the mechanical relationship between glucose uptake in the intestine and intestinal flows is unclear. In the intestine of the nematode Caenorhabditis elegans, the defecation motor program (DMP) causes reciprocating intestinal flows. Although the DMP is frequently activated in the intestines, its physiological function is unknown. We evaluated the mechanical signature of enhanced glucose uptake by the DMP in worms. Glucose uptake tended to increase with increasing flow velocity during the DMP because of mechanical mixing and transport. However, the increase in input energy required for the DMP was low compared with the calorie intake. The findings suggest that animals with gastrointestinal motility exploit the reciprocating intestinal flows caused by peristalsis to promote nutrient absorption by intestinal cells.
“…The total duration of the DMP is approximately 5 s; it is repeated at intervals of 45 ± 3 s (mean ± standard deviation) in healthy wild-type worms 35 , 36 . Because digestion and nutrient uptake associated with microbiota in C. elegans has been evaluated as a model experiment of pathogenic bacteria on symbiotic microbiota 37 , the mechanical role of DMP might have contributions involving nutrient uptake and host health 38 . Figure 1 Body structures and intestinal functions of C. elegans .…”
Despite its physiological and pathological importance, the mechanical relationship between glucose uptake in the intestine and intestinal flows is unclear. In the intestine of the nematode Caenorhabditis elegans, the defecation motor program (DMP) causes reciprocating intestinal flows. Although the DMP is frequently activated in the intestines, its physiological function is unknown. We evaluated the mechanical signature of enhanced glucose uptake by the DMP in worms. Glucose uptake tended to increase with increasing flow velocity during the DMP because of mechanical mixing and transport. However, the increase in input energy required for the DMP was low compared with the calorie intake. The findings suggest that animals with gastrointestinal motility exploit the reciprocating intestinal flows caused by peristalsis to promote nutrient absorption by intestinal cells.
“…Biofilms are composed of microorganisms bound together by a matrix of extracellular polymeric substances (EPS) that are secreted by the cells 7 , 8 . The matrix responds to mechanical stress by exhibiting elastic strain and viscous creep 9 – 12 and its chemical composition facilitates nutrient capture 13 . By modulating their viscoelasticity and chemical composition through genetic expression, biofilms are capable of adapting to their mechanical and chemical environments 14 – 17 .…”
We present a numerical model to simulate the growth and deformation of a viscoelastic biofilm in shear flow under different nutrient conditions. The mechanical interaction between the biofilm and the fluid is computed using the Immersed Boundary Method with viscoelastic parameters determined a priori from measurements reported in the literature. Biofilm growth occurs at the biofilm-fluid interface by a stochastic rule that depends on the local nutrient concentration. We compare the growth, migration, and morphology of viscoelastic biofilms with a common relaxation time of 18 min over the range of elastic moduli 10–1000 Pa in different nearby nutrient source configurations. Simulations with shear flow and an upstream or a downstream nutrient source indicate that soft biofilms grow more if nutrients are downstream and stiff biofilms grow more if nutrients are upstream. Also, soft biofilms migrate faster than stiff biofilms toward a downstream nutrient source, and although stiff biofilms migrate toward an upstream nutrient source, soft biofilms do not. Simulations without nutrients show that on the time scale of several hours, soft biofilms develop irregular structures at the biofilm-fluid interface, but stiff biofilms deform little. Our results agree with the biophysical principle that biofilms can adapt to their mechanical and chemical environment by modulating their viscoelastic properties. We also compare the behavior of a purely elastic biofilm to a viscoelastic biofilm with the same elastic modulus of 50 Pa. We find that the elastic biofilm underestimates growth rates and downstream migration rates if the nutrient source is downstream, and it overestimates growth rates and upstream migration rates if the nutrient source is upstream. Future modeling can use our comparison to identify errors that can occur by simulating biofilms as purely elastic structures.
“…A number of studies on the rheological properties of biofilms using several measurement techniques, including rheometry, uniaxial compression, atomic force microscopy and hydrodynamic load, indicated that biofilms are viscoelastic [4,[17][18][19][20][21]. The elastic modulus and viscosity of biofilms vary widely between cell types and growth stages, with shear modulus ranging from 10 −2 to 10 6 Pa [1]. Shaw et al [4] investigated the relaxation time of Streptococcus mutans and P. aeruginosa biofilms with the rheometer creep test.…”
Section: Introductionmentioning
confidence: 99%
“…Biofilms are colonies of bacteria encased in a self-excreted matrix of extracellular polymeric substances (EPS) [ 1 , 2 ]. In nature, biofilms can be found on rocks, plant surfaces, soil, etc.…”
Bacterial biofilms, which can be found wherever there is water and a substrate, can cause chronic infections and clogging of industrial flow systems. Despite intensive investigation of the dynamics and rheological properties of biofilms, the impact of their rheological properties on streamer growth remains unknown. We numerically simulated biofilm growth in a pillar-flow and investigated the effects of rheological properties of a filamentous flow-shaped biofilm, called a ‘streamer’, on its formation by varying the viscoelasticity. The flow-field is assumed to be a Stokes flow and is solved by a boundary element method. A Maxwell model is used for extracellular matrix-mediated streamer growth to express the fluidity of streamer formations. Both high elastic modulus and viscosity are needed for streamer formation, and high viscosity promotes streamer growth at low cell concentrations. Our findings are consistent with experimental observations and can explain the relationship between the cell concentrations and viscosity at which streamers form.
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