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Modeling of the Bacillus subtilis Bacterial Biofilm Growing on an Agar Substrate.

Wang X, Wang G, Hao M - Comput Math Methods Med (2015)

Bottom Line: Bacterial biofilms are organized communities composed of millions of microorganisms that accumulate on almost any kinds of surfaces.Our results show biofilm growth evolution characteristics such as biofilm thickness, active biomass, and nutrient concentration in the agar substrate.We provide an alternative mathematical method to describe other kinds of biofilm growth such as multiple bacterial species biofilm and also biofilm growth on various complex substrates.

View Article: PubMed Central - PubMed

Affiliation: School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China ; School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.

ABSTRACT
Bacterial biofilms are organized communities composed of millions of microorganisms that accumulate on almost any kinds of surfaces. In this paper, a biofilm growth model on an agar substrate is developed based on mass conservation principles, Fick's first law, and Monod's kinetic reaction, by considering nutrient diffusion between biofilm and agar substrate. Our results show biofilm growth evolution characteristics such as biofilm thickness, active biomass, and nutrient concentration in the agar substrate. We quantitatively obtain biofilm growth dependence on different parameters. We provide an alternative mathematical method to describe other kinds of biofilm growth such as multiple bacterial species biofilm and also biofilm growth on various complex substrates.

No MeSH data available.


Related in: MedlinePlus

Characterization of growing Bacillus subtilis biofilm. (a) Time-lapse images of a growing Bacillus subtilis biofilm growing on top of nutritive agar medium at 12-hour intervals. Upon excitation, the motile, matrix-producing, and sporulating phenotypes produce different fluorescent colors and are observed using red, blue, and yellow filters, respectively. The transmission images are shown at the bottom and are used to determine the optical density. Green line serves as guide indicating at 48 hours that the extension of the matrix-producing region is comparable to the motile cells and exceeds that of the sporulating cells.
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fig2: Characterization of growing Bacillus subtilis biofilm. (a) Time-lapse images of a growing Bacillus subtilis biofilm growing on top of nutritive agar medium at 12-hour intervals. Upon excitation, the motile, matrix-producing, and sporulating phenotypes produce different fluorescent colors and are observed using red, blue, and yellow filters, respectively. The transmission images are shown at the bottom and are used to determine the optical density. Green line serves as guide indicating at 48 hours that the extension of the matrix-producing region is comparable to the motile cells and exceeds that of the sporulating cells.

Mentions: We make time-lapse movies of the growing biofilm by recording the three fluorescent channels and the transmitted channel. After about 12 h the biofilm becomes visible to the naked eye and continues to grow in a circular fashion such that after 48 h its diameter is 16 mm as shown in Figure 2(a). The images show that three different phenotypes are spatially and temporally organized; details will be described below. To estimate the biofilm thickness from the transmission images, we develop a novel calibration procedure involving cross sections of biofilms. Similar to previous studies [14, 29, 30], we use the Beer-Lambert law to estimate the biofilm thickness h from the optical density, OD, through the agar and bacterial colony:(11)OD=hλ,where λ is the attenuation length. The optical density is defined as(12)OD=−log10⁡II0,where I is intensity of the transmitted light through the substrate and colony and I0 is that of the substrate alone, which is transparent agar. To determine λ, we compare the transmission (taken from above) with the height obtained from a side view. We reinforce the biofilm for subsequent manipulations by covering it with agar. We cut a thin slab of the biofilm on the agar substrate, whose top view is shown by the transmission image in the top of Figure 2(b). The transmission, I/I0, is determined from the ratio of the transmitted light relative to that of the agar substrate alone and averaged along the narrow, that is, transverse, direction. We next obtain the biofilm's height by flipping the slab onto its side and image its cross section based on the constitutive fluorescent channel as shown in the bottom of Figure 2(b). Finally, we characterize the biofilm's growth based upon the height profiles obtained from the optical density, as shown in Figures 2(c) and 2(b).


Modeling of the Bacillus subtilis Bacterial Biofilm Growing on an Agar Substrate.

Wang X, Wang G, Hao M - Comput Math Methods Med (2015)

Characterization of growing Bacillus subtilis biofilm. (a) Time-lapse images of a growing Bacillus subtilis biofilm growing on top of nutritive agar medium at 12-hour intervals. Upon excitation, the motile, matrix-producing, and sporulating phenotypes produce different fluorescent colors and are observed using red, blue, and yellow filters, respectively. The transmission images are shown at the bottom and are used to determine the optical density. Green line serves as guide indicating at 48 hours that the extension of the matrix-producing region is comparable to the motile cells and exceeds that of the sporulating cells.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4556878&req=5

fig2: Characterization of growing Bacillus subtilis biofilm. (a) Time-lapse images of a growing Bacillus subtilis biofilm growing on top of nutritive agar medium at 12-hour intervals. Upon excitation, the motile, matrix-producing, and sporulating phenotypes produce different fluorescent colors and are observed using red, blue, and yellow filters, respectively. The transmission images are shown at the bottom and are used to determine the optical density. Green line serves as guide indicating at 48 hours that the extension of the matrix-producing region is comparable to the motile cells and exceeds that of the sporulating cells.
Mentions: We make time-lapse movies of the growing biofilm by recording the three fluorescent channels and the transmitted channel. After about 12 h the biofilm becomes visible to the naked eye and continues to grow in a circular fashion such that after 48 h its diameter is 16 mm as shown in Figure 2(a). The images show that three different phenotypes are spatially and temporally organized; details will be described below. To estimate the biofilm thickness from the transmission images, we develop a novel calibration procedure involving cross sections of biofilms. Similar to previous studies [14, 29, 30], we use the Beer-Lambert law to estimate the biofilm thickness h from the optical density, OD, through the agar and bacterial colony:(11)OD=hλ,where λ is the attenuation length. The optical density is defined as(12)OD=−log10⁡II0,where I is intensity of the transmitted light through the substrate and colony and I0 is that of the substrate alone, which is transparent agar. To determine λ, we compare the transmission (taken from above) with the height obtained from a side view. We reinforce the biofilm for subsequent manipulations by covering it with agar. We cut a thin slab of the biofilm on the agar substrate, whose top view is shown by the transmission image in the top of Figure 2(b). The transmission, I/I0, is determined from the ratio of the transmitted light relative to that of the agar substrate alone and averaged along the narrow, that is, transverse, direction. We next obtain the biofilm's height by flipping the slab onto its side and image its cross section based on the constitutive fluorescent channel as shown in the bottom of Figure 2(b). Finally, we characterize the biofilm's growth based upon the height profiles obtained from the optical density, as shown in Figures 2(c) and 2(b).

Bottom Line: Bacterial biofilms are organized communities composed of millions of microorganisms that accumulate on almost any kinds of surfaces.Our results show biofilm growth evolution characteristics such as biofilm thickness, active biomass, and nutrient concentration in the agar substrate.We provide an alternative mathematical method to describe other kinds of biofilm growth such as multiple bacterial species biofilm and also biofilm growth on various complex substrates.

View Article: PubMed Central - PubMed

Affiliation: School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China ; School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.

ABSTRACT
Bacterial biofilms are organized communities composed of millions of microorganisms that accumulate on almost any kinds of surfaces. In this paper, a biofilm growth model on an agar substrate is developed based on mass conservation principles, Fick's first law, and Monod's kinetic reaction, by considering nutrient diffusion between biofilm and agar substrate. Our results show biofilm growth evolution characteristics such as biofilm thickness, active biomass, and nutrient concentration in the agar substrate. We quantitatively obtain biofilm growth dependence on different parameters. We provide an alternative mathematical method to describe other kinds of biofilm growth such as multiple bacterial species biofilm and also biofilm growth on various complex substrates.

No MeSH data available.


Related in: MedlinePlus