Updated: Jun 5, 2026

Single-cell Microfluidic Analysis of Bacillus subtilis
Published on: January 26, 2018
Chyi-Liang Chen1, Sau-Ching Wu, Wai Mui Tjia
1Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
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This study explored a new way to display proteins on the surface of Bacillus subtilis cells using a module from a cell wall hydrolase called LytE. The module, called CWBM(LytE), was found to bind tightly to the cell wall and could anchor other proteins like β-lactamase. Researchers tested how fusion proteins, with β-lactamase attached at different ends of the module, affected binding and display. They found that the module could support up to 12 million molecules per cell, and even more when cells formed long filaments. The proteins were evenly spread on the cell surface and remained functional. This approach could be useful for biotechnology applications that rely on surface-displayed proteins.
Area of Science:
Background:
Prior research has shown that cell wall-binding modules can be used to anchor proteins to bacterial surfaces. However, the specific binding affinities and display capacities of these modules remain unclear. It was already known that LysM motifs are commonly used in bacterial cell wall interactions. Yet, no prior work had resolved how these motifs influence fusion protein binding efficiency. This gap motivated the investigation of LytE-derived modules for surface display in Bacillus subtilis. The uncertainty around fusion protein positioning and functionality also drove this study. No existing literature had quantified the number of displayed molecules per cell in filamentous cell forms. That uncertainty drove the need for a detailed analysis of CWBM(LytE) and its fusion constructs.
Purpose Of The Study:
This study aimed to assess the cell wall-binding capacity of a module derived from LytE in Bacillus subtilis. The specific problem addressed was the potential of this module for high-density surface display of proteins. The motivation was to determine how fusion protein configuration affects binding and display efficiency. Researchers proposed to evaluate the module's affinity for cell wall sites and its ability to retain function in fusion constructs. The goal was to quantify the maximum number of displayed molecules per cell. The study also sought to examine the impact of filamentous cell formation on display capacity. By analyzing fusion protein positioning and functionality, the authors aimed to optimize surface display systems. This approach could improve applications in biotechnology and protein engineering.
The LytE-derived module, CWBM(LytE), can bind to cell wall sites and display up to 1.2 × 10⁷ molecules per cell.
Fusion proteins with β-lactamase at either end showed lower binding affinity than the module alone.
To confirm surface exposure and accessibility of displayed proteins on Bacillus subtilis cells.
Filamentous cells increased the total number of displayed β-lactamase molecules per cell.
Main Methods:
The study focused on the N-terminal LysM motifs of LytE as a cell wall-binding module. Researchers constructed fusion proteins by attaching β-lactamase to either end of the module. They tested binding affinity using cell wall interactions and quantified molecule display per cell. Immunofluorescence microscopy was used to confirm surface exposure and accessibility of the proteins. The number of binding sites and their affinities were measured using biochemical assays. The effect of fusion protein orientation on binding was analyzed by comparing N- and C-terminal constructs. Filamentous cell formation was observed to assess its impact on display capacity. The distribution of proteins on the cell surface was examined to evaluate display uniformity.
Main Results:
The LytE-derived module, CWBM(LytE), showed strong cell wall-binding capability with two distinct binding site classes. The lower-affinity sites were three times more abundant than the higher-affinity ones. Fusion proteins with β-lactamase at either end had reduced binding affinity compared to the module alone. The number of wall-bound fusion proteins was lower than that of the module itself. This effect was less pronounced when CWBM(LytE) was at the N-terminal end of the fusion. Both CWBM(LytE) and β-lactamase retained functionality regardless of their position in the fusion. In optimal conditions, 1.2 × 10⁷ molecules were displayed per cell. Filamentous cells allowed up to 1.1 × 10⁸ β-lactamase molecules per filamentous cell.
Conclusions:
The LytE-derived module demonstrated effective cell wall binding and could support high-density surface display. The module's affinity for cell wall sites varied, with lower-affinity sites being more abundant. Fusion protein configuration significantly affected binding efficiency and display capacity. Positioning of CWBM(LytE) within the fusion influenced these effects, with N-terminal placement being less disruptive. Both CWBM(LytE) and β-lactamase remained functional in fusion constructs. The study confirmed that displayed proteins were accessible and evenly distributed on the cell surface. Filamentous cell formation increased the total number of displayed molecules per cell. These findings suggest that CWBM(LytE) is a viable module for surface display applications.
Two classes of binding sites were identified, with lower-affinity sites being three times more abundant.
Both CWBM(LytE) and β-lactamase retained functionality regardless of their position in the fusion.