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Hexagonal surface array in a protein-secreting bacterium, Bacillus brevis 47
Abstract:
Bacillus brevis 47, a protein-secreting bacterium, contained two major proteins with approximate molecular weights of 150 000 and 130 000 in the cell wall. The cell surface was covered with a hexagonally arranged array of six structural units about 4 nm in diameter with a lattice constant of 14.5 nm. The regular array structure as well as the chemical composition of cell envelopes remained the same regardless of the growth conditions. A mutant, strain 47-57, which was isolated as a phage resistant colony, contained only the 150 000 protein as a major cell wall protein. Although the mutant had hexagonally arranged arrays with the same lattice constant as that of wild-type cells, the distribution of mass in the unit cell differed considerably from that of the wild-type cells. The number of structural units in the unit cell of the mutant was reduced from six to three. Taking these results together with filtered images of the wild-type and mutant envelopes, two possible models for the surface array of B. brevis 47 are discussed.
Insights
Bacillus brevis 47 cell walls feature a hexagonal protein array. A mutant lacking a key protein altered this array structure, impacting its unit cell composition.
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- Bacillus brevis 47 is a protein-secreting bacterium.
- Its cell wall possesses a distinct hexagonal array of structural units.
Purpose of the Study:
- To investigate the structural organization of the Bacillus brevis 47 cell surface array.
- To understand the role of major cell wall proteins in maintaining this array structure.
Main Methods:
- Analysis of cell wall proteins using molecular weight determination.
- Electron microscopy and image processing of wild-type and mutant cell envelopes.
- Comparison of surface array structures between wild-type and mutant strains.
Main Results:
- Wild-type Bacillus brevis 47 cell walls contain 150,000 and 130,000 molecular weight proteins, forming a hexagonal array with six units per cell.
- A mutant strain (47-57) lacking the 130,000 protein showed altered array structure with three units per cell, despite maintaining the same lattice constant.
- The array structure and composition were consistent across different growth conditions.
Conclusions:
- The 130,000 molecular weight protein is crucial for the complete formation of the Bacillus brevis 47 surface array structure.
- The study proposes two models for the surface array based on the observed differences between wild-type and mutant strains.