The inhibitory effect of Nisin on Bacillus

Nisin is a natural antibacterial peptide produced by Lactococcus lactis, and it has a significant inhibitory effect on Bacillus. Its action process covers multiple links from the germination of Bacillus spores to cell lysis, which are specifically as follows:

I. Spore Germination Stage

Inhibiting Spore Activation: Bacillus spores begin to germinate under suitable environmental conditions. Nisin can act on the cortex of the spores, prevent the spores from absorbing water, and interfere with the osmotic regulation mechanism within the spores, making it impossible for the spores to be normally activated, thus inhibiting the germination process. For example, in a medium containing nisin, the spore germination rate of Bacillus is significantly lower than that of the control group, indicating that nisin can effectively inhibit the initial activation step of the spores.

Interfering with Germination Signal Transduction: A series of signal transduction processes are required to initiate spore germination. Nisin may bind to specific receptors on the surface of the spores and interfere with these signal transduction pathways. Studies have found that it can affect the activities of protein kinases and phosphatases related to germination in Bacillus, thus blocking the transmission of germination signals and preventing the spores from entering the germination state.

II. Vegetative Cell Growth Stage

Inhibiting Cell Wall Synthesis: After the spores successfully germinate to form vegetative cells, nisin acts on the cell wall synthesis process. It can specifically bind to key enzymes in the cell wall synthesis process, such as peptidoglycan synthase, and inhibit their activities, resulting in the obstruction of peptidoglycan synthesis in the cell wall. Since the cell wall is an important part of maintaining the cell's shape and structural integrity, the obstruction of cell wall synthesis makes the cell vulnerable to external osmotic pressure during the growth process, resulting in phenomena such as cell deformation and rupture.

Damaging the Integrity of the Cell Membrane: Nisin has an amphiphilic structure and can insert into the cell membrane to form transmembrane channels. This increases the permeability of the cell membrane, causes the leakage of important substances in the cell, such as amino acids and nucleotides, disrupts the ion balance and metabolic environment within the cell, and thus affects the normal physiological functions of the cell, inhibiting cell growth and reproduction. For example, microscopic observation shows that in Bacillus cells treated with nisin, the cell membrane exhibits obvious damage and shrinkage.

III. Cell Lysis Stage

Inducing the Activity of Autolysins: Nisin can induce the production of autolysins in Bacillus. These autolysins can hydrolyze the peptidoglycan in the cell wall, leading to the destruction of the cell wall structure. With the gradual degradation of the cell wall, the cell loses its supporting structure and swells under the action of the intracellular osmotic pressure, ultimately leading to cell lysis. Studies have shown that in Bacillus cells treated with nisin, the activity of autolysins increases significantly, and the degree of cell lysis is positively correlated with the activity of autolysins.

Promoting the Leakage of Cell Contents: Due to the damage to the cell membrane and the degradation of the cell wall, the contents inside the cell, such as the cytoplasm and nucleic acids, will gradually leak out. Nisin may further expand the channels in the cell membrane or disrupt the connection between the cell membrane and the cell wall, accelerating the leakage process of cell contents and ultimately causing the complete lysis and death of the cell.

Nisin effectively inhibits Bacillus by playing multiple roles at different stages, including spore germination, vegetative cell growth, and cell lysis, and thus has broad application prospects in fields such as food preservation and medical care.