[Conditions for nisin adsorption by Streptococcus lactis cells]

Area of Science:

• Microbiology
• Biochemistry
• Food Science

Background:

• Nisin is a polypeptide antibiotic produced by *Lactococcus lactis*.
• Understanding nisin absorption is crucial for its application in food preservation and medicine.
• Factors influencing nisin-cell interactions require detailed investigation.

Purpose of the Study:

• To investigate the conditions affecting the adsorption of nisin by *Streptococcus lactis* cells.
• To quantify nisin adsorption based on culture age, growth medium, and cell treatment.
• To assess the adsorption of nisin by other bacterial species.

Main Methods:

• Studying nisin adsorption kinetics and equilibrium.
• Utilizing cells of *Streptococcus lactis* at different growth phases (logarithmic vs. stationary).
• Comparing adsorption on cells grown in "poor" versus "rich" media and thermally shocked cells.
• Testing desorption with acid ethanol and bivalent cations.
• Evaluating nisin adsorption by *Bacillus brevis* and *Bacillus polymyxa*.

Main Results:

• Nisin adsorption was significantly higher in the late stationary phase compared to the logarithmic phase.
• Cells grown in "poor" medium adsorbed 85-90% of nisin, while those in "rich" medium adsorbed 50%.
• Thermal shock treatment increased nisin adsorption compared to live cells; desorption was minimal.

Conclusions:

• Culture age and growth medium composition are key factors influencing nisin adsorption by *Streptococcus lactis*.
• Cellular stress, like thermal shock, enhances nisin uptake.
• Nisin adsorption varies among different bacterial species, indicating specific interaction mechanisms.