Evaluation of the effect of some environmental parameters on the level of bacteriocin activity

Abstract

Bacillus megaterium 22, a soil isolate, produced a bacteriocin that exhibited a broad range of inhibitory activity against
food-spoilage microorganisms including Salmonella typhimurium and Staphylococcus aureus. The antimicrobial
activity peaked at the early stationary phase. De Man Rogosa Shrarpe (MRS) was the best medium for bacteriocin
production, where growth of B. megaterium 22 for 12 - 18 h at 30oC, pH 6 - 6.5 resulted in maximum inhibitory effect on
the pathogenic indicator strains. Supplemen-tation and/or replacement of medium nutrients demonstrated higher
values of bacteriocin activity in the presence of 5 - 10% sucrose, 1% beef extract, and under limited aeration.
Bacteriocin activity was significantly stimulated at concentrations of up to 3% NaCl, or 1% KCl. Low levels of spices
(curry, red and Black pepper) synergistically stimulated the bacteriocin activity, except for garlic and rosemary where
higher concentrations (1%) considerably influenced the activity. The bacteriocin was heat stable for 15 min of exposure
to a wide range of temperatures, and over a pH range of 2 - 8 after 1 h of expo-sure. The bacteriocin was stable for up
to 30 min of exposure to UV light, and when stored at 4oC for 90 days. The activity was inhibited by proteolytic enzymes
and tested organic solvents. SDS-PAGE revealed that the apparent molecular weight of the partially purified
bacteriocin ranged from 3.496 to 6.512 kDa. Results presented here support the idea that the bacteriocin may propose
some industrial advantages that render it as a good natural food bio preservative candidate.