Related Experiment Video
Updated: Aug 18, 2026
Monitoring Intraspecies Competition in a Bacterial Cell Population by Cocultivation of Fluorescently Labelled Strains
Published on: January 18, 2014
[Joint culturing of Streptococcus lactis, strain MGU with Proteus vulgaris and Bacillus mesentericus]
Abstract:
Nisin synthesis by Streptococcus lactis, strain MGU, grown as a combined culture together with Proteus vulgaris and Bacillus mesentericus under stationary conditions or with stirring does not depend on the quantity of inoculated associated cells. Nisin synthesis in the combined culture drops down by 10-20% at the initial pH 7.5 of the growth medium which is unfavourable for S. lactis producing nisin. The level of nisin biosynthesis does not rise when the pH of the medium is adjusted (either naturally or artificially) to 6.6-6.8 in the presence of glucose and yeast autolysate. S. lactis inhibits the growth of B. mesentericus when grown together with it whereas P. vulgaris inhibits the growth of S. lactis in their combined culture.
Insights
Nisin synthesis by Streptococcus lactis is unaffected by other microbes
Area of Science:
- Microbiology
- Bacteriology
- Food Science
Background:
- Nisin is a bacteriocin produced by Streptococcus lactis.
- Understanding nisin production in co-cultures is crucial for optimizing its use.
Purpose of the Study:
- To investigate the impact of co-culturing Streptococcus lactis with Proteus vulgaris and Bacillus mesentericus on nisin synthesis.
- To determine the influence of initial pH and medium composition on nisin production in these mixed cultures.
Main Methods:
- Culturing Streptococcus lactis (strain MGU) in combination with Proteus vulgaris and Bacillus mesentericus under stationary and stirred conditions.
- Monitoring nisin synthesis at different initial pH levels (7.5 and 6.6-6.8) and in media supplemented with glucose and yeast autolysate.
- Assessing the growth inhibition effects between the co-cultured species.
Main Results:
- Nisin synthesis by Streptococcus lactis was independent of the quantity of inoculated associated cells.
- Nisin synthesis decreased by 10-20% at an initial pH of 7.5, which is suboptimal for Streptococcus lactis.
- Adjusting the pH to 6.6-6.8 did not enhance nisin biosynthesis, even with glucose and yeast autolysate.
- Streptococcus lactis inhibited Bacillus mesentericus growth, while Proteus vulgaris inhibited Streptococcus lactis growth.
Conclusions:
- The presence of Proteus vulgaris and Bacillus mesentericus does not significantly alter the nisin synthesis levels of Streptococcus lactis under the tested conditions.
- Suboptimal initial pH (7.5) negatively impacts nisin production.
- Further optimization of growth conditions, potentially beyond pH and basic nutrient supplementation, may be needed to improve nisin yields in complex microbial environments.
