Use of artificial neural networks and a gamma-concept-based approach to model growth of and bacteriocin production by Streptococcus macedonicus ACA-DC 198 under simulated conditions of Kasseri cheese production

Growth of and bacteriocin production by Streptococcus macedonicus ACA-DC 198 were assessed and modeled under conditions simulating Kasseri cheese production. Controlled fermentations were performed in milk supplemented with yeast extract at different combinations of temperature (25, 40, and 55 degrees C), constant pH (pHs 5 and 6), and added NaCl (at concentrations of 0, 2, and 4%, wt/vol). The data obtained were used to construct two types of predictive models, namely, a modeling approach based on the gamma concept, as well as a model based on artificial neural networks (ANNs). The latter computational methods were used on 36 control fermentations to quantify the complex relationships between the conditions applied (temperature, pH, and NaCl) and population behavior and to calculate the associated biokinetic parameters, i.e., maximum specific growth and cell count decrease rates and specific bacteriocin production. The functions obtained were able to estimate these biokinetic parameters for four validation fermentation experiments and obtained good agreement between modeled and experimental values. Overall, these experiments show that both methods can be successfully used to unravel complex kinetic patterns within biological data of this kind and to predict population kinetics. Whereas ANNs yield a better correlation between experimental and predicted results, the gamma-concept-based model is more suitable for biological interpretation. Also, while the gamma-concept-based model has not been designed for modeling of other biokinetic parameters than the specific growth rate, ANNs are able to deal with any parameter of relevance, including specific bacteriocin production.     

Temperature and pH conditions that prevail during fermentation of sausages are optimal for production of the antilisterial bacteriocin sakacin K

Sakacin K is an antilisterial bacteriocin produced by Lactobacillus sake CTC 494, a strain isolated from Spanish dry fermented sausages. The biokinetics of cell growth and bacteriocin production of L. sake CTC 494 in vitro during laboratory fermentations were investigated by making use of MRS broth. The data obtained from the fermentations was used to set up a predictive model to describe the influence of the physical factors temperature and pH on microbial behavior. The model was validated successfully for all components. However, the specific bacteriocin production rate seemed to have an upper limit. Both cell growth and bacteriocin activity were very much influenced by changes in temperature and pH. The production of biomass was closely related to bacteriocin activity, indicating primary metabolite kinetics, but was not the only factor of importance. Acidity dramatically influenced both the production and the inactivation of sakacin K; the optimal pH for cell growth did not correspond to the pH for maximal sakacin K activity. Furthermore, cells grew well at 35 degrees C but no bacteriocin production could be detected at this temperature. L. sake CTC 494 shows special promise for implementation as a novel bacteriocin-producing sausage starter culture with antilisterial properties, considering the fact that the temperature and acidity conditions that prevail during the fermentation process of dry fermented sausages are optimal for the production of sakacin K.     

An Exported Inducer Peptide Regulates Bacteriocin Production in Enterococcus faecium CTC492

Production of the bacteriocins enterocin A and enterocin B in Enterococcus faecium CTC492 was dependent on the presence of an extracellular peptide produced by the strain itself. This induction factor (EntF) was purified, and amino acid sequencing combined with DNA sequencing of the corresponding gene identified it as a peptide of 25 amino acids. The gene encodes a prepeptide of 41 amino acids, including a 16-amino-acid leader peptide of the double-glycine type. Environmental factors influenced the level of bacteriocin production in E. faecium CTC492. The optimal pH for bacteriocin production was 6.2. At pH 5.5, growth was slow, and very little bacteriocin was formed. The presence of NaCl or ethanol (EtOH) was also inhibitory to bacteriocin production, and at high concentrations of these solutes, no bacteriocin production was observed. The induction factor induced its own synthesis, and by dilution of the culture 10⁶ times or more, nonproducing cultures were obtained. Bacteriocin production was induced in these cultures by addition of EntF. The response was linear, and low bacteriocin production could be induced by about 10⁻¹⁷ M EntF. This response was attenuated by low pH or the presence of high concentrations of NaCl or EtOH, and 300 times more EntF was needed to induce detectable bacteriocin production in the presence of 6.5% NaCl. High levels of bacteriocin production in cultures grown at low pH or in the presence of high concentrations of NaCl or EtOH were obtained by addition of sufficient amounts of EntF.     

Modelling the growth and bacteriocin production by Lactobacillus amylovorus DCE 471 in batch cultivation

A model was set up to describe the production of amylovorin L471 by Lactobacillus amylovorus DCE 471, on a laboratory scale, in which the cells are grown in MRS (deMau-Rogosa-Sharpe) broth. The main features of the dynamic model are : (i) increase of the biomass according to a logistic equation ; (ii) non-growth-associated consumption of substrate (maintenance metabolism) ; and (iii) primary metabolite kinetics for the bacteriocin production. The main purpose was to set up a simple empirical model to examine growth and bacteriocin production in different conditions. Parameters estimated from a fermentation with 20 g l⁻¹ glucose (w/v) could be used to predict the evolution of cell dry mass, glucose and lactic acid concentration of fermentations, performed with 5, 30, 40 and 60 g l⁻¹ initial glucose. The influence of the operating temperature (30, 37 and 45 °C) on the model parameters was also investigated. The proposed model was able to describe growth and bacteriocin production in all cases. The specific bacteriocin production rate was found to vary strongly with temperature, with 30 °C as the best value. Variation of the operating temperature from 37 to 30 °C appeared to significantly enhance the specific bacteriocin production.     

Sodium Chloride Reduces Production of Curvacin A, a Bacteriocin Produced by Lactobacillus curvatus Strain LTH 1174, Originating from Fermented Sausage

Lactobacillus curvatus LTH 1174, a strain originating in fermented sausage, produces the antilisterial bacteriocin curvacin A. Its biokinetics of cell growth and bacteriocin production as a function of various concentrations of salt (sodium chloride) were investigated in vitro during laboratory fermentations using modified MRS medium. A model was set up to describe the effects of different NaCl concentrations on microbial behavior. Both cell growth and bacteriocin activity were affected by changes in the salt concentration. Sodium chloride clearly slowed down the growth of L. curvatus LTH 1174, but more importantly, it had a detrimental effect on specific curvacin A production (k_B) and hence on overall bacteriocin activity. Even a low salt concentration (2%, wt/vol) decreased bacteriocin production, while growth was unaffected at this concentration. The inhibitory effect of NaCl was mainly due to its role as an a_w-lowering agent. Further, it was clear that salt interfered with bacteriocin induction. Additionally, when 6% (wt/vol) sodium chloride was added, the minimum biomass concentration necessary to start the production of curvacin A (X_B) was 0.90 g (cell dry mass) per liter. Addition of the cell-free culture supernatant or a protein solution as a source of induction factor resulted in a decrease in X_B, an increase in k_B, and hence an increase in the maximum attainable bacteriocin activity.     

Bacteriocin Production with Lactobacillus amylovorus DCE 471 Is Improved and Stabilized by Fed-Batch Fermentation

Amylovorin L471 is a small, heat-stable, and hydrophobic bacteriocin produced by Lactobacillus amylovorus DCE 471. The nutritional requirements for amylovorin L471 production were studied with fed-batch fermentations. A twofold increase in bacteriocin titer was obtained when substrate addition was controlled by the acidification rate of the culture, compared with the titers reached with constant substrate addition or pH-controlled batch cultures carried out under the same conditions. An interesting feature of fed-batch cultures observed under certain culture conditions (constant feed rate) is the apparent stabilization of bacteriocin activity after obtaining maximum production. Finally, a mathematical model was set up to simulate cell growth, glucose and complex nitrogen source consumption, and lactic acid and bacteriocin production kinetics. The model showed that bacterial growth was dependent on both the energy and the complex nitrogen source. Bacteriocin production was growth associated, with a simultaneous bacteriocin adsorption on the producer cells dependent on the lactic acid accumulated and hence the viability of the cells. Both bacteriocin production and adsorption were inhibited by high concentrations of the complex nitrogen source.     

Growth and bacteriocin production by Enterococcus faecium DPC1146 in batch and continuous culture

Production of the bacteriocin enterocin 1146 (E1146) by Enterococcus faecium DPC1146 was studied in batch and continuous fermentation. Growth was strongly inhibited by lactic acid. In batch fermentations maximum E1146 activity (2.8 MBU L⁻¹) was obtained in 9 h with 20 g L⁻¹ glucose. Increase in initial glucose concentration did not lead to a proportional increase in E1146 activity. A simple linear model was found to be adequate to explain the relationship between specific bacteriocin production rate and specific growth rate in batch fermentations with initial glucose concentration higher than 20 g L⁻¹. Maximum bacteriocin activity (2.9–3.2 MBU L⁻¹) was obtained in continuous fermentations at dilution rates between 0.12 and 0.17 h⁻¹ and specific bacteriocin production rate increased linearly with dilution rate. Received 31 July 1996/ Accepted in revised form 01 November 1996     

Influence of nutrients on growth and bacteriocin production by Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442

The aim of this study was to investigate the effect of complex nutrients on microbial growth and bacteriocin production, in order to improve bacteriocin synthesis during the growth cycle of Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442. The fermentations were conducted at the optimum pH and temperature for bacteriocin production (pH 5.5+/-0.1 and temperature 25+/-0.1 degrees C). Because of their association with the final biomass, conditions favouring the increase of the produced biomass resulted in the increase of bacteriocin activity in the growth medium. Since the produced final biomass and the final concentration of the bacteriocins were associated with the amount of the carbon (glucose) and nitrogen source, better growth of the lactic acid bacterial strains favoured the increase of the specific bacteriocin production. Additionally, the bacteriocin production was influenced by carbon/nitrogen ratio.     

Influence of Complex Nutrient Source on Growth of and Curvacin A Production by Sausage Isolate Lactobacillus curvatus LTH 1174

Lactobacillus curvatus LTH 1174, a fermented sausage isolate, produces the antilisterial bacteriocin curvacin A. Its biokinetics of cell growth and bacteriocin production as a function of various concentrations of a complex nutrient source were investigated in vitro during laboratory fermentations with modified MRS medium. A modification of the nutrient depletion model (Leroy and De Vuyst, Appl. Environ, Microbiol. 67:4470-4473, 2001) was used to fit the data describing growth and bacteriocin production. Both cell growth and bacteriocin activity were influenced by changes in the complex nutrient source concentration. Standard MRS medium clearly limited the growth of L. curvatus LTH 1174. Higher nutrient concentrations, up to a certain degree, led to improved growth, a higher attainable biomass concentration, and a higher bacteriocin activity in the supernatant. A lower concentration of complex nutrient source caused severe growth inhibition, leading to a lower biomass concentration but a much higher specific bacteriocin production. When examining the separate components of the complex nutrient source, a stimulating effect of bacteriological peptone on growth was found without an adverse effect on bacteriocin production, resulting in increased curvacin A activity. Furthermore, specific depletion of the amino acids tyrosine, serine, and asparagine/aspartic acid was observed for this strain.     

The Curing Agent Sodium Nitrite, Used in the Production of Fermented Sausages, Is Less Inhibiting to the Bacteriocin-Producing Meat Starter Culture Lactobacillus curvatus LTH 1174 under Anaerobic Conditions

Curvacin A is a listericidal bacteriocin produced by Lactobacillus curvatus LTH 1174, a strain isolated from fermented sausage. The response of this strain to an added curing agent (sodium nitrite) in terms of cell growth and bacteriocin production was investigated in vitro by laboratory fermentations with modified MRS broth. The strain was highly sensitive to nitrite; even a concentration of 10 ppm of curing agent inhibited its growth and both volumetric and specific bacteriocin production. A meat simulation medium containing 5 ppm of sodium nitrite was tested to investigate the influence of the gas phase on the growth and bacteriocin production of L. curvatus LTH 1174. Aerating the culture during growth had no effect on biomass formation, but the oxidative stress caused a higher level of specific bacteriocin production and led to a metabolic shift toward acetic acid production. Anaerobic conditions, on the other hand, led to an increased biomass concentration and less growth inhibition. Also, higher maximum volumetric bacteriocin activities and a higher level of specific bacteriocin production were obtained in the presence of sodium nitrite than in fermentations under aerobic conditions or standard conditions of air supply. These results indicate that the inhibitory effect of the curing agent is at least partially masked under anaerobic conditions.     

Effects of Different Spices Used in Production of Fermented Sausages on Growth of and Curvacin A Production by Lactobacillus curvatus LTH 1174

Lactobacillus curvatus LTH 1174, a fermented sausage isolate, produces the listericidal bacteriocin curvacin A. The effect of different spices relevant for the production of fermented sausages was investigated in vitro through laboratory fermentations with a meat simulation medium and an imposed pH profile relevant for Belgian-type fermented sausages. The influence on the growth characteristics and especially on the kinetics of curvacin A production with L. curvatus LTH 1174 was evaluated. Pepper, nutmeg, rosemary, mace, and garlic all decreased the maximum specific growth rate, while paprika was the only spice that increased it. The effect on the lag phase was minor except for nutmeg and especially for garlic, which increased it, yet garlic was stimulatory for biomass production. The maximum attainable biomass concentration (X_max) was severely decreased by the addition of 0.40% (wt/vol) nutmeg, while 0.35% (wt/vol) garlic or 0.80% (wt/vol) white pepper increased X_max. Nutmeg decreased both growth and bacteriocin production considerably. Garlic was the only spice enhancing specific bacteriocin production, resulting in higher bacteriocin activity in the cell-free culture supernatant. Finally, lactic acid production was stimulated by the addition of pepper, and this was not due to the manganese present because an amount of manganese that was not growth limiting was added to the growth medium. Addition of spices to the sausage mixture is clearly a factor that will influence the effectiveness of bacteriocinogenic starter cultures in fermented-sausage manufacturing.     

The curing agent sodium nitrite,used in the production of fermented sausages,is less inhibiting to the bacteriocin-producing meat starter culture Lactobacillus curvatus LTH 1174 under anaerobic conditions

Curvacin A is a listericidal bacteriocin produced by Lactobacillus curvatus LTH 1174, a strain isolated from fermented sausage. The response of this strain to an added curing agent (sodium nitrite) in terms of cell growth and bacteriocin production was investigated in vitro by laboratory fermentations with modified MRS broth. The strain was highly sensitive to nitrite; even a concentration of 10 ppm of curing agent inhibited its growth and both volumetric and specific bacteriocin production. A meat simulation medium containing 5 ppm of sodium nitrite was tested to investigate the influence of the gas phase on the growth and bacteriocin production of L. curvatus LTH 1174. Aerating the culture during growth had no effect on biomass formation, but the oxidative stress caused a higher level of specific bacteriocin production and led to a metabolic shift toward acetic acid production. Anaerobic conditions, on the other hand, led to an increased biomass concentration and less growth inhibition. Also, higher maximum volumetric bacteriocin activities and a higher level of specific bacteriocin production were obtained in the presence of sodium nitrite than in fermentations under aerobic conditions or standard conditions of air supply. These results indicate that the inhibitory effect of the curing agent is at least partially masked under anaerobic conditions.     

Sodium chloride reduces production of curvacin A, a bacteriocin produced by Lactobacillus curvatus strain LTH 1174, originating from fermented sausage

Lactobacillus curvatus LTH 1174, a strain originating in fermented sausage, produces the antilisterial bacteriocin curvacin A. Its biokinetics of cell growth and bacteriocin production as a function of various concentrations of salt (sodium chloride) were investigated in vitro during laboratory fermentations using modified MRS medium. A model was set up to describe the effects of different NaCl concentrations on microbial behavior. Both cell growth and bacteriocin activity were affected by changes in the salt concentration. Sodium chloride clearly slowed down the growth of L. curvatus LTH 1174, but more importantly, it had a detrimental effect on specific curvacin A production (k(B)) and hence on overall bacteriocin activity. Even a low salt concentration (2%, wt/vol) decreased bacteriocin production, while growth was unaffected at this concentration. The inhibitory effect of NaCl was mainly due to its role as an a(w)-lowering agent. Further, it was clear that salt interfered with bacteriocin induction. Additionally, when 6% (wt/vol) sodium chloride was added, the minimum biomass concentration necessary to start the production of curvacin A (X(B)) was 0.90 g (cell dry mass) per liter. Addition of the cell-free culture supernatant or a protein solution as a source of induction factor resulted in a decrease in X(B), an increase in k(B), and hence an increase in the maximum attainable bacteriocin activity.     

Production, recovery and purification of bacteriocins from lactic acid bacteria

Bacteriocins produced by lactic acid bacteria are a heterogeneous group of peptide inhibitors which include lantibiotics (class I, e.g. nisin), small heat-stable peptides (class II, e.g. pediocin AcH/PA1) and large heat-labile proteins (class III, e.g. helveticin J). Many bacteriocins belonging to the first two groups can be successfully used to inhibit undesirable microorganisms in foods, but only nisin is produced industrially and is licensed for use as a food preservative in a partially purified form. This review focuses on the production and purification of class I and class II bacteriocins from lactic acid bacteria. Bacteriocin production is growth associated but the yield of bacteriocin per unit biomass is affected by several factors, including the producing strain, media (carbohydrate and nitrogen sources, cations, etc.) and fermentation conditions (pH, temperature, agitation, aeration and dilution rate in continuous fermentations). Continuous fermentation processes with cell recycle or immobilized cells can result in a dramatic improvement in productivity over batch fermentations. Several simple recovery processes, based on adsorbing bacteriocin on resins or silica compounds, have been developed and can be used to build integrated production processes. Received: 29 December 1998 / Received revision: 23 April 1999 / Accepted: 23 April 1999     

Application of a mathematical model and Differential Evolution algorithm approach to optimization of bacteriocin production by Lactococcus lactis C7

The effect of pH and temperature on cell growth and bacteriocin production in Lactococcus lactis C7 was investigated in order to optimize the production of bacteriocin. The study showed that the bacteriocin production was growth-associated, but declined after reaching the maximum titer. The decrease of bacteriocin was caused by a cell-bound protease. Maximum bacteriocin titer was obtained at pH 5.5 and at 22°C. In order to obtain a global optimized solution for production of bacteriocin, the optimal temperature for bacteriocin production was further studied. Mathematical models were developed for cell growth, substrate consumption, lactic acid production and bacteriocin production. A Differential Evolution algorithm was used both to estimate the model parameters from the experimental data and to compute a temperature profile for maximizing the final bacteriocin titer and bacteriocin productivity. This simulation showed that maximum bacteriocin production was obtained at the optimal temperature profile, starting at 30°C and terminating at 22°C, which was validated by experiment. This temperature profile yielded 20% higher maximum bacteriocin productivity than that obtained at a constant temperature of 22°C, although the total amount of bacteriocin obtained was slightly decreased.     

Influence of pH,temperature and culture media on the growth and bacteriocin production by vaginal Lactobacillus salivarius CRL 1328

AIMS: To study the influence of pH, temperature and culture medium on the growth and bacteriocin production by vaginal Lactobacillus salivarius subsp. salivarius CRL 1328. METHODS AND RESULTS: The study was performed using a complete factorial experimental design. Lactobacillus salivarius was cultivated in LAPTg and MRS broths, adjusted to specific initial pH, and at different temperatures of incubation. The growth, which was evaluated by the Gompertz model, was higher in MRS broth than in LAPTg broth. The initial pH of the culture medium and the temperature had a dramatic effect on the production of bacteriocin. The optimal conditions for bacteriocin production were different to those for optimal growth. The decrease in the pH of the culture medium was parallel to the growth; pH had similar final values in both the MRS and the LAPTg broths. CONCLUSIONS: The optimal growth conditions were recorded in MRS broth, with an initial pH of 6.5 and a temperature of 37 degrees C. The maximum bacteriocin activity was obtained in LAPTg after 6 h at 37 degrees C, and at an initial pH of 6.5 or 8.0. SIGNIFICANCE AND IMPACT OF THE STUDY: The application of a complete factorial design, and the evaluation of the growth parameters through the Gompertz model, enabled a rapid and simultaneous exploration of the influence of pH, temperature and growth medium on both growth and bacteriocin production by vaginal Lact. salivarius CRL 1328.     

Identification and production of a bacteriocin from Enterococcus mundtii QU 2 isolated from soybean

AIMS: Identification of the bacteriocin produced by Enterococcus mundtii QU 2 newly isolated from soybean and fermentative production of the bacteriocin. METHODS AND RESULTS: The bacteriocin produced by Ent. mundtii QU 2 inhibited the growth of various indicator strains, including Enterococcus, Lactobacillus, Leuconostoc, Pediococcus and Listeria. The bacteriocin activity was stable at wide pH range and against heat treatment, but completely abolished by proteolytic enzymes. The bacteriocin was purified from the culture supernatant by the three-step chromatographic procedure. Mass spectrometry, amino acid sequencing and DNA sequencing revealed that the bacteriocin was similar to class IIa bacteriocins produced by other Ent. mundtii strains. The bacteriocin production decreased in the absence of glucose, nitrogen sources, or Tween 80 in MRS medium. Additionally, it was strongly suppressed by addition of Ca(2+) (CaCO(3) or CaCl(2)). In pH-controlled fermentations, the highest bacteriocin production was achieved at pH 6.0, whereas the highest cell growth was obtained at pH 7.0. CONCLUSIONS: Ent. mundtii QU 2 produced a class IIa bacteriocin. Some growth factors (e.g. Ca(2+) and pH) influenced the bacteriocin production. SIGNIFICANCE AND IMPACT OF THE STUDY: A new soybean isolate, Ent. mundtii QU 2 was found to be a class IIa bacteriocin producer. Factors influencing the bacteriocin production described herein are valuable for applications of the bacteriocins from Ent. mundtii strains.     

Factors affecting production of an antilisterial bacteriocin by Carnobacterium piscicola strain A9b in laboratory media and model fish systems

AIMS: To investigate factors influencing bacteriocin production and bacteriocin stability of the bioprotective culture Carnobacterium piscicola strain A9b. METHODS AND RESULTS: Maximum activity was obtained in MRS7 broth (MRS adjusted to pH 7.2), with or without glucose. No bacteriocin was produced in APT broth when a low inoculum level (0.001%) was used. In contrast, inoculum level did not influence bacteriocin production in BHI and MRS7 without glucose. Bacteriocin production in APT was induced by the presence of an extracellular compound present in the sterile, filtered, cell-free supernatant fluid of a stationary-phase culture. Increasing concentrations of NaCl (2-7%) reduced bacteriocin production and maximum cell density of C. piscicola A9b when grown in cooked fish juice at 4 degrees C. CONCLUSION: Media composition, inoculum level and sodium chloride concentration affected production. SIGNIFICANCE AND IMPACT OF THE STUDY: The influence of NaCl on bacteriocin production may negate the inhibitory effect of C. piscicola A9b against Listeria monocytogenes in salty foods.     

Optimization of Bacteriocin Production by Batch Fermentation of Lactobacillus plantarum LPCO10

Optimization of bacteriocin production by Lactobacillus plantarum LPCO10 was explored by an integral statistical approach. In a prospective series of experiments, glucose and NaCl concentrations in the culture medium, inoculum size, aeration of the culture, and growth temperature were statistically combined using an experimental 2³_5-2 fractional factorial two-level design and tested for their influence on maximal bacteriocin production by L. plantarum LPCO10. After the values for the less-influential variables were fixed, NaCl concentration, inoculum size, and temperature were selected to study their optimal relationship for maximal bacteriocin production. This was achieved by a new experimental 3²_3-1 fractional factorial three-level design which was subsequently used to build response surfaces and analyzed for both linear and quadratic effects. Results obtained indicated that the best conditions for bacteriocin production were shown with temperatures ranging from 22 to 27°C, salt concentration from 2.3 to 2.5%, and L. plantarum LPCO10 inoculum size ranging from 10^7.3 to 10^7.4 CFU/ml, fixing the initial glucose concentration at 2%, with no aeration of the culture. Under these optimal conditions, about 3.2 × 10⁴ times more bacteriocin per liter of culture medium was obtained than that used to initially purify plantaricin S from L. plantarum LPCO10 to homogeneity. These results indicated the importance of this study in obtaining maximal production of bacteriocins from L. plantarum LPCO10 so that bacteriocins can be used as preservatives in canned foods.     

Influence of pH on growth and bacteriocin production byLactococcus lactis subsp.lactis 14ONWC during batch fermentation

The influence of pH on growth, and lactic acid and bacteriocin production byLactococcus lactis subsp.lactis 140 NWC was studied during batch fermentation in a lactose-based complex medium. Growth and lactic acid production were modelled using a simple logistic equation while substrate consumption was found to be a function growth and lactic acid production rate. The optimal pH for growth and lactic acid production was between 6.0 and 6.5. Bacteriocin production showed primary metabolite kinetics. pH had a dramatic effect on the production of the bacteriocin, lactococcin 140. A maximum activity of 15.4 × 10⁶ AU (arbitrary units) 1^–1 was obtained after 7 h at pH 5.5. Maximum bacteriocin activity was achieved before the end of growth and was followed by a decrease in activity, which was due to adsorption to the cells of the producing organism, possibly followed by degradation by specific proteases. Both bacteriocin production and degradation rates were higher at pH 5.0 and 5.5, resulting in sharper activity peaks than at pH 6.0 or 6.5. On the basis of the experimental results a qualitative model for bacteriocin production is proposed.