Biphasic kinetics of growth and bacteriocin production with Lactobacillus amylovorus DCE 471 occur under stress conditions

Abstract

Micro-organisms used during the production of fermented foods are subjected to several abiotic stresses. Microbial survival during these processes strongly depends on the ability of the cells to adapt and become more tolerant to the environmental conditions. Cultivation of Lactobacillus amylovorus DCE 471, a potential strain for use during type II sourdough fermentations, at low temperatures, unfavourable pH and high salt concentrations resulted in biphasic growth patterns. In addition, two separate bacteriocin peaks, as well as a dramatic change in cellular morphology, were observed. In general, an increase of the specific bacteriocin production occurred during the second growth phase. Finally, the observed sugar consumption profiles were affected by the applied fermentation temperature. Moreover, the highest bacteriocin activity occurred during maltose consumption at a low constant temperature of 28˚C and a constant pH of 5?4. Plate counts from both growth phases revealed the existence of two colony types. Irregular colonies were found to outnumber smoother colonies during the first growth phase, while the second growth phase was characterized by a greater number of smooth colonies. Electron microscopy was used to investigate the observed morphological switch at the single-cell level. Single, rod-shaped cells changed into elongated cells that grew in chains. Colony and cell morphology changes coincided with the biphasic growth pattern.

Immunochemical Characterization of Temperature-Regulated Production of Enterocin L50 (EntL50A and EntL50B), Enterocin P, and Enterocin Q byEnterococcus faeciumL50

“…Moreover, good cell growth does not necessarily result in large bacteriocin production (44,53). In this respect, biosynthesis of bacteriocins is often stimulated by stress conditions leading to lower growth rates and cell yields but higher bacteriocin activity (19,55). Considering that laboratory fermentations under optimal conditions differ from real food fermentations, it is of utmost importance to estimate the influence of technological factors and specific environmental conditions that prevail in the food matrix on bacterial cell growth and bacteriocin activity and production (44), as it is of interest to select the optimal growth conditions leading to the maximum bacteriocin activity (1,32,42,44,58).…”

Impact of stress conditions on the growth of Lactobacillus acidophilus IBB 801 and production of acidophilin 801

“…They have evolved adaptive responses, depending on bacterial species and stress conditions, mainly the synthesis of some specifi c proteins, observed especially under various cold or heat stresses and acid stress, but also changes in membrane fatty acid composition (Wang et al, 2005). Recent studies have been focused on the impact of the stress factors on bacteriocin production by lactic acid bacteria (Leroy and De Vuyst, 1999a, b;Neysens et al, 2003;Raykova et al, 2008). In the present study, L. acidophilus IBB 801 was grown at different temperatures, but also in the presence of sodium chloride or ethanol as stress factors.…”

The bacteriocin producer Lactobacillus amylovorus DCE 471 is a competitive starter culture for type II sourdough fermentations

“…Preparation of the L. amylovorus DCE 471 inoculum was done as described previously. 28,29 Fermentations were carried out under uncontrolled pH conditions and at a controlled temperature of 37…”