Two 2[5H]-Furanones as Possible Signaling Molecules inLactobacillus helveticus

Abstract

Two 2[5H]-furanones, in association with medium-chain fatty acids, were released in whey by Lactobacillus helveticus exposed to oxidative and heat stresses. This species plays an important role in cheese technology, particularly for Swiss-type cheeses and Grana cheese. Moreover, it significantly contributes to cheese ripening by means of an early autolysis and the release of enzymes during processing. Experimental evidence of the involvement of the two 2[5H]-furanones, detected by a gas chromatography-mass spectrometry/solid-phase microextraction technique, in the autolysis phenomenon has been obtained. Zymograms performed by using renaturing sodium dodecyl sulfate-polyacrylamide gels were used to detect the bioactivity of the supernatants containing the two furanones on fresh cells of the same strain. In addition to bands corresponding to known autolysins, new autolysins were detected concomitant with the exposure of Lactobacillus helveticus to the supernatants, which can be regarded as conditioned media (CM), and to a commercial furanone, 5-ethyl-3-hydroxy-4-methyl-2[5H]-furanone (HEMFi), having spectral data similar to those of the newly described 2[5H]-furanones. Morphological changes were observed when fresh cells were exposed to CM containing the two 2[5H]-furanones and HEMFi. The two furanones produced by Lactobacillus helveticus, which met a number of criteria to be included in cell-cell signaling molecules, have a presumptive molecular mass lower than those of already known 3[2H]-furanones having an autolytic activity and being produced by gram-negative bacteria. Moreover, they present a different chemical structure with respect to the furanones already identified as products of Lactococcus lactis subsp. cremoris or to those identified in some cheeses with Lactobacillus helveticus as a starter culture.

Functional Analysis ofluxSin the Probiotic StrainLactobacillus rhamnosusGG Reveals a Central Metabolic Role Important for Growth and Biofilm Formation

“…In this way, we could confirm that LuxS is responsible for the observed AI-2 production in L. rhamnosus GG, which we reported previously (14). This is an important finding since some lactobacilli are known to produce furanone-like molecules by other pathways that do not directly involve luxS (42). Additionally, we found that the luxS mutation causes a medium-dependent growth defect in L. rhamnosus GG, especially in AOAC medium.…”

Dynamic Stresses of Lactic Acid Bacteria Associated to Fermentation Processes

“…Analysing the oxidative and heat stresses in L. helveticus two new 2[5H]-furanones released by this strain both as a possible signalling molecules and as possible important flavouring compounds has been identified by GC-MS-SPME [9]. On the contrary the study of nonvolatile metabolites can be performed by normal chromatographic technique (HPLC), especially for amino acids and sugars [15], or by Fast Protein Liquid Chromatography (FPLC) separation for peptides, followed by a mass spectrometry identification [127].…”

“…With this perspective the use of GC-MS-SPME as a potent and easy tool to study the generation of volatile metabolite compounds such as flavoring molecules or aroma precursors was widely adopted [9,[11][12][13]15] and contributed to rationalize the process and optimize the products. In particular, the effects of HPH on different species of Lactobacillus involved in dairy product fermentation and ripening, monitoring the changes in volatile compounds as indicators of metabolic profiles has been studied [11].…”

“…These changes might eventually lead to competitive advantages for the population, more effective adaptation and responses to changing environmental conditions, or the co-ordination of interactions between bacteria and their abiotic and biotic environments [7]. In fact, microorganisms produce diffusible chemicals for the purpose of communication and it has been reported that the stress caused by the exposure of microbial cells to their own cell free conditioned media, containing metabolites and bioactive compounds including ''quorum sensing" molecules, including 2(5H)-furanones, promotes cell differentiation, autolysis and overproduction of specific metabolites [12,80,9,10]. In this way the microbial cultures used in food fermentations can also contribute (by "secondary" reactions and relations) to the formation of flavor and texture [81].…”

Acid Stress-Mediated Metabolic Shift in Lactobacillus sanfranciscensis LSCE1

“…More specifically, the exposure of different microbial species to osmotic, acid, oxidative, and chemical stresses gave rise to an accumulation (20-to 30-fold) of 3-methylbutanoic acid generated in the leucine (Leu) degradation pathway (3,23,34,36,48,51). Systematic investigations regarding 3-methylbutanoic acid overproduction were previously performed (23,33,51).…”