ABSTRACT
AIMS: Oxylipins are regarded as unsaturated fatty acids (UFAs) oxidation products, whose accumulation in plants and fungi is associated with stress. The aim of this study was to investigate if a metabolic pathway from UFAs to oxylipins was present also in lactic acid bacteria (LAB). METHODS AND RESULTS: A strain of Lactobacillus helveticus, incubated in the presence of oleic, linoleic and linolenic acids released, after 2 h, fatty acid oxidation products, mainly C6 , C8 , C9 aldehydes and alcohols. An experiment with total carbon labelled linoleic acid, in the presence or not of an oxidative stress, demonstrated that oxylipins, such as hexanal, octanal, nonanal, 2-octenal, 2-octanal, originated mainly from the oxidation of this fatty acid. CONCLUSIONS: Since lipoxygenase, dioxygenase and cytochrome P450 genes have never been found in L. helveticus, a possible pathway for linoleic conversion and oxylipins formation could include, as a first step, the transient formation of hydroxylated linoleic acids by fatty acids hydratases. However, the sequence of steps from the linoleic acid to the C6 and C8 aldehydes needs to be more deeply investigated. SIGNIFICANCE AND IMPACT OF THE STUDY: Due to the multiple role of oxylipins which are flavouring agents, antimicrobial compounds and interspecific signalling molecules, the knowledge of the mechanisms involved in their biosynthesis in food related bacteria could have an important biotechnological impact, also allowing the overproduction of selected bioactive molecules.
ABSTRACT
The effect of non-inhibitory concentrations of capric, lauric and alpha-linolenic acids (C10:0, C12:0 and C18:3 respectively) on the division time distribution of single cells of Staphylococcus aureus was evaluated at pH 7 and pH 5. The effect of the initial cell concentration on the lag time of growing cell populations was also assessed. The statistical properties of the division times (defined as the time interval from birth to next binary fission for a single cell) were studied using the method of Elfwing et al. [Elfwing, A., Le Marc, Y., Baranyi, J., Ballagi, A., 2004. Observing the growth and division of large number of individual bacteria using image analysis. Applied and Environmental Microbiology 70, 675-678]. The division times were significantly longer in the presence of free fatty acids than in the control. Shorter division intervals were detected at pH 7 than at pH 5 in the control experiment and in the presence of C10:0. However, both C12:0 and C18:3 slowed down the growth, regardless of the pH. The observed division time distributions were used to simulate growth curves from different inoculum sizes using the stochastic birth process described by Pin and Baranyi [Pin, C., Baranyi, J., 2006. Kinetics of single cells: observation and modelling of a stochastic process. Applied and Environmental Microbiology 72, 2163-2169]. The output of the simulation results were compared with observed data. The lag times fitted to simulated growth curves were in good agreement with those fitted to growth curves measured by plate counts. The averaged out effect of the population masked the effect of the free fatty acids and pH on the division times of single cells.
