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Yeast metabolism depends on growing conditions, which include the chemical composition of the medium, temperature and growth time. Historically, fatty acid profiles have been used to differentiate yeasts growing in liquid media. The present study determined the fatty acids of Saccharomyces species in colonies. Using the same method, the effect of that the number of colonies and growth time had on solid media allowed us to determine the metabolomic profiles of the cells. Our results showed that the lipid and metabolomic profiles of the cells evolved as the colony grew. Interestingly, some strains of Saccharomyces cerevisiae have been were differentiated using the fatty acid profile of a colony; concretely indeed EC1118 and QA23 strains were separated from ICV-K1 and BM4x4. The synthesis of saturated fatty acids was greater than that of unsaturated fatty acids during the first two days of cell growth on a solid medium compared to a liquid medium. Unsaturated fatty acids subsequently became predominant. Finally, this methodology could be useful for carrying out physiological studies in a complete or defined solid growth medium allowing the supplementation of compounds, which inhibit or activate the growth of yeasts.

The use of non-Saccharomyces yeast together with S. cerevisiae in winemaking is a current trend. Apart from the organoleptic modulation of the wine, the composition of the resulting yeast lees is different and may thus impact malolactic fermentation (MLF). Yeasts of Saccharomyces cerevisiae, Torulaspora delbrueckii and Metschnikowia pulcherrima were inactivated and added to a synthetic wine. Three different strains of Oenococcus oeni were inoculated and MLF was monitored. Non-Saccharomyces lees, especially from some strains of T. delbrueckii, showed higher compatibility with some O. oeni strains, with a shorter MLF and a maintained bacterial cell viability. The supplementation of lees increased nitrogen compounds available by O. oeni. A lower mannoprotein consumption was related with longer MLF. Amino acid assimilation by O. oeni was strain specific. There may be many other compounds regulating these yeast lees-O. oeni interactions apart from the well-known mannoproteins and amino acids. This is the first study of MLF with different O. oeni strains in the presence of S. cerevisiae and non-Saccharomyces yeast lees to report a strain-specific interaction between them.

The thioredoxin system protects against oxidative stress through the reversible oxidation of the thioredoxin active center dithiol to a disulphide. The genome of Oenococcus oeni PSU-1 contains three thioredoxin genes (trxA1, trxA2, trxA3), one thioredoxin reductase (trxB) and one ferredoxin reductase (fdr) which, until recently, was annotated as a second thioredoxin reductase. For the first time, the entire thioredoxin system in several O. oeni strains isolated from wine has been analysed. Comparisons at the DNA and protein levels have been undertaken between sequences from O. oeni and other genera and species, and the genera Leuconostoc and Lactobacillus were found to present the highest similarities. The gene most frequently absent from a collection of 34 strains and the sequences annotated in the NCBI database was trxA1. Moreover, phylogenetic analysis suggested that this gene was horizontally transferred from Lactobacillus to O. oeni. Strain-dependent expression profiles were determined in rich and in wine-like media. General over-expression was detected after inoculation into wine-like medium, with trxA3 being the most highly expressed gene. The increased transcriptional levels of the thioredoxin genes are indicative of the crucial role of this system in the O. oeni response to wine harsh conditions.

Table olives are one of the main fermented vegetables in the world. Olives can be processed as treated or natural. Both have to be fermented but treated green olives have to undergo an alkaline treatment before they are placed in brine to start their fermentation. It has been generally established that lactic acid bacteria (LAB) are responsible for the fermentation of treated olives. However, LAB and yeasts compete for the fermentation of natural olives. Yeasts play a minor role in some cases, contributing to the flavour and aroma of table olives and in LAB development. The main microbial genus isolated in table olives is Lactobacillus. Other genera of LAB have also been isolated but to a lesser extent. Lactobacillus plantarum and Lactobacillus pentosus are the predominant species in most fermentations. Factors influencing the correct development of fermentation and LAB, such as pH, temperature, the amount of NaCl, the polyphenol content or the availability of nutrients are also reviewed. Finally, current research topics on LAB from table olives are reviewed, such as using starters, methods of detection and identification of LAB, their production of bacteriocins, and the possibility of using table olives as probiotics.

Near one hundred isolates of Lactobacillus paraplantarum, Lactobacillus pentosus and Lactobacillus plantarum from table olives were studied. Strains were genotyped by rep-PCR. Although the technique failed to differentiate some isolates at the species level, it proved a robust and easy procedure that could be useful for distinguishing between related strains of L. paraplantarum, L. pentosus and L. plantarum from a large pool of unrelated strains of these species. A PCR-based screening revealed the presence of the plantaricin encoding genes plnA, plnB, plnC, plnD, plnE/F, plnF, plnI, plnJ, plnK, plnG and plnN in most isolates of the three species. Sequences of bacteriocin genes present in L. paraplantarum and L. pentosus were homologous to L. plantarum genes. Through a discriminating analysis of the bacteriocin gene profiles, it was possible to establish a relationship between the origin of isolation and the LAB isolates, regardless of species.

The accumulation of citrulline and ornithine in wine or beer as a result of the arginine catabolism of some lactic acid bacteria (LAB) species increases the risk of ethyl carbamate and putrescine formation, respectively. Several LAB species, which are found as spoilage bacteria in alcoholic beverages, have been reported to be arginine degrading. This study evaluates the effect of ethanol content and low pH on the excretion of citrulline and ornithine by two strains belonging to the potential contaminant species Lactobacillus brevis and Pediococcus pentosaceus. In the conditions that most affected cell viability, arginine consumption per cell increased noticeably, indicating that arginine utilization may be a stress responsive mechanism. L. brevis showed a higher accumulation of ornithine in the media than P. pentosaceus. In the presence of ethanol, a higher expression of the arcC gene was found in P. pentosaceus, which resulted in a lower excretion of citrulline and ornithine than in L. brevis. This suggests that L. brevis is more likely to produce these amino acids, which are precursors of ethyl carbamate and putrescine.

This research studied the influence of sodium chloride on bacteriocin activity of table olives’ strain Lactobacillus pentosus B96. The strain was cultured in MRS under different NaCl concentrations (0, 4, 6 and 8%, in w/v). In MRS, maximum bacteriocin activity was achieved 9 h later. A medium containing 4 or 6% NaCl (w/v) increased the total bioactivity of the strain and an 8% NaCl reduced it. Real-time PCR was used to monitor the genetic expression of the bacteriocin genes plnA, plnB, plnC, plnE/F, plnJ, plnK, plnN and plantaricin S. Cultured in MRS, plantaricin S reached its maximum expression during the lag phase while plnE/F expresses during the exponential phase. The presence of sodium chloride in the medium moved the maximum expression of plantaricin S to the stationary phase, independently of the concentration. 4% (w/v) of NaCl didn’t affect the expression pattern of plnE/F while promotes the expression of plnN during both the lag and the exponential phases. More sodium chloride, 6% (w/v) maintained the expression of plnN in the pag phase but not in the exponential and moved plnE/F expression to the stationary phase. Plantaricin S, plnE/F and plnN over-expressed during the stationary phase in the higher sodium chloride concentration assayed, 8% (w/v). The relative expression level of plsA was 1000-fold higher than that of the plnE/F and plnN genes and even the ldhD constitutive gene used. Under our conditions, expression of plnA, plnB, plnC, plnJ and plnK genes was not observed.

The production of Arbequina naturally green olives is a traditional and spontaneous process in which lactic acid bacteria (LAB) and yeasts are present. To better control the fermentation of olives, strains of LAB and yeasts that had been isolated from brines were used in this study. A strain of Lactobacillus pentosus selected from an industrial olive fermentation was used as a starter culture for the traditional fermentation of Arbequina naturally green olives. Three more strains isolated from Arbequina olive brines were selected: one yeast, (Candida diddensiae), and two Lactobacillus (one L. plantarum and the other L. pentosus). The individual fermentation profile of all the strains and the co-inoculation profile of each one of the three with the first selected L. pentosus were studied in pilot-scale fermentations. The results showed that all the strains used as a starter, and particularly the yeast C. diddensiae, reduced the Enterobacteriaceae survival period in comparison with the spontaneous process. Only when a L. pentosus strain was inoculated were the LAB counts above 106 cfu ml−1 throughout the process. The C. diddensiae starter failed to colonize the brine until the end of the process and no LAB were detected. Results of rep-PCR using the primer GTG5 showed that both L. pentosus starters were able to colonize the brine by the end of the process but when they were co-inoculated only one strain was dominant. The L. plantarum starter failed to colonize the brine. In the control fermentation, various autochthonous strains of L. pentosus and L. plantarum were detected. The pH only reached desirable levels when a L. pentosus strain was inoculated. From the results of the sensory evaluation, panellists found significant differences between the different starters used for fermenting olives.

The consumption of citrate by the malolactic bacterium Oenococcus oeni changes the aromatic profile of wines due to the production of volatile compounds such as diacetyl and acetic acid. In this study, the expression of genes related to citrate utilization in the O. oeni strain PSU-1 was investigated to further understand the role of this metabolic pathway in the adaptation to wine environment and its impact on organoleptic qualities. Different conditions of ethanol content (0% and 10%) and pH (3.5 and 4.0) were assayed to evaluate the transcriptional response to both these stress factors. In the presence of ethanol, metabolic and transcriptional behavior was different than the observed when ethanol was absent. The expression of citrate pathway genes was mainly affected by ethanol, while pH showed a lower effect. Among the studied genes, citE, ackA and alsD were the genes revealing a distinctive transcriptional response. The differences observed in gene expression were in correlation with the different content of end products such as acetic acid and diacetyl. The increment of gene expression observed in the presence of ethanol at low pH suggests the participation of citrate metabolism in the response to stress conditions.