The fate of linoleic acid on Saccharomyces cerevisiae metabolism under aerobic and anaerobic conditions.

INTRODUCTION: Saccharomyces cerevisiae has been widely used for fermenting food and beverages for over thousands years. Its metabolism together with the substrate composition play an important role in determining the characteristics of the final fermented products. We previously showed that the polyunsaturated fatty acid, linoleic acid, which is present in the grape juice at trace levels, significantly affected the development of aroma compounds of the wines. However, the effect of linoleic acid on the overall cell metabolism of S. cerevisiae is still not clear. Therefore, we aimed to unlock the metabolic response of S. cerevisiae to linoleic acid using metabolomics and isotope labelling experiments. METHODS: We cultured the cells on a minimal mineral medium supplementing them with linoleic acid isomers and 13C-linoleic acid. Both intracellular and extracellular metabolite profiles were determined using gas chromatography coupled to mass spectrometry (GC-MS) to investigate which S. cerevisiae pathways were affected by linoleic acid supplementation. RESULTS: The utilisation of linoleic acid by S. cerevisiae had a significant impact on the primary carbon metabolism increasing the glucose consumption and the ethanol production under anaerobic condition. The energetic state of the cell was, therefore, affected and the glycolytic pathway, the TCA cycle and the amino acid production were up-regulated. We also observed that linoleic acid was transported into the cell and converted into other fatty acids affecting their profile even under anaerobic condition. CONCLUSION: Our data clearly shows that linoleic acid supplementation in growth medium increased glucose consumption and ethanol production by S. cerevisiae under anaerobic condition. We also suggest that S. cerevisiae might be able to perform an alternative anaerobic pathway to ß-oxidation, which has not been reported yet.

Sphingomonas turrisvirgatae sp. nov., an agar-degrading species isolated from freshwater.

A yellow pigmented and agar-pitting colony was isolated from a water sample obtained from a drainage ditch within a disused system of constructed wetlands. The strain was purified and named MCT13T. This rod-shaped, Gram-negative, oxidase- and catalase-positive, aerobic, non-spore-forming, and non-motile strain formed round colonies and grew optimally at pH 7.5±0.2, at 28-30 °C on LB agar, with 0-0.5 % NaCl. The 16S rRNA gene sequence analysis placed the MCT13T isolate within the Sphingomonas (sensu stricto) cluster. The DNA G+C content was 65.3 %. The only observed ubiquinone was Q10. The major fatty acids included C17 : 1ω6c and C18 : 1ω7c/C18 : 1ω6c. The major polar lipids were sphingoglycolipid, diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylglycerol. The major polyamine was spermidine. The 16S rRNA gene phylogenetic analysis performed on the whole sequence, showed the closest relative of MCT13T to be Sphingomonas koreensis (98.52 %); however, there are several genotypic and phenotypic differences between the novel isolate and the type strain JSS26T of S. koreensis. On the basis of these results, strain MCT13T represents a novel species in the genus Sphingomonas, for which the name Sphingomonas turrisvirgatae sp. nov. is proposed. The type strain is MCT13T (=DSM 105457T=BAC RE RSCIC 7T).

The effect of linoleic acid on the Sauvignon blanc fermentation by different wine yeast strains.

The level of linoleic acid in the Sauvignon blanc (SB) grape juice affects the development of different aroma compounds during fermentation by Saccharomyces cerevisiae EC1118, including key varietal thiols such as 3-mercaptohexanol (3MH) and 3-mercaptohexyl acetate (3MHA). However, it is still unknown if linoleic acid would affect in a similar way other commonly used S. cerevisiae wine strains. Here we investigated the effect of grape juice linoleic acid on the development of aroma compounds and other metabolites of SB wines using different wine yeast strains: EC1118, AWRI796 and VIN13. Linoleic acid clearly affected the levels of acetylated aroma compounds, several amino acids, and antioxidant molecules, independent of yeast strain, but the production of 3MH was affected by linoleic acid in a strain-specific manner. Moreover, the supplementation of deuterium-labelled 3MH also affected the production of varietal thiols in a strain-specific way. Linoleic acid reduced the acetylation process probably by inhibiting an acetyltransferase, an effect that was independent of the yeast strain. However, regulation of the 3MH biosynthesis is strain-specific, which suggests a mindful consideration not only towards the wine yeast but also to the linoleic acid concentration in the grape juice in order to obtain the desired wine aroma characteristics.

The efficacy of commercial decontamination agents differs between standardised test settings and research laboratory usage for a variety of bacterial species.

Decontamination of surfaces and items plays an important role in reducing the spread of infectious microorganisms in many settings including hospitals and research institutes. Regardless of the location, appropriate decontamination procedures are required for maintaining biosafety and biosecurity. For example, effective decontamination of microbial cultures is essential to ensure proper biocontainment and safety within microbiological laboratories. To this end, many commercial decontamination agents are available which have been tested to a prescribed standard to substantiate their efficacy. However, these standardised tests are unlikely to accurately reflect many conditions encountered in medical and biomedical research. Despite this, laboratory workers and other users of decontamination agents may assume that all decontamination agents will work in all situations. We tested commonly used commercial decontamination agents against a range of bacterial species to determine their efficacy under real-world research laboratory conditions. As each decontamination agent has a different recommended dilution for use, to compare their efficacy we calculated their 'effective ratio' which reflects the difference between the manufacturer-recommended dilution and the dilution needed to achieve decontamination under real-world research laboratory conditions. Effective ratios above one indicate that the agent was effective at a dilution more dilute than recommended whereas effective ratios lower than one indicate that the agent required a higher concentration than recommended. Our results show that the quaternary ammonium agents TriGene Advance and Chemgene HLD4L were the most effective out of the agents tested, with biocidal activity measured at up to 64 times the recommended dilution. In contrast, hypochlorite (bleach) and Prevail™ (stabilised hydrogen peroxide) had the lowest effective ratios amongst the tested agents. In conclusion, our data suggests that not all decontamination agents will work at the recommended dilutions under real-world research laboratory conditions. We recommend that the protocols for the use of decontamination agents are verified under the specific conditions required to ensure they are fit for purpose.

Dealing with Hidden Threats: The Antimicrobial Effect of the Embalming Process.

Individuals naturally carry bacteria and other microbes as part of their natural flora, with some being opportunistic pathogens. Approximately 30% of the population is known to carry Staphylococcus aureus in their nasal cavity, an organism that causes infections ranging from soft tissue abscesses to toxic shock syndrome. This problem is compounded by the presence of antibiotic-resistant strains such as Methicillin-Resistant Staphylococcus aureus (MRSA). Commensal bacteria present on cadavers pose a risk to those who handle the body. As a Medical School Anatomy laboratory that performs hands-on cadaveric dissection, we wanted to know whether the embalming process is sufficient to kill all commensal bacteria that pose a risk to staff and students. Even if these strains do not cause disease in these individuals, secondary transmission could occur to friends and family, who may be at higher risk of acquiring an infection. Embalming is assumed to eliminate all microbial contamination on the body. However, there are limited studies to confirm this. This study characterises the incidence of antibiotic sensitive and resistant bacteria in cadavers donated for medical teaching and research. We have screened for Methicillin-Resistant Organisms (MRO) and Extended-Spectrum Beta-Lactamase (ESBL) producing bacteria. In this study group of cadavers, approximately 46% (16/35) carry an MRO, while 51% (18/35) carry an ESBL positive organism prior to embalming. By determining the organisms' presence pre- and post-embalming, we can evaluate the embalming procedure's effectiveness. Our results show embalming eliminates detectable microbes in about 51% (18/35) of the cadavers. MRO dropped by 75% (16 to 4 positive cadavers), while ESBL organisms went down by almost 95% (from 18 to 1 positive cadaver). There was a further decrease in the number of positive cadavers after storage at 4 °C to 6% (2/32). Thus, although the embalming process does not immediately sterilise all the cadavers, prolonged storage at 4 °C can further reduce the number of viable bacteria.