Overproduction of isoprenoids by Saccharomyces cerevisiae in a synthetic grape juice medium in the absence of plant genes.

The objective of this work is to demonstrate if the hexaprenyl pyrophosphate synthetase Coq1p might be involved in monoterpenes synthesis in Saccharomyces cerevisiae, although its currently known function in yeast is to catalyze the first step in ubiquinone biosynthesis. However, in a BY4743 laboratory strain, the presence of an empty plasmid in a chemically defined grape juice medium results in a statistically significant increase of linalool, (E)-nerolidol and (E,E)-farnesol. When COQ1 is overexpressed from a plasmid, the levels of the volatile isoprenoids are further increased. Furthermore, overexpression of COQ1 in the same genetic context but with a mutated farnesyl pyrophosphate synthetase (erg20 mutation K197E), results in statistically significant higher levels of linalool (above 750 µg/L), geraniol, α-terpineol, and the sesquiterpenes, farnesol and nerolidol (total concentration of volatile isoprenoids surpasses 1300 µg/L). We show that the levels of monoterpenes and sesquiterpenes that S. cerevisiae can produce, in the absence of plant genes, depend on the composition of the medium and the genetic context. To the best of our knowledge, this is the highest level of linalool produced by S. cerevisiae up to now. Further research will be needed for understanding how COQ1 and the medium composition might interact to increase flavor complexity of fermented beverages.

Transcriptional regulation of lipid homeostasis in mycobacteria.

Mycolic acids are major components of the cell envelope of mycobacteria, such as Mycobacterium tuberculosis, and play an important role in its architecture, impermeability and interaction with the environment. Synthesis of mycolic acids is carried out by two types of fatty acid synthases (FAS) working in concert: type I FAS, a multifunctional enzyme capable of de novo synthesis of medium-chain fatty acids, and type II FAS, responsible for their elongation. In this article we report the identification and characterization of a transcriptional regulator (MabR), whose binding to the FAS-II promoter region was demonstrated in vitro and in vivo. Overexpression and knock-down studies in Mycobacterium smegmatis revealed the repressor nature of MabR, with reduced amounts of FAS-II transcripts and fatty acids in the overproducing strain. Under these conditions, downregulation of fas transcription was also observed, thereby suggesting the existence of cross-talk between the two FAS, mediated by MabR. Finally, the finding that a mabR knock-out mutant could only be obtained in a merodiploid strain of M. smegmatis, confirmed the predicted essentiality, thus implying an essential role for MabR in mycobacterial fatty acid metabolism.

[Application of a new transport and storage material for improving the quality of drinking water in rural African areas]. / Application d'un nouveau matériel de transport et de stockage pour l'amélioration de la qualité de l'eau de boisson en milieu rural africain.

Although boreholes in rural african areas deliver safe drinking water, there is a daily consumption of water polluted by fecal bacteria. Contamination occurs during transport, storage and domestic allocation of water. This is directly attributable to ignorance of the rules of hygiene, and the use of traditional jars ineffective in maintaining water quality. Their replacement with more modern recipients and the initiation of sanitary education markedly decrease bacterial water contamination, however, WHO standards which define portable water are rarely attained. In fact, it seems that established WHO conditions can only be achieved with piped water or after chemical disinfection.