Regulated expression of green fluorescent protein in Debaryomyces hansenii

High-resolution live cell imaging to define ultrastructural and dynamic features of the halotolerant yeast Debaryomyces hansenii

Although some budding yeasts have proved tractable and intensely studied models, others are more recalcitrant. Debaryomyces hansenii, an important yeast species in food and biotechnological industries with curious physiological characteristics, has proved difficult to manipulate genetically and remains poorly defined. To remedy this, we have combined live cell fluorescent dyes with high-resolution imaging techniques to define the sub-cellular features of D. hansenii, such as the mitochondria, nuclei, vacuoles and the cell wall. Using these tools, we define biological processes like the cell cycle, organelle inheritance and various membrane trafficking pathways of D. hansenii for the first time. Beyond this, reagents designed to study Saccharomyces cerevisiae proteins were used to access proteomic information about D. hansenii. Finally, we optimised the use of label-free holotomography to image yeast, defining the physical parameters and visualising sub-cellular features like membranes and vacuoles. Not only does this work shed light on D. hansenii but this combinatorial approach serves as a template for how other cell biological systems, which are not amenable to standard genetic procedures, can be studied.

A CRISPR/Cas9 method facilitates efficient oligo-mediated gene editing in Debaryomyces hansenii

Halophilic and osmotolerant yeast Debaryomyces hansenii has a high potential for cell factory applications due to its resistance to harsh environmental factors and compatibility with a wide substrate range. However, currently available genetic techniques do not allow the full potential of D. hansenii as a cell factory to be harnessed. Moreover, most of the currently available tools rely on the use of auxotrophic markers that are not suitable in wild-type prototrophic strains. In addition, the preferred non-homologous end-joining (NHEJ) DNA damage repair mechanism poses further challenges when precise gene targeting is required. In this study, we present a novel plasmid-based CRISPRCUG/Cas9 method for easy and efficient gene editing of the prototrophic strains of D. hansenii. Our toolset design is based on a dominant marker and facilitates quick assembly of the vectors expressing Cas9 and single or multiple single-guide RNAs (sgRNAs) that provide the possibility for multiplex gene engineering even in prototrophic strains. Moreover, we have constructed NHEJ-deficient D. hansenii that enable our CRISPRCUG/Cas9 tools to support the highly efficient introduction of point mutations and single/double gene deletions. Importantly, we also demonstrate that 90-nt single-stranded DNA oligonucleotides are sufficient for direct repair of DNA breaks induced by sgRNA-Cas9, resulting in precise edits reaching 100% efficiencies. In conclusion, tools developed in this study will greatly advance basic and applied research in D. hansenii. In addition, we envision that our tools can be rapidly adapted for gene editing of other non-conventional yeast species including the ones belonging to the CUG clade.

New kids on the block: emerging oleaginous yeast of biotechnological importance

There is growing interest in using oleaginous yeast for the production of a variety of fatty acids and fatty acid-derived oleochemicals. This is motivated by natural propensity for high flux through lipid biosynthesis that has naturally evolved, making them a logical starting point for additional genetic engineering to improve titers and productivities. Much of the academic and industrial focus has centered on yeast that have significant genetic engineering tool capabilities, such as Yarrowia lipolytica, and those that have naturally high lipid accumulation, such as Rhodosporidium toruloides and Lipomyces starkeyi; however, there are oleaginous yeast with phenotypes better aligned with typically inhibitory process conditions, such as high salt concentrations and lignocellulosic derived inhibitors. This review addresses the foundational work in characterizing two emerging oleaginous yeast of interest: Debaryomyces hansenii and Trichosporon oleaginosus. We focus on the physiological and metabolic properties of these yeast that make each attractive for bioprocessing of lignocellulose to fuels and chemicals, discuss their respective genetic engineering tools and highlight the critical barriers facing the broader implementation of these oleaginous yeast.

Chemistry, Antioxidant, Antibacterial and Antifungal Activities of Volatile Oils and their Components

The present paper reports the chemical composition, antioxidant and antibacterial activities of several essential oils and their components. Analysis showed that three oils (Carum carvi L., Verbena officinalis L. and Majorana hortensis L.) contained predominantly oxygenated monoterpenes, while others studied (Pimpinella anisum L., Foeniculum vulgare Mill.) mainly contained anethole. C. carvi, V. officinalis and M. hortensis oils exhibited the most potent antioxidant activity, due their contents of carvacrol, anethole and estragol. Antibacterial action was assessed against a range of pathogenic and useful bacteria and fungi of agro-food interest. V. officinalis and C. carvi oils proved the most effective, in particular against Bacillus cereus and Pseudomonas aeruginosa. Carvacrol proved most active against Escherichia coli, and completely inhibited the growth of Penicillium citrinum. The oils proved inactive towards some Lactobacilli strains, whereas single components showed an appreciable activity. These results may be important for use of the essential oils as natural preservatives for food products.

Chemical composition and in vitro antimicrobial and mutagenic activities of seven Lamiaceae essential oils

Deeper knowledge of the potentiality of aromatic plants can provide results of economic importance for food and pharmacological industry. The essential oils of seven Lamiaceae species were analyzed by gas chromatography-mass spectrometry and assayed for their antibacterial, antifungal and mutagenic activities. Monoterpenes in the oils ranged between 82.47% (hyssop oil) and 97.48% (thyme oil), being mainly represented by oxygenated compounds. The antibacterial activity was evaluated against six pathogenic and five non-pathogenic bacterial strains. Oregano and thyme oils showed the strongest antibacterial activity against the pathogenic ones. The antifungal activity was evaluated against six fungal strains of agrifood interest: the oils tested exhibited variable degrees of activity. Two Salmonella typhimurium strains were used to assess the possible mutagenic activity. No oil showed mutagenic activity. Data obtained let us hypothesise that the use of essential oils could be a viable and safe way to decrease the utilisation of synthetic food preservatives. Further research is needed to obtain information regarding the practical effectiveness of essential oils to prevent the growth of food borne and spoiling microbes under specific application conditions.

Debaryomyces hansenii — an extremophilic yeast with biotechnological potential

We illuminate the ecological, physiological and genetic characteristics of the yeast Debaryomyces hansenii in the view of our belief that this metabolically versatile, non-pathogenic, osmotolerant and oleaginous microorganism represents an attractive target for fundamental and applied biotechnological research. To this end, we give a broad overview of extant biotechnological procedures using D. hansenii, e.g. in the manufacture of various foods, and propose research into the heterologous synthesis of a range of fine chemicals.

Mechanisms underlying the halotolerant way of

The yeast Debaryomyces hansenii is usually found in salty environments such as the sea and salted food. It is capable of accumulating sodium without being intoxicated even when potassium is present at low concentration in the environment. In addition, sodium improves growth and protects D. hansenii in the presence of additional stress factors such as high temperature and extreme pH. An array of advantageous factors, as compared with Saccharomyces cerevisiae, is putatively involved in the increased halotolerance of D. hansenii: glycerol, the main compatible solute, is kept inside the cell by an active glycerol-Na+ symporter; potassium uptake is not inhibited by sodium; sodium protein targets in D. hansenii seem to be more resistant. The whole genome of D. hansenii has been sequenced and is now available at http://cbi.labri.fr/Genolevures/ and, so far, no genes specifically responsible for the halotolerant behaviour of D. hansenii have been found.