New insights into the effect of medium-chain-length lactones on yeast membranes. Importance of the culture medium

A sustainable bioprocess technology for producing food-flavour (+)-γ-decalactone from castor oil-derived ricinoleic acid using enzymatic activity of Candida parapsilosis: Scale-up optimization and purification using novel composite

Ricinoleic acid (RA) from castor oil was employed in biotransformation of peach-flavoured γ-decalactone (GDL), using a Candida parapsilosis strain (MTCC13027) which was isolated from waste of pineapple crown base. Using four variables-pH, cell density, amount of RA, and temperature-the biotransformation parameters were optimized using RSM and BBD. Under optimized conditions (pH 6, 10 % of microbial cells, 10 g/L RA at 28°C), the conversion was maximum and resulted to 80 % (+)-GDL (4.4 g/L/120 h) yield in shake flask (500 mL). Furthermore, optimization was achieved by adjusting the aeration and agitation parameters in a 3 L bioreactor, which were then replicated in a 10 L bioreactor to accurately determine the amount of (+)-GDL. In bioreactor condition, 4.7 g/L (>85 %) of (+)-GDL is produced with 20 % and 40 % dissolved oxygen (1.0 vvm) at 150 rpm in 72 h and 66 h, respectively. Further, a new Al-Mg-Ca-Si composite column-chromatography method is developed to purify enantiospecific (+)-GDL (99.9 %). This (+)-GDL is 100 % nature-identical as validated through 14C-radio-carbon dating. Thorough chemical investigation of enantiospecific (+)-GDL is authenticated for its use as flavour. This bioflavour has been developed through a cost-effective biotechnological process in response to the demand from the food industry on commercial scale.

A review on variation in crude glycerol composition, bio-valorization of crude and purified glycerol as carbon source for lipid production

Crude glycerol (CG) is a by-product formed during the trans-esterification reaction for biodiesel production. Although crude glycerol is considered a waste stream of the biodiesel industry, it can replace expensive carbon substrates required for lipid production by oleaginous micro-organisms. However, crude glycerol has several impurities, such as methanol, soap, triglycerides, fatty acids, salts and metals, which are created during the trans-esterification process and may affect the cellular metabolism involved in lipid synthesis. This review aims to critically present a variation in crude glycerol composition depending on trans-esterification process and impact of impurities present in the crude glycerol on the cell growth and lipid accumulation by oleaginous microbes. This study also draws comparison between purified and crude glycerol for lipid production. Several techniques for crude glycerol purification (chemical treatment, thermal treatment, membrane technology, ion-exchange chromatography and adsorption) have been presented and discussed with reference to cost and environmental effects.

Spindle pole body duplication defective yeast cells are more prone to membrane damage

Correct separation of chromosomes during mitosis is essential for preventing genetic instability and aneuploidy. Such separation is dependent on correct duplication of the nuclear-associated microtubular organizing center, i.e., spindle pole body (SPB), in fungi. MonoPolar Spindle 2 (MPS2) is an essential gene, encoding a membrane protein required for the insertion of SPB into the nuclear envelope. We recently reported that the SESA complex, which is composed of Smy2, Eap1, Scp160, and Asc1, suppresses the essential role of MPS2 (Sezen et al. 2009, Genes & Development 23:1559-1570), i.e., in SESA-active cells Mps2 becomes nonessential. We also proposed that the SESA network facilitates this insertion by altering the membrane lipid composition (Sezen 2015, FEMS Yeast Research 15:fov089). In addition, we are interested in the antifungal properties of essential oils and previously reported that membrane integrity of yeast cells is impaired upon exposure to turpentine, thyme, oregano, and orange peel essential oils (Konuk and Ergüden 2017, BioCell 41:13-18). Due to our continuing interest in the SESA system and the mechanisms by which essential oils affect yeast cells, we aimed to investigate the effects of essential oils on yeast cell membranes. Herein, we show that mps2∆ 2µm-SMY2 and mps2∆ pom34∆ cells, in which the SESA complex is active and SPB duplication is defective, are more prone to membrane damage upon treatment with essential oils.

Fluorescence Lifetime and UV-Vis Spectroscopy to Evaluate the Interactions Between Quercetin and Its Yeast Microcapsule

Quercetin is a fragile bioactive compound. Several works have tried to preserve it by encapsulation but the form of encapsulation (mono- or supra-molecular structure, tautomeric form), though important for stability and bioavailability, remains unknown. The present work aims at developing a fluorescence lifetime technique to evaluate the structure of quercetin during encapsulation in a vector capsule that has already proven efficiency, yeast cells. Molecular stabilization was observed during a 4-month storage period. The time-correlated single-photon counting (TCSPC) technique was used to evaluate the interaction between quercetin molecules and the yeast capsule. The various tautomeric forms, as identified by UV-Vis spectroscopy, result in various lifetimes in TCSPC, although they varied also with the buffer environment. Quercetin in buffer exhibited a three-to-four longer long-time after 24 h (changing from 6-7 to 18-23 ns), suggesting an aggregation of molecules. In yeast microcapsules, the long-time population exhibited a longer lifetime (around 27 ns) from the beginning and concerned about 20% of molecules compared to dispersed quercetin. This shows that lifetime analysis can show the monomolecular instability of quercetin in buffer and the presence of interactions between quercetin molecules and their microcapsules.

Effect of crude glycerol impurities on lipid preparation by Rhodosporidium toruloides yeast 32489

Crude glycerol (byproduct of biodiesel preparation) was utilised as the carbon source to produce lipid using oleaginous yeast Rhodosporidium toruloides 32489. Under the same conditions, lipid production with crude glycerol was higher than those produced with glucose and pure glycerol. The effects of 4 main impurities in crude glycerol (methyl oleate, sodium oleate, NaCl and methanol) on lipid production were investigated. Compared with utilising pure glycerol, addition of methyl oleate, sodium oleate, and NaCl impurities increased lipid production by 47.0%, 68.0% and 64.0%, respectively, while methanol decreased lipid production by 17.7%. However, when methanol was mixed with other impurities, its inhibition effect was alleviated due to the promoting effect of other impurities. Hence, crude glycerol could be used as a renewable and low-cost carbon source to replace pure glucose or glycerol for lipid preparation.

Advanced fluorescence technologies help to resolve long-standing questions about microbial vitality

Advances in fundamental physical and optical principles applied to novel fluorescence methods are currently resulting in rapid progress in cell biology and physiology. Instrumentation devised in pioneering laboratories is becoming commercially available, and study findings are now becoming accessible. The first results have concerned mainly higher eukaryotic cells but many more developments can be expected, especially in microbiology. Until now, some important problems of cell physiology have been difficult to investigate due to interactions between probes and cells, excretion of probes from cells and the inability to make in situ observations deep within the cell, within tissues and structures. These technologies will enable microbiologists to address these topics. This Review aims at introducing the limits of current physiology evaluation techniques, the principles of new fluorescence technologies and examples of their use in this field of research for evaluating the physiological state of cells in model media, biofilms or tissue environments. Perspectives on new imaging technologies, such as super-resolution imaging and non-linear highly sensitive Raman microscopy, are also discussed. This review also serves as a reference to those wishing to explore how fluorescence technologies can be used to understand basic cell physiology in microbial systems.