Oleaginous yeasts for biochemicals, biofuels and food from lignocellulose-hydrolysate and crude glycerol

Microbial lipids produced from lignocellulose and crude glycerol (CG) can serve as sustainable alternatives to vegetable oils, whose production is, in many cases, accompanied by monocultures, land use changes or rain forest clearings. Our projects aim to understand the physiology of microbial lipid production by oleaginous yeasts, optimise the production and establish novel applications of microbial lipid compounds. We have established methods for fermentation and intracellular lipid quantification. Following the kinetics of lipid accumulation in different strains, we found high variability in lipid formation even between very closely related oleaginous yeast strains on both, wheat straw hydrolysate and CG. For example, on complete wheat straw hydrolysate, we saw that one Rhodotorula glutinis strain, when starting assimilating D-xylosealso assimilated the accumulated lipids, while a Rhodotorula babjevae strain could accumulate lipids on D-xylose. Two strains (Rhodotorula toruloides CBS 14 and R. glutinis CBS 3044) were found to be the best out of 27 tested to accumulate lipids on CG. Interestingly, the presence of hemicellulose hydrolysate stimulated glycerol assimilation in both strains. Apart from microbial oil, R. toruloides also produces carotenoids. The first attempts of extraction using the classical acetone-based method showed that β-carotene is the major carotenoid. However, there are indications that there are also substantial amounts of torulene and torularhodin, which have a very high potential as antioxidants.

Oleaginous yeasts respond differently to carbon sources present in lignocellulose hydrolysate

BACKGROUND

Microbial oils, generated from lignocellulosic material, have great potential as renewable and sustainable alternatives to fossil-based fuels and chemicals. By unravelling the diversity of lipid accumulation physiology in different oleaginous yeasts grown on the various carbon sources present in lignocellulose hydrolysate (LH), new targets for optimisation of lipid accumulation can be identified. Monitoring lipid formation over time is essential for understanding lipid accumulation physiology. This study investigated lipid accumulation in a variety of oleaginous ascomycetous and basidiomycetous strains grown in glucose and xylose and followed lipid formation kinetics of selected strains in wheat straw hydrolysate (WSH).

RESULTS

Twenty-nine oleaginous yeast strains were tested for their ability to utilise glucose and xylose, the main sugars present in WSH. Evaluation of sugar consumption and lipid accumulation revealed marked differences in xylose utilisation capacity between the yeast strains, even between those belonging to the same species. Five different promising strains, belonging to the species Lipomyces starkeyi, Rhodotorula glutinis, Rhodotorula babjevae and Rhodotorula toruloides, were grown on undiluted wheat straw hydrolysate and lipid accumulation was followed over time, using Fourier transform-infrared (FTIR) spectroscopy. All five strains were able to grow on undiluted WSH and to accumulate lipids, but to different extents and with different productivities. R. babjevae DVBPG 8058 was the best-performing strain, accumulating 64.8% of cell dry weight (CDW) as lipids. It reached a culture density of 28 g/L CDW in batch cultivation, resulting in a lipid content of 18.1 g/L and yield of 0.24 g lipids per g carbon source. This strain formed lipids from the major carbon sources in hydrolysate, glucose, acetate and xylose. R. glutinis CBS 2367 also consumed these carbon sources, but when assimilating xylose it consumed intracellular lipids simultaneously. Rhodotorula strains contained a higher proportion of polyunsaturated fatty acids than the two tested Lipomyces starkeyi strains.

CONCLUSIONS

There is considerable metabolic diversity among oleaginous yeasts, even between closely related species and strains, especially when converting xylose to biomass and lipids. Monitoring the kinetics of lipid accumulation and identifying the molecular basis of this diversity are keys to selecting suitable strains for high lipid production from lignocellulose.

FT-NIR: a tool for rapid intracellular lipid quantification in oleaginous yeasts

BACKGROUND

Lipid extraction for quantification of fat content in oleaginous yeasts often requires strong acids and harmful organic solvents; it is laborious and time-consuming. Therefore, in most cases just endpoint measurements of lipid accumulation are performed and kinetics of intracellular lipid accumulation is difficult to follow. To address this, we created a prediction model using Fourier-transform near-infrared (FT-NIR) spectroscopy. This method allows to measure lipid content in yeast.

METHODS

The FT-NIR calibration sets were constructed from spectra of freeze-dried cells of the oleaginous yeasts Rhodotorula toruloides CBS 14, Lipomyces starkeyi CBS 1807 and Yarrowia lipolytica CBS 6114. The yeast cells were obtained from different cultivation conditions. Freeze-dried cell pellets were scanned using FT-NIR in the Multi Purpose Analyser (MPA) from Bruker. The obtained spectra were assigned corresponding to total fat content, obtained from lipid extraction using a modified Folch method. Quantification models using partial least squares (PLS) regression were built, and the calibration sets were validated on independently cultivated samples. The R. toruloides model was additionally tested on Rhodotorula babjevae DBVPG 8058 and Rhodotorula glutinis CBS 2387.

RESULTS

The R ² of the FT-NIR model for R. toruloides was 98%, and the root mean square error of cross-validation (RMSECV) was 1.53. The model was validated using a separate set of R. toruloides samples with a root mean square error of prediction (RMSEP) of 3.21. The R ² of the Lipomyces model was 96%, with RMSECV 2.4 and RMSEP 3.8. The R ² of the mixed model, including all tested yeast strains, was 90.5%, with RMSECV 2.76 and RMSEP 3.22, respectively. The models were verified by predicting the total fat content in newly cultivated and freeze-dried samples. Additionally, the kinetics of lipid accumulation of a culture were followed and compared with standard lipid extraction methods.

CONCLUSIONS

Using FT-NIR spectroscopy, we have developed a faster, less laborious and non-destructive quantification of yeast intracellular lipid content compared to methods using lipid extraction.

Biochemical profiling, prediction of total lipid content and fatty acid profile in oleaginous yeasts by FTIR spectroscopy

BACKGROUND

Oleaginous yeasts are considered as a potential lipid source for food, feed and biofuel production. In order to make the yeast-based lipid production environmentally and economically sustainable, there is a need for screening studies in order to find the best yeast lipid producers on different substrates, and to optimize cultivation conditions. Since the target parameter of such screening studies are lipid amounts and profiles, an analytical technique that is able to perform lipid analyses rapidly, reproducible and with high precision is highly desirable. The main objective of this study was to establish the non-invasive high-throughput Fourier transform infrared (FTIR) spectroscopy analysis for the prediction of lipid content and profile in oleaginous yeasts.

RESULTS

High-throughput FTIR spectroscopy allowed characterizing the total biochemical profile of oleaginous yeasts and enabled us to identify strains and substrate(s) providing the highest total lipid content. Some of the yeast strains grown under nitrogen-limiting conditions with glucose/xylose/mixture of glucose and xylose as carbon sources were accumulating lipids with a high proportion of free fatty acids. FTIR spectra were used to predict gravimetric and gas chromatography data by establishing multivariate calibration models. Coefficients of determination (R ²) for calibration models were obtained in a range between 0.62 and 0.92 for predicting lipid content. When using an independent test set, R ² values between 0.53 and 0.79 were achieved for predicting fatty acid profile. The best spectral region(s) for the prediction of total lipid content was 3100-2800 cm^-1 combined with 1800-700 cm^-1, and for prediction of summed saturated (SAT), monounsaturated (MUFA) and polyunsaturated (PUFA) fatty acids: 3100-2800 cm^-1, 3100-2800 cm^-1 combined with 1700-1715 cm^-1 and 3100-2800 cm^-1 combined with 1800-1715 cm^-1, respectively. The highest lipid accumulation was observed for strains Rhodotorula babjevae DBVPG 8058 on glucose and mixture of glucose and xylose and Lipomyces starkeyi CBS 2512 on xylose.

CONCLUSIONS

Applying FTIR spectroscopy combined with multivariate data analysis allows performing rapid, non-invasive, reproducible and precise quantitative predictions of total lipid content and lipid profile. It allows also detecting different lipid fractions as triacylglycerols (TAGs) and free fatty acids and evaluating the total biochemical profile of cells. Several yeast strains with high lipid accumulation were identified.

Proteome analysis of xylose metabolism in Rhodotorula toruloides during lipid production

BACKGROUND

Rhodotorula toruloides is a promising platform organism for production of lipids from lignocellulosic substrates. Little is known about the metabolic aspects of lipid production from the lignocellolosic sugar xylose by oleaginous yeasts in general and R. toruloides in particular. This study presents the first proteome analysis of the metabolism of R. toruloides during conversion of xylose to lipids.

RESULTS

Rhodotorula toruloides cultivated on either glucose or xylose was subjected to comparative analysis of its growth dynamics, lipid composition, fatty acid profiles and proteome. The maximum growth and sugar uptake rate of glucose-grown R. toruloides cells were almost twice that of xylose-grown cells. Cultivation on xylose medium resulted in a lower final biomass yield although final cellular lipid content was similar between glucose- and xylose-grown cells. Analysis of lipid classes revealed the presence of monoacylglycerol in the early exponential growth phase as well as a high proportion of free fatty acids. Carbon source-specific changes in lipid profiles were only observed at early exponential growth phase, where C18 fatty acids were more saturated in xylose-grown cells. Proteins involved in sugar transport, initial steps of xylose assimilation and NADPH regeneration were among the proteins whose levels increased the most in xylose-grown cells across all time points. The levels of enzymes involved in the mevalonate pathway, phospholipid biosynthesis and amino acids biosynthesis differed in response to carbon source. In addition, xylose-grown cells contained higher levels of enzymes involved in peroxisomal beta-oxidation and oxidative stress response compared to cells cultivated on glucose.

CONCLUSIONS

The results obtained in the present study suggest that sugar import is the limiting step during xylose conversion by R. toruloides into lipids. NADPH appeared to be regenerated primarily through pentose phosphate pathway although it may also involve malic enzyme as well as alcohol and aldehyde dehydrogenases. Increases in enzyme levels of both fatty acid biosynthesis and beta-oxidation in xylose-grown cells was predicted to result in a futile cycle. The results presented here are valuable for the development of lipid production processes employing R. toruloides on xylose-containing substrates.

Oleaginous yeast as a component in fish feed

This study investigates the replacement of vegetable oil (VO) in aquaculture feed for Arctic char (Salvelinus alpinus) with oil produced by the oleaginous yeast Lipomyces starkeyi grown in lignocellulose (wheat straw) hydrolysate. VO is extensively used to partially replace fish oil in aquaculture feed, which can be seen as non-sustainable. VO itself is becoming a limited resource. Plant oils are used in many different applications, including food, feed and biodiesel. Its replacement in non-food applications is desirable. For this purpose, yeast cells containing 43% lipids per g dry weight were mechanically disrupted and incorporated into the fish feed. There were no significant differences in this pilot study, regarding weight and length gain, feed conversion ratio, specific growth rate, condition factor and hepatosomatic index between the control and the yeast oil fed group. Fatty and amino acid composition of diet from both groups was comparable. Our results in fish demonstrate that it is possible to replace VO by yeast oil produced from lignocellulose, which may broaden the range of raw materials for food production and add value to residual products of agriculture and forestry.

Bioethanol and lipid production from the enzymatic hydrolysate of wheat straw after furfural extraction

This study investigates biofuel production from wheat straw hydrolysate, from which furfural was extracted using a patented method developed at the Latvian State Institute of Wood Chemistry. The solid remainder after furfural extraction, corresponding to 67.6% of the wheat straw dry matter, contained 69.9% cellulose of which 4% was decomposed during the furfural extraction and 26.3% lignin. Enzymatic hydrolysis released 44% of the glucose monomers in the cellulose. The resulting hydrolysate contained mainly glucose and very little amount of acetic acid. Xylose was not detectable. Consequently, the undiluted hydrolysate did not inhibit growth of yeast strains belonging to Saccharomyces cerevisiae, Lipomyces starkeyi, and Rhodotorula babjevae. In the fermentations, average final ethanol concentrations of 23.85 g/l were obtained, corresponding to a yield of 0.53 g ethanol per g released glucose. L. starkeyi generated lipids with a rate of 0.08 g/h and a yield of 0.09 g per g consumed glucose. R. babjevae produced lipids with a rate of 0.18 g/h and a yield of 0.17 per g consumed glucose. In both yeasts, desaturation increased during cultivation. Remarkably, the R. babjevae strain used in this study produced considerable amounts of heptadecenoic, α,- and γ-linolenic acid.

Lipid production from hemicellulose with Lipomyces starkeyi in a pH regulated fed-batch cultivation

This study investigated lipid production from the hemicellulosic fraction of birch wood by the oleaginous yeast Lipomyces starkeyi. Birch wood chips were thermochemically pretreated by hot water extraction, and the liquid phase, containing 45.1 g/l xylose as the major sugar, 13.1 g/l acetic acid and 4.7 g/l furfural, was used for cultivations of L. starkeyi CBS1807. The hydrolysate strongly inhibited yeast growth; the strain could only grow in medium containing 30% hydrolysate at pH 6. At pH 5, growth stopped already upon the addition of about 10% hydrolysate. In fed-batch cultures fed with hydrolysate or a model xylose-acetic acid mixture, co-consumption of xylose and acetic acid was observed, which resulted in a pH increase. This phenomenon was utilized to establish a pH-stat fed-batch cultivation in which, after an initial feeding, hydrolysate or model mixture was connected to the pH-regulation system of the bioreactor. Under these conditions we obtained growth and lipid production in cultures grown on either xylose or glucose during the batch phase. In cultivations fed with model mixture, a maximum lipid content of 60.5% of the cell dry weight (CDW) was obtained; however, not all xylose was consumed. When feeding hydrolysate, growth was promoted and carbon sources were completely consumed, resulting in higher CDW with maximum lipid content of 51.3%. In both cultures the lipid concentration was 8 g/l and a lipid yield of 0.1 g/g carbon source was obtained. Lipid composition was similar in all cultivations, with C18:1 and C16:0 being the most abundant fatty acids. Copyright © 2016 John Wiley & Sons, Ltd.

The acute effects of performing drop jumps of different intensities on concentric squat strength

AIM

To investigate the acute effects of performing drop jumps of different intensities on subsequent squat 1 repetition maximum (1RM).

METHODS

14 participants with strength training experience completed two familiarization sessions to become accustomed with the testing procedures and 1RM-like loads. Following this, four different 1RM testing sessions were completed. In each testing session subjects performed a 5-min bicycle warm-up followed by a series of sets with increasingly heavier loads until squat 1RM was achieved. During the first of these four sessions squat 1RM was assessed without the addition of drop jumps to the 1RM warm-up routine, thus was designated the control (CTRL) condition. In the final 3 testing sessions, two drop jumps from either 30 (DJ30), 45 (DJ45), or 60 (DJ60) cm were added to the warm-up routine that preceded squat 1RM assessment. EMG activity of the vastus lateralis was also monitored during 1RM testing.

RESULTS

Squat 1RM without prior plyometric activity was 128.4±36.1 kg. Following DJ30, DJ45, and DJ60 squat 1RM equaled 130.4±36.4 kg, 130.9±38.3 kg, 131.0±38.9 kg, respectively. A repeated measures ANOVA uncovered a significant main effect of warm-up condition (P=0.021). Post hoc analysis revealed that differences in the 1RM values were only significant between DJ30 and CTRL (P=0.002). No significant differences in muscle activation of the vastus lateralis were noted between the conditions.

CONCLUSION

These findings indicate lower body strength in individuals familiar with resistance training can be acutely enhanced when preceded by a warm-up incorporating a low volume of low intensity drop jumps.

Acute neuromuscular responses to resistance training performed at different loads

The aim of this study was to compare the acute neuromuscular responses during resistance exercise performed with different loading protocols. Thirteen (N=13) college-aged male subjects experienced in weight training completed two different weight training protocols involving a single elbow flexion exercise. During both protocols subjects performed three sets of the exercise with a 3-min rest between each set. One protocol required the subjects to perform each set to failure using 100% 10 repetition maximum (RM) load whereas the second protocol required the subjects to perform 10 repetitions for the first two sets using 90% 10RM load and only go to failure on the third set. Maximal voluntary isometric contraction (MVIC), integrated EMG recording (iEMG) of the biceps brachii, and blood lactate were measured before and upon completion of the two training protocols. Subjects were able to perform a significantly greater volume of work (total repetitionsxload) in the 90% 10RM protocol compared to the 100% 10RM protocol. Both protocols elicited similar cumulative levels of fatigue as reflected by a decrease in MVIC and iEMG(max) and an increase in blood lactate (p< or =0.05). As a result of the drop in repetitions performed in successive sets, it was concluded that training with 100% 10RM while exercising to failure in each set may not optimise the training volume, which may have implications for chronic muscle adaptation.

Biotinylated fluorescent peptide substrates for the sensitive and specific determination of cathepsin D activity

Cathepsin D (CatD) is a member of the mammalian aspartic protease family and is involved in cellular protein degradation and in several pathological processes. A sensitive and specific assay for the determination of CatD activity in biological samples was developed. The peptide amide substrates Amca-EDKPILF downward arrowFRLGK(biotin)-CONH2 (I), Amca-EEKPIC(Acm)F downward arrowFRLGK(biotin)-CONH2 (II) and Amca-EEKPISF downward arrowFRLGK(biotin)-CONH2 (III) contain a CatD cleavage site (F downward arrowF) flanked by a N-terminal Amca-fluorophore (7-amino-4-methylcoumarin-3-acetic acid) and a C-terminal biotin moiety. Substrates II and III proved to be specific substrates containing only one cleavage site for CatD. After cleavage of the Phe-Phe bond by CatD all biotin conjugated peptides were removed with streptavidin-coated magnetic beads. The remaining fluorescent peptides in solution represent the amount of digested substrate. The versatility of this CatD digest and pull down assay was demonstrated by measuring the activity of CatD in different subcellular fractions of human EBV-transformed B cells and human monocytes. The described method based on the designed CatD substrates represents a valuable tool for routine assays.

Human B lymphoblastoid cells contain distinct patterns of cathepsin activity in endocytic compartments and regulate MHC class II transport in a cathepsin S-independent manner

Endocytic proteolysis represents a major functional component of the major histocompatibility complex class II antigen-presentation machinery. Although transport and assembly of class II molecules in the endocytic compartment are well characterized, we lack information about the pattern of endocytic protease activity along this pathway. Here, we used chemical tools that visualize endocytic proteases in an activity-dependent manner in combination with subcellular fractionation to dissect the subcellular distribution of the major cathepsins (Cat) CatS, CatB, CatH, CatD, CatC, and CatZ as well as the asparagine-specific endoprotease (AEP) in human B-lymphoblastoid cells (BLC). Endocytic proteases were distributed in two distinct patterns: CatB and CatZ were most prominent in early and late endosomes but absent from lysosomes, and CatH, CatS, CatD, CatC, and AEP distributed between late endosomes and lysosomes, suggesting that CatB and CatZ might be involved in the initial proteolytic attack on a given antigen. The entire spectrum of protease activity colocalized with human leukocyte antigen-DM and the C-terminal and N-terminal processing of invariant chain (Ii) in late endosomes. CatS was active in all endocytic compartments. Surprisingly and in contrast with results from dendritic cells, inhibition of CatS activity by leucine-homophenylalanine-vinylsulfone-phenol prevented N-terminal processing of Ii but did not alter the subcellular trafficking or surface delivery of class II complexes, as deferred from pulse-chase analysis in combination with subcellular fractionation and biotinylation of cell-surface protein. Thus, BLC contain distinct activity patterns of proteases in endocytic compartments and regulate the intracellular transport and surface-delivery of class II in a CatS-independent manner.

Circadian changes in the response of the rabbits retina to flashes

It was previously shown that in rabbits the electroretinogram (ERG) and the visually evoked potential show a circadian rhythm consisting of a stable phase during which the animals respond to flashes with day time potentials and another phase with night time potentials (NTPs) and that the occurrence of the sharp phase transitions is programmed by the time course of the preceding light-dark schedule. From the present investigation it follows that photic sensitivity to flashes is markedly higher during the NTP-phase than in the other phase, whereas dark adaptation runs the same time course in both phases. With respect to the ERG it appears that, over a wide range of flash intensities its b wave only is affected by phase of the rhythm. The differences in photic responses between the 2 phases are discussed in the light of possibly synchronous changes in the influence of sympathetic nerve fibres on eye structures.

Treatment of frontal sinus mucoceles with the osteoplastic flap technique

The osteoplastic flap technique for treating frontal sinus mucoceles is described. This procedure has the advantages of: being a direct approach, which allows exposure of the entire sinus, provides complete obliteration of the sinus to prevent recurrence of the sinus disease, and prevents blind curettage of any exposed dura mater; leaving no facial deformity after the operation; being a relatively atraumatic procedure with low morbidity and minimum postoperative care; and allowing simultaneous surgery on both frontal sinuses when indicated.