Rhodotorula toruloides: an ideal microbial cell factory to produce oleochemicals, carotenoids, and other products

Requirement of clean energy sources urges us to find substitutes for fossil fuels. Microorganisms provide an option to produce feedstock for biofuel production by utilizing inexpensive, renewable biomass. Rhodotorula toruloides (Rhodosporidium toruloides), a non-conventional oleaginous yeast, can accumulate intracellular lipids (single cell oil, SCO) more than 70% of its cell dry weight. At present, the SCO-based biodiesel is not a price-competitive fuel to the petroleum diesel. Many efforts are made to cut the cost of SCO by strengthening the performance of genetically modified R. toruloides strains and by valorization of low-cost biomass, including crude glycerol, lignocellulosic hydrolysates, food and agro waste, wastewater, and volatile fatty acids. Besides, optimization of fermentation and SCO recovery processes are carefully studied as well. Recently, new R. toruloides strains are developed via metabolic engineering and synthetic biology methods to produce value-added chemicals, such as sesquiterpenes, fatty acid esters, fatty alcohols, carotenoids, and building block chemicals. This review summarizes recent advances in the main aspects of R. toruloides studies, namely, construction of strains with new traits, valorization of low-cost biomass, process detection and optimization, and product recovery. In general, R. toruloides is a promising microbial cell factory for production of biochemicals.

Oleaginous yeasts- substrate preference and lipid productivity: a view on the performance of microbial lipid producers

Background

Oleaginous yeasts are promising microbial platforms for sustainable, bio-based production of biofuels and oleochemical building blocks. Bio-based residues provide sustainable and cost-effective carbon sources for fermentative yeast oil production without land-use change. Considering the regional abundancy of different waste streams, we chose complex biomass residue streams of marine origin; macroalgae hydrolysate, and terrestrial origin; wheat straw hydrolysate in the presence, and absence of corn steep liquor as a complex nitrogen source. We investigated the biomass and lipid yields of an array of well-described oleaginous yeasts; R. glutinis, T. asahii, R. mucilaginosa, R. toruloides, C. oleaginosus growing on these hydrolysates. Furthermore, their sugar utilization, fatty acid profile, and inhibitory effect of the hydrolysates on yeast growth were compared. For correlative reference, we initially performed comparative growth experiments for the strains on individual monomeric sugars separately. Each of these monomeric sugars was a dominant carbon source in the complex biomass hydrolysates evaluated in this study. In addition, we evaluated N-acetylglucosamine, the monomeric building block of chitin, as a low-cost nitrogen and carbon source in yeast fermentation.

Results

C. oleaginosus provided the highest biomass and lipid yields. In the wheat straw and brown algae hydrolysates, this yeast strain gained 7.5 g/L and 3.8 g/L lipids, respectively. Cultivation in algae hydrolysate resulted in a higher level of unsaturated fatty acids in the lipids accumulated by all yeast strains. R. toruloides and C. oleaginosus were able to effectively co-utilize mannitol, glucose, and xylose. Growth rates on wheat straw hydrolysate were enhanced in presence of corn steep liquor.

Conclusions

Among the yeast strains investigated in this study, C. oleaginosus proved to be the most versatile strain in terms of substrate utilization, productivity, and tolerance in the complex media. Various fatty acid profiles obtained on each substrate encourage the manipulation of culture conditions to achieve the desired fatty acid composition for each application. This could be accomplished by combining the element of carbon source with other formerly studied factors such as temperature and oxygen. Moreover, corn steep liquor showed promise for enhancement of growth in the oleaginous strains provided that carbon substrate is available.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01710-3.

Phosphate removal combined with acetate supplementation enhances lipid production from water hyacinth by Cutaneotrichosporon oleaginosum

BACKGROUND

Microbial lipids derived from various lignocellulosic feedstocks have emerged as a promising candidate for the biodiesel industry and a potential substitute for high value-added fats. However, lignocellulosic biomass, especially herbaceous biomass, such as water hyacinth, contains high concentrations of nitrogenous components. These compounds impede microbial lipid production, as lipid biosynthesis is commonly induced by imposing a nutrient deficiency, especially nitrogen starvation. Novel strategies and bioprocesses are pivotal for promoting lipid production from nitrogen-rich biomass.

RESULTS

Here a combined strategy of phosphate removal and acetate supplementation was described for enhanced microbial lipid production on water hyacinth hydrolysates by Cutaneotrichosporon oleaginosum (formerly Cryptococcus curvatus). Lipid production was significantly improved, when the phosphorus limitation and sugars/acetate co-utilization strategies were used separately. In this case, acetate and glucose were consumed simultaneously. Lipid production was observed by the combination of phosphate removal with acetate supplementation. Lipid titer, content, and yield were determined to be 7.3 g/L, 59.7% and 10.1 g/100 g raw water hyacinth, respectively. These data were increased by 4.2, 4.6, and 4.3 times, respectively, compared to those from the unprocessed hydrolysates. The fatty acid compositions of the resulting lipids bear a marked resemblance to those of rapeseed oil, indicating their applicability to the biodiesel industry.

CONCLUSIONS

The combination of phosphate removal and acetate supplementation was successful in significantly enhancing microbial lipid production. This strategy offers a valuable solution for nitrogen-rich lignocellulosic feedstocks utilization, which should foster more economical nitrogen-rich biomass-to-lipid bioprocesses.

A two-stage process facilitating microbial lipid production from N-acetylglucosamine by Cryptococcus curvatus cultured under non-sterile conditions

N-acetylglucosamine (GlcNAc), the monomeric constituent of chitin, is rarely studied for lipid production by oleaginous species. This study demonstrated that Cryptococcus curvatus had a great capacity to convert GlcNAc into lipid with high yield using a two-stage production process. Optimal inoculum age and inoculation size strongly improved the two-stage lipid production efficiency. More interestingly, this process rendered superior lipid production under non-sterile condition. The acetate liberated from GlcNAc was consumed timely, while the NH₄⁺ released was rarely assimilated. Lipid titre, lipid content and lipid yield reached 9.9 g/L, 56.9% and 0.23 g/g, respectively, which were significantly higher than those from the conventional process where cell growth and lipid accumulation were coupled. The resulting lipid samples had similar fatty acid compositional profiles to those of vegetable oil, suggesting their potential for biodiesel production. These findings strongly supported the two-stage process as an attractive strategy for better techno-economics of the chitin-to-biodiesel routes.

Characterization and robust nature of newly isolated oleaginous marine yeast Rhodosporidium spp. from coastal water of Northern China

A total of ten marine yeast strains isolated from Bohai Sea, Northern China were identified to be members of three genera Rhodosporidium, Rhodotorula, and Cryptococcus. Two representative strains Rhodosporidium TJUWZ4 and Cryptococcus TJUWZA11 with high lipid content based on Nile red staining method were further characterized. A wide range of culture conditions (C and N sources, pH, temperature, salinity and C/N ratio) were tested to characterize the biomass and lipid production (yield and productivity) of these strains. Results indicated that Rhodosporidium TJUWZ4 was capable of achieving lipid yield up to 44% and 0.09 g/l-h productivity on glucose and peptone medium at pH 4, 20 °C, 30% salinity, and C/N 80. Three fatty acids, namely oleic acid (18:1), palmitic acid (C16:0) and linoleic acid (18:2) were the major intracellular fatty acids, which accounted for 90% of total lipids. With promising features for intracellular lipid accumulation, Rhodosporidium TJUWZ4 is a robust strain with great potentials for application in biodiesel production from renewable feedstocks.

The novel oleaginous bacterium Sphingomonas sp. EGY1 DSM 29616: a value added platform for renewable biodiesel

Oleaginous microorganisms are regarded as efficient, renewable cell factories for lipid biosynthesis, a biodiesel precursor, to overwhelm the cosmopolitan energy crisis with affordable investment capital costs. Present research highlights production and characterization of lipids by a newly isolated oleaginous bacterium, Sphingomonas sp. EGY1 DSM 29616 through an eco-friendly approach. Only sweet whey [42.1% (v/v)] in tap water was efficiently used as a growth medium and lipid production medium to encourage cell growth and trigger lipid accumulation simultaneously. Cultivation of Sphingomonas sp. EGY1 DSM 29616 in shake flasks resulted in the accumulation of 8.5 g L^-1 lipids inside the cells after 36 h at 30 °C. Triglycerides of C16:C18 saturated and unsaturated fatty acids showed a similar pattern to tripalmitin or triolein; deduced from gas chromatography (GC), thin layer chromatography (TLC), and Matrix-assisted laser desorption/ionization time-of-flight-mass spectra analysis (MALDI-TOF-MS) analyses. Batch cultivation 2.5 L in a laboratory scale fermenter led to 13.8 g L^-1 accumulated lipids after 34 h at 30 °C. Present data would underpin the potential of Sphingomonas sp. EGY1 DSM 29616 as a novel renewable cell factory for biosynthesis of biodiesel.

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.

Integrated in situ transesterification for improved biodiesel production from oleaginous yeast: a value proposition for possible industrial implication

An integrated in situ transesterification process was developed in this study for energy and cost-efficient biodiesel production from oleaginous yeast biomass.