Trichosporon Fermentans Research Articles

Computer assisted design and flow field analysis of a multi-tube airlift reactor for biological treatment of oily wastewater

The rational design of a bioreactor plays an important role in establishing an efficient biological wastewater treatment process. In this study, a multi-tube parallel airlift reactor (MP-ALR) composed of multiple draft tubes was designed and developed by computational fluid dynamics (CFD), and was applied to oily wastewater treatment. The CFD results showed that the gas holdup and liquid velocity of MP-ALR were higher than those in a traditional airlift reactor (T-ALR), and the flow field distribution of MP-ALR was more uniform. The optimum number of parallel draft tubes was determined to be 3 in the design of a 280 L reactor with a high aspect ratio. The experimental results of using Trichosporon fermentans to treat refined soybean oil wastewater (RSOW) in a 32 L MP-ALR showed that the maximum biomass concentration increased by 2.39 g/L and the chemical oxygen demand (COD) removal was increased by 17.73 % compared with those in T-ALR. The MP-ALR developed in this study not only improves the efficiency of the biological treatment of oily wastewater, but also provides a new idea for the design of bioreactors.

The dispersion of Trichosporon fermentans was controlled by optimizing the shear environment in the reactor to improve the cell sedimentation and separation performance

The morphology of pseudomycelium in Trichosporon fermentans is not conducive to the accumulation of lipids and the recovery of yeast cells by sedimentation. In this study, the computational fluid dynamics method was used to study the effects of shear force on the flow field distribution and on the dimorphism transition and dispersion of yeast cells in a 5 L stirred bioreactor, and to explore the sedimentation performance of yeast cells in different forms. It was shown that under the condition of moderate shear force, such as 3.45 Pa corresponding to a stirring speed of 300 rpm as selected in this experiment, most of the yeast cells in the fermentation broth were spherical or short rod-shaped, and there were almost no pseudohyphal yeasts, which contributed to the good sedimentation performance of the yeast cells. The results showed that the appropriate shear force could effectively inhibit the transformation of yeast cells into pseudohyphae, retain a large number of cells in a single cell shape, enhance cell dispersion and facilitate cell contact, absorption and utilization of organic substrates, as well as increase the lipid accumulation in yeast cells. By controlling the shear force, after 40 h of treatment of RSOW using Trichosporon fermentans, the chemical oxygen demand and oil content removal were approximately 95.81% and 88.09%, respectively, which indicate a significant improvement compared with those before optimizing the shear environment. Therefore, based on shear control of the cell morphology to improve yeast cell dispersion and sedimentation performance, the oily wastewater treatment method established in this study can be used to guide the process design of fermented Trichosporon fermentans for the treatment of RSOW and the resource recycling of yeasts.

Cunninghamella echinulata produced from soybean wastewater cleanly harvests oleaginous yeasts in soybean oil refinery effluent by efficient adhesion and improves microbial lipid quality

The oleaginous yeast Trichosporon fermentans can degrade oils and fats in soybean oil refinery effluent (SORE) and accumulate intracellular lipids. Effective harvesting techniques for oleaginous yeasts can improve their utilization efficiency. Considering its excellent adhesion properties, Cunninghamella echinulata, a lipid-producing fungus, was introduced to harvest the yeast in SORE via a two-step process. Compared with C. echinulata cultured in traditional medium, namely, potato starch wastewater (PSW), C. echinulata produced from soybean wastewater (SW) achieved a better adhesion for the yeast, reaching 95.24%. Based on kinetic and thermodynamic analysis, it was found that yeasts are gathered by mycelium pellets of C. echinulata by physical adsorption, and the process is controlled by liquid film diffusion and intraparticle diffusion. The porosity of these mycelium pellets was as high as 79.3 ± 0.5%, which contributed significantly to C. echinulata's ability to adhere to the yeasts. However, when the pH was between 6 and 7, an electric neutralization effect was responsible for the higher adhesion of C. echinulata from SW to T. fermentans compared with that of C. echinulata from PSW. Because the microbial lipids produced by C. echinulata are rich in unsaturated fatty acids (UFAS), the highest proportion of UFAS reached 79.8% of the total fatty acids in microbial lipids extracted from the adhesion products. Compared with the traditional techniques used for harvesting oleaginous yeasts, the efficient adhesion of C. echinulata from SW to the yeasts in SORE represented a cleaner harvest process and improved the quality of the microbial lipids.

Computational fluid dynamics analysis of Trichosporon fermentans flocculation in refined soybean oil wastewater and flocculation rate prediction method

Trichosporon fermentans can be used to treat refined soybean oil wastewater (RSOW) and produce microbial lipids. Bioflocculation is an effective method to recover Trichosporon fermentans which accumulates intracellular oils from wastewater. During the flocculation, the hydrodynamic distribution and parameters in the reactor are important limiting factors of yeast flocculation performance. In a 0.25 L flocculation device, it was found that the appropriate range of turbulence kinetic energy was within 0.00065–0.00073 m2/s2, the dissipation rate was within 0.119–0.317 m2/s3, and the shear force was less than 0.433 Pa by computational fluid dynamics. In this case, the flocculation rate (Fr) of Trichosporon fermentans could reach more than 90%. The empirical formula associated Fr of Trichosporon fermentans with hydrodynamic parameters was obtained by Matlab, and improved in the enlargement of flocculation device, displaying an error of less than 3.03%. A conical draft tube airlift circulating reactor for flocculation was designed based on the empirical formula, and the Fr reached 91.3%. The study shows that it is feasible to predict Fr of Trichosporon fermentans according to hydrodynamic parameters by numerical simulation, and design the industrial reactor for flocculation harvesting yeasts. It is also helpful for large-scale treatment of RSOW in a safe environment.

Incorporating corn oil refining wastewater improves lipid accumulation and self-settling property of Trichosporon fermentans in corn starch wastewater

• The wastewater rich in oils was helpful to inhibit of yeast-to-hypha transition. • Mixing corn processing wastewaters improved the self-settling property of yeasts. • The lipid content of yeasts was increased by mixing corn processing wastewaters. • The mycelium morphology of yeasts can be reflected by thermogravimetric analysis. Corn starch wastewater (CSW) and corn oil refining wastewater (CORW) produced by corn processing industry can be used as substrates for oleaginous yeasts, but the problem of separating yeasts from wastewaters hinders industrial applications of the technology. A method for morphological analysis of mycelia based on thermogravimetric analysis was established in this work, and it was found that most of the Trichosporon fermentans in CSW showed mycelium form and exhibited undesirable self-settling property. When equivalent CORW was incorporated to CSW, hypha formation was inhibited, and the yeasts could be settled quickly. Trichosporon fermentans could achieve better wastewater treatment and produce 2.88 times more of lipids in the wastewater consisted of equivalent CSW and CORW than in CSW. This study contributes a new way to treat wastewater from corn processing industry, and is helpful for industrial application of wastewater treatment technology using oleaginous yeasts.

High-level expression and characterization of a lipase from Trichosporon fermentans Y3 and its application as an aquafeed additive for grouper (Epinephelus coioides)

A lipase gene was cloned from Trichosporon fermentans Y3, subcloned into pPICZαA, and then expressed in Pichia pastoris X33. The lipase (lipRT), which was obtained using a 50-L bioreactor, had maximum activity of 6000 U/mL. It had an optimum pH 8.0 and remained stable between pH 3.0 and 11.0, while its optimum temperature was 45 °C, maintaining more than 55% of optimum activity between 20 and 35 °C. To evaluate the potential application of lipRT as an aquafeed additive for juvenile grouper (Epinephelus coioides), fish with initial weight 13.31 ± 0.26 g were randomly divided into 12 sea cages and fed five formulated diets (labeled diets 1 to 4). Diets 1–4 were formulated to include 8% crude lipid and serial levels of lipRT (0 U/kg, 50 U/kg, 500 U/kg, and 1000 U/kg). The results showed that WG, FE, and PER of fish as well as ACH50, LSZ, and O2− production ratio in serum of fish on diets 3 and 4 were significantly (P < 0.05) higher than those on diets 1 and 2. The present data suggests that lipRT could improve the utilization of lipid and some nonspecific immunological parameters, and therefore could potentially be used as an aquafeed additive.

Pyrolysis of oleaginous yeast biomass from wastewater treatment: Kinetics analysis and biocrude characterization

Pyrolysis of Trichosporon fermentans biomass, a type of oleaginous yeast from the fermentation of refined soybean oil wastewater, was studied in the present work. Based on the TG/DTG curves, the activation energy values for the thermal decomposition of Trichosporon fermentans biomass were evaluated by the KAS method (111.69 kJ/mol) and FWO method (116.93 kJ/mol), respectively. The pyrolysis behavior was represented by considering the parallel degradation of four components, namely carbohydrates, proteins, lipids, and others, and the fitting degree of the simulated curve was over 0.99. According to the FTIR spectra of the end-products, the increasing hydrocarbons at a temperature around 400 °C indicated the lipid degradation. Biocrude oil was collected from a fixed bed reactor and the chemical composition was characterized by GC-TOF/MS. The yield of hydrocarbons in the bio-oil was identified as being over 28% when the pyrolysis temperature was higher than 500 °C, whilst the content of nitrogen compounds was less than 18%. The fractional yield distributions of the end-products at different pyrolysis temperatures were compared and the maximum yield of bio-oil was achieved (around 42%) at 500 °C. This study proposed a cost-effective and environmentally friendly method for the preparation of biofuel from oleaginous yeast pyrolysis.

Single cell oil and ethanol production by the oleaginous yeast Trichosporon fermentans utilizing dried sweet sorghum stalks

The ability of the oleaginous yeast Trichosporon fermentans to efficiently produce lipids when cultivated in dried sweet sorghum was evaluated. First, lipid production was evaluated in synthetic media mimicking the composition of sweet sorghum stalks and optimized based on the nitrogen source and C: N ratio. Under optimum conditions, the lipid production reached 3.66 g/L with 21.91% w/w lipid content by using a mixture of sucrose, glucose and fructose and peptone at C: N ratio 160. Cultivation on pre-saccharified sweet sorghum stalks offered 1.97 g/L, while it was found that sweet sorghum stalks can support yeast growth and lipid production without the need for external nitrogen source addition. At an attempt to increase the carbon source concentration for optimizing lipid production, the Crabtree effect was observed in T. fermentans. To this end, the yeast was evaluated for its potential to produce ethanol under anaerobic conditions in synthetic media and sweet sorghum. The ethanol concentration at 100 g/L glucose was 40.31 g/L, while utilizing sweet sorghum by adding a distinct saccharification step and external nitrogen source offered ethanol concentration equal to 23.5 g/L. To the authors’ knowledge, this is the first time that the Crabtree effect is observed in T. fermentans.

Trichosporon fermentans biomass flocculation from soybean oil refinery wastewater using bioflocculant produced from Paecilomyces sp. M2-1.

The soybean oil refinery (SOR) wastewater contains a high concentration of chemical oxygen demand (COD) and lipid, so the direct emissions of SOR wastewater will result in environmental pollution and waste of resources. Oleaginous yeast Trichosporon fermentans can consume organic materials in SOR wastewater to synthesize microbial oil, which achieves the purpose of SOR wastewater resource utilization. The effective harvesting technology of oleaginous yeasts can improve the utilization efficiency. In this study, Paecilomyces sp. M2-1 with high flocculating activity was isolated. The flocculants produced by M2-1 (MBF2-1) include 75% (w/w) polysaccharides, rely on cations, and display the flocculation percentage of above 77% in the range of pH2-11. Especially under alkaline conditions, the flocculation percentage can be kept above 97%. The results of scanning electron microscope observation and zeta potential measurements suggested that the bridging, net trapping, and sweeping were the main flocculation mechanism of MBF2-1. MBF2-1 could flocculate T. fermentans that was used to reduce the organic matter in SOR wastewater and to produce microbial oil. Under the optimum conditions, the flocculation percentage of MBF2-1 against T. fermentans from SOR wastewater can reach 95%. Fatty acid content percent in microbial oil from T. fermentans was not almost affected by flocculation of MBF2-1. Moreover, MBF2-1 can further remove 55% and 53% of COD and oil content in the fermented SOR wastewater, respectively. The properties and high flocculating percentage displayed by MBF2-1 indicated its potential application prospect in oleaginous yeast harvest and food industry wastewater treatment.

Refined soybean oil wastewater treatment and its utilization for lipid production by the oleaginous yeast Trichosporon fermentans

BackgroundThe release of refined soybean oil wastewater (RSOW) with a high chemical oxygen demand (COD) and oil content burdens the environment. The conversion of RSOW into lipids by oleaginous yeasts may be a good way to turn this waste into usable products.ResultsThe oleaginous yeast Trichosporon fermentans was used for treating the RSOW without sterilization, dilution, or nutrient supplementation. It was found that the COD and oil content of the RSOW were removed effectively; microbial oil was abundantly produced in 48 h; and the phospholipids in the RSOW tended to contribute to a higher biomass and microbial lipid content. With Plackett–Burman design and response surface design experiments, the optimal wastewater treatment conditions were determined: temperature 28.3 °C, amount of inoculum 5.9% (v/v), and initial pH 6.1. The optimized conditions were used in a 5-L bioreactor to treat the RSOW. The maximum COD degradation of 94.7% was obtained within 40 h, and the removal of the oil content was 89.9%. The biomass was 7.9 g/L, the lipid concentration was 3.4 g/L, and the lipid content was 43% (w/w). The microbial oil obtained, with a main component of unsaturated fatty acids, was similar to vegetable oils and was suggested as a potential raw material for biodiesel production.ConclusionTrichosporon fermentans can be effectively used for RSOW treatment, and lipid production and can complete pretreatment and biochemical treatment simultaneously, allowing the utilization of RSOW, which both solves an environmental problem and positively impacts the use of resources. These results provide valuable information for developing and designing more efficient waste-into-lipid bioprocesses.

Agro-industrial waste recycling by Trichosporon fermentans: conversion of waste sweetpotato vines alone into lipid.

Agro-industrial waste can be used to replace traditional carbohydrates, such as sucrose, starch, and glucose in many industrial fermentation processes. This study investigated the conversion of pre-treated waste sweetpotato vines (SV) into lipid by Trichosporon fermentans under the separate hydrolysis and fermentation (SHF) and the simultaneous saccharification and fermentation (SSF) processes. The results showed that SV autoclaving significantly increased the lipid accumulation of T. fermentans compared with acid or alkaline hydrolysis. The effects of different pre-treatments on SV were also studied by scanning electron microscopy and Fourier transform infrared spectroscopy, which showed the partial removal of the aliphatic fractions, hemicelluloses, and lignin during pre-treatment. Moreover, the lipid yield of T. fermentans in SSF was 6.98gL-1, which was threefold higher than that (2.79gL-1) in SHF, and the lipid contents of yeast in SSF and SHF were 36 and 25%, respectively. Overall, this study indicated that SSF using autoclaved SV could increase the growth and lipid production of T. fermentans and provided an efficient way to realize the resource utilization of waste SV.

Efficient Conversion of Fructose-Based Biomass into Lipids with Trichosporon fermentans Under Phosphate-Limited Conditions.

Limiting nitrogen supply has been routinely used as the master regulator to direct lipid biosynthesis. However, this strategy does not work with nitrogen-rich substrates, such as Jerusalem artichoke (JA), a fructose-based biomass, while it is difficult to obtain a high carbon-to-nitrogen (C/N) molar ratio. In this study, an alternative strategy to promote lipid accumulation by the oleaginous yeast Trichosporon fermentans CICC 1368 was developed by limiting phosphorous supply, and this strategy was implemented with JA hydrolysate as substrate. We showed that lipid accumulation was directly correlated with the C/P ratio of the culture media for T. fermentans. The time course of cell growth and lipid production was analyzed in a media with an initial C/P ratio of 6342, and the cellular lipid content could reach up to 48.5% of dry biomass. Moreover, JA hydrolysates were used as substrate for microbial lipid accumulation, under high C/P molar ratio condition, lipid yield, lipid content, and lipid coefficient increased by 10, 30, and 34%, respectively. It showed that by limiting phosphorus, the conversion of sugar into lipids can be improved effectively. Limiting phosphorus provides a promising solution to the problem of microbial lipid production with nitrogen-rich natural materials.

Use of Crude Glycerol as Sole Carbon Source for Microbial Lipid Production by Oleaginous Yeasts.

Crude glycerol, discharged from biodiesel production process, is a potential carbon source for microbial lipid production. The capability of using crude glycerol as sole carbon source for microbial lipid production by oleaginous yeasts Trichosporon fermentans and Trichosporon cutaneum was investigated for the first time. T. fermentans and T. cutaneum could use crude glycerol for efficient lipid production, and the optimal glycerol concentration for which were 50 and 70g/L, respectively. The optimum nitrogen source, C/N, inoculum concentration, and pH were yeast extract + peptone, 60, 10.0%, and 6.0, respectively. The most suitable culture temperature for T. fermentans and T. cutaneum were 28 and 30°C, respectively. Under the optimal conditions, the maximum biomass, lipid content, lipid yield, and lipid coefficient of T. fermentans and T. cutaneum were 16.0g/L, 32.4%, 5.2g/L, and 16.5%, and 17.4g/L, 32.2%, 5.6g/L, and 17.0%, respectively. Moreover, it was found that methanol present in the crude glycerol had minor influence on the lipid production. Addition of surfactant potassium oleate into the medium could slightly stimulate the cell growth and lipid accumulation of both yeasts. This study shows that T. fermentans and T. cutaneum are promising strains for lipid production on crude glycerol.

Mechanistic insights into the effect of imidazolium ionic liquid on lipid production by Geotrichum fermentans.

BackgroundIonic liquid (IL) pretreatment has emerged as a promising technique that enables complete utilization of lignocellulosic biomass for biofuel production. However, imidazolium IL has recently been shown to exhibit inhibitory effect on cell growth and product formation of industrial microbes, such as oleaginous microorganisms. To date, the mechanism of this inhibition remains largely unknown.ResultsIn this study, the feasibility of [Bmim][OAc]-pretreated rice straw hydrolysate as a substrate for microbial lipid production by Geotrichum fermentans, also known as Trichosporon fermentans, was evaluated. The residual [Bmim][OAc] present in the hydrolysate caused a reduction in biomass and lipid content (43.6 and 28.1%, respectively) of G. fermentans, compared with those of the control (7.8 g/L and 52.6%, respectively). Seven imidazolium ILs, [Emim][DEP], [Emim]Cl, [Amim]Cl, [Bmim]Cl, [Bzmim]Cl, [Emim][OAc], and [Bmim][OAc], capable of efficient pretreatment of lignocellulosic biomass were tested for their effects on the cell growth and lipid accumulation of G. fermentans to better understand the impact of imidazolium IL on the lipid production. All the ILs tested inhibited the cell growth and lipid accumulation. In addition, both the cation and the anion of IL contributed to IL toxicity. The side chain of IL cations showed a clear impact on toxicity. On examining IL anions, [OAc]− was found to be more toxic than those of [DEP]− and Cl−. IL exhibited its toxicity by inhibiting sugar consumption and key enzyme (malic enzyme and ATP-citrate lyase) activities of G. fermentans. Cell membrane permeability was also altered to different extents in the presence of various ILs. Scanning electron microscopy revealed that IL induces fibrous structure on the surface of G. fermentans cell, which might represent an adaptive mechanism of the yeast to IL.ConclusionsThis work gives some mechanistic insights into the impact of imidazolium IL on the cell growth and lipid accumulation of oleaginous yeast, which is important for IL integration in lignocellulosic biofuel production, especially for microbial lipid production.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0682-z) contains supplementary material, which is available to authorized users.

Utilization of Seawater for the Biorefinery of Lignocellulosic Biomass: Ionic Liquid Pretreatment, Enzymatic Hydrolysis, and Microbial Lipid Production

The biorefineries of lignocellulosic biomass have attracted increasing interest recently. However, large water consumption in the large-scale biorefineries remains a major problem. In this work, utilization of abundant seawater as an alternative to freshwater for ionic liquid (IL) pretreatment of lignocellulosic biomass was reported for the first time. In addition, enzymatic hydrolysis of IL-pretreated biomass and microbial lipid production from wheat straw hydrolysate were conducted in seawater. It was found that seawater had no significantly negative effect on enzymatic hydrolysis as well as IL pretreatment. After grass lignocelluloses were pretreated by 50% cholinium IL–seawater mixtures at 90 °C for 6 h and washed by seawater, the residues became highly susceptible to enzymatic hydrolysis; the reducing sugar yields of 54–72% were obtained in pH 4.8 seawater in the subsequent enzymatic hydrolysis of the residues. The lipid yield of 4.5 g/L and lipid coefficient of 0.21 g/g of sugar were achieved after cultivation of Trichosporon fermentans on wheat straw hydrolysate with the sugar concentration of approximately 30 g/L for 3 days.

Comparative genome analysis of the oleaginous yeast Trichosporon fermentans reveals its potential applications in lipid accumulation

In this work, Trichosporon fermentans CICC 1368, which has been shown to accumulate cellular lipids efficiently using industry-agricultural wastes, was subjected to preliminary genome analysis, yielding a genome size of 31.3 million bases and 12,702 predicted protein-coding genes. Our analysis also showed a high degree of gene duplications and unique genes compared with those observed in other oleaginous yeasts, with 3–4-fold more genes related to fatty acid elongation and degradation compared with those in Rhodosporidium toruloides NP11 and Yarrowia lipolytica CLIB122. Phylogenetic analysis with other oleaginous microbes suggested that the lipogenic capacity of T. fermentans was obtained during evolution after the divergence of genera. Thus, our study provided the first draft genome and comparative analysis of T. fermentans, laying the foundation for its genetic improvement to facilitate cost-effective lipid production.

Evaluating the effects of biocompatible cholinium ionic liquids on microbial lipid production by Trichosporon fermentans.

BackgroundMicrobial lipid is a potential raw material for large-scale biodiesel production and lignocellulosic hydrolysate has been considered as promising low-cost substrate for lipid fermentation. Lignocellulosic biomass needs to be pretreated before enzymatic hydrolysis, and biocompatible cholinium ionic liquids (ILs) have been demonstrated to be highly efficient for pretreatment. However, the impact of these ILs residues in hydrolysates on downstream biotransformation remains unknown. Therefore, the influence of three typical cholinium ILs on the lipid production by Trichosporon fermentans was first investigated.ResultsThe cell growth of T. fermentans was stimulated in the presence of cholinium lysine ([Ch][Lys]) and cholinium serine ([Ch][Ser]), while the lipid accumulation was inhibited by [Ch][Lys]) and [Ch][Ser]. Both cell growth and lipid accumulation of T. fermentans were inhibited in the presence of cholinium acetate ([Ch][OAc]). Despite the reduction in lipid content, the lipid production by T. fermentans was improved in the presence of low concentrations of [Ch][Lys] (≤30 mM) and [Ch][Ser] (≤20 mM) due to the remarkable increase of biomass. It was found that cholinium cation had minor influence on lipid production. However, the anions of [Ch][Lys] and [Ch][Ser] could be assimilated as nitrogen source by T. fermentans and the reduced C/N ratio accounts for the inhibition of lipid accumulation, which could be alleviated by improving C/N ratio of medium. In addition, the anion of [Ch][OAc] could be metabolized by T. fermentans, leading to a rapid alkaline-pH shift and strong inhibition of lipid production. And this inhibitory effect on lipid production could be significantly reduced by controlling culture pH.ConclusionsThe anions of [Ch][Lys], [Ch][Ser] and [Ch][OAc] play an important role in affecting the cell growth and lipid accumulation of T. fermentans, and the inhibition of these three ILs on lipid production can be alleviated by careful fermentation condition control. Hence, T. fermentans is a promising strain for microbial lipid production from cholinium ILs-pretreated lignocellulosic hydrolysates.

Effects of Acetic Acid and pH on the Growth and Lipid Accumulation of the Oleaginous Yeast Trichosporon fermentans

Acetic acid, one major inhibitor released during the hydrolysis of lignocellulosic biomass, can be utilized by the oleaginous yeast Trichosporon fermentans without glucose repression. The effect of acetic acid on the cell growth and lipid accumulation of T. fermentans under controlled pH conditions was investigated in a 5-L fermentor. Undissociated acetic acid with concentrations of 0.026, 0.052, and 0.096 g L-1 in media contributed to approximately 12-, 24-, and 48-h lag phases, respectively, indicating that undissociated acetic acid is the inhibitory molecular form. The inhibition of cell growth was correlated with undissociated acetic acid concentration. However, acetic acid had little influence on the lipid accumulation of T. fermentans at different pH conditions. The specific glucose consumption rate decreased with increasing acetic acid concentration, but the impact of acetic acid on the specific xylose consumption rate was not pronounced. In addition, the variation of pH and acetic acid concentration had no significant influence on the fatty acid composition of the lipids. Acetic acid showed more severe inhibition under low pH conditions. The reduction of intracellular pH partly explains this inhibitory effect.

Microbial lipid production from pectin-derived carbohydrates by oleaginous yeasts

Pectin-rich biomass is relatively less studied as feedstock for the production of biofuel and chemicals, partially because the major compositional carbohydrates galacturonate and arabinose are generally disfavored substrates for microorganisms. To explore the capability of microbial lipid production from pectic biomass, 10 oleaginous yeasts were evaluated by using galacturonate as sole carbon sources. Three strains belonging to Trichosporon cutaneum, Trichosporon fermentans and Cryptococcus curvatus were found to effectively convert galacturonate into lipid with lipid yields up to 0.12g/g. Slightly higher lipid yields were also obtained on beet pulp hydrolysates, and cellular lipid contents were higher than 40.0% except for the T. fermentans strain. All of these lipid samples had long chain fatty acid compositional profiles similar to those of vegetable oils. The results demonstrate the potential of lipid production from pectic biomass, which is of great significance in terms of integrating wastes management and biofuel production.

Kinetics and Mechanism Analysis on Microbial Oil Production by Trichosporon fermentans in Rice Straw Hydrolysate

To give an insight into the kinetics of microbial oil fermentation with lignocellulosic hydrolysate as substrate, lipid production by Trichosporon fermentans in rice straw hydrolysate was investigated in a 5 L fermentor. For comparison, fermentation in its simulated medium was also performed to evaluate the effect of inhibitors present in the rice straw hydrolysate on the cell growth and lipid accumulation of T. fermentans. The optimum fermentation time, maximum biomass, and lipid content of T. fermentans in the rice straw hydrolysate were 10.5 days, 28.6 g/L, and 43.9%, respectively, while the corresponding values in the simulated medium were 8.5 days, 27.0 g/L, and 65.0%, respectively, indicating that the inhibitors in the rice straw hydrolysate did show some inhibition on the cell growth and lipid accumulation of T. fermentans. Kinetic models of lipid fermentation with T. fermentans showed the maximum specific growth rate and the correlation coefficient of lipid synthesis to cell growth in the rice straw hydrolysate were 0.40 and 0.51, respectively, which are much lower than those in the simulated medium (0.58 and 0.73). To better understand the influential mechanism of inhibitors in the rice straw hydrolysate on the growth and lipid accumulation of T. fermentans, the physiological and biochemical changes of cells in the fermentation were further investigated. The reduced activities of adenosine triphosphate (ATP) citrate lyase, malic enzyme, and xylose reductase, and the elongation of cells at the beginning of fermentation, partly account for the inhibitory effect of inhibitors in the rice straw hydrolysate.