Xue-Fang Chen

Single cell oil production from low-cost substrates: The possibility and potential of its industrialization

Currently, single cell oils (SCO) attract much attention because of their bi-function as a supplier of functional oils and feedstock for biodiesel production. However, high fermentation costs prevent their further application, and the possibility and potential of their industrialization is suspected. Therefore, various low-cost, hydrophilic and hydrophobic substrates were utilized for SCO production. Of these substrates, lignocellulosic biomass, which is the most available and renewable source in nature, might be an ideal raw material for SCO production. Although many reviews on SCO have been published, few have focused on SCO production from low-cost substrates or evaluated the possibility and potential of its industrialization. Therefore, this review mainly presents information on SCO and its production using low-cost substrates and mostly focuses on lignocellulosic biomass. Finally, the possibility and potential of SCO industrialization is evaluated.

Oil production by the yeast Trichosporon dermatis cultured in enzymatic hydrolysates of corncobs

Corncob was hydrolyzed with Trichoderma reesei cellulase and used as substrate for growth by the oleaginous yeast Trichosporon dermatis without detoxification or addition of a nitrogen source or trace elements. A total biomass of 24.4g/L with a lipid content of 40.1% (corresponding to a lipid yield of 9.8g/L), and a high lipid coefficient (lipid yield per mass of sugar, %g/g) of 16.7 could be achieved after cultivation for 7days. Therefore, T. dermatis is a promising strain for microbial oil production from lignocellulosic biomass.

Evaluating the effect of medium composition and fermentation condition on the microbial oil production by Trichosporon cutaneum on corncob acid hydrolysate.

The effect of medium composition and cultural condition on the growth and lipid accumulation of oleaginous yeast Trichosporon cutaneum on corncob acid hydrolysate was systematically investigated. Glucose, xylose, and cellobiose were shown to be promising sugar for lipid production by T. cutaneum. Adding other nitrogen sources into the hydrolysate was not beneficial for the lipid production possibly due to the existence of other nitrogen sources in it. Interestingly, adding MgSO4·7H2O, CuSO4·5H2O, MnSO4·H2O, and KCl (optimal concentration were 0.3, 3.0×10(-3), 3.0×10(-3), and 0.4 g/L, respectively) could stimulate the lipid production by T. cutaneum. Additionally, inoculum concentration, temperature, and initial pH (optimal value were 5%, 28 °C, and 6.0, respectively) showed influence on the lipid production of T. cutaneum. Under the optimum conditions, the biomass (22.9 g/L) had a weak increase (3.6%), while the lipid content (45.4%) and lipid coefficient (22.9%) increased obviously (about 26.5% and 31.6%) compared with the initial conditions.

Engineering Clostridium acetobutylicum for alcohol production.

While Clostridium acetobutylicum has been used for large-scale butanol production (ABE fermentation), its by-product acetone cannot be used as a biofuel. In this study, C. acetobutylicum was engineered for alcohol titers (butanol plus ethanol). The adc gene was inactivated to eliminate acetone production, and glutathione biosynthetic capability was introduced into C. acetobutylicum to improve the strains robustness by expressing Escherichia colis gshAB genes in the adc locus. Acetone production was reduced from 2.64±0.22 g/L to 0.15±0.08 g/L in the engineered strain 824adc::gsh, whereas butanol production was increased from 5.17±0.26 g/L to 8.27±0.27 g/L. To further improve the alcohol titers, the metabolic flux in the alcohol biosynthesis pathways was enhanced. Overlapping PCR was used to generate expression cassette EC, which expresses the hbd, thl, crt, and bcd genes, and the Sol operon was amplified to express the adhE and ctfAB genes. Butanol and alcohol production reached 14.86±0.26 g/L and 18.11±0.66 g/L, respectively, in 824adc::gsh Sol-EC. Furthermore, the butanol and alcohol yields were 0.336 g/g and 0.409 g/g, respectively, in 824adc::gsh Sol-EC. This study provided a combined strategy for enhancing alcohol production in C. acetobutylicum.

Using wastewater after lipid fermentation as substrate for bacterial cellulose production by Gluconacetobacter xylinus

In this study, lipid fermentation wastewater (fermentation broth after separation with yeast biomass) with high Chemical Oxygen Demand (COD) value of 25,591 mg/L was used as substrate for bacterial cellulose (BC) production by Gluconacetobacter xylinus for the first time. After 5 days of fermentation, the highest BC yield (0.659 g/L) was obtained. Both monosaccharide and polysaccharides present in lipid fermentation wastewater could be utilized by G. xylinus simultaneously during fermentation. By this bioconversion, 30.0% of COD could be removed after 10 days of fermentation and the remaining wastewater could be used for further BC fermentation. The crystallinity of BC samples in lipid fermentation wastewater increased gradually during fermentation but overall the environment of lipid fermentation wastewater showed small influence on BC structure by comparison with that in traditional HS medium by using FE-SEM, FTIR, and XRD. By this work, the possibility of using lipid fermentation wastewater containing low value carbohydrate polymer (extracellular polysaccharides) for high value carbohydrate polymer (BC) production was proven.

Bacterial cellulose production from the litchi extract by Gluconacetobacter xylinus

ABSTRACT Although litchi has both nutrient and edible value, the extremely short preservation time limited its further market promotion. To explore processed litchi products with longer preservation time, litchi extract was selected as an alternative feedstock for production of bacterial cellulose (BC). After 2 weeks of static fermentation, 2.53 g/L of the BC membrane was obtained. The trace elements including magnesium (Mg) and sodium (Na) in the litchi extract were partly absorbed in the BC membrane, but no potassium (K) element was detected in it, curiously. Scanning electron microscope (SEM) photographs exhibited an ultrafine network nanostructure for the BC produced in the litchi extract. Analysis of the fourier-transform infrared spectroscopy (FTIR) confirmed the pellicles to be a cellulosic material. Interestingly, X-ray diffraction (XRD) results showed the BC membrane obtained from litchi extract had higher crystallinity of 94.0% than that from HS medium. Overall, the work showed the potential of producing high value-added polymer from litchi resources.

Beneficial Effect of Corncob Acid Hydrolysate on the Lipid Production by Oleaginous Yeast Trichosporon dermatis

In this work, corncob acid hydrolysate and its simulated medium whose sugar composition was the same as the corncob acid hydrolysate were used as fermentation substrate for lipid production by oleaginous yeast Trichosporon dermatis. On the corncob acid hydrolysate, after 7 days of fermentation, the biomass, lipid content, lipid yield, and lipid coefficient of T. dermatis were 17.3 g/L, 40.2%, 7.0 g/L, and 16.5%, respectively. Interestingly, during the lipid fermentation on the corncob acid hydrolysate, glucose, xylose, arabinose, and even acetic acid could be well utilized as carbon sources by T. dermatis. Surprisingly, the lipid yield (7.0 g/L) of T. dermatis on the corncob acid hydrolysate was much higher than that (3.8 g/L) on the simulated medium, in spite of the fact that the lipid coefficient (17.4%) on the simulated medium was a little higher. This phenomenon further showed that lignocellulosic acid hydrolysate was a suitable substrate for lipid fermentation by T. dermatis. This work would help the comprehensive utilization of lignocellulosic biomass for lipid production.

Recent advances and industrial viewpoint for biological treatment of wastewaters by oleaginous microorganisms.

Recently, technology of using oleaginous microorganisms for biological treatment of wastewaters has become one hot topic in biochemical and environmental engineering for its advantages such as easy for operation in basic bioreactor, having potential to produce valuable bio-products, efficient wastewaters treatment in short period, etc. To promote its industrialization, this article provides some comprehensive analysis of this technology such as its advances, issues, and outlook especially from industrial viewpoint. In detail, the types of wastewaters can be treated and the kinds of oleaginous microorganisms used for biological treatment are introduced, the potential of industrial application and issues (relatively low COD removal, low lipid yield, cost of operation, and lack of scale up application) of this technology are presented, and some critical outlook mainly on co-culture method, combination with other treatments, process controlling and adjusting are discussed systematically. By this article, some important information to develop this technology can be obtained.

Enhanced enzymatic hydrolysis and acetone-butanol-ethanol fermentation of sugarcane bagasse by combined diluted acid with oxidate ammonolysis pretreatment.

This study aims to propose a biorefinery pretreatment technology for the bioconversion of sugarcane bagasse (SB) into biofuels and N-fertilizers. Performance of diluted acid (DA), aqueous ammonia (AA), oxidate ammonolysis (OA) and the combined DA with AA or OA were compared in SB pretreatment by enzymatic hydrolysis, structural characterization and acetone-butanol-ethanol (ABE) fermentation. Results indicated that DA-OA pretreatment improves the digestibility of SB by sufficiently hydrolyzing hemicellulose into fermentable monosaccharides and oxidating lignin into soluble N-fertilizer with high nitrogen content (11.25%) and low C/N ratio (3.39). The enzymatic hydrolysates from DA-OA pretreated SB mainly composed of glucose was more suitable for the production of ABE solvents than the enzymatic hydrolysates from OA pretreated SB containing high ratio of xylose. The fermentation of enzymatic hydrolysates from DA-OA pretreated SB produced 12.12g/L ABE in 120h. These results suggested that SB could be utilized efficient, economic, and environmental by DA-OA pretreatment.

Use of elephant grass (Pennisetum purpureum) acid hydrolysate for microbial oil production by Trichosporon cutaneum

ABSTRACT Elephant grass (Pennisetum purpureum) dilute acid hydrolysate contains 34.6 g/L total sugars. The potential of lipid production by oleaginous yeast Trichosporon cutaneum grown on elephant grass acid hydrolysate was investigated for the first time. During the fermentation process on the elephant grass acid hydrolysate, glucose, xylose, and arabinose could be well utilized as carbon sources by T. cutaneum. Interestingly, xylose was almost no use before glucose was consumed completely. This illustrated that simultaneous saccharification of xylose and glucose by T. cutaneum did not occur on elephant grass acid hydrolysate. The highest biomass, lipid content, lipid yield, and lipid coefficient of T. cutaneum were measured after the sixth day of fermentation and were 22.76 g/L, 24.0%, 5.46 g/L, and 16.1%, respectively. Therefore, elephant grass is a promising raw material for microbial oil production by T. cutaneum.