Lian Xiong

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.

Bioconversion of elephant grass (Pennisetum purpureum) acid hydrolysate to bacterial cellulose by Gluconacetobacter xylinus

To evaluate the possibility of elephant grass acid hydrolysate converting into bacterial cellulose (BC) produced by Gluconacetobacter xylinus CH001 and to characterize the morphology and structure of the cellulose produced.

Evaluating the possibility of using acetone-butanol-ethanol (ABE) fermentation wastewater for bacterial cellulose production by Gluconacetobacter xylinus

To reduce the cost of bacterial cellulose (BC) production, the possibility of using acetone‐butanol‐ethanol (ABE) fermentation wastewater with high COD value (18 050 mg l−1) for BC production by Gluconacetobacter xylinus was evaluated. After 7 days of fermentation, the highest BC yield (1·34 g l−1) was obtained. The carbon sources including sugars (glucose and xylose), organic acids (acetic acid and butyric acid) and alcohol compounds (ethanol and butanol) were utilized by G. xylinus simultaneously during fermentation. Although the COD decrease ratio (about 14·7%) was low, the highest BC yield on COD consumption (56·2%, g g−1) was relatively high and the remaining wastewater could be used for further BC fermentation. Besides, the environment of ABE fermentation wastewater showed small influence on the BC structure by comparison with the BC products obtained in traditional HS medium using field emission scanning electron microscope (FE‐SEM), Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD). Overall, ABE fermentation wastewater is one promising substrate for BC production.

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.

Preparation of Esterified Bacterial Cellulose for Improved Mechanical Properties and the Microstructure of Isotactic Polypropylene/Bacterial Cellulose Composites

Bacterial cellulose (BC) has great potential to be used as a new filler to reinforce isotactic polypropylene (iPP) due to its high crystallinity, biodegradability, and efficient mechanical properties. In this study, esterification was used to modify BC, which improved the surface compatibility of the iPP and BC. The results indicated that the cellulose octoate (CO) changed the surface properties from hydrophilic to lipophilic. Compared to the pure iPP, the tensile strength, charpy notched impact strength, and tensile modulus of the iPP/BC composites increased by 9.9%, 7.77%, and 15.64%, respectively. However, the addition of CO reinforced the iPP/CO composites. The tensile strength, charpy notched impact strength, and tensile modulus of the iPP/CO composites increased by 14.23%, 14.08%, and 17.82% compared to the pure iPP. However, the elongation at break of both the composites is decreased. The SEM photographs and particle size distribution of the composites showed improvements when the change of polarity of the BC surface, interface compatibility, and dispersion of iPP improved.

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.