Jijiao Zeng

Feasibility of filamentous fungi for biofuel production using hydrolysate from dilute sulfuric acid pretreatment of wheat straw

BackgroundLipids produced from filamentous fungi show great promise for biofuel production, but a major limiting factor is the high production cost attributed to feedstock. Lignocellulosic biomass is a suitable feedstock for biofuel production due to its abundance and low value. However, very limited study has been performed on lipid production by culturing oleaginous fungi with lignocellulosic materials. Thus, identification of filamentous fungal strains capable of utilizing lignocellulosic hydrolysates for lipid accumulation is critical to improve the process and reduce the production cost.ResultsThe growth performances of eleven filamentous fungi were investigated when cultured on glucose and xylose. Their dry cell weights, lipid contents and fatty acid profiles were determined. Six fungal strains with high lipid contents were selected to culture with the hydrolysate from dilute sulfuric acid pretreatment of wheat straw. The results showed that all the selected fungal strains were able to grow on both detoxified liquid hydrolysate (DLH) and non-detoxified liquid hydrolysate (NDLH). The highest lipid content of 39.4% was obtained by Mortierella isabellina on NDLH. In addition, NDLH with some precipitate could help M. isabellina form pellets with an average diameter of 0.11 mm.ConclusionThis study demonstrated the possibility of fungal lipid production from lignocellulosic biomass. M. isabellina was the best lipid producer grown on lignocellulosic hydrolysates among the tested filamentous fungi, because it could not only accumulate oils with a high content by directly utilizing NDLH to simplify the fermentation process, but also form proper pellets to benefit the downstream harvesting. Considering the yield and cost, fungal lipids from lignocellulosic biomass are promising alternative sources for biodiesel production.

Biological pretreatment of wheat straw by Phanerochaete chrysosporium supplemented with inorganic salts

Inorganic salts and tween 80 are known to induce the lignin degrading peroxidase expression of Phanerochaete chrysosporium in submerged culture. In this study, the wheat straw pretreatment supplemented with inorganic salts (salts group), tween 80 (plus) and no supplementation to the biomass (minus) were examined. Among the solid state fermentation groups, salts group resulted in a substantial degradation of wheat straw within one week, along with the highest lignin loss (25%) and ∼250% higher efficiency for the total sugar release through enzymatic hydrolysis. The results were correlated with pyrolysis GC-MS (Py-GC-MS), thermogravimetric (TG)/differential thermogravimetric (DTG) and X-ray diffraction (XRD). The results suggested that the supplementation of inorganic salts in the solid state fermentation of wheat straw significantly enhances the degradation rate of the biomass by P. chrysosporium which can be exploited as an alternative means to existing pretreatment technologies.

Lignocellulosic biomass as a carbohydrate source for lipid production by Mortierella isabellina

Various carbon sources including monosugars, disaccharides and carboxymethyl-cellulose (CMC) were used for single-cell oil production by the filamentous fungus Mortierella isabellina. In addition, the inhibitory effects of lignocellulose-derived compounds (lignin aldehydes, furan aldehydes and weak acid) were investigated. C6 sugars were preferably used for growth compared to C5 sugars. CMC was not an usable substrate, implying the absence of a cellulase system in this fungus. Lignin derivatives showed the most inhibitory effects, but acetic and formic acids at concentrations of 4 g/L improved lipid production, achieving 6.81 ± 0.07 g/L and 6.66 ± 0.33 g/L respectively, which was twice as high as that of the control. A 16.8% lipid yield from hydrolysate suggested that this fungus could be useful for microbial lipid production.

Microbial lipid production from xylose by Mortierella isabellina.

Culture conditions including nitrogen source and concentration, xylose concentration, and inoculum level were evaluated for the effect on cell growth and lipid production of an oleaginous fungus, Mortierella isabellina, grown on xylose. Yeast extract and ammonium sulfate were found to be the best amongst the organic and inorganic nitrogen sources tested, respectively. Subsequent combination of these two nitrogen sources at a nitrogen ratio of 1:1 further enhanced lipid production. The highest cell biomass 28.8 g L(-1) and lipid 18.5 g L(-1) were obtained on a medium containing 100 g L(-1) xylose and 50.4 mM nitrogen with a spore concentration of 10(8) mL(-1). Specifically, nitrogen concentration and inoculum level were demonstrated to be important for obtaining a high lipid yield on xylose consumed of 0.182 g g(-1). The results suggest that M. isabellina holds great potential to be a candidate for biofuel production from xylose, the second most abundant sugar from lignocellulose.

Increasing manganese peroxidase productivity of Phanerochaete chrysosporium by optimizing carbon sources and supplementing small molecules

Aims:  To overproduce manganese peroxidase (MnP) using Phanerochaete chrysosporium. Effects of carbon sources, agricultural by‐products and small molecules were tested to enhance the MnP productivity.

Improved lipid accumulation by morphology engineering of oleaginous fungus Mortierella isabellina

Oleaginous fungi capable of accumulating a considerable amount of lipids are promising sources for lipid‐based biofuel production. The specific productivities of filamentous fungi in submerged fermentation are often correlated with morphological forms. However, the relationship between morphological development and lipid accumulation is not known. In this study, distinct morphological forms of oleaginous fungus Mortierella isabellina including pellets of different sizes, free dispersed mycelia, and broken hyphal fragments were developed by additions of different concentrations of magnesium silicate microparticles. Different morphological forms led to different levels of lipid accumulation as well as different spatial patterns of lipid distribution within pellets/mycelial aggregates. Significant higher lipid content (0.75 g lipid/g cell biomass) and lipid yield (0.18 g lipid/g glucose consumed) were achieved in free dispersed mycelia than in pellets. Moreover, extracellular metabolite analysis showed that production of undesirable by‐product malate was repressed in free dispersed mycelium form. Unveiling the desired morphological form of M. isabellina for lipid accumulation provided insights into molecular mechanism of lipid biosynthesis linked with morphological development, as well as design and optimization of bioprocess to produce lipid‐based biofuels. Biotechnol. Bioeng. 2014;111: 1758–1766.

DEGRADATION OF NATIVE WHEAT STRAW LIGNIN BY STREPTOMYCES VIRIDOSPORUS T7A

Lignin is one of the major contributing factors toward the recalcitrance of lignocellulosic biomass. Understanding the process of lignin degradation in natural biological processes will provide useful information to develop novel biomass conversion technologies. Functional group changes in the lignin entities during the process may contribute to the cellulose degradation (utilization) by the microorganisms. In this study, compositional and advanced Fourier transform infrared, pyrolysis gas chromatography/mass spectrometry and 13C cross polarization/magic angle spinning nuclear magnetic resonance analysis were performed to explore the mechanism of biodegradation of wheat straw by Streptomyces viridosporus T7A. The results indicated that S. viridosporus T7A removed lignin and hemicelluloses as indicated by the increased carbohydrate/lignin ratio. Significant modification of carbonyl and methoxyl groups in the complex lignin structure was also evident. Most importantly, the quantitative results showed that lignin degradation was featured by deduction of guaiacyl unit. The results provide new insight for understanding lignin degradation by bacteria.

Effects of lignin modification on wheat straw cell wall deconstruction by Phanerochaete chrysosporium

BackgroundA key focus in sustainable biofuel research is to develop cost-effective and energy-saving approaches to increase saccharification of lignocellulosic biomass. Numerous efforts have been made to identify critical issues in cellulose hydrolysis. Aerobic fungal species are an integral part of the carbon cycle, equip the hydrolytic enzyme consortium, and provide a gateway for understanding the systematic degradation of lignin, hemicelluloses, and cellulose. This study attempts to reveal the complex biological degradation process of lignocellulosic biomass by Phanerochaete chrysosporium in order to provide new knowledge for the development of energy-efficient biorefineries.ResultsIn this study, we evaluated the performance of a fungal biodegradation model, Phanerochaete chrysosporium, in wheat straw through comprehensive analysis. We isolated milled straw lignin and cellulase enzyme-treated lignin from fungal-spent wheat straw to determine structural integrity and cellulase absorption isotherms. The results indicated that P. chrysosporium increased the total lignin content in residual biomass and also increased the cellulase adsorption kinetics in the resulting lignin. The binding strength increased from 117.4 mL/g to 208.7 mL/g in milled wood lignin and from 65.3 mL/g to 102.4 mL/g in cellulase enzyme lignin. A detailed structural dissection showed a reduction in the syringyl lignin/guaiacyl lignin ratio and the hydroxycinnamate/lignin ratio as predominant changes in fungi-spent lignin by heteronuclear single quantum coherence spectroscopy.ConclusionP. chrysosporium shows a preference for degradation of phenolic terminals without significantly destroying other lignin components to unzip carbohydrate polymers. This is an important step in fungal growth on wheat straw. The phenolics presumably locate at the terminal region of the lignin moiety and/or link with hemicellulose to form the lignin-carbohydrate complex. Findings may inform the development of a biomass hydrolytic enzyme combination to enhance lignocellulosic biomass hydrolysis and modify the targets in plant cell walls.

New Insights into Microbes in the Midgut of Termite Coptotermes formosanus

Wood-feeding termites have evolved unique capability to effectively digest lignocellulosic material, using it for both energy and nutrition. This ability depends mainly on the mutualistic interaction between symbiotic gut microbiota and the termite itself. This study investigated microorganisms in the midgut of termite Coptotermes formosanus, a segment that has been less studied than the hindgut. Fluorescence in situ hybridization (FISH) was initially used to visualize and identify individual bacteria and archaea in the termite’s midgut. After isolation of microorganisms with six different media, preliminary screening was carried out on plates by testing the capability to oxidize guaiacol as well as decolorize the dye azure B. Two selected strains; B207 and L201 were identified as Streptomyces sp. through 16S rRNA gene sequence analysis. Submerged state fermentation of the strains with softwood biomass as substrate was further performed. The analysis results of attenuated total reflectance fourier transform infrared (ATR-FTIR), chromatography/mass spectrometry (GC/MS) and pyrolysis-gas chromatography/ mass spectrometry (Py-GC/MS) indicated that streptomyces strains B207 and L201 have certain lignocellulose decomposition capabilities.