Xiaojun Su

Comparison of γ-irradiation with other pretreatments followed with simultaneous saccharification and fermentation on bioconversion of microcrystalline cellulose for bioethanol production.

The effect of γ-irradiation pretreatment was compared with other pretreatment methods including ionic liquids (ILs), 1% HCl, 1% H2SO4, acidic aqueous Ils (AA-ILs), on the bioconversion efficiency of microcrystalline cellulose (MCC) for bioethanol production. The efficiency of MCC pretreatment followed with simultaneous saccharification and fermentation (SSF) was firstly evaluated according to the variations of the irradiation-derived compounds and structure of MCC, as well as yeast growth curve and bioethanol yield. Results showed that the appropriate irradiation dose (891 kGy used in our work) could eliminate the negative effect of toxic irradiation-derived compounds on SSF for ethanol bioconversion with the yield value of 67%. Analyses of SEM, FT-IR, reducing sugar and bioethanol yield showed that the efficiency of pretreatment on MCC was ILs ≈ irradiation pretreatment > AA-ILs pretreatment > 1% HCl pretreatment > 1% H2SO4 pretreatment.

Insights into the effects of γ-irradiation on the microstructure, thermal stability and irradiation-derived degradation components of microcrystalline cellulose (MCC)

It has been demonstrated that radiation pretreatment can cause a significant breakdown of the stubborn cellulose structure, which will increase the accessibility of cellulose and enhance enzyme hydrolysis in bio-fuel processes. In this study, using microcrystalline cellulose (MCC) as a model substrate, the impacts of irradiation dose on the microstructure, thermal stability and irradiated-degradation components of cellulose under 60Co γ-irradiation (0–1400 kGy) was comprehensively investigated. FT-IR, EPR and NMR analyses show that irradiation destroys the glycosidic bond and inter- and intra-molecular hydrogen bond of cellulose, resulting in the generation of reductive carbonyl groups and free radicals. SEM, XRD and GPC analyses confirm that irradiation can damage the crystalline microstructure and surface morphology of MCC, which reduces its degree of polymerization from 183 045 kDa to 4413 kDa. TGA and DGA curves indicate that the activated energy (Ea) and thermal stability of treated MCC decrease with the increasing irradiation dose. Ion chromatography (IC) analysis demonstrates that there exist fermentation sugars such as glucose (10.73 mg g−1), xylose (1.58 mg g−1), arabinose (0.46 mg g−1), fructose (4.31 mg g−1), and cellobiose (1.90 mg g−1) as well as low amounts of glucuronic acid (0.35 mg g−1) and galacturonic acid (1.46 mg g−1) in the irradiation-derived degradation components. Therefore, the findings in this study suggest that γ-irradiation processing is an environment-friendly, promising and effective approach to treat lignocellulose biomass.

Isolation and characterization of a novel 2-methyl-4-chlorophenoxyacetic acid-degrading Enterobacter sp. strain SE08.

A bacterial strain (SE08) capable of utilizing 2-methyl-4-chlorophenoxy acetic acid (MCPA) as the sole carbon and energy source for growth was isolated by continuous enrichment culturing in minimal salt medium (MSM) from a long term MCPA exposed soil. This bacterial strain was identified as Enterobacter sp. based on morphological, physiological and biochemical tests, as well as 16S rRNA sequence analysis. Its ability to degrade MCPA was determined using high performance liquid chromatography. The strain SE08 can tolerate unusually high MCPA concentrations (125-2000mg/L). The influences of culturing factors (initial concentration, pH, and temperature) on the bacterial growth and substrate degradation were studied. The results showed that the optimal MCPA degradation occurred at an MCPA concentration of 500mg/L, 30°C and pH 6.0. Under these conditions, 68.5 percent of MCPA in MSM was degraded by SE08, and the OD600nm reached 0.64 after culturing for 72h. The degradation of MCPA could be enhanced by addition of both carbon and nitrogen sources. At an initial MCPA concentration of 500mg/L, when 5g/L glucose and 2.5g/L yeast extract were added into the MSM media, the MCPA degradation was significantly increased to 83.8 percent, and OD600nm was increased to 1.09 after incubation at 30°C and pH 6.0 for 72h. This is the first study showing that an Enterobacter sp. strain is capable of degrading MCPA, which might provide a new approach for the remediation of MCPA contaminated soil and contribute to the limited knowledge about the function of Enterobacter species.

Ethanol production from xylose by Fusarium oxysporum and the optimization of culture conditions

Abstract Bioethanol is the most commonly used renewable biofuel as an alternative to fossil fuels. Many microbial strains can convert lignocellulosics into bioethanol. However, very few natural strains with a high capability of fermenting pentose sugars and simultaneously utilizing various sugars have been reported. In this study, fermentation of sugar by Fusarium oxysporum G was performed for the production of ethanol to improve the performance of the fermentation process. The influences of pH, substrate concentration, temperature, and rotation speed on ethanol fermentation are investigated. The three significant factors (pH, substrate concentration, and temperature) are further optimized by quadratic orthogonal rotation regression combination design and response surface methodology (RSM). The optimum conditions are pH 4, 40 g/L of xylose, 32 °C, and 110 rpm obtained through single factor experiment design. Finally, it is found that the maximum ethanol production (10.0 g/L) can be achieved after 7 d of fermentation under conditions of pH 3.87, 45.2 g/L of xylose, and 30.4 °C. Glucose is utilized preferentially for the glucose–xylose mixture during the initial fermentation stage, but glucose and xylose are synchronously consumed without preference in the second period. These findings are significant for the potential industrial application of this strain for bioethanol production.