Effect of physicochemical pre-treatment of rice straw on its digestibility by <Emphasis Type="Italic">Clostridium cellulolyticum</Emphasis>

Rice straw (RS) may serve as a low-cost biomass for the production of biofuels and biochemicals, but its native structure is resistant to enzymatic and microbial deconstruction. Therefore, an efficient pre-treatment method is required to modify crystalline cellulose to a more reactive amorphous form. This work investigated pre-treatments of rice straw involving size reduction (S) followed by either sodium hydroxide (NaOH) or diluted sulfuric acid (H₂SO₄) and liquid hot water (LHW). The shrinkage of the vascular bundles in the rice straw structure pre-treated with NaOH–LHW–S was higher than that with LHW–S and H₂SO₄–LHW–S pre-treatments. The highest levels of total fermentative products and residual sugars were obtained at the concentrations of 7.8 ± 0.2 and 2.1 ± 0.3 g/L, respectively, after fermentation by Clostridium cellulolyticum for NaOH–LHW–S pre-treated rice straw at 121 °C for 120 min. Overall, the combined physicochemical pre-treatment of RS led to improved microbial hydrolysis during cellulose degradation at the percentage of 85.5 ± 0.5.     

Characteristics of hydrogen sulfide removal in a carrier-packed biological deodorization system

The relationship between the characteristics of carriers in a carrier-packed biological deodorization (CPBD) reactor and the efficiency of H(2)S removal was studied. From the result of a deodorization experiment using three different carriers (each of which obtained a high level of H(2)S removal), the best carrier was cylindrical and the surface and inside of the carrier had macro pores (about 1mm in diameter). The carrier also had large porosity and surface area. Each of these characteristics, with the exception of the large surface area, corresponded to the characteristics that resulted in a high discharge efficiency of sulfuric acid. A deodorization experiment using two carriers that differed only in size showed that K(G)a was a very important operating parameter of the apparatus. Therefore, the size of the carrier should be as small as possible within certain technical limitations.     

Re-engineering Escherichia coli KJ122 to enhance the utilization of xylose and xylose/glucose mixture for efficient succinate production in mineral salt medium

Applied Microbiology and Biotechnology - Escherichia coli KJ122 was previously engineered to produce high concentration and yield of succinate in mineral salt medium containing glucose and sucrose...     

Production of succinic acid from sucrose and sugarcane molasses by metabolically engineered Escherichia coli

Sucrose-utilizing genes (cscKB and cscA) from Escherichia coli KO11 were cloned and expressed in a metabolically engineered E. coli KJ122 to enhance succinate production from sucrose. KJ122 harboring a recombinant plasmid, pKJSUC, was screened for the efficient sucrose utilization by growth-based selection and adaptation. KJ122-pKJSUC-24T efficiently utilized sucrose in a low-cost medium to produce high succinate concentration with less accumulation of by-products. Succinate concentrations of 51 g/L (productivity equal to 1.05 g/L/h) were produced from sucrose in anaerobic bottles, and concentrations of 47 g/L were produced in 10 L bioreactor within 48 h. Antibiotics had no effect on the succinate production by KJ122-pKJSUC-24T. In addition, succinate concentrations of 62 g/L were produced from sugarcane molasses in anaerobic bottles, and concentrations of 56 g/L in 10 L bioreactor within 72 h. These results demonstrated that KJ122-pKJSUC-24T would be a potential strain for bio-based succinate production from sucrose and sugarcane molasses.     

Effect of biomass concentration on the specific solvent productivity ofClostridium acetobutylicum in chemostat culture

Summary Using a defined medium in chemostat culture, an inverse relationship between the biomass concentration and the specific butanol productivity has been observed. It is suggested that this is due to the cell population not being homogeneous, and that a change in the nutrient balance leads to a cha in the relative proportions of acidogenic, solventogenic and inert cells (spores).     

Effect of phosphate and ammonium ion concentrations on solvent production in defined medium byClostridium acetobutylicum

Summary Experiments have been performed in batch fermentation, using a defined medium, to investigate the effects of phosphate and ammonium ion concentrations on solvent production usingClostridium acetobutylicum. Solvent production occurred under conditions of either ammonium- or phosphate-limitation, but the optimum conditions were observed to be where both of these nutrients were slightly in excess of growth requirements. A greater excess of nutrients caused the fermentation to be acidogenic rather than solventogenic.