Yota Tsuge

Toward the complete utilization of rice straw: Methane fermentation and lignin recovery by a combinational process involving mechanical milling, supporting material and nanofiltration

Rice straw was mechanically milled using a process consuming 1.9MJ/kg-biomass, and 10g/L of unmilled or milled rice straw was used as the carbon source for methane fermentation in a digester containing carbon fiber textile as the supporting material. Milling increased methane production from 226 to 419mL/L/day at an organic loading rate of 2180mg-dichromate chemical oxygen demand/L/day, corresponding to 260mLCH4/gVS. Storage of the fermentation effluent at room temperature decreased the weight of the milled rice straw residue from 3.81 to 1.00g/L. The supernatant of the effluent was subjected to nanofiltration. The black concentrates deposited on the nanofiltration membranes contained 53.0-57.9% lignin. Solution nuclear magnetic resonance showed that lignin aromatic components such as p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) were retained primarily, and major lignin interunit structures such as the β-O-4-H/G unit were absent. This combinational process will aid the complete utilization of rice straw.

Design of Wall-Destructive but Membrane-Compatible Solvents

We report an extremely biocompatible solvent for plant cell walls based on a polar liquid zwitterion that dissolves cellulose, the most recalcitrant component of the plant cell walls. The polar liquid zwitterion does not affect the viability and activity of Escherichia coli, even at high concentrations. We demonstrate conversion of cell walls to ethanol via a starch-like process, namely successive dissolution, hydrolysis and fermentation in the same reaction pot.

Comparative metabolic state of microflora on the surface of the anode electrode in a microbial fuel cell operated at different pH conditions

The metabolic state of microflora (mixed microbial cultures) in microbial fuel cells (MFCs) is currently unclear. Metabolomic analyses were conducted of microflora growing on the anodic electrodes of MFCs operated at pH 7.0, 5.5, or 4.0 and utilizing starch as the major carbon substrate. A much higher current was produced at pH 7.0 than at pH 5.5 and 4.0, correlating with an increased population ratio of Geobacter species to the total bacteria growing on the electrode. Most intracellular metabolites related to the tricarboxylic acid (TCA) cycle were present at a higher level at pH 7.0 than at pH 5.5 and 4.0, and the levels of metabolites correlated well with the obtained current densities. A high intracellular adenosine triphosphate (ATP)/adenosine diphosphate (ADP) ratio at pH 7.0, compared to at pH 5.5 and 4.0, likewise supported current production. Overall, the metabolomic analyses demonstrated that activation of the TCA cycle and increased ATP generation are critical parameters for electricity generation by microflora.

Application of microalgae hydrolysate as a fermentation medium for microbial production of 2-pyrone 4,6-dicarboxylic acid

Actual biomass of microalgae was tested as a fermentation substrate for microbial production of 2-pyrone 4,6-dicarboxylic acid (PDC). Acid-hydrolyzed green microalgae Chlorella emersonii (algae hydrolysate) was diluted to adjust the glucose concentration to 2xa0g/L and supplemented with the nutrients of Luria-Bertani (LB) medium (tryptone 10xa0g/L and yeast extract 5xa0g/L). When the algae hydrolysate was used as a fermentation source for recombinant Escherichia coli producing PDC, 0.43xa0g/L PDC was produced with a yield of 20.1% (mol PDC/mol glucose), whereas 0.19xa0g/L PDC was produced with a yield of 8.6% when LB medium supplemented with glucose was used. To evaluate the potential of algae hydrolysate alone as a fermentation medium for E.xa0coli growth and PDC production, the nutrients of LB medium were reduced from the algae hydrolysate medium. Interestingly, 0.17xa0g/L PDC was produced even without additional nutrient, which was comparable to the case using pure glucose medium with nutrients of LB medium. When using a high concentration of hydrolysate without additional nutrients, 1.22xa0g/L PDC was produced after a 24-h cultivation with the yield of 16.1%. Overall, C.xa0emersonii has high potential as cost-effective fermentation substrate for the microbial production of PDC.

Lignocellulose nanofibers prepared by ionic liquid pretreatment and subsequent mechanical nanofibrillation of bagasse powder: Application to esterified bagasse/polypropylene composites

In the present study, we examined the efficacy of choline acetate (ChOAc, a cholinium ionic liquid))-assisted pretreatment of bagasse powder for subsequent mechanical nanofibrillation to produce lignocellulose nanofibers. Bagasse sample with ChOAc pretreatment and subsequent nanofibrillation (ChOAc/NF-bagasse) was prepared and compared to untreated control bagasse sample (control bagasse), bagasse sample with nanofibrillation only (NF-bagasse) and with ChOAc pretreatment only (ChOAc-bagasse). The specific surface area was 0.83m2/g, 3.1m2/g, 6.3m2/g, and 32m2/g for the control bagasse, ChOAc-bagasse, NF-bagasse, and the ChOAc/NF-bagasse, respectively. Esterified bagasse/polypropylene composites were prepared using the bagasse samples. ChOAc/NF-bagasse exhibited the best dispersion in the composites. The tensile toughness of the composites was 0.52J/cm3, 0.73J/cm3, 0.92J/cm3, and 1.29J/cm3 for the composites prepared using control bagasse, ChOAc-bagasse, NF-bagasse, and ChOAc/NF-bagasse, respectively. Therefore, ChOAc pretreatment and subsequent nanofibrillation of bagasse powder resulted in enhanced tensile toughness of esterified bagasse/polypropylene composites.

Sucrose purification and repeated ethanol production from sugars remaining in sweet sorghum juice subjected to a membrane separation process

The juice from sweet sorghum cultivar SIL-05 (harvested at physiological maturity) was extracted, and the component sucrose and reducing sugars (such as glucose and fructose) were subjected to a membrane separation process to purify the sucrose for subsequent sugar refining and to obtain a feedstock for repeated bioethanol production. Nanofiltration (NF) of an ultrafiltration (UF) permeate using an NTR-7450 membrane (Nitto Denko Corporation, Osaka, Japan) concentrated the juice and produced a sucrose-rich fraction (143.2xa0gxa0L−1 sucrose, 8.5xa0gxa0L−1 glucose, and 4.5xa0gxa0L−1 fructose). In addition, the above NF permeate was concentrated using an ESNA3 NF membrane to provide concentrated permeated sugars (227.9xa0gxa0L−1) and capture various amino acids in the juice, enabling subsequent ethanol fermentation without the addition of an exogenous nitrogen source. Sequential batch fermentation using the ESNA3 membrane concentrate provided an ethanol titer and theoretical ethanol yield of 102.5–109.5xa0gxa0L−1 and 84.4–89.6%, respectively, throughout the five-cycle batch fermentation by Saccharomyces cerevisiae BY4741. Our results demonstrate that a membrane process using UF and two types of NF membranes has the potential to allow sucrose purification and repeated bioethanol production.

Metabolic engineering of Corynebacterium glutamicum for production of sunscreen shinorine

Abstract Ultraviolet-absorbing chemicals are useful in cosmetics and skin care to prevent UV-induced skin damage. We demonstrate here that heterologous production of shinorine, which shows broad absorption maxima in the UV-A and UV-B region. A shinorine producing Corynebacterium glutamicum strain was constructed by expressing four genes from Actinosynnema mirum DSM 43827, which are responsible for the biosynthesis of shinorine from sedoheptulose-7-phosphate in the pentose phosphate pathway. Deletion of transaldolase encoding gene improved shinorine production by 5.2-fold. Among the other genes in pentose phosphate pathway, overexpression of 6-phosphogluconate dehydrogenase encoding gene further increased shinorine production by 60% (19.1 mg/L). The genetic engineering of the pentose phosphate pathway in C. glutamicum improved shinorine production by 8.3-fold in total, and could be applied to produce the other chemicals derived from sedoheptulose-7-phosphate. Microbial production of sunscreen shinorine.

Dimethyl sulfoxide enhances both the cellulose dissolution ability and biocompatibility of a carboxylate-type liquid zwitterion

The cellulose dissolution ability of a liquid zwitterion, the most biocompatible cellulose solvent, was improved by adding a co-solvent, dimethylsulfoxide. Moreover, the biocompatibility of the liquid zwitterion was also improved by adding dimethylsulfoxide although it is toxic relative to the liquid zwitterion. This mixture is an efficient and extremely biocompatible cellulose solvent.

Enhanced production of d-lactate from mixed sugars in Corynebacterium glutamicum by overexpression of glycolytic genes encoding phosphofructokinase and triosephosphate isomerase

The use of mixed sugars containing glucose and xylose in lignocellulosic biomass is desirable for the microbial production of chemicals and fuels. We investigated the effect of individual or simultaneous overexpression of glycolytic genes on d-lactate production from a mixture of glucose and xylose by a recombinant xylose-assimilating Corynebacterium glutamicum strain. The individual overexpression of genes encoding phosphofructokinase (PFK) and triosephosphate isomerase (TPI) increased d-lactate production rate by 71% and 34%, respectively, with corresponding increases (2.4- and 1.8-fold) in the glucose consumption; however, the amount of xylose consumed not altered. d-Lactate yield was also increased by 5.5%, but only in the strain overexpressing the gene encoding PFK. In the parent strain and the strains overexpressing the genes encoding PFK or TPI, a reduction in d-lactate production occurred at approximately 900xa0mM after 32xa0h. However, the strain that simultaneously overexpressed the genes encoding PFK and TPI continued to produce d-lactate after 32xa0h, with the eventual production of 1326xa0mM after production for 80xa0h in mineral salts medium. Our findings contribute to the cost-effective, large-scale production of d-lactate from mixed sugars.

Changes in the microbial consortium during dark hydrogen fermentation in a bioelectrochemical system increases methane production during a two-stage process

BackgroundBioelectrochemical systems (BESs) are an innovative technology developed to influence conventional anaerobic digestion. We examined the feasibility of applying a BES to dark hydrogen fermentation and its effects on a two-stage fermentation process comprising hydrogen and methane production. The BES used low-cost, low-reactivity carbon sheets as the cathode and anode, and the cathodic potential was controlled at −u20091.0xa0V (vs. Ag/AgCl) with a potentiostat. The operation used 10xa0g/L glucose as the major carbon source.ResultsThe electric current density was low throughout (0.30–0.88xa0A/m2 per electrode corresponding to 0.5–1.5xa0mM/day of hydrogen production) and water electrolysis was prevented. At a hydraulic retention time of 2xa0days with a substrate pH of 6.5, the BES decreased gas production (hydrogen and carbon dioxide contents: 52.1 and 47.1%, respectively), compared to the non-bioelectrochemical system (NBES), although they had similar gas compositions. In addition, a methane fermenter (MF) was applied after the BES, which increased gas production (methane and carbon dioxide contents: 85.1 and 14.9%, respectively) compared to the case when the MF was applied after the NBES. Meta 16S rRNA sequencing revealed that the BES accelerated the growth of Ruminococcus sp. and Veillonellaceae sp. and decreased Clostridium sp. and Thermoanaerobacterium sp., resulting in increased propionate and ethanol generation and decreased butyrate generation; however, unknowingly, acetate generation was increased in the BES.ConclusionsThe altered redox potential in the BES likely transformed the structure of the microbial consortium and metabolic pattern to increase methane production and decrease carbon dioxide production in the two-stage process. This study showed the utility of the BES to act on the microbial consortium, resulting in improved gas production from carbohydrate compounds.