Grace M. Nisola

High yield production of D-xylonic acid from D-xylose using engineered Escherichia coli.

An engineered Escherichia coli was constructed to produce D-xylonic acid, one of the top 30 high-value chemicals identified by US Department of Energy. The native pathway for D-xylose catabolism in E. coli W3110 was blocked by disrupting xylose isomerase (XI) and xylulose kinase (XK) genes. The native pathway for xylonic acid catabolism was also blocked by disrupting two genes both encoding xylonic acid dehydratase (yagE and yjhG). Through the introduction of a D-xylose dehydrogenase from Caulobacter crescentus, a D-xylonic acid producing E. coli was constructed. The recombinant E. coli produced up to 39.2 g L(-1) D-xylonic acid from 40 g L(-1) D-xylose in M9 minimal medium. The average productivity was as high as 1.09 g L(-1) h(-1) and no gluconic acid byproduct was produced. These results suggest that the engineered E. coli has a promising application for the industrial-scale production of D-xylonic acid.

Combination of Entner-Doudoroff pathway with MEP increases isoprene production in engineered Escherichia coli.

Embden-Meyerhof pathway (EMP) in tandem with 2-C-methyl-D-erythritol 4-phosphate pathway (MEP) is commonly used for isoprenoid biosynthesis in E. coli. However, this combination has limitations as EMP generates an imbalanced distribution of pyruvate and glyceraldehyde-3-phosphate (G3P). Herein, four glycolytic pathways—EMP, Entner-Doudoroff Pathway (EDP), Pentose Phosphate Pathway (PPP) and Dahms pathway were tested as MEP feeding modules for isoprene production. Results revealed the highest isoprene production from EDP containing modules, wherein pyruvate and G3P were generated simultaneously; isoprene titer and yield were more than three and six times higher than those of the EMP module, respectively. Additionally, the PPP module that generates G3P prior to pyruvate was significantly more effective than the Dahms pathway, in which pyruvate production precedes G3P. In terms of precursor generation and energy/reducing-equivalent supply, EDP+PPP was found to be the ideal feeding module for MEP. These findings may launch a new direction for the optimization of MEP-dependent isoprenoid biosynthesis pathways.

Dye/water separation through supported liquid membrane extraction

The separation of synthetic dye Rhodamine 6G (R6G) and water was investigated using blended organic liquids in a supported liquid membrane (SLM) extraction system. Liquid membrane (LM) components include octyl alcohol (OcOH) as the dye extractant and a polysiloxane liquid as the stabilizing agent. Initial permeation results revealed the suitability of poly (phenyl methyl) siloxane (PPMS) over poly (octyl methyl) siloxane as the blending agent. The most acceptable condition for dye extraction was determined at feed solution pH congruent with 1, wherein highest distribution coefficient, K(D) (OcOH/H(2)O)=18, was attained. Though permeability decreased at optimal blending condition of 1:1 (w/w) OcOH/PPMS, SLM longevity was exhibited with>98% LM retention after 15 h operation in contrast to pure OcOH SLM system (>60% LM loss). Equilibrium experiments reveal that dye extraction followed Langmuir adsorption principle. The dye transport was elucidated using mass transfer analysis wherein it showed a decrease in overall coefficient (k(o)) at increasing feed concentrations. This was a direct consequence of K(D) decline, which becomes more apparent at higher concentrations when SLM saturation point is approached. At varied hydrodynamic conditions, improved k(o) values were observed up to Re(omega)=10,000 when minimal variation in film resistance is attained. Beyond this condition, k(o) becomes independent from stirring rate effect nonetheless SLM stability is compromised due to shear-induced LM losses.

Silver nanoparticles in a polyether - block - polyamide copolymer towards antimicrobial and antifouling membranes

The potential of hydrophilic polyether-block-polyamide copolymer (PEBA) with antimicrobial silver nanoparticles (nano-Ag) to alleviate membrane biofouling was investigated. PEBA solutions of different nano-Ag content were prepared as dense films and as coating materials for ultrafiltration polysulfone (PSf) membranes. Disc diffusion and surface contact tests revealed the capability of the PEBA/nano-Ag films to inhibit the growth of Escherichia coli (E. coli). Contact angle measurements confirmed the hydrophilisation of the PSf surface after coating with PEBA. Field emission scanning electron microscopy, atomic force microscopy (AFM) and fourier transform infrared spectroscopy were performed to confirm the surface modification of PSf. As a proof-of-concept, filtration performances of bare PSf, PEBA coated-and PEBA/nano-Ag coated PSf were compared using a simulated solution inoculated with E. coli as the feed. The results revealed that the hydrophilisation of PSf by coating with PEBA improved the fouling resistance of the membrane as indicated by the retarded flux reduction rate and higher flux recovery. However, PSf exhibited the highest antifouling resistance when coated with PEBA/nano-Ag. The AFM images of used membranes showed that PEBA/nano-Ag minimized the attachment and growth of E. coli on the membrane which abated irreversible biofouling, a problem that was most severe on bare PSf.

Brown algae hydrolysis in 1-n-butyl-3-methylimidazolium chloride with mineral acid catalyst system.

The amenability of three brown algal species, Sargassum fulvellum, Laminaria japonica and Undaria pinnatifida, to hydrolysis were investigated using the ionic liquid (IL), 1-n-butyl-3-methylimidazolium chloride ([BMIM]Cl). Compositional analyses of the brown algae reveal that sufficient amounts of sugars (15.5-29.4 wt.%) can be recovered. Results from hydrolysis experiments show that careful selection of the type of mineral acid as catalyst and control of acid loading could maximize the recovery of sugars. Optimal reaction time and temperature were determined from the kinetic studies on the sequential reducing sugar (TRS) formation and degradation. Optimal reaction times were determined based on the extent of furfurals formation as TRS degradation products. X-ray diffraction and environmental scanning electron microscopy confirmed the suitability of [BMIM]Cl as solvent for the hydrolysis of the three brown algae. Overall results show the potential of brown algae as renewable energy resources for the production of valuable chemicals and biofuels.

Metal-free mild oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran

The potential of 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl (4-hydroxy-TEMPO radical) as an oxidant with [bis(acetoxy)-iodo]benzene (BAIB) and acetic acid (CH3COOH) as co-oxidants to convert 5-hydroxymethylfurfural (5-HMF) into 2,5-diformylfuran (2,5-DFF) was investigated. The effects of oxidant/acid dosages, choice of appropriate solvent, reaction temperature and time were determined to maximize the 2,5-DFF yield. Optimally, 66% 2,5-DFF yield was achieved in TEMPO/BAIB/CH3COOH system at 30 °C after 45 min in ethyl acetate. The reaction system is environmentally benign (metal-free) and energy efficient (mild at short reaction period). With scarce reports on 2,5-DFF production, the developed system provides an alternative route for a better access and wider application of this important platform chemical.

One-pot synthesis of 2,5-diformylfuran from fructose using a magnetic bi-functional catalyst

A magnetic bi-functional WO3HO-VO(salten)-SiO2@Fe3O4 nanocatalyst was prepared to directly synthesize 2,5-diformylfuran (2,5-DFF) from fructose. The chlorosilylated SiO2@Fe3O4 (Cl-SiO2@Fe3O4) nanoparticles served as the platform for the two functionalities. Tungstic acid was generated via protonation of sodium tungstate, which was directly attached on the platform via nucleophilic –Cl displacement. Meanwhile, oxovanadium was complexed with a salten ligand which was functionalized on the Cl-SiO2@Fe3O4. Characterization results confirmed the successful preparation of the WO3HO-VO(salten)-SiO2@Fe3O4 nanocatalyst. Under the optimal one-pot system, tungstic acid-mediated fructose dehydration afforded 82% 5-hydroxymethylfurfural (5-HMF) in 1 h. Upon co-oxidant H2O2 addition, in situ 5-HMF oxidation by the activated oxoperoxovanadium species produced 71% of 2,5-DFF after 15 h under ambient air. The stability of 5-HMF formation was found critical to 2,5-DFF production. Aside from the catalytic efficiency and process simplicity, the WO3HO-VO(salten)-SiO2@Fe3O4 nanocatalyst was readily retrieved magnetically and re-used multiple times with marginal losses in its activity.

Liquid–liquid extraction of Li+ using mixed ion carrier system at room temperature ionic liquid

AbstractAn environmentally benign technique for the separation and recovery of lithium (Li+) from aqueous streams, containing mixed metal ions was developed via liquid–liquid extraction (LLE). Hydrophobic room temperature ionic liquids (RTIL) were tested as the main extracting solvents. To increase the metal extraction, a proton-ionizable agent bis(2-ethylhexyl) phosphoric acid (DEHPA) was added into the RTIL. To enhance the metal uptake selectivity, three Li+-selective neutral ion carriers such as 6-hydroxy-dibenzo-14-crown-4, dibenzo-14-crown-4, and tri-n-octyl-phosphine (TOPO) were also used and tested as extractant additives. Among the tested RTILs, phosphonium-based CYPHOS IL 109 was the most stable extractant as it exhibited the lowest loss when contacted with water. Addition of proton-ionizable agent DEHPA in CYPHOS IL 109 afforded a high extraction of multivalent cations with negligible recovery of monovalent metals. On the other hand, the addition of neutral ion carrier TOPO in DEHPA/CYPHOS IL 10...

Enhanced yield of ethylene glycol production from d-xylose by pathway optimization in Escherichia coli

The microbial production of renewable ethylene glycol (EG) has been gaining attention recently due to its growing importance in chemical and polymer industries. EG has been successfully produced biosynthetically from d-xylose through several novel pathways. The first report on EG biosynthesis employed the Dahms pathway in Escherichia coli wherein 71% of the theoretical yield was achieved. This report further improved the EG yield by implementing metabolic engineering strategies. First, d-xylonic acid accumulation was reduced by employing a weak promoter which provided a tighter control over Xdh expression. Second, EG yield was further improved by expressing the YjgB, which was identified as the most suitable aldehyde reductase endogenous to E. coli. Finally, cellular growth, d-xylose consumption, and EG yield were further increased by blocking a competing reaction. The final strain (WTXB) was able to reach up to 98% of the theoretical yield (25% higher as compared to the first study), the highest reported value for EG production from d-xylose.

SBA-15 supported ionic liquid phase (SILP) with H2PW12O40− for the hydrolytic catalysis of red macroalgal biomass to sugars

A supported ionic liquid phase (SILP) catalyst for biomass hydrolysis was prepared via immobilization of an acidic ionic liquid (IL) with a phosphotungstic counter-anion H2PW12O40− (HPW) on ordered mesoporous silica (SBA-15). Characterization results from XRD, N2 physisorption, FT-IR, TGA and SEM/TEM image analyses confirmed the successful preparation of the SILP catalyst (SBA-IL–HPW). Meanwhile, its catalytic performance was evaluated in terms of sugar production from the hydrolysis of different biomasses in water. Under optimal hydrolysis conditions, SBA-IL–HPW yielded 73% D-galactose from agarose and 58% D-glucose from cellobiose. Moreover, SBA-IL–HPW effectively hydrolyzed the red macroalgae G. amansii as it afforded 55% total reducing sugar and 38% D-galactose yields. SBA-IL–HPW was easily separated from the hydrolysates after reaction and was re-used five times without significant loss of activity. Overall findings reveal the potential of SBA-IL–HPW as a durable, environmentally benign catalyst for sugar production from renewable resources.