Preparation of levoglucosan by pyrolysis of cellulose and its citric acid fermentation

Citric Acid: Properties, Microbial Production, and Applications in Industries

Citric acid finds broad applications in various industrial sectors, such as the pharmaceutical, food, chemical, and cosmetic industries. The bioproduction of citric acid uses various microorganisms, but the most commonly employed ones are filamentous fungi such as Aspergillus niger and yeast Yarrowia lipolytica. This article presents a literature review on the properties of citric acid, the microorganisms and substrates used, different fermentation techniques, its industrial utilization, and the global citric acid market. This review emphasizes that there is still much to explore, both in terms of production process techniques and emerging new applications of citric acid.

Bioupgrading of the aqueous phase of pyrolysis oil from lignocellulosic biomass: a platform for renewable chemicals and fuels from the whole fraction of biomass

Pyrolysis, a thermal decomposition without oxygen, is a promising technology for transportable liquids from whole fractions of lignocellulosic biomass. However, due to the hydrophilic products of pyrolysis, the liquid oils have undesirable physicochemical characteristics, thus requiring an additional upgrading process. Biological upgrading methods could address the drawbacks of pyrolysis by utilizing various hydrophilic compounds as carbon sources under mild conditions with low carbon footprints. Versatile chemicals, such as lipids, ethanol, and organic acids, could be produced through microbial assimilation of anhydrous sugars, organic acids, aldehydes, and phenolics in the hydrophilic fractions. The presence of various toxic compounds and the complex composition of the aqueous phase are the main challenges. In this review, the potential of bioconversion routes for upgrading the aqueous phase of pyrolysis oil is investigated with critical challenges and perspectives.

Metal vs. Metal-Free Catalysts for Oxidation of 5-Hydroxymethylfurfural and Levoglucosenone to Biosourced Chemicals

Lignocellulosic feedstocks, such as forestry biomass and agricultural crop residues, can be utilized to generate biofuels and biochemicals. Converting these organic waste materials into biochemicals is widely regarded as a remedial approach to develop a sustainable, clean, and green energy source. Nevertheless, are these methods sustainable and clean? Prior studies have shown that most such conversions use metals - including heavy metals or noble metals - as catalysts. In addition to the fact that many metals (e. g., aluminum, cobalt, titanium, platinum) have been listed as critical minerals, these methods suffer from high cost, deactivation, and leakage problems and the release of toxic wastes. This Review summarizes catalytic methods using metal and metal-free catalysts for the oxidation of the platform molecules 5-hydroxymethylfurfural and levoglucosenone and demonstrates the potential and effectiveness of metal-free catalysts.

Fast pyrolysis as a tool for obtaining levoglucosan after pretreatment of biomass with niobium catalysts

Levoglucosan (LGA) is a promising chemical platform derived from the pyrolysis of biomass that offers access to a variety of value-added products. We report an efficient route to produce LGA via the pretreatment of biomass with niobium compounds (oxalate, chloride and oxide) followed by fast pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC-MS) at temperatures of 350-600 °C. Catalytic pretreatment reduces the quantity of lignin in the biomass, concentrates the cellulose and enhance LGA formation during fast pyrolysis. The pretreatment also removes alkaline metals, preventing competitive side reactions. The effect of several parameters such as catalyst weight, time, temperature, and solvent, with the optimal pretreatment conditions determined to be 3 (wt.%) niobium oxalate for 1 h at 23 °C in water. Pretreatment increased the LGA yields by 6.40-fold for sugarcane bagasse, 4.15-fold for elephant grass, 4.13-fold for rice husk, 2.86-fold for coffee husk, and 1.86-fold for coconut husk as compared to the raw biomasses. These results indicate that biomass pretreatment using niobium derivates prior fast pyrolysis can be a promising technique for biomass thermochemical conversion in LGA and others important pyrolytic products.

Effect of acid additives on sugarcane bagasse pyrolysis: Production of high yields of sugars

The aim of this work was to improve sugarcane bagasse thermochemical conversion to pyrolytic sugars production, particularly to levoglucosan. The experiments were carried out evaluating the effect of acid washing with HNO₃ (0.1wt.%) followed by H₂SO₄ addition (0.1, 0.2 and 0.3wt.%) at pyrolysis temperatures of 350, 400, 450, 500, 550 and 600°C was studied by Py-GC/MS. The experimental results showed that HNO₃ washing, followed by H₂SO₄ concentration of 0.2wt.% at 350°C resulted in an increase in levoglucosan yield between 5 and 7 times the yield obtained when the raw bagasse was processed. Thus, these results are very attractive to improve pyrolytic sugars production in sugarcane bagasse by previously acid treatment to pyrolysis technology.

Evaluation of Pyrolysis Oil as Carbon Source for Fungal Fermentation

Pyrolysis oil, a complex mixture of several organic compounds, produced during flash pyrolysis of organic lignocellulosic material was evaluated for its suitability as alternative carbon source for fungal growth and fermentation processes. Therefore several fungi from all phyla were screened for their tolerance toward pyrolysis oil. Additionally Aspergillus oryzae and Rhizopus delemar, both established organic acid producers, were chosen as model organisms to investigate the suitability of pyrolysis oil as carbon source in fungal production processes. It was observed that A. oryzae tolerates pyrolysis oil concentrations between 1 and 2% depending on growth phase or stationary production phase, respectively. To investigate possible reasons for the low tolerance level, eleven substances from pyrolysis oil including aldehydes, organic acids, small organic compounds and phenolic substances were selected and maximum concentrations still allowing growth and organic acid production were determined. Furthermore, effects of substances to malic acid production were analyzed and compounds were categorized regarding their properties in three groups of toxicity. To validate the results, further tests were also performed with R. delemar. For the first time it could be shown that small amounts of phenolic substances are beneficial for organic acid production and A. oryzae might be able to degrade isoeugenol. Regarding pyrolysis oil toxicity, 2-cyclopenten-1-on was identified as the most toxic compound for filamentous fungi; a substance never described for anti-fungal or any other toxic properties before and possibly responsible for the low fungal tolerance levels toward pyrolysis oil.

Engineering levoglucosan metabolic pathway in Rhodococcus jostii RHA1 for lipid production

Oleaginous strains of Rhodococcus including R. jostii RHA1 have attracted considerable attention due to their ability to accumulate triacylglycerols (TAGs), robust growth properties and genetic tractability. In this study, a novel metabolic pathway was introduced into R. jostii by heterogenous expression of the well-characterized gene, lgk encoding levoglucosan kinase from Lipomyces starkeyi YZ-215. This enables the recombinant R. jostii RHA1 to produce TAGs from the anhydrous sugar, levoglucosan, which can be generated efficiently as the major molecule from the pyrolysis of cellulose. The recombinant R. jostii RHA1 could grow on levoglucosan as the sole carbon source, and the consumption rate of levoglucosan was determined. Furthermore, expression of one more copy of lgk increased the enzymatic activity of LGK in the recombinant. However, the growth performance of the recombinant bearing two copies of lgk on levoglucosan was not improved. Although expression of lgk in the recombinants was not repressed by the glucose present in the media, glucose in the sugar mixture still affected consumption of levoglucosan. Under nitrogen limiting conditions, lipid produced from levoglucosan by the recombinant bearing lgk was up to 43.54 % of the cell dry weight, which was comparable to the content of lipid accumulated from glucose. This work demonstrated the technical feasibility of producing lipid from levoglucosan, an anhydrosugar derived from the pyrolysis of lignocellulosic materials, by the genetically modified rhodococci strains.

Bioconversion of anhydrosugars: Emerging concepts and strategies

As methods for the use of anhydrosugars in chemical and biofuel production continue to develop, our collective knowledge of anhydrosugar processing enzymes continues to improve, including their mechanistic details, structural dynamics and modes of substrate binding. Of particular interest, anhydrosugar kinases, such as levoglucosan kinase (LGK) and 1,6-anhydro-N-acetylmuramic acid kinase (AnmK), utilize an unusual mechanism whereby the sugar substrate is both cleaved and phosphorylated. The phosphorylated sugar can then be routed to other metabolic pathways, thereby allowing its further bioconversion. Advanced engineering efforts to improve the catalytic efficiency and stability of LGK have been steadily progressing. Other enzymes that cleave the glycosidic bond of disaccharide sugars containing an anhydrosugar component are also being identified and characterized. Accordingly, the potential future use of these enzymes in large-scale production strategies is becoming increasingly viable. Here, a mini-review of the observed characteristics of anhydrosugar processing enzymes is presented along with recent developments in the bioconversion of these sugars. © 2016 IUBMB Life 68(9):700-708, 2016.

Identification of Soil Microbes Capable of Utilizing Cellobiosan

Approximately 100 million tons of anhydrosugars, such as levoglucosan and cellobiosan, are produced through biomass burning every year. These sugars are also produced through fast pyrolysis, the controlled thermal depolymerization of biomass. While the microbial pathways associated with levoglucosan utilization have been characterized, there is little known about cellobiosan utilization. Here we describe the isolation and characterization of six cellobiosan-utilizing microbes from soil samples. Each of these organisms is capable of using both cellobiosan and levoglucosan as sole carbon source, though both minimal and rich media cellobiosan supported significantly higher biomass production than levoglucosan. Ribosomal sequencing was used to identify the closest reported match for these organisms: Sphingobacterium multivorum, Acinetobacter oleivorans JC3-1, Enterobacter sp SJZ-6, and Microbacterium sps FXJ8.207 and 203 and a fungal species Cryptococcus sp. The commercially-acquired Enterobacter cloacae DSM 16657 showed growth on levoglucosan and cellobiosan, supporting our isolate identification. Analysis of an existing database of 16S rRNA amplicons from Iowa soil samples confirmed the representation of our five bacterial isolates and four previously-reported levoglucosan-utilizing bacterial isolates in other soil samples and provided insight into their population distributions. Phylogenetic analysis of the 16S rRNA and 18S rRNA of strains previously reported to utilize levoglucosan and our newfound isolates showed that the organisms isolated in this study are distinct from previously described anhydrosugar-utilizing microbial species.

Mathematical modeling of the fermentation of acid-hydrolyzed pyrolytic sugars to ethanol by the engineered strain Escherichia coli ACCC 11177

Pyrolysate from waste cotton was acid hydrolyzed and detoxified to yield pyrolytic sugars, which were fermented to ethanol by the strain Escherichia coli ACCC 11177. Mathematical models based on the fermentation data were also constructed. Pyrolysate containing an initial levoglucosan concentration of 146.34 g/L gave a glucose yield of 150 % after hydrolysis, suggesting that other compounds were hydrolyzed to glucose as well. Ethyl acetate-based extraction of bacterial growth inhibitors with an ethyl acetate/hydrolysate ratio of 1:0.5 enabled hydrolysate fermentation by E. coli ACCC 11177, without a standard absorption treatment. Batch processing in a fermenter exhibited a maximum ethanol yield and productivity of 0.41 g/g and 0.93 g/L·h(-1), respectively. The cell growth rate (r x ) was consistent with a logistic equation [Formula: see text], which was determined as a function of cell growth (X). Glucose consumption rate (r s ) and ethanol formation rate (r p ) were accurately validated by the equations [Formula: see text] and [Formula: see text], respectively. Together, our results suggest that combining mathematical models with fermenter fermentation processes can enable optimized ethanol production from cellulosic pyrolysate with E. coli. Similar approaches may facilitate the production of other commercially important organic substances.

Biomass pyrolysis liquid to citric acid via 2-step bioconversion

Background

The use of fossil carbon sources for fuels and petrochemicals has serious impacts on our environment and is unable to meet the demand in the future. A promising and sustainable alternative is to substitute fossil carbon sources with microbial cell factories converting lignocellulosic biomass into desirable value added products. However, such bioprocesses require tolerance to inhibitory compounds generated during pretreatment of biomass. In this study, the process of sequential two-step bio-conversion of biomass pyrolysis liquid containing levoglucosan (LG) to citric acid without chemical detoxification has been explored, which can greatly improve the utilization efficiency of lignocellulosic biomass.

Results

The sequential two-step bio-conversion of corn stover pyrolysis liquid to citric acid has been established. The first step conversion by Phanerochaete chrysosporium (P. chrysosporium) is desirable to decrease the content of other compounds except levoglucosan as a pretreatment for the second conversion. The remaining levoglucosan in solution was further converted into citric acid by Aspergillus niger (A. niger) CBX-209. Thus the conversion of cellulose to citric acid is completed by both pyrolysis and bio-conversion technology. Under experimental conditions, levoglucosan yield is 12% based on the feedstock and the citric acid yield can reach 82.1% based on the levoglucosan content in the pyrolysis liquid (namely 82.1 g of citric acid per 100 g of levoglucosan).

Conclusion

The study shows that P. chrysosporium and A. niger have the potential to be used as production platforms for value-added products from pyrolyzed lignocellulosic biomass. Selected P. chrysosporium is able to decrease the content of other compounds except levoglucosan and levoglucosan can be further converted into citric acid in the residual liquids by A. niger. Thus the conversion of cellulose to citric acid is completed by both pyrolysis and bio-conversion technology.

Fermentation of levoglucosan with oleaginous yeasts for lipid production

This paper reports the production of lipids from non-hydrolyzed levoglucosan (LG) by oleaginous yeasts Rhodosporidium toruloides and Rhodotorula glutinis. Enzyme activity tests of LG kinases from both yeasts indicated that the phosphorylation pathway of LG to glucose-6-phosphate existed. The highest enzyme activity obtained for R. glutinis was 0.22 U/mg of protein. The highest cell mass and lipid production by R. glutinis were 6.8 and 2.7 g/L, respectively from pure LG, and 3.3 and 0.78 g/L from a pyrolytic LG aqueous phase detoxified by ethyl acetate extraction, rotary evaporation and activated carbon. This corresponded to a lipid yield of 13.5 wt.% for pure LG and only 3.9 wt.% for LG in pyrolysis oil.

Hybrid thermochemical processing: fermentation of pyrolysis-derived bio-oil

Thermochemical processing of biomass by fast pyrolysis provides a nonenzymatic route for depolymerization of biomass into sugars that can be used for the biological production of fuels and chemicals. Fermentative utilization of this bio-oil faces two formidable challenges. First is the fact that most bio-oil-associated sugars are present in the anhydrous form. Metabolic engineering has enabled utilization of the main anhydrosugar, levoglucosan, in workhorse biocatalysts. The second challenge is the fact that bio-oil is rich in microbial inhibitors. Collection of bio-oil in distinct fractions, detoxification of bio-oil prior to fermentation, and increased robustness of the biocatalyst have all proven effective methods for addressing this inhibition.

Molecular basis of 1,6-anhydro bond cleavage and phosphoryl transfer by Pseudomonas aeruginosa 1,6-anhydro-N-acetylmuramic acid kinase

Anhydro-N-acetylmuramic acid kinase (AnmK) catalyzes the ATP-dependent conversion of the Gram-negative peptidoglycan (PG) recycling intermediate 1,6-anhydro-N-acetylmuramic acid (anhMurNAc) to N-acetylmuramic acid-6-phosphate (MurNAc-6-P). Here we present crystal structures of Pseudomonas aeruginosa AnmK in complex with its natural substrate, anhMurNAc, and a product of the reaction, ADP. AnmK is homodimeric, with each subunit comprised of two subdomains that are separated by a deep active site cleft, which bears similarity to the ATPase core of proteins belonging to the hexokinase-hsp70-actin superfamily of proteins. The conversion of anhMurNAc to MurNAc-6-P involves both cleavage of the 1,6-anhydro ring of anhMurNAc along with addition of a phosphoryl group to O6 of the sugar, and thus represents an unusual enzymatic mechanism involving the formal addition of H3PO4 to anhMurNAc. The structural complexes and NMR analysis of the reaction suggest that a water molecule, activated by Asp-182, attacks the anomeric carbon of anhMurNAc, aiding cleavage of the 1,6-anhydro bond and facilitating the capture of the γ phosphate of ATP by O6 via an in-line phosphoryl transfer. AnmK is active only against anhMurNAc and not the metabolically related 1,6-anhydro-N-acetylmuramyl peptides, suggesting that the cytosolic N-acetyl-anhydromuramyl-l-alanine amidase AmpD must first remove the stem peptide from these PG muropeptide catabolites before anhMurNAc can be acted upon by AnmK. Our studies provide the foundation for a mechanistic model for the dual activities of AnmK as a hydrolase and a kinase of an unusual heterocyclic monosaccharide.

Catalytic fast pyrolysis of cellulose to prepare levoglucosenone using sulfated zirconia

Sulfated zirconia was employed as catalyst for fast pyrolysis of cellulose to prepare levoglucosenone (LGO), a very important anhydrosugar for organic synthesis. The yield and the selectivity of LGO were studied in a fixed-bed reactor at different temperatures and cellulose/catalyst mass ratios. The experiments of catalyst recycling were also carried out. The results displayed that from 290 to 400 °C, the liquid and solid accounted for more than 95 wt % of products, and the higher temperature led to more liquid and less solid products. The introduction of SO₄²⁻/ZrO₂ could promote cellulose conversion and LGO production. The temperature had a similar effect on the yield and selectivity of LGO at different cellulose/catalyst mass ratios. The maximum yield was obtained at 335 °C. Although the structure of the parent ZrO₂ was retained after recycles, which was confirmed by X-ray diffraction and N₂ adsorption-desorption measurements, the activity of SO₄²⁻/ZrO₂ could only be partially recovered by simply calcination. The catalytic activity decrease could be mainly attributed to SO₄²⁻ leaching, and the activity could be restored by further impregnation of H₂SO₄.

The preparation of high-grade bio-oils through the controlled, low temperature microwave activation of wheat straw

The low temperature microwave activation of biomass has been investigated as a novel, energy efficient route to bio-oils. The properties of the bio-oil produced were considered in terms of fuel suitability. Water content, elemental composition and calorific value have all been found to be comparable to and in many cases better than conventional pyrolysis oils. Compositional analysis shows further differences with conventional pyrolysis oils including simpler chemical mixtures, which have potential as fuel and chemical intermediates. The use of simple additives, e.g. HCl, H(2)SO(4) and NH(3), affects the process product distribution, along with changes in the chemical composition of the oils. Clearly the use of our low temperature technology gives significant advantages in terms of preparing a product that is much closer to that which is required for transport fuel applications.

Catalytic pyrolysis of cellulose with sulfated metal oxides: a promising method for obtaining high yield of light furan compounds

Pyrolysis-gas chromatography/mass-spectrometry (Py-GC/MS) was employed to achieve fast pyrolysis of cellulose and on-line analysis of the pyrolysis vapors. Three sulfated metal oxides (SO(4)(2-)/TiO(2), SO(4)(2-)/ZrO(2) and SO(4)(2-)/SnO(2)) were prepared and used for catalytic cracking of the pyrolysis vapors. The distribution of the pyrolytic products was significantly altered by the catalysts. Those important primary pyrolytic products, such as levoglucosan and hydroxyacetaldehyde, were significantly decreased or even completely eliminated. Meanwhile, the catalysis increased three light furan compounds (5-methyl furfural, furfural and furan) greatly. In regard to the selectivity of the three catalysts, the SO(4)(2-)/SnO(2) was the most effective catalyst for obtaining 5-methyl furfural, while the SO(4)(2-)/TiO(2) favored the formation of furfural and the SO(4)(2-)/ZrO(2) favored the formation of furan.

Synthesis of pentasaccharide and heptasaccharide derivatives and their effects on plant growth

Two oligosaccharide derivatives, beta-D-Glcp-(1-6)-beta-D-Glcp-(1-6)-beta-D-Glcp-(1-6)-beta-D-Glcp-(1-4)-alpha-D-ManpOMe (1) and beta-D-Glcp-(1-6)-beta-D-Glcp-(1-6)-beta-D-Glcp-(1-6)-beta-D-Glcp-(1-6)-beta-D-Glcp-(1-6)-beta-D-Glcp-(1-4)-alpha-D-ManpOMe (2), have been synthesized efficiently using a convergent glycosylation strategy of 2 + 3 and 2 + 5. 1,6-Anhydro-beta-D-glucopyranose, which was prepared from cotton pyrolysis, was applied as a key synthon in the synthesis, significantly simplifying the preparation. The bioassay suggested that these two oligosaccharides can both stimulate the growth of maize cultured in liquid medium at a concentration of 3 ppm.

Ethanol fermentation from biomass resources: current state and prospects

In recent years, growing attention has been devoted to the conversion of biomass into fuel ethanol, considered the cleanest liquid fuel alternative to fossil fuels. Significant advances have been made towards the technology of ethanol fermentation. This review provides practical examples and gives a broad overview of the current status of ethanol fermentation including biomass resources, microorganisms, and technology. Also, the promising prospects of ethanol fermentation are especially introduced. The prospects included are fermentation technology converting xylose to ethanol, cellulase enzyme utilized in the hydrolysis of lignocellulosic materials, immobilization of the microorganism in large systems, simultaneous saccharification and fermentation, and sugar conversion into ethanol.

Screening and identification of the levoglucosan kinase gene (lgk) fromAspergillus nigerby LC-ESI-MS/MS and RT-PCR

A protein of 75,000 Daltons with levoglucosan kinase activity was purified from Aspergillus niger. After in-gel digestion by trypsin, a 14-mer peptide was sequenced and analyzed by LC-ESI-MS/MS. Using a primer derived from the 14-mer peptide in combination with Oligo-(dT)18, a cDNA fragment was obtained by RT-PCR. A search of the GenBank database indicated that the protein had not been identified before. A similar protein named hypothetical protein FG07802.1 (EAA77996.1) was found to exist in Gibberella zeae by Blastx search. Using a primer derived from the protein, a cDNA fragment of second RT-PCR was cloned into plasmid pAJ401, which was transformed to Saccharomyces cerevisiae H158 and expressed. Two positive levoglucosan assimilating recombinants were selected. The lgk gene was screened and identified.

Ethanol fermentation of acid-hydrolyzed cellulosic pyrolysate with Saccharomyces cerevisiae

The acid hydrolysis of cellulosic pyrolysate to glucose and its fermentation to ethanol were investigated. The maximum glucose yield (17.4%) was obtained by the hydrolysis with 0.2 mol sulfuric acid per liter pyrolysate using autoclaving at 121 degrees C for 20 min. The fermentation by Saccharomyces cerevisiae of a hydrolysate medium containing 31.6 g/l glucose gave 14.2 g/l ethanol in 24 h, whereas the fermentation of the medium containing 31.6 g/l pure glucose gave 13.7 g/l ethanol in 18 h. The results showed that the acid-hydrolyzed pyrolysate could be used for ethanol production. Different nitrogen sources were evaluated and the best ethanol concentration (15.1 g/l) was achieved by single urea. S. cerevisiae (R) was obtained by adaptation of S. cerevisiae to the hydrolysate medium for 12 times, and 40.2 g/l ethanol was produced by S. cerevisiae (R) in the fermentation with the hydrolysate medium containing 95.8 g/l glucose, which was about 47% increase in ethanol production compared to its parent strain.

Identification, characterization of levoglucosan kinase, and cloning and expression of levoglucosan kinase cDNA from Aspergillus niger CBX-209 in Escherichia coli

The first enzyme responsible for assimilating levoglucosan in Aspergillus niger CBX-209 was corroborated to be levoglucosan kinase that catalyzes the transfer of a phosphate group from ATP to levoglucosan to yield a glucose 6-phosphate in the presence of magnesium ion and ATP by FAB-mass spectrometric method combined with previous observations from HPLC and enzymological experiments. Levoglucosan kinase was purified to apparent homogeneity by using a combination of seven purification steps. SDS-PAGE revealed a single protein band of 56 KDa. It is a monomeric enzyme and maximal enzyme activity was measured at pH 9.3 and 30 degrees C. This kinase is stable below 20 degrees C at a quite broad pHs ranging from 6 to 10 and levoglucosan could protect the enzyme from thermal inactivation. Exclusive substrate specificity for levoglucosan suggested that not only the structure of the intramolecular glucosidic linkage but also the configuration of the pyranose frame would be specific for recognition by levoglucosan kinase. The K(m) values of this enzyme were 71.2mM for levoglucosan and 0.25 mM for ATP, determined by double reciprocal plottings and ADP inhibited on the enzyme activity competitively with a Ki value of 0.20mM. A cDNA library from A. niger was constructed in Escherichia coli DH5alpha. The library was screened for levoglucosan kinase gene on NCE selective medium and three positive recombinants were selected after a five day culture. Detection of activities of levoglucosan kinase in the cell extracts indicated that levoglucosan kinase gene (lgk) was expressed by the recombinant strain of E. coli DH5alpha.