Selective synthesis of 2-furoic acid and 5-hydroxymethyl-2-furancarboxylic acid from bio-based furans by recombinant Escherichia coli cells

Identification of marker compounds in fermented Benincasa hispida and validation of the method for its analysis

Fermentation is a process that improves health functionality by inducing the production and increase of bioactive compounds. In this study, to standardize the fermentation process for Benincasa hispida, marker compounds that are increased or produced during fermentation were identified based on UPLC-QTOF-MS/MS. Analysis method verification and content analysis were conducted using HPLC-PDA. The marker compounds produced or increased in content were identified as 2-furoic acid, 2,3-dihydroxybenzoic acid, and rubinaphthin A by comparing their retention times, UV and MS spectra, and molecular formulas with those reported in previous studies. In addition, the increase in the content of the marker compounds by fermentation was confirmed, and the analytical method was validated by measuring its specificity, linearity, limit of detection and quantitation, precision, and accuracy. These results suggest that the developed fermentation process, marker compound identification, and verified analysis method can be applied to develop potential functional food ingredients from fermented B. hispida.

Efficient Synthesis of Biobased Furoic Acid from Corncob via Chemoenzymatic Approach

Valorization of lignocellulosic materials into value-added biobased chemicals is attracting increasing attention in the sustainable chemical industry. As an important building block, furoic acid has been commonly utilized to manufacture polymers, flavors, perfumes, bactericides, fungicides, etc. It is generally produced through the selective oxidation of furfural. In this study, we provide the results of the conversion of biomass-based xylose to furoic acid in a chemoenzymatic cascade reaction with the use of a heterogeneous chemocatalyst and a dehydrogenase biocatalyst. For this purpose, NaOH-treated waste shrimp shell was used as a biobased carrier to prepare high activity and thermostability of biobased solid acid catalysts (Sn-DAT-SS) for the dehydration of corncob-valorized xylose into furfural at 170 °C in 30 min. Subsequently, xylose-derived furfural and its derivative furfuryl alcohol were wholly oxidized into furoic acid with whole cells of E. coli HMFOMUT at 30 °C and pH 7.0. The productivity of furoic acid was 0.35 g furoic acid/(g xylan in corncob). This established chemoenzymatic process could be utilized to efficiently valorize biomass into value-added furoic acid.

Whole Cell Biocatalysis of 5-Hydroxymethylfurfural for Sustainable Biorefineries

The implementation of cost-effective and sustainable biorefineries to substitute the petroleum-based economy is dependent on coupling the production of bioenergy with high-value chemicals. For this purpose, the US Department of Energy identified a group of key target compounds to be produced from renewable biomass. Among them, 5-hydroxymethylfurfural (HMF) can be obtained by dehydration of the hexoses present in biomass and is an extremely versatile molecule that can be further converted into a wide range of higher value compounds. HMF derivatives include 2,5-bis(hydroxymethyl)furan (BHMF), 5-hydroxymethyl-furan-2-carboxylic acid (HMFCA), 2,5-diformylfuran (DFF), 5-formyl-2-furancarboxylic acid (FFCA) and 2,5-furandicarboxylic acid (FDCA), all presenting valuable applications, in polymers, bioplastics and pharmaceuticals. Biocatalysis conversion of HMF into its derivatives emerges as a green alternative, taking into account the high selectivity of enzymes and the mild reaction conditions used. Considering these factors, this work reviews the use of microorganisms as whole-cell biocatalysts for the production of HMF derivatives. In the last years, a large number of whole-cell biocatalysts have been discovered and developed for HMF conversion into BHMF, FDCA and HMFCA, however there are no reports on microbial production of DFF and FFCA. While the production of BHMF and HMFCA mainly relies on wild type microorganisms, FDCA production, which requires multiple bioconversion steps from HMF, is strongly dependent on genetic engineering strategies. Together, the information gathered supports the possibility for the development of cell factories to produce high-value compounds, envisioning economical viable biorefineries.

Valorisation of corncob into furfuryl alcohol and furoic acid via chemoenzymatic cascade catalysis

Heterogeneous tin-based sulfonated graphite (Sn-GP) catalyst was prepared with graphite as carrier. The physicochemical properties of Sn-GP were captured by FT-IR, XRD, SEM and BET. Organic acids with different pKa values were used to assist Sn-GP for transforming corncob (CC), and a linear equation (Furfural yield  = - 7.563 ×  pKa  + 64.383) (R2  =  0.9348) was fitted in acidic condition. Using sugarcane bagasse, reed leaf, chestnut shell, sunflower stalk and CC as feedstocks, co-catalysis of CC (75.0 g/L) with maleic acid (pKa  =  1.92) (0.5 wt%) and Sn-GP (3.6 wt%) yielded the highest furfural yield (47.3%) for 0.5 h at 170 °C. An effective furfural synthesis was conducted via co-catalysis with Sn-GP and maleic acid. Subsequently, E. coli CG-19 and TS completely catalyzed the conversion of corncob-derived FAL to furfurylalcohol and furoic acid, respectively. Valorisation of available renewable biomass to furans was successfully developed in tandem chemoenzymatic reaction.

An NAD-Specific 6-Hydroxy-3-Succinoyl-Semialdehyde-Pyridine Dehydrogenase from Nicotine-Degrading Agrobacterium tumefaciens Strain S33

Agrobacterium tumefaciens strain S33 can catabolize nicotine via a hybrid of the pyridine and pyrrolidine pathways. Most of the enzymes involved in this biochemical pathway have been identified and characterized, except for the one catalyzing the oxidation of 6-hydroxy-3-succinoyl-semialdehyde-pyridine to 6-hydroxy-3-succinoylpyridine. Based on a previous genomic and transcriptomic analysis, an open reading frame (ORF) annotated to encode aldehyde dehydrogenase (Ald) in the nicotine-degrading cluster was predicted to be responsible for this step. In this study, we heterologously expressed the enzyme and identified its function by biochemical assay and mass spectrum analysis. It was found that Ald catalyzes the NAD-specific dehydrogenation of 6-hydroxy-3-succinoyl-semialdehyde-pyridine to 6-hydroxy-3-succinoylpyridine. With the nonhydroxylated analog 3-succinoyl-semialdehyde-pyridine (SAP) as a substrate, Ald had a specific activity of 10.05 U/mg at pH 9.0 and apparent K_m values of around 58.68 μM and 0.41 mM for SAP and NAD⁺, respectively. Induction at low temperature and purification and storage in low-salt buffers were helpful to prevent its aggregation and precipitation. Disruption of the ald gene caused a lower growth rate and biomass of strain S33 on nicotine but not on 6-hydroxy-3-succinoylpyridine. Ald has a broad range of substrates, including benzaldehyde, furfural, and acetaldehyde. Recombinant Escherichia coli cells harboring the ald gene can efficiently convert furfural to 2-furoic acid at a specific rate of 0.032 mmol min⁻¹ g dry cells⁻¹, extending the application of Ald in the catalysis of bio-based furan compounds. These findings provide new insights into the biochemical mechanism of the nicotine-degrading hybrid pathway and the possible application of Ald in industrial biocatalysis.

IMPORTANCE Nicotine is one of the major toxic N-heterocyclic aromatic alkaloids produced in tobacco plants. Manufacturing tobacco and smoking may lead to some environmental and public health problems. Microorganisms can degrade nicotine by various biochemical pathways, but the biochemical mechanism for nicotine degradation has not been fully elucidated. In this study, we identified an aldehyde dehydrogenase responsible for the oxidation of 6-hydroxy-3-succinoyl-semialdehyde-pyridine to 6-hydroxy-3-succinoylpyridine; this was the only uncharacterized enzyme in the hybrid of the pyridine and pyrrolidine pathways in Agrobacterium tumefaciens S33. Similar to the known aldehyde dehydrogenase, the NAD-specific homodimeric enzyme presents a broad substrate range with high activity in alkaline and low-salt-containing buffers. It can catalyze not only the aldehyde from nicotine degradation but also those of benzaldehyde, furfural, and acetaldehyde. It was found that recombinant Escherichia coli cells harboring the ald gene could efficiently convert furfural to valuable 2-furoic acid, demonstrating its potential application for enzymatic catalysis.

Recent advances in the conversion of furfural into bio-chemicals through chemo- and bio-catalysis

Furfural is a promising renewable platform molecule derived from hemi-cellulose, which can be further converted to fossil fuel alternatives and valuable chemicals due to its highly functionalized molecular structure. This mini-review summarizes the recent progress in the chemo-catalytic and/or bio-catalytic conversion of furfural into high-value-added chemicals, including furfurylamine, C₆ carboxylic acid, i.e., furandicarboxylic acid, furfural alcohol, aromatics, levulinic acid, maleic acid, succinic acid, furoic acid, and cyclopentanone, particularly the advances in the catalytic valorization of furfural into useful chemicals in the last few years. The possible reaction mechanisms for the conversion of furfural into bio-chemicals are summarized and discussed. The future prospective and challenges in the utilization of furfural through chemo- and bio-catalysis are also put forward for the further design and optimization of catalytic processes for the conversion of furfural.

Improved Bio-Synthesis of 2,5-bis(hydroxymethyl)furan by Burkholderia contaminans NJPI-15 With Co-substrate

Upgrading of biomass derived 5-hydroxymethylfurfural (HMF) has attracted considerable interest recently. A new highly HMF-tolerant strain of Burkholderia contaminans NJPI-15 was isolated in this study, and the biocatalytic reduction of HMF into 2,5-bis(hydroxymethyl)furan (BHMF) using whole cells was reported. Co-substrate was applied to improve the BHMF yield and selectivity of this strain as well as HMF-tolerant level. The catalytic capacity of the cells can be substantially improved by Mn²⁺ ion. The strain exhibited good catalytic performance at a pH range of 6.0–9.0 and a temperature range of 25°C–35°C. In addition, 100 mM HMF could be reduced to BHMF by the B. contaminans NJPI-15 resting cells in presence of 70 mM glutamine and 30 mM sucrose, with a yield of 95%. In the fed-batch strategy, 656 mM BHMF was obtained within 48 h, giving a yield of 93.7%. The reported utilization of HMF to produce BHMF is a promising industrially sound biocatalytic process.

Biotechnological production and high potential of furan-based renewable monomers and polymers

Of the 25 million tons of plastic waste produced every year in Europe, 40% of these are not reused or recycled, thus contributing to environmental pollution, one of the major challenges of the 21st century. Most of these plastics are made of petrochemical-derived polymers which are very difficult to degrade and as a result, a lot of research efforts have been made on more environmentally friendly alternatives. Bio-based monomers, derived from renewable raw materials, constitute a possible solution for the replacement of oil-derived monomers, with furan derivatives that emerged as platform molecules having a great potential for the synthesis of biobased polyesters, polyamides and their copolymers. This review article summarizes the latest developments in biotechnological production of furan compounds that can be used in polymer chemistry as well as in their conversion into polymers. Moreover, the biodegradability of the resulting materials is discussed.

Selective Biosynthesis of Furoic Acid From Furfural by Pseudomonas Putida and Identification of Molybdate Transporter Involvement in Furfural Oxidation

Upgrading of furanic aldehydes to their corresponding furancarboxylic acids has received considerable interest recently. Herein we reported selective oxidation of furfural (FAL) to furoic acid (FA) with quantitative yield using whole-cells of Pseudomonas putida KT2440. The biocatalytic capacity could be substantially promoted through adding 5-hydroxymethylfurfural into media at the middle exponential growth phase. The reaction pH and cell dosage had notable impacts on both FA titer and selectivity. Based on the validation of key factors for FAL conversion, the capacity of P. putida KT2440 to produce FAL was substantially improved. In batch bioconversion, 170 mM FA was produced with selectivity nearly 100% in 2 h, whereas 204 mM FA was produced with selectivity above 97% in 3 h in fed-batch bioconversion. Particularly, the role of molybdate transporter in oxidation of FAL and 5-hydroxymethylfurfural was demonstrated for the first time. The furancarboxylic acids synthesis was repressed markedly by destroying molybdate transporter, which implied Mo-dependent enzyme/molybdoenzyme played pivotal role in such oxidation reactions. This research further highlights the potential of P. putida KT2440 as next generation industrial workhorse and provides a novel understanding of molybdoenzyme in oxidation of furanic aldehydes.

Chemoenzymatic conversion of Sorghum durra stalk into furoic acid by a sequential microwave-assisted solid acid conversion and immobilized whole-cells biocatalysis

In this study, chemoenzymatic conversion of Sorghum durra stalk (SDS) into furoic acid was developed by a sequential microwave-assisted solid acid conversion and immobilized whole-cells biocatalysis method. Dry dewaxed SDS (75 g/L) was catalyzed into furfural at 57.8% yield with heterogeneous Sn-argil (2.0 wt% dosage) in n-ethyl butyrate-H₂O (1:1, v:v) biphasic system using a microwave (600 W) for 10 min at 180 °C. In this biphasic media (pH 6.5), SDS-derived furfural (125.0 mM) was biologically oxidized to furoic acid by immobilized Brevibacterium lutescens cells harboring furfural-oxidizing activity at 30 °C, and furfural was wholly transformed to furoic acid within 24 h. Finally, the recovery and reuse of the Sn-argil catalyst and immobilized biocatalysts were conducted for synthesizing furoic acid from SDS in the biphasic system. This chemoenzymatic route can be attractive for furoic acid production.

Improved biosynthesis of 5-hydroxymethyl-2-furancarboxylic acid and furoic acid from biomass-derived furans with high substrate tolerance of recombinant Escherichia coli HMFOMUT whole-cells

The main aim of this work was to firstly develop a selective oxidation approach for biologically converting 5-hydroxymethylfurfural and furfural into the corresponding furan-based carboxylic acids with recombinant Escherichia coli HMFOMUT. Whole-cells of this recombinant strain harbored good biocatalytic activity in a narrow pH range (pH 6.5-7.0), which had high tolerance toward furfural (up to 50 mM) and 5-hydroxymethylfurfural (up to 150 mM), well-known potential inhibitors against microorganisms. 5-Hydroxymethyl-2-furancarboxylic acid and furoic acid could be obtained at 96.9% and 100% yield from 5-hydroxymethylfurfural (150 mM) and furfural (50 mM) at 30 °C and pH 7.0. The improved substrate tolerance of Escherichia coli HMFOMUT is gaining a great interest to synthesize value-added furan-based carboxylic acids, which has potential industrial applications.

Efficient biotransformation of 5-hydroxymethylfurfural to 5-hydroxymethyl-2-furancarboxylic acid by a new whole-cell biocatalyst Pseudomonas aeruginosa PC-1

An efficient HMFCA production strategy was developed using a new whole-cell biocatalyst from Pseudomonas aeruginosa PC-1.