An acidic feruloyl esterase from the mushroom Lactarius hatsudake : A potential animal feed supplement

Recovery of green phenolic compounds from lignin-based source: Role of ferulic acid esterase towards waste valorization and bioeconomic perspectives

The production of chemicals/products so far relies on fossil-based resources with the creation of several environmental problems at the global level. In this situation, a sustainable and circular economy model is necessitated to mitigate global environmental issues. Production of biowaste from various processing industries also creates environmental issues which would be valorized for the production of industrially important reactive and bioactive compounds. Lignin acts as a vital part in biowaste composition which can be converted into a wide range of phenolic compounds. The phenolic compounds have attracted much attention, owing to their influence on diverse not only organoleptic parameters, such as taste or color, but also active agents for active packaging systems. Crop residues of varied groups, which are an affluent source of lignocellulosic biomass could serve as a renewable resource for the biosynthesis of ferulic acid (FA). FA is obtained by the FA esterase enzyme action, and it can be further converted into various tail end phenolic flavor green compounds like vanillin, vanillic acid and hydroxycinnamic acid. Lignin being renewable in nature, processing and management of biowastes towards sustainability is the need as far as the global industrial point is concerned. This review explores all the approaches for conversion of lignin into value-added phenolic compounds that could be included to packaging applications. These valorized products can exhibit the antioxidant, antimicrobial, cardioprotective, anti-inflammatory and anticancer properties, and due to these features can emerge to incorporate them into production of functional foods and be utilization of them at active food packaging application. These approaches would be an important step for utilization of the recovered bioactive compounds at the nutraceutical and food industrial sectors.

Nutritional value, elemental bioaccumulation and antioxidant activity of fruiting bodies and mycelial cultures of an unrecorded wild Lactarius hatsudake from Nanyue mountainous region in China

An unrecorded wild mushroom Lactarius hatsudake from Nanyue mountainous region in China was identified. Subsequently, comparative investigation on the nutritional value, elemental bioaccumulation, and antioxidant activity was performed in the fruiting body (FB) and mycelium (MY) samples of this species. It revealed that the contents of moisture (87.66 ± 0.16 g/100 g fw) and ash (6.97 ± 0.16 g/100 g dw) were significantly higher in FB, and the total carbohydrate, fat, and protein concentrations of FB were similar to those in MY. Among nutritionally important elements, FB possessed higher concentrations of potassium (37808.61 ± 1237.38 mg/kg dw), iron (470.69 ± 85.54 mg/kg dw), and zinc (136.13 ± 5.16 mg/kg dw), whereas MY was a better source of magnesium (1481.76 ± 18.03 mg/kg dw), calcium (2203.87 ± 69.61 mg/kg dw), and sodium (277.44 ± 22.93 mg/kg dw). According to the health risk estimation, FB might pose an aluminum-related health problem when a prolonged period of exposure, while MY was risk-free for consumers. The results of antioxidant capacity (1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) assays) in FB and MY were within the range of 104.19 ± 5.70 mg ascorbic acid equivalents (AAE)/g to 169.50 ± 4.94 mg AAE/g, and half maximal effective concentration EC50 values ranged from 0.23 ± 0.01 mg/mL to 0.62 ± 0.05 mg/mL. The aqueous extracts of MY demonstrated a strong ABTS radical scavenging capacity with the highest AAE value.

Diversity and Network Relationship Construction of Soil Fungal Communities in Lactarius hatsudake Tanaka Orchard during Harvest

Lactarius hatsudake Tanaka is a mycorrhizal edible mushroom with rich economic and nutritional value. Although it is artificially planted, its yield is unstable. Soil fungi, including L. hatsudake, coexist with many other microorganisms and plants. Therefore, complex microbial communities have an influence on the fruiting body formation of L. hatsudake. L. hatsudake and its interactions with the rest of the fungal community over time are not completely understood. In this study, we performed high-throughput sequencing of microorganisms in the basal soil of the fruiting body (JT), mycorrhizosphere soil (JG), and non-mushroom-producing soil (CK) in a 6-year-old L. hatsudake plantation at harvest. The results showed that the soil of the L. hatsudake plantation was rich in fungal communities and a total of 10 phyla, 19 classes, 53 orders, 90 families, 139 genera, and 149 species of fungi were detected. At the phylum level, the major groups were Basidiomycota and Ascomycota. At the genus level, the dominant groups were Lactarius, Trichoderma, Suillus, and Penicillium. Among them, L. hatsudake had an absolute dominant position in the soil fungal community of the plantation, and was the only group of Lactarius in the plantation soil. Penicillium cryptum and Penicillium adametzii were unique to the JT soil sample. Chaetopsphaeria, Myxocephala, Devriesia, and Psathyrella were positively correlated with L. hatsudake. In the constructed fungal network, the total number of nodes were ranked in descending order as JG (441) > CK (405) > JT (399), while the total number of edges were ranked in descending order as CK (1360) > JG (647) > JT (586). Analysis of the fungal assembly process revealed that groups CK and JG have determinative processes that dominated community building, while the JT group exhibited a dominant random process with a 0.60 probability. The results indicated that L. hatsudake was successfully colonized in the plantation soil. During harvest, the CK group exhibited the largest network size and the most complex fungal interactions, while the fungal community structure in the mushroom cultivation zone (JT and JG) was stable and less susceptible to external environmental interference. L. hatsudake affects the fungal community in the soil surrounding its fruiting body.

Characterization of Feruloyl Esterase from Klebsiella oxytoca Z28 and Its Application in the Release of Ferulic Acid from De-Starching Wheat Bran

Feruloyl esterase (EC3.1.1.73; FAE) can degrade biomass to release ferulic acid (FA), which has a high application in bioprocessing, food, pharmaceutical, paper, feed, and other industrial fields. A strain of Klebsiella oxytoca Z28 with ferulic esterase activity was screened from Daqu. In addition, the FAE gene was expressed in Escherichia coli BL21 (DE3). The enzyme consists of 340 amino acids with a molecular mass of 37.7 kDa. The FAE enzyme activity was 463 U/L when the substrate was ethyl 4-hydroxy-3-methoxycinnamate and the optimum temperature and pH were 50 °C and 8.0, respectively. The enzyme had good stability at temperatures of 25-40 °C and a pH of 8.0. Ba²⁺, Cu²⁺, Mn²⁺, and Ca²⁺ had a strong inhibitory effect on the enzyme activity, and Na⁺ had a promotive effect on the enzyme activity. The de-starching wheat bran was degraded by KoFAE, and the FA release was up to 227.15 µg/g. This indicated that the heterologous expression of KoFAE from Klebsiella oxytoca Z28 in E. coli had a certain potential of biodegradation, which can be applied to the degradation of agricultural waste to obtain high value-added FA products.

Penicillium chrysogenum as a fungal factory for feruloyl esterases

Plant biomass is a promising substrate for biorefinery, as well as a source of bioactive compounds, platform chemicals, and precursors with multiple industrial applications. These applications depend on the hydrolysis of its recalcitrant structure. However, the effective biological degradation of plant cell walls requires several enzymatic groups acting synergistically, and novel enzymes are needed in order to achieve profitable industrial hydrolysis processes. In the present work, a feruloyl esterase (FAE) activity screening of Penicillium spp. strains revealed a promising candidate (Penicillium rubens Wisconsin 54-1255; previously Penicillium chrysogenum), where two FAE-ORFs were identified and subsequently overexpressed. Enzyme extracts were analyzed, confirming the presence of FAE activity in the respective gene products (PrFaeA and PrFaeB). PrFaeB-enriched enzyme extracts were used to determine the FAE activity optima (pH 5.0 and 50-55 °C) and perform proteome analysis by means of MALDI-TOF/TOF mass spectrometry. The studies were completed with the determination of other lignocellulolytic activities, an untargeted metabolite analysis, and upscaled FAE production in stirred tank reactors. The findings described in this work present P. rubens as a promising lignocellulolytic enzyme producer. KEY POINTS: • Two Penicillium rubens ORFs were first confirmed to have feruloyl esterase activity. • Overexpression of the ORFs produced a novel P. rubens strain with improved activity. • The first in-depth proteomic study of a P. rubens lignocellulolytic extract is shown.

A high-quality genome assembly of Lactarius hatsudake strain JH5

Lactarius hatsudake is a species of Lactarius commonly found in pine forests, is edible with a delicious and nutritious fruiting body, and exhibits medicinal properties. It is an ideal natural multifunctional food with bioactive components including fungal polysaccharides, crude fiber, unsaturated fatty acids, nucleic acid derivatives, various amino acids, and vitamins. However, biological and genomic analyses of this mycorrhizal mushroom are sparse, thereby hindering large-scale cultivation. Previously, we isolated and screened L. hatsudake JH5 strains and have applied our garnered knowledge to the large-scale cultivation of mycorrhizal seedlings. In this study, we produced a high-quality genome assembly of L. hatsudake JH5 by combining Illumina paired-end and PacBio single molecule real-time sequencing, resulting in PacBio single molecule real-time reads of 7.67 Gb and Illumina Pair-End reads of 1,560 Mb. Based on the distribution of k-mer frequencies, the genome size of this strain was estimated to be 63.84 Mb (1.14% heterozygosity). Based on de novo genome assembly, the final genome size was determined to be 76.7 Mb, with scaffold N50 of 223.2 kb and N90 of 54.5 kb, and a GC content of 54.38%. BUSCO assessment showed that genome completeness was 89.0%. The N50 length of the JH5 genome was 43.6% longer than that of the previously published L. hatsudake MG20 genome. This high-quality L. hatsudake genome assembly will facilitate research on the functional genome, molecular breeding, yield enhancement, and sustainability of L. hatsudake cultivation.

Molecular and Biochemical Analyses of a Novel Trifunctional Endoxylanase/Endoglucanase/Feruloyl Esterase from the Human Colonic Bacterium Bacteroides intestinalis DSM 17393

A novel enzyme Bi76 comprising GH10, E_set_Esterase_N, and CE1 modules was identified, with the highest homology (62.9%) with a bifunctional endoxylanase/feruloyl esterase among characterized enzymes. Interestingly, Bi76 hydrolyzed glucan substrates besides xylans and feruloylated substrates, suggesting that it is the first characterized trifunctional endoxylanase/endoglucanase/feruloyl esterase. Analyses of truncation variants revealed that GH10 and E_set_Esterase_N + CE1 modules encoded endoxylanase/endoglucanase and feruloyl esterase activities, respectively. Synergism analyses indicated that endoxylanase, α-l-arabinofuranosidase, and feruloyl esterase acted cooperatively in releasing ferulic acid (FA) and xylooligosaccharides from feruloylated arabinoxylan. The interdomain synergism of Bi76 overmatched the intermolecular synergism of TM1 and TM2. Importantly, Bi76 exhibited good capacity in producing FA, releasing 5.20, 4.38, 2.12, 1.35, 0.46, and 0.19 mg/g from corn bran, corn cob, wheat bran, corn stover, rice husk, and rice bran, respectively. This study expands the trifunctional endoxylanase/endoglucanase/feruloyl esterase repertoire and demonstrates the great potential of Bi76 in agricultural residue utilization.

Biochemical characterization of a novel feruloyl esterase from Burkholderia pyrrocinia B1213 and its application for hydrolyzing wheat bran

In this study, a novel feruloyl esterase (BpFae) from Burkholderia pyrrocinia B1213 was purified, biochemically characterized, and applied in releasing ferulic acid from wheat bran. The molecular mass of BpFae was approximately 60 kDa by SDS-PAGE, and the enzyme was a homomultimer in solution. BpFae displayed maximum activity at pH 4.5-5.0 and was stable at pH 3.0-7.0. The optimal temperature for BpFae was 50 °C. BpFae activity was not affected by most metal ions tested and was significantly increased by Tween-20 and Triton-100. Purified BpFae exhibited a preference for methyl ferulate (41.78 U mg^-1) over methyl p-coumarate (38.51 U mg^-1) and methyl caffeate (35.36 U mg^-1) and had the lowest activity on methyl sinapate (1.79 U mg^-1). Under the optimum conditions, the K _m and V _max for methyl ferulate were 0.53 mM and 86.74 U mg^-1, respectively. Residues Ser209, His492, and Glu245 in the catalytic pocket of BpFae could form hydrogen bonds with the substrate and were crucial for catalytic activity and substrate specificity. When G11 xylanase XynA and BpFae were used separately for hydrolyzing de-starched wheat bran (DSWB), the ferulic acid released was undetectable and 1.78%, respectively, whereas it was increased to 59.26% using the mixture of the two enzymes. Thus, BpFae is considered an attractive candidate for the production of ferulic acid from agricultural by-products.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03066-2.

Comparison of Enzyme Secretion and Ferulic Acid Production by Escherichia coli Expressing Different Lactobacillus Feruloyl Esterases

Construction of recombinant Escherichia coli strains carrying feruloyl esterase genes for secretory expression offers an attractive way to facilitate enzyme purification and one-step production of ferulic acid from agricultural waste. A total of 10 feruloyl esterases derived from nine Lactobacillus species were expressed in E. coli BL21 (DE3) to investigate their secretion and ferulic acid production. Extracellular activity determination showed all these Lactobacillus feruloyl esterases could be secreted out of E. coli cells. However, protein analysis indicated that they could be classified as three types. The first type presented a low secretion level, including feruloyl esterases derived from Lactobacillus acidophilus and Lactobacillus johnsonii. The second type showed a high secretion level, including feruloyl esterases derived from Lactobacillus amylovorus, Lactobacillus crispatus, Lactobacillus gasseri, and Lactobacillus helveticus. The third type also behaved a high secretion level but easy degradation, including feruloyl esterases derived from Lactobacillus farciminis, Lactobacillus fermentum, and Lactobacillus reuteri. Moreover, these recombinant E. coli strains could directly release ferulic acid from agricultural waste. The highest yield was 140 μg on the basis of 0.1 g de-starched wheat bran by using E. coli expressed L. amylovorus feruloyl esterase. These results provided a solid basis for the production of feruloyl esterase and ferulic acid.

Efficient ferulic acid and xylo-oligosaccharides production by a novel multi-modular bifunctional xylanase/feruloyl esterase using agricultural residues as substrates

Liberating high value-added compounds ferulic acid (FA) and xylo-oligosaccharides (XOSs) from agricultural residues is a promising strategy for the utilization of lignocellulose. In this study, a bifunctional xylanase/feruloyl esterase from bacterial consortium EMSD5 was heterogeneously expressed in Escherichia coli. Depending on the inter-domain synergism of the recombinant enzyme rXyn10A/Fae1A, high yields of FA (2.78, 1.82, 1.15 and 7.31 mg/g substrate, respectively) were obtained from 20 mg in-soluble wheat arabinoxylan, de-starched wheat bran, ultrafine-grinding corn stover and steam-exploded corncob. Meanwhile, 3.210, 1.235, 1.215 and 0.823 mg xylose/XOSs were also released. For cost-saving enzyme production, we firstly constructed a recombinant E. coli, which could secrete the bifunctional xylanase/feruloyl esterase out of cells. When the recombinant E. coli was cultured in medium containing 200 mg de-starched wheat bran, 474 μg FA and 18.2 mg xylose/XOSs were also detected. Hence, rXyn10A/Fae1A and the recombinant strain showed great applied potential for FA and XOSs production.

Does glucose affect the de-esterification of methyl ferulate by Lactobacillus buchneri?

Silage, the fermented product from anaerobic storage of forage crops with high water contents (50%–70%), is normally used as animal feed but also for the production of biofuels and value‐added products. To improve the utilization of plant fibers during ensiling, previous attempts have aimed at breaking linkages between lignin and hemicellulose by use of Lactobacillus buchneri LN 4017 (ATCC PTA‐6138), a feruloyl esterase (FAE)‐producing strain, but results have been inconsistent. Normally, there are sufficient amounts of readily available substrates for bacterial growth in silage. We thus hypothesized that the inconsistent effect of L. buchneri LN 4017 on the digestibility of silage fibers is due to the catabolic repression of FAE activity by substrates present in silage (e.g., glucose). To test this hypothesis, we analyzed the effect of glucose on the de‐esterification of methyl ferulate (MF), a model substrate used for FAE activity assays. At three glucose:MF ratios (0:1, 1:1, and 13:1), the bacteria continued hydrolyzing MF with increasing glucose:MF ratios, indicating that the de‐esterification reaction was not repressed by glucose. We therefore conclude that the de‐esterification activity of L. buchneri LN 4017 is not repressed by silage substrates during ensiling.

New Insights Into Cinnamoyl Esterase Activity of Oenococcus oeni

Some strains of Oenococcus oeni possess cinnamoyl esterase activity that can be relevant in the malolactic stage of wine production liberating hydroxycinnamic acids that are precursors of volatile phenols responsible for sensory faults. The objective of this study was to better understand the basis of the differential activity between strains. After initial screening, five commercial strains of O. oeni were selected, three were found to exhibit cinnamoyl esterase activity (CE+) and two not (CE-). Although the use of functional annotation of genes revealed genotypic variations between the strains, no specific genes common only to the three CE+ strains could explain the different activities. Pasteurized wine was used as a natural source of tartrate esters in growth and metabolism experiments conducted in MRS medium, whilst commercial trans-caftaric acid was used as substrate for enzyme assays. Detoxification did not seem to be the main biological mechanism involved in the activity since unlike its phenolic cleavage products and their immediate metabolites (trans-caffeic acid and 4-ethylcatechol), trans-caftaric acid was not toxic toward O. oeni. In the case of the two CE+ strains OenosTM and CiNeTM, wine-exposed samples showed a more rapid degradation of trans-caftaric acid than the unexposed ones. The CE activity was present in all cell-free extracts of both wine-exposed and unexposed strains, except in the cell-free extracts of the CE- strain CH11TM. This activity may be constitutive rather than induced by exposure to tartrate esters. Trans-caftaric acid was totally cleaved to trans-caffeic acid by cell-free extracts of the three CE+ strains, whilst cell-free extracts of the CE- strain CH16TM showed significantly lower activity, although higher for the strains in experiments with no prior wine exposure. The EstB28 esterase gene, found in the genomes of the 5 strains, did not reveal any difference on the upstream regulation and transport functionality between the strains. This study highlights the complexity of the basis of this activity in wine related O. oeni population. Variable cinnamoyl esterases or/and membrane transport activities in the O. oeni strains analyzed and a possible implication of wine molecules could explain this phenomenon.

Extracellular secretion of feruloyl esterase derived from Lactobacillus crispatus in Escherichia coli and its application for ferulic acid production

A feruloyl esterase producing strain was isolated and identified as Lactobacillus crispatus S524. Its putative feruloyl esterase was heterogeneously expressed in Escherichia coli BL21 (DE3). Interestingly, the feruloyl esterase (FaeLcr) could be secreted into the culture medium with a relative high purity of 201.7 mg/L. FaeLcr was purified from the cell-free culture supernatant and appeared as a single protein band with the molecular mass of 28 kDa by SDS-PAGE. The optimal temperature and pH were determined as 65 °C and 7.0, and it showed prominent thermo-stability and alkali-stability. Furthermore, the purified FarLcr could release a maximal amount of 199 µg ferulic acid from 0.2 g de-starched wheat bran. Meanwhile, when cultured this recombinant E. coli strain in medium supplemented with 2 g de-starched wheat bran, 1.86 mg ferulic acid was also detected. These results suggested that the recombinant strain has a great potential application in feruloyl esterase and ferulic acid production.

Molecular cloning, expression and characterization of a novel feruloyl esterase from a soil metagenomic library with phthalate-degrading activity

OBJECTIVES

To discover novel feruloyl esterases (FAEs) by the function-driven screening procedure from soil metagenome.

RESULTS

A novel FAE gene bds4 was isolated from a soil metagenomic library and over-expressed in Escherichia coli. The recombinant enzyme BDS4 was purified to homogeneity with a predicted molecular weight of 38.8 kDa. BDS4 exhibited strong activity (57.05 U/mg) toward methyl ferulate under the optimum pH and temperature of 8.0 and 37°C. Based on its amino acid sequence and model substrates specificity, BDS4 was classified as a type-C FAE. The quantity of the releasing ferulic acid can be enhanced significantly in the presence of xylanase compared with BDS4 alone from de-starched wheat bran. In addition, BDS4 can also hydrolyze several phthalates such as diethyl phthalate, dimethyl phthalate and dibutyl phthalate.

CONCLUSION

The current investigation discovered a novel FAE with phthalate-degrading activity and highlighted the usefulness of metagenomic approaches as a powerful tool for discovery of novel FAEs.

Feruloyl esterases: Biocatalysts to overcome biomass recalcitrance and for the production of bioactive compounds

Ferulic acid and its hydroxycinnamate derivatives represent one of the most abundant forms of low molecular weight phenolic compounds in plant biomass. Feruloyl esterases are part of a microorganism's plant cell wall-degrading enzymatic arsenal responsible for cleaving insoluble wall-bound hydroxycinnamates and soluble cytosolic conjugates. Stimulated by industrial requirements, accelerating scientific discoveries and knowledge transfer, continuous improvement efforts have been made to identify, create and repurposed biocatalysts dedicated to plant biomass conversion and biosynthesis of high-added value molecules. Here we review the basic knowledge and recent advances in biotechnological characteristics and the gene content encoding for feruloyl esterases. Information about several enzymes is systematically organized according to their function, biochemical properties, substrate specificity, and biotechnological applications. This review contributes to further structural, functional, and biotechnological R&D both for obtaining hydroxycinnamates from agricultural by-products as well as for lignocellulose biomass treatments aiming for production of bioethanol and other derivatives of industrial interest.

Carbohydrate Esterases: An Overview

Carbohydrate esterases are a group of enzymes which release acyl or alkyl groups attached by ester linkage to carbohydrates. The CAZy database, which classifies enzymes that assemble, modify, and break down carbohydrates and glycoconjugates, classifies all carbohydrate esterases into 16 families. This chapter is an overview of the research for nearly 50 years around the main groups of carbohydrate esterases dealing with the degradation of polysaccharides, their main biochemical and molecular traits, as well as its application for the synthesis of high added value esters.