Effects of inoculating feruloyl esterase-producing Lactiplantibacillus plantarum A1 on ensiling characteristics, in vitro ruminal fermentation and microbiota of alfalfa silage

BACKGROUND

Ferulic acid esterase (FAE)-secreting Lactiplantibacillus plantarum A1 (Lp A1) is a promising silage inoculant due to the FAE's ability to alter the plant cell wall structure during ensiling, an action that is expected to improve forage digestibility. However, little is known regarding the impacts of Lp A1 on rumen microbiota. Our research assessed the influences of Lp A1 in comparison to a widely adopted commercial inoculant Lp MTD/1 on alfalfa's ensilage, in vitro rumen incubation and microbiota.

RESULTS

Samples of fresh and ensiled alfalfa treated with (either Lp A1 or Lp MTD/1) or without additives (as control; CON) and ensiled for 30, 60 and 90 d were used for fermentation quality, in vitro digestibility and batch culture study. Inoculants treated silage had lower (P < 0.001) pH, acetic acid concentration and dry matter (DM) loss, but higher (P = 0.001) lactic acid concentration than the CON during ensiling. Compared to the CON and Lp MTD/1, silage treated with Lp A1 had lower (P < 0.001) aNDF, ADF, ADL, hemicellulose, and cellulose contents and higher (P < 0.001) free ferulic acid concentration. Compared silage treated with Lp MTD/1, silage treated with Lp A1 had significantly (P < 0.01) improved ruminal gas production and digestibility, which were equivalent to those of fresh alfalfa. Real-time PCR analysis indicated that Lp A1 inoculation improved the relative abundances of rumen's total bacteria, fungi, Ruminococcus albus and Ruminococcus flavefaciens, while the relative abundance of methanogens was reduced by Lp MTD/1 compared with CON. Principal component analysis of rumen bacterial 16S rRNA gene amplicons showed a clear distinction between CON and inoculated treatments without noticeable distinction between Lp A1 and Lp MTD/1 treatments. Comparison analysis revealed differences in the relative abundance of some bacteria in different taxa between Lp A1 and Lp MTD/1 treatments. Silage treated with Lp A1 exhibited improved rumen fermentation characteristics due to the inoculant effects on the rumen microbial populations and bacterial community.

CONCLUSIONS

Our findings suggest that silage inoculation of the FAE-producing Lp A1 could be effective in improving silage quality and digestibility, and modulating the rumen fermentation to improve feed utilization.

Characterization of isogenic mutants with single or double deletions of four phenolic acid esterases in Lactiplantibacillus plantarum TMW1.460

In plants, hydroxycinnamic and hydroxybenzoic acids occur mainly as esters. This study aimed to determine the contribution of individual phenolic acid esterases in Lp. plantarum TMW1.460, which encodes for four esterases: TanA, Lp_0796, Est_1092 and a homolog of Lj0536 and Lj1228 that was termed HceP. To determine which of the phenolic acid esterases present in Lp plantarum TMW1.460 are responsible for esterase activity, mutants with deletions in lp_0796, est_1092, tanB, hceP, or hceP and est_1092 were constructed. The phenotype of wild type strain and mutants was determined with esters of hydroxycinnamic acids (chlorogenic acid and ethyl ferulate) and of hydroxybenzoic acids (methyl gallate, tannic acid and epigallocatechin-3-gallate). Lp. plantarum TMW1.460 hydrolysed chlorogenic acid, methyl ferulate and methyl gallate but not tannic acid or epigallocatechin gallate. The phenotype of mutant strains during growth in mMRS differed from the wild type as follows: Lp. plantarum TMW1.460ΔhceP did not hydrolyse esters of hydroxycinnamic acids; Lp. plantarum TMW1.460ΔtanB did not hydrolyse esters of hydroxybenzoic acids; disruption of est_1092 or Lp_0796 did not alter the phenotype. The phenotype of Lp. plantarum TMW1.460ΔΔhceP/est_1092 was identical to Lp. plantarum TMW1.460ΔhceP. The metabolism of phenolic acids during growth of the mutant strains in broccoli puree and wheat sourdough did not differ from metabolism of the wild type strain. In conclusion, esters of hydroxycinnamic and hydroxybenzoic acids each are hydrolysed by dedicated enzymes. The hydroxycinnamic acid esterase HceP is not expressed, or not active during growth of Lp. plantarum TMW1.460 in all food substrates.

Probiotic effect of ferulic acid esterase-producing Lactobacillus plantarum inoculated alfalfa silage on digestion, antioxidant, and immunity status of lactating dairy goats

A feeding experiment was conducted to determine the effects of inoculating alfalfa silage with a ferulic acid esterase-producing inoculum on feed digestibility, rumen fermentation, antioxidant, and immunity status of lactating dairy goats. Twenty dairy goats were distributed into 2 experimental groups consisting of control diet (Lp MTD/1, including Lactobacillus plantarum MTD/1 inoculated silage) against diet containing silage treated with ferulic acid esterase-producing L. plantarum A1 (Lp A1). Alfalfa silage inoculated with a ferulic acid esterase-producing Lp A1 had better fermentation quality than the Lp MTD/1 inoculation. The application of Lp A1 improved silage antioxidant capacity as indicated by greater total antioxidant capacity (T-AOC), superoxide dismutase (SOD) and glutathion peroxidase (GSH-Px) activities in Lp A1 treated silage versus Lp MTD/1 treatment. Compared with Lp MTD/1 treated group, inoculation of silage with Lp A1 increased apparent total tract digestibility of dietary dry matter, organic matter and crude protein, and ruminal concentrations of total volatile fatty acids, acetate, propionate and isobutyrate as well. The results of current study also demonstrated improved antioxidant capacity and immune performance of dairy goats with Lp A1 inoculation. Feeding Lp A1-treated silage increased dairy goats' serum antioxidase activity, such as T-AOC, SOD, GSH-Px and catalase, and the serum concentration of immunoglobulin A, while decreased tumor necrosis factor α, interleukin (IL)-2 and IL-6. In addition, compared with Lp MTD/1, diet containing alfalfa silage inoculated with Lp A1 endowed dairy goats' milk with greater fat and protein contents, improved dairy goat milk quality without affecting feed efficiency.

Microbial mechanisms of using feruloyl esterase-producing Lactobacillus plantarum A1 and grape pomace to improve fermentation quality and mitigate ruminal methane emission of ensiled alfalfa for cleaner animal production

This study was conducted to investigate the influence of feruloyl esterase-producing Lactobacillus plantarum A1 (Lp A1) and grape pomace (GP) alone, or in combination (LG) on ensiling characteristics and bacterial community, in vitro ruminal fermentation, methane (CH₄) emission, and the microbiota of ensiled alfalfa. Alfalfa at 42% dry matter (DM) was treated in a 2 × 2 factorial design: with the application of Lp A1 at 0 (control) or 1 × 10⁶ cfu/g of fresh forage, and GP at 0 or 5% of fresh forage. After 60 d of ensiling, a decrease in nonprotein nitrogen (NPN) was observed in GP treated silage. Lp A1 inoculated silage had a lower fiber content than silages without Lp A1. The lowest NPN was found in silage treated with LG, and an obvious increase in the relative abundance of Lactobacillus paracasei was detected in silages treated with Lp A1 and LG, respectively. In vitro ruminal experiments indicated that, although the application of GP deceased ruminal total gas, CH₄ production, nitrogen degradation and the number of methanogenic archaea in alfalfa silage, it also reduced silage DM digestibility. In contrast, inoculation with Lp A1 not only increased DM digestibility and populations of ruminal Ruminococcus flavefaciens and fungi, but also improved ruminal total gas and CH₄ production. As expected, LG treatment decreased alfalfa silage ruminal total gas and CH₄ production relative to Lp A1 treatment alone, and increased silage DM digestibility compared with GP treated silage. In conclusion, the application of LG before ensiling alfalfa, balanced silage proteolysis, feed digestibility, and CH₄ emission, and could be a promising strategy for using food industry by-products to produce a nutritional and environmentally-friendly legume silage that will mitigate N and greenhouse gas emissions from ruminants.

One-pot microbial bioconversion of wheat bran ferulic acid to biovanillin

Due to growing consumer preference towards natural ingredients in food products, the production of flavors by microbial biotransformation of agrowastes provides an eco-friendly, cost-effective and sustainable pathway for biovanillin production. In the present study, biovanillin was produced by microbial biotransformation of ferulic acid (FA) using Streptomyces sp. ssr-198. The strain was able to grow in glucose medium supplemented with 1 g/L FA and produce 20.91 ± 1.11 mg/L vanillin within 96 h, along with 5.78 ± 0.13 mg/L vanillic acid in 144 h. Estimation of enzymes involved in FA degradation detected maximum feruloyl-CoA synthetase activity (1.21 ± 0.03 U/mg protein) at 96 h and maximum vanillin dehydrogenase activity (0.31 ± 0.008 U/mg protein) at 168 h, with small amounts of ferulic acid esterase activity (0.13 ± 0.002 U/mg protein) in the fermentation medium. Further, the glucose deficient production medium supplemented with 3 g/L of ferulic acid when inoculated with Streptomyces sp. ssr-198 (6% wet weight) produced maximum vanillin (685 ± 20.11 mg/L) within 72 h at 37 °C under agitation (150 rpm) and declined thereafter. Furthermore, in a one-pot experiment, wherein crude ferulic acid esterase (700 IU/g of substrate) from Enterococcus lactis SR1 was added into 10% w/v wheat bran (natural source of ferulic acid) based medium and was inoculated with 1% w/v of Streptomyces sp. ssr-198 resulted in maximum vanillin production (1.02 ± 0.02 mg/g of substrate) within 60 h of incubation. The study provides an insight into synergistic effect of using FAE of E. lactis SR1 and Streptomyces sp. ssr-198 for bioproduction of biovanillin using agro residues.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03006-0.

A biorefinery approach for the production of ferulic acid from agroresidues through ferulic acid esterase of lactic acid bacteria

Ferulic acid is a known precursor for vanillin production but the significance of agro waste as substrates for its extraction, in combination with microbes is a less explored option. Various lactic acid bacteria were screened for the production of ferulic acid esterase (FAE) and Enterococcus lactis SR1 was found to produce maximum FAE (7.54 ± 0.15 IU/ml) in the synthetic medium under submerged fermentation. To make the process cost effective, various lignocellulosic agroresidues were evaluated for the production of FAE from the bacterium. It was found that wheat bran serves as the best substrate for FAE production (4.18 ± 0.12 IU/ml) from E. lactis SR1. Further, optimization of fermentation conditions for FAE production from E. lactis SR1 using wheat bran as carbon source led to an increase in the enzyme production (7.09 ± 0.21 IU/ml) by 1.5 fold. The FAE produced was used alone or in combination with commercial holocellulase for biological release of FA from the tested agroresidues. The highest release of FA (mg/g) by enzymatic extraction occurred in sugarbeet pulp (2.56), followed by maize bran (1.45), wheat bran (1.39) and rice bran (0.87), when both the enzymes (FAE and holocellulase) were used together. Alkaline extraction and purification of ferulic acid (FA) from these agro residues also showed that sugarbeet pulp contains the highest amount of FA (5.5 mg/g) followed by maize bran (3.0 mg/g), wheat bran (2.8 mg/g) and rice bran (1.9 mg/g), similar to the trend obtained in biological/enzymatic extraction of FA from these residues. Furthermore, the substrates were found to release higher reducing sugars when both commercial holocellulase and FAE were used in combination than by the use of holocellulase alone. Thus, FAEs not only release FA but also enabled hemicellulase and cellulase to release more sugars from plant material.

Pretreatment of Pennisetum sinese silages with ferulic acid esterase-producing lactic acid bacteria and cellulase at two dry matter contents: Fermentation characteristics, carbohydrates composition and enzymatic saccharification

The impact of Lactobacillus plantarum A1 producing ferulic acid esterase and Acremonium cellulase on Pennisetum sinese silages was investigated at two dry matter contents by studying the ensiling characteristics, lignocellulosic degradation and enzymatic saccharification properties. The P. sinese was treated with nothing (control), Acremonium cellulase (AC), L. plantarum A1 (Lp) and AC + Lp and ensiled for 60 d. All additive treatments effectively preserved P. sinese and promoted the degradation of lignocellulose in comparison with control. Pretreatment with AC exhibited better effects in degradation of lignocellulose and enhancing enzymatic saccharification of P. sinese silage with low dry matter content (L-DM), while AC + Lp performed better in lignocellulose degradation in silages with high dry matter content (H-DM). Application of Lp exhibited a better performance in reducing the concentration of acid detergent lignin in treated silages. In addition, Lp enhanced enzymatic saccharification at 72 h in H-DM silage relative to other treatments.

Simultaneous production of cellulase and ferulic acid esterase by Penicillium decumbens with rice straw as the sole carbon source

As well as cellulose and hemicelluloses, rice straw contains phenolic acids. The simultaneous production of monosaccharides and phenolic acids could improve the value of rice straw. In this study, it was confirmed that Penicillium decumbens produces more ferulic acid esterase (FAE) than other cellulase-producing fungi. Cellulose, destarched wheat bran (DSWB), and rice straw were used as carbon sources. Little phenolic acid was released by cellulose- and DSWB-based enzymes during the saccharification of rice straw, whereas rice straw was a favorable carbon source for the simultaneous production of cellulase and FAE. High-performance liquid chromatography showed that during enzyme production, phenolic acids were released from rice straw, and ball-milling affected this release of phenolic acids. Small amounts of phenolic acids induced FAE production. Although the enzymes produced with rice straw showed lower FAE activity than those produced with DSWB, phenolic acids were produced efficiently during the saccharification of rice straw in response to the synergistic effects of cellulase and FAE. Therefore, we suggest that the production of enzymes by P. decumbens on rice straw as the sole carbon source will allow the production of more valuable products from rice straw, making the utilization of rice straw more economic.

Identification and characterization of ferulic acid esterase from Penicillium chrysogenum 31B: de-esterification of ferulic acid decorated with l-arabinofuranoses and d-galactopyranoses in sugar beet pectin

We previously described the fungus Penicillium chrysogenum 31B, which has high performance to produce the ferulic acid esterase (FAE) for de-esterifying ferulic acids (FAs) from sugar beet pulp. However, the characteristics of this fungus have not yet been determined. Therefore, in this study, we evaluated the molecular characteristics and natural substrate specificity of the Pcfae1 gene from Penicillium chrysogenum and examined its synergistic effects on sugar beet pectin. The Pcfae1 gene was cloned and overexpressed in Pichia pastoris KM71H, and the recombinant enzyme, named PcFAE1, was characterized. The 505 amino acids of PcFAE1 possessed a GCSTG motif (Gly164 to Gly168), characteristic of the serine esterase family. By comparing the amino acid sequence of PcFAE1 with that of the FAE (AoFaeB) of Aspergillus oryzae, Ser166, Asp379, and His419 were identified as the catalytic triad. PcFAE1 was purified through two steps using anion-exchange column chromatography. Its molecular mass without the signal peptide was 75 kDa. Maximum PcFAE1 activity was achieved at pH 6.0-7.0 and 50 °C. The enzyme was stable up to 37 °C and at a pH range of 3-8. PcFAE1 activity was only inhibited by Hg²⁺, and the enzyme had activity toward methyl FA, methyl caffeic acid, and methyl p-coumaric acid, with specific activities of 6.97, 4.65, and 9.32 U/mg, respectively, but not on methyl sinapinic acid. These results indicated that PcFAE1 acted similar to FaeB type according the Crepin classification. PcFAE1 de-esterified O-[6-O-feruloyl-β-d-galactopyranosyl-(1→4)]-d-galactopyranose, O-[2-O-feruloyl-α-l-arabinofuranosyl-(1→5)]-l-arabinofuranose, and O-[5-O-feruloyl-α-l-arabinofuranosyl-(1→3)]-O-β-d-xylopyranosyl-(1→4)-d-xylopyranose, indicating that the enzyme could de-esterify FAs decorated with both β-d-galactopyranosidic and α-l-arabinofuranosidic residues in pectin and xylan. PcFAE1 acted in synergy with endo-α-1,5-arabinanase and α-l-arabinofuranosidase, which releases FA linked to arabinan, to digest the sugar beet pectin. Moreover, when PcFAE1 was allowed to act on sugar beet pectin together with Driselase, approximately 90% of total FA in the substrate was released. Therefore, PcFAE1 may be an interesting candidate for hydrolysis of lignocellulosic materials and could have applications as a tool for production of FA from natural substrates.

Effects of ferulic acid esterase-producing Lactobacillus fermentum and cellulase additives on the fermentation quality and microbial community of alfalfa silage

Background

Alfalfa (Medicago sativa) is an important forage material widely used for animal feed production. Ensiling is an effective method for preserving alfalfa, but it has shown some limitations in the production of high-quality alfalfa silage due to its low water soluble carbohydrates (WSC) content and high buffering capacity. Lactic acid bacteria (LAB) and cellulase are often used as silage additives to promote the ensiling process and enhance fermentation quality.

Methods

Experiments were conducted to investigate the effects of ferulic acid esterase (FAE)-producing Lactobacillus fermentum 17SD-2 (LF) and cellulase (CE) on the fermentation quality and microbial community of alfalfa silage. After 60 days of ensiling, analysis of fermentation quality and bacterial diversity in alfalfa silages were conducted using high-performance liquid chromatography and high-throughput sequencing methods.

Results

Alfalfa was ensiled with additives (LF, CE, and LF+CE) or without additives for 60 days. All additives increased lactic acid and decreased pH values and ammonia-N contents compared to control. Among all treatments, the combined addition of LF and CE showed lowest pH (4.66) and ammonia-N (NH₃-N, 0.57% DM) content, highest contents of lactic acid (LA, 10.51% DM), dry matter (DM, 22.54%) and crude protein (CP, 24.60% DM). Combined addition of LF and CE performed better in reducing neutral detergent fiber (NDF, 29.76% DM) and acid detergent fiber (ADF, 22.86% DM) contents than the addition of LF (33.71, 27.39% DM) or CE (32.07, 25.45% DM) alone. Moreover, the microbial analysis indicated that LF+CE treatments increased the abundance of desirable Lactobacillus and inhibited the growth of detrimental Enterobacter and Clostridia in alfalfa silage.

Discussion

Combined addition of FAE-producing LF and CE is more effective than treatments of LF or CE alone in improving fermentation quality and nutrition values of alfalfa silage. This is likely due to a synergistic effect of CE and FAE produced by LF on plant cell wall degradation, indicating that these additives promote each other to improve fiber degradation and silage fermentation. In conclusion, combined addition of FAE-producing LF and CE could be a feasible way to improve alfalfa silage quality.

Ferulic acid esterase-producing lactic acid bacteria and cellulase pretreatments of corn stalk silage at two different temperatures: Ensiling characteristics, carbohydrates composition and enzymatic saccharification

The effects of Acremonium cellulase and L. plantarum A1 with ferulic acid esterase activity on corn stalk silage fermentation characteristics, carbohydrate composition and enzymatic saccharification were studied at 25 and 40 °C, respectively. Corn stalk was ensiled without additive (C), Acremonium cellulase (AC), L. plantarum A1 (Lp) and AC + Lp for 60 days. Pretreatment with Lp or AC + Lp promoted the better silage fermentation and the degradation of lignocellulose as indicated by high lactic acid and low pH and lignocellulose content compared to control silages at 25 °C. AC + Lp performed better in reducing lignocellulose and DM loss. In addition, Lp alone enhanced enzymatic saccharification of corn stalk silage. However, the influence of L. plantarum A1 on corn stalk silage was not obvious at 40 °C. Corn stalk ensiled with combined additive is a suitable pretreatment method for subsequent biofuel production at 25 °C, but addition of Acremonium cellulase alone at 40 °C may be a promising method.

Novel xylanolytic triple domain enzyme targeted at feruloylated arabinoxylan degradation

A three catalytic domain multi-enzyme; a CE1 ferulic acid esterase, a GH62 α-l-arabinofuranosidase and a GH10 β-d-1,4-xylanase was identified in a metagenome obtained from wastewater treatment sludge. The capability of the CE1-GH62-GH10 multi-enzyme to degrade arabinoxylan was investigated to examine the hypothesis that CE1-GH62-GH10 would degrade arabinoxylan more efficiently than the corresponding equimolar mix of the individual enzymes. CE1-GH62-GH10 efficiently catalyzed the production of xylopyranose, xylobiose, xylotriose, arabinofuranose and ferulic acid (FA) when incubated with insoluble wheat arabinoxylan (WAX-I) (k_cat = 20.8 ± 2.6 s^-1). Surprisingly, in an equimolar mix of the individual enzymes a similar k_cat towards WAX-I was observed (k_cat = 17.3 ± 3.8 s^-1). Similarly, when assayed on complex plant biomass the activity was comparable between CE1-GH62-GH10 and an equimolar mix of the individual enzymes. This suggests that from a hydrolytic point of view a CE1-GH62-GH10 multi-enzyme is not an advantage. Determination of the melting temperatures for CE1-GH62-GH10 (71.0 ± 0.05 °C) and CE1 (69.9 ± 0.02), GH62 (65.7 ± 0.06) and GH10 (71 ± 0.05 °C) indicates that CE1 and GH62 are less stable as single domain enzymes. This conclusion was corroborated by the findings that CE1 lost ˜50% activity within 2 h, while GH62 retained ˜50% activity after 24 h, whereas CE1-GH62-GH10 and GH10 retained ˜50% activity for 72 h. GH62-GH10, when appended to each other, displayed a higher specificity constant (k_cat/K_m = 0.3 s^-1 mg^-1 ml) than the individual GH10 (k_cat/K_m = 0.12 s^-1 ± 0.02 mg^-1 ml) indicating a synergistic action between the two. Surprisingly, CE1-GH62, displayed a 2-fold lower k_cat towards WAX-I than GH62, which might be due to the presence of a putative carbohydrate binding module appended to CE1 at the N-terminal. Both CE1 and CE1-GH62 released insignificant amounts of FA from WAX-I, but FA was released from WAX-I when both CE1 and GH10 were present, which might be due to GH10 releasing soluble oligosaccharides that CE1 can utilize as substrate. CE1 also displayed activity towards solubilized 5-O-trans-feruloyl-α-l-Araf (k_cat = 36.35 s^-1). This suggests that CE1 preferably acts on soluble oligosaccharides.

Cloning and expression of ferulic acid esterase gene and its effect on wort filterability

OBJECTIVES

To optimize the expression of type A ferulic acid esterase (FaeA) from Aspergillus niger in Pichia pastoris X-33 using codon optimization.

RESULTS

Recombinant FaeA was purified from the fermentation broth, with the maximum specific activity of 48.4 ± 0.1 U mg^-1. Adding it during mashing process for beer brewing raised the filtration rate by 14.5% while the turbidity and viscosity declined by 22 and 6.9%, respectively. Addition of FaeA increased the concentrations of free ferulic acid (FA) and arabinoxylan (AX) in the wort, while the polymeric arabinoxylans content declined significantly.

CONCLUSIONS

Recombinant FaeA was capable to prevent the oxidative gelation of PAX formation by breaking the cross-linking of FA among AX chains and improve the filtration performance of wort.

A type D ferulic acid esterase from Streptomyces werraensis affects the volume of wheat dough pastries

A type D ferulic acid esterase (FAE) was identified in the culture supernatant of Streptomyces werraensis, purified, sequenced, and heterologously produced in E. coli BL21(DE3)Star by co-expressing chaperones groES-groEL (69 U L^-1). The unique enzyme with a mass of about 48 kDa showed no similarity to other FAEs, and only moderate homology (78.5%) to a Streptomycete β-xylosidase. The purified reSwFAED exhibited a temperature optimum of 40 °C, a pH optimum in the range from pH seven to eight and a clear preference for bulky natural substrates, such as 5-O-trans-feruloyl-L-arabinofuranose (FA) and β-D-xylopyranosyl-(1→2)-5-O-trans-feruloyl-L-arabinofuranose (FAX), compared to the synthetic standard substrate methyl ferulate. Treatment of wheat dough with as little as 0.03 U or 0.3 U kg^-1 reSwFAED activity resulted in a significant increase of the bun volume (8.0 or 9.7%, resp.) after baking when combined with polysaccharide-degrading enzymes from Aspergillus. For the first time, the long-standing, but rarely proven positive effect of a FAE in baking was confirmed.

Enrichment of maize and triticale bran with recombinant Aspergillus tubingensis ferulic acid esterase

Ferulic acid is a natural antioxidant found in various plants and serves as a precursor for various fine chemicals, including the flavouring agent vanillin. However, expensive extraction methods have limited the commercial application of ferulic acid, in particular for the enrichment of food substrates. A recombinant Aspergillus tubingensis ferulic acid esterase Type A (FAEA) was expressed in Aspergillus niger D15#26 and purified with anion-exchange chromatography (3487 U/mg, K_m  = 0.43 mM, K_cat = 0.48/min on methyl ferulate). The 36-kDa AtFAEA protein showed maximum ferulic acid esterase activity at 50 °C and pH 6, suggesting potential application in industrial processes. A crude AtFAEA preparation extracted 26.56 and 8.86 mg/g ferulic acid from maize bran and triticale bran, respectively, and also significantly increased the levels of p-coumaric and caffeic acid from triticale bran. The cost-effective production of AtFAEA could therefore allow for the enrichment of brans generally used as food and fodder, or for the production of fine chemicals (such as ferulic and p-coumaric acid) from plant substrates. The potential for larger-scale production of AtFAEA was demonstrated with the A. niger D15[AtfaeA] strain yielding a higher enzyme activity (185.14 vs. 83.48 U/ml) and volumetric productivity (3.86 vs. 1.74 U/ml/h) in fed-batch than batch fermentation.

Expression of a fungal ferulic acid esterase in suspension cultures of tall fescue (Festuca arundinacea) decreases cell wall feruloylation and increases rates of cell wall digestion

In the cell walls of grasses ferulic acid is esterified to arabinosyl residues in arabinoxylans that can then undergo oxidative coupling reactions to form ferulate dehydrodimers, trimers and oligomers which function to cross-link cell-wall polysaccharides, limiting cell wall degradability. Fungal ferulic acid esterase can release both esterified monomeric and dimeric ferulic acids from these cell wall arabinoxylans making the cell wall more susceptible to further enzymatic attack and increasing cell wall degradability. Non-embryogenic cell suspension cultures of Festuca arundinacea expressing a Aspergillus niger ferulic acid esterase (faeA) targeted to either the apoplast, or endoplasmic reticulum under the control of a constitutive actin promoter, or to the vacuole under the control of a soybean heat shock promoter, were established and FAE activity determined in the cells and medium during a growth cycle. Analysis of the ester-linked ferulates of the cell walls showed that all three transformed cell lines had both reduced ferulate levels and increased levels of xylanase mediated release of wall phenolics on autodigestion as well as increased rates of cell wall digestion in a simulated rumen environment, when compared to control non-transformed cells.

A halotolerant type A feruloyl esterase from Pleurotus eryngii

An extracellular feruloyl esterase (PeFaeA) from the culture supernatant of Pleurotus eryngii was purified to homogeneity using cation exchange, hydrophobic interaction, and size exclusion chromatography. The length of the complete coding sequence of PeFaeA was determined to 1668 bp corresponding to a protein of 555 amino acids. The catalytic triad of Ser-Glu-His demonstrated the uniqueness of the enzyme compared to previously published FAEs. The purified PeFaeA was a monomer with an estimated molecular mass of 67 kDa. Maximum feruloyl esterase (FAE) activity was observed at pH 5.0 and 50 °C, respectively. Metal ions (5 mM), except Hg(2+), had no significant influence on the enzyme activity. Substrate specificity profiling characterized the enzyme as a type A FAE preferring bulky natural substrates, such as feruloylated saccharides, rather than small synthetic ones. Km and kcat of the purified enzyme for methyl ferulate were 0.15 mM and 0.85 s(-1). In the presence of 3 M NaCl activity of the enzyme increased by 28 %. PeFaeA alone released only little ferulic acid from destarched wheat bran (DSWB), whereas after addition of Trichoderma viride xylanase the concentration increased more than 20 fold.