Efficient Extraction of Ferulic Acid from Sugar Beet Pulp Using the Culture Supernatant of Penicillium chrysogenum

Penicillium chrysogenum: Beyond the penicillin

Almost one century after the Sir Alexander Fleming's fortuitous discovery of penicillin and the identification of the fungal producer as Penicillium notatum, later Penicillium chrysogenum (currently reidentified as Penicillium rubens), the molecular mechanisms behind the massive production of penicillin titers by industrial strains could be considered almost fully characterized. However, this filamentous fungus is not only circumscribed to penicillin, and instead, it seems to be full of surprises, thereby producing important metabolites and providing expanded biotechnological applications. This review, in addition to summarizing the classical role of P. chrysogenum as penicillin producer, highlights its ability to generate an array of additional bioactive secondary metabolites and enzymes, together with the use of this microorganism in relevant biotechnological processes, such as bioremediation, biocontrol, production of bioactive nanoparticles and compounds with pharmaceutical interest, revalorization of agricultural and food-derived wastes or the enhancement of food industrial processes and the agricultural production.

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.

Gelation of konjac glucomannan by acetylmannan esterases from Aspergillus oryzae

Konjac glucomannan (KGM) is a principal component of the gelatinous food Konjac. Konjac production through alkali treatment releases an undesirable amine-odor. Two acetylesterases (AME1 and AME2) active against konjac glucomannan (polymer or oligomer) were purified from the supernatant of Aspergillus oryzae RIB40 culture. We cloned the genes encoding AME1 and AME2 based on the genomic information of A. oryzae, constructed their expression systems in A. oryzae, and obtained the recombinant enzymes (rAME1 and rAME2). rAME1 did not act on the KGM polymer but only on the KGM oligomer, releasing approximately 60% of the acetic acid in the substrate. However, rAME2 was active against both KGM substrates, releasing approximately 80% and 100% of acetic acid from the polymer and oligomer, respectively. Both enzymes were active against xylan and exhibited a trace activity on ethyl ferulate. The acetyl group position specificities of both enzymes were analyzed via heteronuclear single quantum correlation NMR using oligosaccharides of glucomannan prepared from Aloe vera (AGM), which has a higher acetyl group content than KGM. rAME1 acted specifically on single-substituted acetyl groups and not on double-substituted ones. In contrast, rAME2 appeared to act on all the acetyl groups in AGM. Treatment of 3% KGM with rAME2 followed by heating to 90 °C resulted in gel formation under weakly acidic conditions. This is the first study to induce gelation of KGM under these conditions. A comparison of the breaking and brittleness properties of gels formed by alkaline and enzymatic treatments revealed similar texture of the two gels. Furthermore, scanning electron microscopy of the surface structure of both gels revealed that both formed a fine mesh structure. Our findings on enzymatic gelation of KGM should lead to the development of new applications in food manufacturing industry.

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.

Advances and Prospects of Phenolic Acids Production, Biorefinery and Analysis

Biotechnological production of phenolic acids is attracting increased interest due to their superior antioxidant activity, as well as other antimicrobial, dietary, and health benefits. As secondary metabolites, primarily found in plants and fungi, they are effective free radical scavengers due to the phenolic group available in their structure. Therefore, phenolic acids are widely utilised by pharmaceutical, food, cosmetic, and chemical industries. A demand for phenolic acids is mostly satisfied by utilising chemically synthesised compounds, with only a low quantity obtained from natural sources. As an alternative to chemical synthesis, environmentally friendly bio-based technologies are necessary for development in large-scale production. One of the most promising sustainable technologies is the utilisation of microbial cell factories for biosynthesis of phenolic acids. In this paper, we perform a systematic comparison of the best known natural sources of phenolic acids. The advances and prospects in the development of microbial cell factories for biosynthesis of these bioactive compounds are discussed in more detail. A special consideration is given to the modern production methods and analytics of phenolic acids.

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.

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.

Secreted protein extract analyses present the plant pathogen Alternaria alternata as a suitable industrial enzyme toolbox

Lignocellulosic plant biomass is the most abundant carbon source in the planet, which makes it a potential substrate for biorefinery. It consists of polysaccharides and other molecules with applications in pharmaceutical, food and feed, cosmetics, paper and textile industries. The exploitation of these resources requires the hydrolysis of the plant cell wall, which is a complex process. Aiming to discover novel fungal natural isolates with lignocellulolytic capacities, a screening for feruloyl esterase activity was performed in samples taken from different metal surfaces. An extracellular enzyme extract from the most promising candidate, the natural isolate Alternaria alternata PDA1, was analyzed. The feruloyl esterase activity of the enzyme extract was characterized, determining the pH and temperature optima (pH 5.0 and 55-60 °C, respectively), thermal stability and kinetic parameters, among others. Proteomic analyses derived from two-dimensional gels allowed the identification and classification of 97 protein spots from the extracellular proteome. Most of the identified proteins belonged to the carbohydrates metabolism group, particularly plant cell wall degradation. Enzymatic activities of the identified proteins (β-glucosidase, cellobiohydrolase, endoglucanase, β-xylosidase and xylanase) of the extract were also measured. These findings confirm A. alternata PDA1 as a promising lignocellulolytic enzyme producer.

SIGNIFICANCE

Although plant biomass is an abundant material that can be potentially utilized by several industries, the effective hydrolysis of the recalcitrant plant cell wall is not a straightforward process. As this hydrolysis occurs in nature relying almost solely on microbial enzymatic systems, it is reasonable to infer that further studies on lignocellulolytic enzymes will discover new sustainable industrial solutions. The results included in this paper provide a promising fungal candidate for biotechnological processes to obtain added value from plant byproducts and analogous substrates. Moreover, the proteomic analysis of the secretome of a natural isolate of Alternaria sp. grown in the presence of one of the most used vegetal substrates on the biofuels industry (sugar beet pulp) sheds light on the extracellular enzymatic machinery of this fungal plant pathogen, and can be potentially applied to developing new industrial enzymatic tools. This work is, to our knowledge, the first to analyze in depth the secreted enzyme extract of the plant pathogen Alternaria when grown on a lignocellulosic substrate, identifying its proteins by means of MALDI-TOF/TOF mass spectrometry and characterizing its feruloyl esterase, cellulase and xylanolytic activities.

Diversity of fungal feruloyl esterases: updated phylogenetic classification, properties, and industrial applications

Feruloyl esterases (FAEs) represent a diverse group of carboxyl esterases that specifically catalyze the hydrolysis of ester bonds between ferulic (hydroxycinnamic) acid and plant cell wall polysaccharides. Therefore, FAEs act as accessory enzymes to assist xylanolytic and pectinolytic enzymes in gaining access to their site of action during biomass conversion. Their ability to release ferulic acid and other hydroxycinnamic acids from plant biomass makes FAEs potential biocatalysts in a wide variety of applications such as in biofuel, food and feed, pulp and paper, cosmetics, and pharmaceutical industries. This review provides an updated overview of the knowledge on fungal FAEs, in particular describing their role in plant biomass degradation, diversity of their biochemical properties and substrate specificities, their regulation and conditions needed for their induction. Furthermore, the discovery of new FAEs using genome mining and phylogenetic analysis of current publicly accessible fungal genomes will also be presented. This has led to a new subfamily classification of fungal FAEs that takes into account both phylogeny and substrate specificity.

Crystal structure of a feruloyl esterase belonging to the tannase family: a disulfide bond near a catalytic triad

Feruloyl esterase (FAE) catalyzes the hydrolysis of the ferulic and diferulic acids present in plant cell wall polysaccharides, and tannase catalyzes the hydrolysis of tannins to release gallic acid. The fungal tannase family in the ESTHER database contains various enzymes, including FAEs and tannases. Despite the importance of FAEs and tannases in bioindustrial applications, three-dimensional structures of the fungal tannase family members have been unknown. Here, we determined the crystal structure of FAE B from Aspergillus oryzae (AoFaeB), which belongs to the fungal tannase family, at 1.5 Å resolution. AoFaeB consists of a catalytic α/β-hydrolase fold domain and a large lid domain, and the latter has a novel fold. To estimate probable binding models of substrates in AoFaeB, an automated docking analysis was performed. In the active site pocket of AoFaeB, residues responsible for the substrate specificity of the FAE activity were identified. The catalytic triad of AoFaeB comprises Ser203, Asp417, and His457, and the serine and histidine residues are directly connected by a disulfide bond of the neighboring cysteine residues, Cys202 and Cys458. This structural feature, the "CS-D-HC motif," is unprecedented in serine hydrolases. A mutational analysis indicated that the novel structural motif plays essential roles in the function of the active site.