Characterization and application of a novel class II thermophilic peroxidase from Myceliophthora thermophila in biosynthesis of polycatechol

Tandem metalloenzymes gate plant cell entry by pathogenic fungi

Global food security is endangered by fungal phytopathogens causing devastating crop production losses. Many of these pathogens use specialized appressoria cells to puncture plant cuticles. Here, we unveil a pair of alcohol oxidase-peroxidase enzymes to be essential for pathogenicity. Using Colletotrichum orbiculare, we show that the enzyme pair is cosecreted by the fungus early during plant penetration and that single and double mutants have impaired penetration ability. Molecular modeling, biochemical, and biophysical approaches revealed a fine-tuned interplay between these metalloenzymes, which oxidize plant cuticular long-chain alcohols into aldehydes. We show that the enzyme pair is involved in transcriptional regulation of genes necessary for host penetration. The identification of these infection-specific metalloenzymes opens new avenues on the role of wax-derived compounds and the design of oxidase-specific inhibitors for crop protection.

Exploring the Diversity of Fungal DyPs in Mangrove Soils to Produce and Characterize Novel Biocatalysts

The functional diversity of the New Caledonian mangrove sediments was examined, observing the distribution of fungal dye-decolorizing peroxidases (DyPs), together with the complete biochemical characterization of the main DyP. Using a functional metabarcoding approach, the diversity of expressed genes encoding fungal DyPs was investigated in surface and deeper sediments, collected beneath either Avicennia marina or Rhizophora stylosa trees, during either the wet or the dry seasons. The highest DyP diversity was observed in surface sediments beneath the R. stylosa area during the wet season, and one particular operational functional unit (OFU1) was detected as the most abundant DyP isoform. This OFU was found in all sediment samples, representing 51–100% of the total DyP-encoding sequences in 70% of the samples. The complete cDNA sequence corresponding to this abundant DyP (OFU 1) was retrieved by gene capture, cloned, and heterologously expressed in Pichia pastoris. The recombinant enzyme, called DyP1, was purified and characterized, leading to the description of its physical–chemical properties, its ability to oxidize diverse phenolic substrates, and its potential to decolorize textile dyes; DyP1 was more active at low pH, though moderately stable over a wide pH range. The enzyme was very stable at temperatures up to 50 °C, retaining 60% activity after 180 min incubation. Its ability to decolorize industrial dyes was also tested on Reactive Blue 19, Acid Black, Disperse Blue 79, and Reactive Black 5. The effect of hydrogen peroxide and sea salt on DyP1 activity was studied and compared to what is reported for previously characterized enzymes from terrestrial and marine-derived fungi.

Fed-batch production of Thermothelomyces thermophilus lignin peroxidase using a recombinant Aspergillus nidulans strain in stirred-tank bioreactor

Enzymatic lignin depolymerization is considered a favorable approach to utilize lignin due to the higher selectivity and less energy requirement when compared to thermochemical lignin valorization. Lignin peroxidase (LiP) is one of the key enzymes involved in lignin degradation and possesses high redox potential to oxidize non-phenolic structures and phenolic compounds in lignin. However, the production of LiP is mainly from white-rot fungi at small scales. It is critical to discover new LiP from other microorganisms and produce LiP at large scales. This study aims to produce a novel LiP originally from Thermothelomyces thermophiles using a recombinant Aspergillus nidulans strain. The LiP production medium was optimized, and different fed-batch strategies for LiP production were investigated to improve LiP activity, yield, and productivity. Results demonstrated that LiP production was enhanced by using multi-pulse fed-batch fermentation. A maximum LiP activity of 1,645 mU/L with a protein concentration of 0.26 g/L was achieved.

A novel thermophile β-galactosidase from Thermothielavioides terrestris producing galactooligosaccharides from acid whey

β-Galactosidases are key enzymes in the food industry. Apart from the hydrolysis of the saccharide bond of lactose, they also catalyze transgalactosylation reactions, producing galactooligosaccharides (GOS) with prebiotic activity. Here we report the heterologous production in Pichia pastoris of a novel β-galactosidase from the fungus Thermothielavioides terrestris. The enzyme (TtbGal1) was purified and characterized, showing optimal activity at 60 °C and pH 4. TtbGal1 is thermostable, retaining almost full activity for 24 h at 50 °C. It was applied to the production of GOS from defined lactose solutions and acid whey, a liquid waste from the Greek yoghurt industry, reaching yields of 19.4 % and 14.8 %, respectively. HILIC-ESI-QTOF-MS analysis revealed the production of GOS with up to 4 saccharide monomers. The results demonstrate efficient GOS production catalyzed by TtbGal1, valorizing acid whey, a waste with a heavy polluting load from the dairy industry.

Screening of Recombinant Lignocellulolytic Enzymes Through Rapid Plate Assays

In the search for novel biomass-degrading enzymes through mining microbial genomes, it is necessary to apply functional tests during high-throughput screenings, which are capable of detecting enzymatic activities directly by way of plate assay. Using the most efficient expression systems of Escherichia coli and Pichia pastoris, the production of a high amount of His-tagged recombinant proteins could be thrived, allowing the one-step isolation by affinity chromatography. Here, we describe simple and efficient assay techniques for the detection of various biomass-degrading enzymatic activities on agar plates, such as cellulolytic, hemicellulolytic, and ligninolytic activities and their isolation using immobilized-metal affinity chromatography.

Thermophilic enzyme systems for efficient conversion of lignocellulose to valuable products: Structural insights and future perspectives for esterases and oxidative catalysts

Thermophilic enzyme systems are of major importance nowadays in all industrial processes due to their great performance at elevated temperatures. In the present review, an overview of the current knowledge on the properties of thermophilic and thermotolerant carbohydrate esterases and oxidative enzymes with great thermostability is provided, with respect to their potential use in biotechnological applications. A special focus is given to the lytic polysaccharide monooxygenases that are able to oxidatively cleave lignocellulose through the use of oxygen or hydrogen peroxide as co-substrate and a reducing agent as electron donor. Structural characteristics of the enzymes, including active site conformation and surface properties are discussed and correlated with their substrate specificity and thermostability properties.

Versatile Fungal Polyphenol Oxidase with Chlorophenol Bioremediation Potential: Characterization and Protein Engineering

Polyphenol oxidases (PPOs) have been mostly associated with the undesirable postharvest browning in fruits and vegetables and have implications in human melanogenesis. Nonetheless, they are considered useful biocatalysts in the food, pharmaceutical, and cosmetic industries. The aim of the present work was to characterize a novel PPO and explore its potential as a bioremediation agent. A gene encoding an extracellular tyrosinase-like enzyme was amplified from the genome of Thermothelomyces thermophila and expressed in Pichia pastoris The recombinant enzyme (TtPPO) was purified and biochemically characterized. Its production reached 40 mg/liter, and it appeared to be a glycosylated and N-terminally processed protein. TtPPO showed broad substrate specificity, as it could oxidize 28/30 compounds tested, including polyphenols, substituted phenols, catechols, and methoxyphenols. Its optimum temperature was 65°C, with a half-life of 18.3 h at 50°C, while its optimum pH was 7.5. The homology model of TtPPO was constructed, and site-directed mutagenesis was performed in order to increase its activity on mono- and dichlorophenols (di-CPs). The G292N/Y296V variant of TtPPO 5.3-fold increased activity on 3,5-dichlorophenol (3,5-diCP) compared to the wild type.IMPORTANCE A novel fungal PPO was heterologously expressed and biochemically characterized. Construction of single and double mutants led to the generation of variants with altered specificity against CPs. Through this work, knowledge is gained regarding the effect of mutations on the substrate specificity of PPOs. This work also demonstrates that more potent biocatalysts for the bioremediation of harmful CPs can be developed by applying site-directed mutagenesis.

Draft Genome Sequence of the Wood-Degrading Ascomycete Kretzschmaria deusta DSM 104547

We report here the draft genome of Kretzschmaria (Ustulina) deusta, an ascomycetous fungus that colonizes and substantially degrades hardwood and can infest living broad-leaved trees. The genome was assembled into 858 contigs, with a total size of 46.5 Mb, and 11,074 protein-coding genes were predicted.

Bioconversion of Biomass-Derived Phenols Catalyzed by Myceliophthora thermophila Laccase

Biomass-derived phenols have recently arisen as an attractive alternative for building blocks to be used in synthetic applications, due to their widespread availability as an abundant renewable resource. In the present paper, commercial laccase from the thermophilic fungus Myceliophthora thermophila was used to bioconvert phenol monomers, namely catechol, pyrogallol and gallic acid in water. The resulting products from catechol and gallic acid were polymers that were partially characterized in respect to their optical and thermal properties, and their average molecular weight was estimated via solution viscosity measurements and GPC. FT-IR and ¹H-NMR data suggest that phenol monomers are connected with ether or C–C bonds depending on the starting monomer, while the achieved molecular weight of polycatechol is found higher than the corresponding poly(gallic acid). On the other hand, under the same condition, pyrogallol was dimerized in a pure red crystalline compound and its structure was confirmed by ¹H-NMR as purpurogallin. The herein studied green synthesis of enzymatically synthesized phenol polymers or biological active compounds could be exploited as an alternative synthetic route targeting a variety of applications.