Bundling the removal of emerging contaminants with the production of ligninolytic enzymes from residual streams

Abstract

Enzymes offer interesting features as biological catalysts for industry: high specificity, activity under mild conditions, accessibility, and environmental friendliness. Being able to produce enzymes in large quantities and having them available in a stable and reusable form reduces the production costs of any enzyme-based process. Agricultural residues have recently demonstrated their potential as substrates to produce ligninolytic enzymes by different white rot fungi. In this study, the biotechnological production of a manganese peroxidase (MnP) by Irpex lacteus was conducted through solid-state fermentation (SSF) with wheat straw as substrate and submerged fermentation (SmF) employing wheat straw extract (WSE). The obtained enzyme cocktail also showed manganese-independent activity (MiP), related to the presence of a short MnP and a dye-decolorizing peroxidase (DyP) which was confirmed by shotgun proteomic analyses. In view of the enhanced production of ligninolytic enzymes in SmF, different parameters such as WSE concentration and nitrogen source were evaluated. The highest enzyme titers were obtained with a medium formulated with glucose and peptone (339 U/L MnP and 15 U/L MiP). The scale-up to a 30 L reactor achieved similar activities, demonstrating the feasibility of enzyme production from the residual substrate at different production scales. Degradation of five emerging pollutants was performed to demonstrate the high oxidative capacity of the enzyme. Complete removal of hormones and bisphenol A was achieved in less than 1 h, whereas almost 30% degradation of carbamazepine was achieved in 24 h, which is a significant improvement compared to previous enzymatic treatments of this compound.

Key points

• Wheat straw extract is suitable for the growth of I. lacteus.

• The enzyme cocktail obtained allows the degradation of emerging contaminants.

• Mn-dependent and Mn-independent activities increases the catalytic potential.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11776-7.

Bioremediation of phenolic pollutant bisphenol A using optimized reverse micelles system of Trametes versicolor laccase in non-aqueous environment

In recent times, there is increased public interest and indeed strong movement against the use of Bisphenol A (4,4'-(propane-2,2,-diphenol)) due to its endocrine disrupting properties. In the present study, biotransformation of Bisphenol A (BPA) was accomplished using Trametes versicolor laccase (E.C. 1.10.3.2) enzyme. The enzyme was entrapped in reverse micelles comprising of bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) and 2,2,4-trimethylpentane (isooctane) for non-aqueous catalysis considering hydrophobicity of BPA. Screening of various parameters that may affect micellar system was carried out using Plackett-Burman experimental design and central composite design (Design Expert 11). According to Design Expert actual concentration of different variables was 0.55, 150 (Wo 30), 0.0035 mM and 175 µg/ml for Mg⁺²ions, Hydration ratio (Wo), 2,6-dimethoxyphenol (2,6 DMP, substrate) and laccase, respectively, at 40 °C and pH 4.5. Under these conditions laccase activity in reverse micelles was increased two folds as compared to unoptimized micellar system. It was evident that the reverse micelles diameter was linearly proportionated to the amount of laccase enzyme incorporated. BPA bioremediation mediated by laccase in non-aqueous environment was found to be 84% in 8 h of treatment. Biotransformation of BPA was monitored using GC-MS. BPA degraded products, such as BPA-O-catechol and 4,4 (Ethane 2-oxy 2-ol) diphenol were identified indicating transformation by oxidation.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02842-4.

Green sustainable process to revalorize purple corn cobs within a biorefinery frame: Co-production of bioactive extracts

Purple corn (Zea mays L.) is used for the preparation of traditional drinks and desserts, generating great quantities of residues. The scarce information about purple corn cob (PCC) is encouraging an interest in exploring its potential as a valuable source of bioactive compounds with benefits for human health. In this study, a green method based on hydrothermal processing was used for the simultaneous extraction of oligosaccharides and phenolic compounds from PCC. For this purpose, the effects of three factors (time, temperature and pH) on the oligosaccharide content (OSC), total phenolic content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC), as well as on the antioxidant activity measured with three different methods (DPPH, ABTS and FRAP) were evaluated. The bioactive extract obtained under optimal conditions presented a high content of bioactive compounds exhibiting a notable antioxidant capacity and moderate inhibitory activities towards xanthine oxidase. This extract was also structurally characterized by FTIR, HPAEC-DAD, MALDI-TOF-MS and TGA, and the HPLC-ESI-MS analysis led to the tentative identification of 15 antioxidant phenolic compounds. Thus, this research demonstrated that this residue from the food industry has a high potential for obtaining several bioactive compounds that can be utilized as multi-functional ingredients in the food and pharmaceutical industries.

Solar Photocatalytic Phenol Polymerization and Hydrogen Generation for Flocculation of Wastewater Impurities

Achieving global sustainability will require balancing encroaching climate changes while maintaining existing quality of life. Using sunlight to purify wastewater while simultaneously generating usable fuels is an opportunity to approach both targets in a cost-efficient manner. In addition, converting biomass products to usable polymers is a sustainable approach for potentially replacing polystyrene or other petroleum derived polymers. Phenols from medical, manufacturing, and agricultural waste are commonly found in many water sources, and they are known to foul common reverse osmosis membranes. Here, we show oxidative polymerization of guaiacol, an aromatic compound derived from biomass, with concurrent hydrogen gas generation by using platinum-seeded cadmium sulfide nanorods (Pt@CdS) as photocatalysts. Rather than forming short oligomers as typically made by enzymes such as laccase and peroxidase, the resulting polymers show higher molecular weights that can more easily flocculate out of water. By comparing guaiacol conversion to molecular weight and dispersity, the guaiacol was found to polymerize via a chain-growth process. We also show that Pt@CdS can polymerize other phenols as well by testing the monomers phenol, 2,6-dihydroxybenzoic acid, gallic acid, and vanillin. Lastly, because the aqueous solubility of these aromatic polymers decreases dramatically with molecular weight, polymerization reactions were also tested in biphasic solutions to determine if chain growth could propagate in the oil phase. We show that the Pt@CdS nanoparticles can form stable Pickering emulsions in various biphasic combinations, and that both H₂ formation and polymer molecular weight correlated with the partition coefficient of guaiacol into the oil phase as well as the solubility of the growing polymer chains. These combined studies demonstrate the possibility of using nanoscale photocatalysts to oxidatively polymerize phenolic substrates via a chain-growth mechanism, thereby providing a path for pretreating water by flocculating out contaminants with concurrent generation of hydrogen.

Laccase Activity as an Essential Factor in the Oligomerization of Rutin

The enzyme-mediated polymerization of bioactive phenolic compounds, such as the flavonoid rutin, has gained interest due to the enhanced physico-chemical and biological properties of the products, which increases their potential application as a nutraceutical. In this work, the influence of enzyme activity on rutin oligomerization was evaluated in reactions with low (1000 U/L) and high (10,000 U/L) initial laccase activities. For both reactions, high molecular weight oligomer fractions showed better properties compared to lower weight oligomers. Products of the reaction with low laccase activity exhibited thermal stability and antioxidant potential similar to control reaction, but led to higher inhibitory activity of xanthine oxidase and apparent aqueous solubility. Oligomers obtained in the reaction with high laccase activity showed better apparent aqueous solubility but decreased biological activities and stability. Their low antioxidant activity was correlated with a decreased phenolic content, which could be attributed to the formation of several bonds between rutin molecules.

Production of lignin based insoluble polymers (anionic hydrogels) by C. versicolor

Unlike previous lignin biodegradation studies, white rot fungi were used to produce functional biopolymers from Kraft lignin. Lignin-based polymers (hydrogel precursors) partially soluble in both aqueous and organic solvents were produced employing a relatively fast (6 days) enzymation of Kraft lignin with basidiomycetes, primarily Coriolus versicolor, pre-grown on kenaf/lignin agar followed by either vacuum evaporation or acid precipitation. After drying followed by a treatment with alkaline water, this intermediate polymer became a pH-sensitive anionic hydrogel insoluble in either aqueous or organic solvents. The yield of this polymer increased from 20 to 72 wt% with the addition of 2% dimethylsulfoxide to distilled water used as a medium. The mechanical stability and buffering capacity of this hydrogel can be adjusted by washing the intermediate polymer/hydrogel precursor prior to drying with solvents of different polarity (water, methanol or ethanol). Any of these polymers featured a significant thermal resilience assessed as a high thermostable “coked” fraction in thermal carbon analysis, apparently resulting from significant covalent cross-linking that occurs during the treatment of their intermediate precursors.