Enzymatic depolymerization of highly crystalline polyethylene terephthalate enabled in moist-solid reaction mixtures

Less than 9% of the plastic produced is recycled after use, contributing to the global plastic pollution problem. While polyethylene terephthalate (PET) is one of the most common plastics, its thermomechanical recycling generates a material of lesser quality. Enzymes are highly selective, renewable catalysts active at mild temperatures; however, they lack activity toward the more crystalline forms of PET commonly found in consumer plastics, requiring the energy-expensive melt-amorphization step of PET before enzymatic depolymerization. We report here that, when used in moist-solid reaction mixtures instead of the typical dilute aqueous solutions or slurries, the cutinase from Humicola insolens can directly depolymerize amorphous and crystalline regions of PET equally, without any pretreatment, with a 13-fold higher space-time yield and a 15-fold higher enzyme efficiency than reported in prior studies with high-crystallinity material. Further, this process shows a 26-fold selectivity for terephthalic acid over other hydrolysis products.

Determination of key-thermodynamic parameters using a kinetic modeling approach to describe the post-consumer poly(ethylene terephthalate) hydrolysis catalyzed by cutinase from Humicola insolens

The search for a straightforward technology for post-consumer poly(ethylene terephthalate) (PC-PET) degradation is essential to develop a circular economy. In this context, PET hydrolases such as cutinases can be used as bioplatforms for this purpose. Humicola insolens cutinase (HiC) is a promising biocatalyst for PC-PET hydrolysis. Therefore, this work evaluated a kinetic model, and it was observed that the HiC seems not to be inhibited by any of the main PET hydrolysis products such as terephthalic acid (TPA), mono-(2-hydroxyethyl) terephthalate (MHET), and bis-(2-hydroxyethyl) terephthalate (BHET). The excellent fitting of the experimental data to a kinetic model based on enzyme-limiting conditions validates its employment for describing the enzymatic PC-PET hydrolysis using two-particle size ranges (0.075-0.250, and 0.250-0.600 mm) and temperatures (40, 50, 55, 60, 70, and 80 ºC). The Arrhenius law provided a reliable parameter (activation energy of 98.9 ± 2.6 kJ mol −1 ) for enzymatic hydrolysis, which compares well with reported values for chemical PET hydrolysis. The thermodynamic parameters of PC-PET hydrolysis corresponded to activation enthalpy of 96.1 ± 3.6 kJ mol -1 and activation entropy of 10.8 ± 9.8 J mol -1 K -1 . Thus, the observed rate enhancement with temperature was attributed to the enthalpic contribution, and this understanding is helpful to the comprehension of enzymatic behavior on hydrolysis reaction.

Study of Associated Fungal Pathogens on Seeds of Eruca sativa Mill., (Gargeer)

The aim of the present study is to identification and classification of different associated fungi from the seeds of Eruca sativa. Total 10 species of fungal pathogens belonging to 7 genera are isolated from the Saudi (Ss) and Indian seeds of Eruca sativa. Saudi seeds affected by the fungal pathogens namely, A. niger, A. flavus, A fumigates, Mucor spp., Pencillium spp., while Indian seeds affected by Aspergillus niger, A. flavus, A. fumigates, Aspergillus terreus, Pencillium spp., Mucor spp., Rhizopus stolonifer, Humicola insolens, Colletotrichum gloeosporioides, Fusarium oxysporum. However, many of the soil borne or seed borne associated fungal pathogens spread the diseases in plants as well as in human beings. So the present study reveals that, the proper identification of fungal pathogens and their symptoms are easily recognized. Then the prevention care could be taken during the agriculture and high yield produced before the spread of symptoms and diseases.

A Novel CreA-Mediated Regulation Mechanism of Cellulase Expression in the Thermophilic Fungus Humicola insolens

The thermophilic fungus Humicola insolens produces cellulolytic enzymes that are of great scientific and commercial interest; however, few reports have focused on its cellulase expression regulation mechanism. In this study, we constructed a creA gene (carbon catabolite repressor gene) disruption mutant strain of H. insolens that exhibited a reduced radial growth rate and stouter hyphae compared to the wild-type (WT) strain. The creA disruption mutant also expressed elevated pNPCase (cellobiohydrolase activities), pNPGase (β-glucosidase activities), and xylanase levels in non-inducing fermentation with glucose. Unlike other fungi, the H. insolens creA disruption mutant displayed lower FPase (filter paper activity), CMCase (carboxymethyl cellulose activity), pNPCase, and pNPGase activity than observed in the WT strain when fermentation was induced using Avicel, whereas its xylanase activity was higher than that of the parental strain. These results indicate that CreA acts as a crucial regulator of hyphal growth and is part of a unique cellulase expression regulation mechanism in H. insolens. These findings provide a new perspective to improve the understanding of carbon catabolite repression regulation mechanisms in cellulase expression, and enrich the knowledge of metabolism diversity and molecular regulation of carbon metabolism in thermophilic fungi.