Biodegradation of plastics for sustainable environment

Towards circular economy: Sustainable soil additives from natural waste fibres to improve water retention and soil fertility

Human activity is accompanied by the introduction of excessive amounts of artificial materials, including geosynthetics, into the environment, causing global environmental pollution. Moreover, climate change continues to negatively affect global water resources. With the intensification of environmental problems, material reusability and water consumption limitations have been proposed. This study replaced synthetic soil additives with biodegradable materials and analysed the potential and sustainable processing of natural fibrous materials, which form problematic waste. Waste fibres are the basis of innovative soil water storage technologies in the form of biodegradable and water-absorbing geocomposites (BioWAG). We analysed the influence of BioWAGs on plant vegetation and the environment through a three-year field experiment. Furthermore, biomass increases, drought effect reductions, and biodegradation mechanisms were analysed. Natural waste fibres had a positive influence, as they released easily accessible nutrients into the soil during biodegradation. BioWAGs had a positive influence on the biometric parameters of grass, increasing biomass growth by 430 %. Our results indicated that this is an effective method of waste fibre management that offers the possibility to manufacture innovative, environmentally friendly materials in compliance with the objectives of circular economy and the expectations of users.

Valorization of lignocellulosic biomass for polyhydroxyalkanoate production: Status and perspectives

With the increasing concerns regarding climate, energy, and plastic crises, bio-based production of biodegradable polymers has become a dire necessity. Significant progress has been made in biotechnology for the production of biodegradable polymers from renewable resources to achieve the goal of zero plastic waste and a net-zero carbon bioeconomy. In this review, an overview of polyhydroxyalkanoate (PHA) production from lignocellulosic biomass (LCB) was presented. Having established LCB-based biorefinery with proper pretreatment techniques, various PHAs could be produced from LCB-derived sugars, hydrolysates, and/or aromatic mixtures employing microorganisms. This provides a clue for addressing the current environmental crises because "biodegradable polymers" could be produced from one of the most abundant resources that are renewable and sustainable in a "carbon-neutral process". Furthermore, the potential future of LCB-to-non-natural PHA production was discussed with particular reference to non-natural PHA biosynthesis methods and LCB-derived aromatic mixture biofunnelling systems.

Insight into bacterial community profiles of oil shale and sandstone in ordos basin by culture-dependent and culture-independent methods

To promote the exploitation of unconventional oil resources by indigenous microorganisms, the bacterial community profiles of oil shale and sandstone in Ordos Basin were investigated using Illumina Miseq sequencing combined with the culture-based method, which was performed and reported in this literature for the first time. A total of 601 operational taxonomic units (OTUs) were obtained from collected samples, the predominant phylum present in all samples was Proteobacteria (76.96%-93.07%). Discriminatory bacterial community profiles existed in those samples by culture-dependent and culture-independent methods, with variations not only in diversity indices but also in the abundance of bacteria at different genus levels. The dominant genera in cultured sandstone sample (SCB), uncultured sandstone sample (SUB), cultured shale sample (YCB), uncultured shale sample (YUB) were Enhydrobacter (71.62%), Acidovorax (42.44%), Pseudomonas (40.13%), Variovorax (70.02%), respectively. Both sample sources and culturing methods were the principal factors affecting the variation, while the communities' structures were favored primarily by culture-dependent or culture-independent approaches. The high abundance of hydrocarbon degradation-related genes was exhibited in YCB, which reveals a great potential for utilization of the culture-dependent method in shale oil exploitation. This study provided guidance for the exploitation of shale oil and sandstone oil by artificial utilization of indigenous bacteria.

Concerted action of extracellular and cytoplasmic esterase and urethane-cleaving activities during Impranil biodegradation by Alicycliphilus denitrificans BQ1

The concerted action of commercial esterases, proteases and amidases has been demonstrated to be relevant in polyurethane (PU) degradation by in vitro experiments. However, the spatial and temporal dynamics of these activities during PU biodegradation by PU-degrading bacteria have not been addressed. Here, we examined the capability of Alicycliphilus denitrificans BQ1 to biodegrade the polyester (PS)-PU Impranil, analyzed the temporal and spatial coordination between the extracellular and cytoplasmic esterase and urethane-cleaving activities, and their independent and combined effects on Impranil biodegradation. A. denitrificans BQ1 grew in Impranil, and its clearing was correlated with the cleavage of ester and urethane groups since early times, with decrements of some Impranil compounds and the appearance of biodegradation products. While extracellular esterase was active at early times with its maximum at 18 h, urethanase appeared at this time and increased up to the end of the analysis (48 h), with the cytoplasmic activities behaving similarly but with lower levels than the extracellular ones. Both enzymatic activities exhibited distinct substrate specificity depending on their cellular localization and cultivation times, suggesting they cleave differentially located groups. As the urethane cleavage occurred since early times, when no urethane-cleaving activity was detected, different proteins should be acting at early and late times. In vitro experiments with independent or combined cellular protein fractions supported the previous deduction and confirmed the concerted action of extracellular and cytoplasmic esterase and urethane-cleaving activities. A two-stage process for Impranil degradation by A. denitrificans BQ1 is proposed.

In Silico Identification of Potential Sites for a Plastic-Degrading Enzyme by a Reverse Screening through the Protein Sequence Space and Molecular Dynamics Simulations

The accumulation of polyethylene terephthalate (PET) seriously harms the environment because of its high resistance to degradation. The recent discovery of the bacteria-secreted biodegradation enzyme, PETase, sheds light on PET recycling; however, the degradation efficiency is far from practical use. Here, in silico alanine scanning mutagenesis (ASM) and site-saturation mutagenesis (SSM) were employed to construct the protein sequence space from binding energy of the PETase–PET interaction to identify the number and position of mutation sites and their appropriate side-chain properties that could improve the PETase–PET interaction. The binding mechanisms of the potential PETase variant were investigated through atomistic molecular dynamics simulations. The results show that up to two mutation sites of PETase are preferable for use in protein engineering to enhance the PETase activity, and the proper side chain property depends on the mutation sites. The predicted variants agree well with prior experimental studies. Particularly, the PETase variants with S238C or Q119F could be a potential candidate for improving PETase. Our combination of in silico ASM and SSM could serve as an alternative protocol for protein engineering because of its simplicity and reliability. In addition, our findings could lead to PETase improvement, offering an important contribution towards a sustainable future.

Development of a Highly Efficient Environmentally Friendly Plasticizer

The purpose of this work is the synthesis of adipic acid ester and the study of the possibility of its use as a PVC plasticizer. The resulting butyl phenoxyethyl adipate was characterized by Fourier-transform infrared spectrometry, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The compatibility, effectiveness and plasticizing effect of butyl phenoxyethyl adipate in comparison with dioctylphthalate (DOP) were determined. The new environmentally friendly plasticizer has good compatibility with PVC and high thermal stability. The effectiveness of the plasticizing action of adipate based on the glass-transition temperature was 132.2 °C in relation to pure PVC and 7.7 °C in comparison to compounds based on DOP. An increase in the fluidity of the melt of polyvinyl chloride (PVC) compounds in the temperature range of 160–205 °C by 19–50% confirms a decrease in the energy intensity of the processes of manufacturing and the processing of polymer materials containing a new additive.