Harnessing recalcitrant lignocellulosic biomass for enhanced biohydrogen production: Recent advances, challenges, and future perspective

Biohydrogen (Bio-H2) is widely recognized as a sustainable and environmentally friendly energy source, devoid of any detrimental impact on the environment. Lignocellulosic biomass (LB) is a readily accessible and plentiful source material that can be effectively employed as a cost-effective and sustainable substrate for Bio-H2 production. Despite the numerous challenges, the ongoing progress in LB pretreatment technology, microbial fermentation, and the integration of molecular biology techniques have the potential to enhance Bio-H2 productivity and yield. Consequently, this technology exhibits efficiency and the capacity to meet the future energy demands associated with the valorization of recalcitrant biomass. To date, several pretreatment approaches have been investigated in order to improve the digestibility of feedstock. Nevertheless, there has been a lack of comprehensive systematic studies examining the effectiveness of pretreatment methods in enhancing Bio-H2 production through dark fermentation. Additionally, there is a dearth of economic feasibility evaluations pertaining to this area of research. Thus, this review has conducted comparative studies on the technological and economic viability of current pretreatment methods. It has also examined the potential of these pretreatments in terms of carbon neutrality and circular economy principles. This review paves the way for a new opportunity to enhance Bio-H2 production with technological approaches.

Potential applications of extremophilic bacteria in the bioremediation of extreme environments contaminated with heavy metals

Protecting the environment from harmful pollutants has become increasingly difficult in recent decades. The presence of heavy metal (HM) pollution poses a serious environmental hazard that requires intricate attention on a worldwide scale. Even at low concentrations, HMs have the potential to induce deleterious health effects in both humans and other living organisms. Therefore, various strategies have been proposed to address this issue, with extremophiles being a promising solution. Bacteria that exhibit resistance to metals are preferred for applications involving metal removal due to their capacity for rapid multiplication and growth. Extremophiles are a special group of microorganisms that are capable of surviving under extreme conditions such as extreme temperatures, pH levels, and high salt concentrations where other organisms cannot. Due to their unique enzymes and adaptive capabilities, extremophiles are well suited as catalysts for environmental biotechnology applications, including the bioremediation of HMs through various strategies. The mechanisms of resistance to HMs by extremophilic bacteria encompass: (i) metal exclusion by permeability barrier; (ii) extracellular metal sequestration by protein/chelator binding; (iii) intracellular sequestration of the metal by protein/chelator binding; (iv) enzymatic detoxification of a metal to a less toxic form; (v) active transport of HMs; (vi) passive tolerance; (vii) reduced metal sensitivity of cellular targets to metal ions; and (viii) morphological change of cells. This review provides comprehensive information on extremophilic bacteria and their potential roles for bioremediation, particularly in environments contaminated with HMs, which pose a threat due to their stability and persistence. Genetic engineering of extremophilic bacteria in stressed environments could help in the bioremediation of contaminated sites. Due to their unique characteristics, these organisms and their enzymes are expected to bridge the gap between biological and chemical industrial processes. However, the structure and biochemical properties of extremophilic bacteria, along with any possible long-term effects of their applications, need to be investigated further.

A critical review on plastic waste life cycle assessment and management: Challenges, research gaps, and future perspectives

The global production and consumption of plastics, as well as their deposition in the environment, are experiencing exponential growth. In addition, mismanaged plastic waste (PW) losses into drainage channels are a growing source of microplastic (MP) pollution concern. However, the complete understanding of their environmental implications throughout their life cycle is yet to be fully understood. Determining the potential extent to which MPs contribute to overall ecotoxicity is possible through the monitoring of PW release and MP removal during remediation. Life cycle assessments (LCAs) have been extensively utilized in many comparative analyses, such as comparing petroleum-based plastics with biomass and single-use plastics with multi-use alternatives. These assessments typically yield unexpected or paradoxical results. Nevertheless, there is still a paucity of reliable data and tools for conducting LCAs on plastics. On the other hand, the release and impact of MP have so far not been considered in LCA studies. This is due to the absence of inventory-related data regarding MP releases and the characterization factors necessary to quantify the effects of MP. Therefore, this review paper conducts a comprehensive literature review in order to assess the current state of knowledge and data regarding the environmental impacts that occur throughout the life cycle of plastics, along with strategies for plastic management through LCA.

Recent advances in sustainable hydrogen production from microalgae: Mechanisms, challenges, and future perspectives

The depletion of fossil fuel reserves has resulted from their application in the industrial and energy sectors. As a result, substantial efforts have been dedicated to fostering the shift from fossil fuels to renewable energy sources via technological advancements in industrial processes. Microalgae can be used to produce biofuels such as biodiesel, hydrogen, and bioethanol. Microalgae are particularly suitable for hydrogen production due to their rapid growth rate, ability to thrive in diverse habitats, ability to resolve conflicts between fuel and food production, and capacity to capture and utilize atmospheric carbon dioxide. Therefore, microalgae-based biohydrogen production has attracted significant attention as a clean and sustainable fuel to achieve carbon neutrality and sustainability in nature. To this end, the review paper emphasizes recent information related to microalgae-based biohydrogen production, mechanisms of sustainable hydrogen production, factors affecting biohydrogen production by microalgae, bioreactor design and hydrogen production, advanced strategies to improve efficiency of biohydrogen production by microalgae, along with bottlenecks and perspectives to overcome the challenges. This review aims to collate advances and new knowledge emerged in recent years for microalgae-based biohydrogen production and promote the adoption of biohydrogen as an alternative to conventional hydrocarbon biofuels, thereby expediting the carbon neutrality target that is most advantageous to the environment.

Strategies for efficient management of microplastics to achieve life cycle assessment and circular economy

The anticipated increase in the influx of plastic waste into aquatic environments has propelled the identification and elimination of plastic waste into the global agenda. The plastics sector generates a significant volume of materials, which, due to their extended durability, accumulate rapidly in natural ecosystems. Consequently, this indiscriminate utilization, along with the deposition of plastic waste (PW) in landfills and inadequate recycling practices, leads to diverse economic, social, and environmental consequences. Microplastics (MPs) are a type of PW that has been fragmented into particles measuring less than 5 mm. These particles have been found in several environments, including the air, soil, freshwater, and ocean ecosystems, where they accumulate in large quantities. In order to gain insight into the ecological risks and resource implications associated with a plastic product, it is strongly advised to conduct life cycle and sustainability analyses. Therefore, this paper examines various strategies aimed at achieving effective management of MP waste in order to develop a conceptual framework for MPs in circular economy and life cycle assessment (LCA). The findings of this study provides a new avenue for future research and contribution to manage MP waste as well as reduce their environmentally hazardous impact.

Decolorization of reactive azo dye using novel halotolerant yeast consortium HYC and proposed degradation pathway

The presence of high salinity levels in textile wastewater poses a significant obstacle to the process of decolorizing azo dyes. The present study involved the construction of a yeast consortium HYC, which is halotolerant and was recently isolated from wood-feeding termites. The consortium HYC was mainly comprised of Sterigmatomyces halophilus SSA-1575 and Meyerozyma guilliermondii SSA-1547. The developed consortium demonstrated a decolourization efficiency of 96.1% when exposed to a concentration of 50 mg/l of Reactive Black 5 (RB5). The HYC consortium significantly decolorized RB5 up to concentrations of 400 mg/l and in the presence of NaCl up to 50 g/l. The effects of physicochemical factors and the degradation pathway were systematically investigated. The optimal pH, salinity, temperature, and initial dye concentration were 7.0, 3%, 35 °C and 50 mg/l, respectively. The co-carbon source was found to be essential, and the addition of glucose resulted in a 93% decolorization of 50 mg/l RB5. The enzymatic activity of various oxido-reductases was assessed, revealing that NADH-DCIP reductase and azo reductase exhibited greater activity in comparison to other enzymes. UV-Visible (UV-vis) spectrophotometry, Fourier-transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC), and gas chromatography-mass spectrometry (GC-MS) were utilized to identify the metabolites generated during the degradation of RB5. Subsequently, a metabolic pathway was proposed. The confirmation of degradation was established through alterations in the functional groups and modifications in molecular weight. The findings indicate that this halotolerant yeast consortium exhibits promising potential of degrading dye compounds. The results of this study offer significant theoretical basis and crucial perspectives for the implementation of halotolerant yeast consortia in the bioremediation of textile and hypersaline wastewater. This approach is particularly noteworthy as it does not produce aromatic amines.

Bioplastic production in terms of life cycle assessment: A state-of-the-art review

The current transition to sustainability and the circular economy can be viewed as a socio-technical response to environmental impacts and the need to enhance the overall performance of the linear production and consumption paradigm. The concept of biowaste refineries as a feasible alternative to petroleum refineries has gained popularity. Biowaste has become an important raw material source for developing bioproducts and biofuels. Therefore, effective environmental biowaste management systems for the production of bioproducts and biofuels are crucial and can be employed as pillars of a circular economy. Bioplastics, typically plastics manufactured from bio-based polymers, stand to contribute to more sustainable commercial plastic life cycles as part of a circular economy in which virgin polymers are made from renewable or recycled raw materials. Various frameworks and strategies are utilized to model and illustrate additional patterns in fossil fuel and bioplastic feedstock prices for various governments' long-term policies. This review paper highlights the harmful impacts of fossil-based plastic on the environment and human health, as well as the mass need for eco-friendly alternatives such as biodegradable bioplastics. Utilizing new types of bioplastics derived from renewable resources (e.g., biowastes, agricultural wastes, or microalgae) and choosing the appropriate end-of-life option (e.g., anaerobic digestion) may be the right direction to ensure the sustainability of bioplastic production. Clear regulation and financial incentives are still required to scale from niche polymers to large-scale bioplastic market applications with a truly sustainable impact.

Can wood-feeding termites solve the environmental bottleneck caused by plastics? A critical state-of-the-art review

The abundance of synthetic polymers has become an ever-increasing environmental threat in the world. The excessive utilization of plastics leads to the accumulation of such recalcitrant pollutants in the environment. For example, during the COVID-19 pandemic, unprecedented demand for personal protective equipment (PPE) kits, face masks, and gloves made up of single-use items has resulted in the massive generation of plastic biomedical waste. As secondary pollutants, microplastic particles (<5 mm) are derived from pellet loss and degradation of macroplastics. Therefore, urgent intervention is required for the management of these hazardous materials. Physicochemical approaches have been employed to degrade synthetic polymers, but these approaches have limited efficiency and cause the release of hazardous metabolites or by-products into the environment. Therefore, bioremediation is a proper option as it is both cost-efficient and environmentally friendly. On the other hand, plants evolved lignocellulose to be resistant to destruction, whereas insects, such as wood-feeding termites, possess diverse microorganisms in their guts, which confer physiological and ecological benefits to their host. Plastic and lignocellulose polymers share a number of physical and chemical properties, despite their structural and recalcitrance differences. Among these similarities are a hydrophobic nature, a carbon skeleton, and amorphous/crystalline regions. Compared with herbivorous mammals, lignocellulose digestion in termites is accomplished at ordinary temperatures. This unique characteristic has been of great interest for the development of a plastic biodegradation approach by termites and their gut symbionts. Therefore, transferring knowledge from research on lignocellulosic degradation by termites and their gut symbionts to that on synthetic polymers has become a new research hotspot and technological development direction to solve the environmental bottleneck caused by synthetic plastic polymers.

Environmental and Human Health Impact of Disposable Face Masks During the COVID-19 Pandemic: Wood-Feeding Termites as a Model for Plastic Biodegradation

The ongoing COVID-19 pandemic has resulted in an unprecedented form of plastic pollution: personal protective equipment (PPE). On the eve of the COVID-19 pandemic, there is a tremendous increase in the production of plastic-based PPE. To control the spread of the virus, face masks (FMs) are used as primary PPE. Thus, the production and usage of FM significantly increased as the COVID-19 pandemic was still escalating. The primary raw materials for the manufacturing of FMs are non-biodegradable synthetic polymers derived from petrochemicals. This calls for an urgent need to develop novel strategies for the efficient degradation of plastics. Furthermore, most of these masks contain plastic or other derivatives of plastic. The extensive usage of FM generates millions of tons of plastic waste for the environment in a short span of time. However, their degradation in the environment and consequences are poorly understood. Therefore, the potential impacts of disposable FM on the environment and human health during the COVID-19 pandemic are clarified in the present study. Despite structural and recalcitrance variations, lignocellulose and plastic polymers have physicochemical features, including carbon skeletons with comparable chemical bonds as well as hydrophobic properties in amorphous and crystalline regions. In this review, we argue that there is much to be learned from termites by transferring knowledge from research on lignocellulose degradation by termites to that on plastic waste.

Biowastes for biodegradable bioplastics production and end-of-life scenarios in circular bioeconomy and biorefinery concept

Due to global urbanization, industrialization, and economic development, biowastes generation represents negative consequences on the environment and human health. The use of generated biowastes as a feedstock for biodegradable bioplastic production has opened a new avenue for environmental sustainability from the circular (bio)economy standpoint. Biodegradable bioplastic production can contribute to the sustainability pillars (environmental, economic, and social). Furthermore, bioenergy, biomass, and biopolymers production after recycling of biodegradable bioplastic can help to maintain the energy-environment balance. Several types of biodegradable bioplastic, such as starch-based, polyhydroxyalkanoates, polylactic acid, and polybutylene adipate terephthalate, can achieve this aim. In this review, an overview of the main biowastes valorization routes and the main biodegradable bioplastic types of production, application, and biodegradability are discussed to achieve the transition to the circular economy. Additionally, end-of-life scenarios (up-cycle and down-cycle) are reviewed to attain the maximum environmental, social, and economic benefit from biodegradable bioplastic products under biorefinery concept.

Exploring the potential of a newly constructed manganese peroxidase-producing yeast consortium for tolerating lignin degradation inhibitors while simultaneously decolorizing and detoxifying textile azo dye wastewater

MnP-YC4, a newly constructed manganese peroxidase-producing yeast consortium, has been developed to withstand lignin degradation inhibitors while degrading and detoxifying azo dye. MnP-YC4 tolerance to major biomass-derived inhibitors was promising. MnP induced by lignin was found to be highly related to dye decolorization by MnP-YC4. Simulated azo dye-containing wastewater supplemented with a lignin co-substrate (3,5-Dimethoxy-4-hydroxybenzaldehyde) decolorized up to 100, 91, and 76% at final concentrations of 20, 40, and 60%, respectively. MnP-YC4 effectively decolorized the real textile wastewater sample, reaching up to 91.4%, and the COD value decreased significantly during the decolorization, reaching 7160 mg/l within 7 days. A possible dye biodegradation pathway was proposed based on the degradation products identified by UV-vis, FTIR, GC/MS, and HPLC techniques, beginning with azo bond cleavage and eventually mineralized to CO₂ and H₂O. When compared to the phytotoxic original dye, the phytotoxicity of MnP-YC4 treated dye-containing wastewater samples confirmed the nontoxic nature.

Could termites be hiding a goldmine of obscure yet promising yeasts for energy crisis solutions based on aromatic wastes? A critical state-of-the-art review

Biodiesel is a renewable fuel that can be produced from a range of organic and renewable feedstock including fresh or vegetable oils, animal fats, and oilseed plants. In recent years, the lignin-based aromatic wastes, such as various aromatic waste polymers from agriculture, or organic dye wastewater from textile industry, have attracted much attention in academia, which can be uniquely selected as a potential renewable feedstock for biodiesel product converted by yeast cell factory technology. This current investigation indicated that the highest percentage of lipid accumulation can be achieved as high as 47.25% by an oleaginous yeast strain, Meyerozyma caribbica SSA1654, isolated from a wood-feeding termite gut system, where its synthetic oil conversion ability can reach up to 0.08 (g/l/h) and the fatty acid composition in yeast cells represents over 95% of total fatty acids that are similar to that of vegetable oils. Clearly, the use of oleaginous yeasts, isolated from wood-feeding termites, for synthesizing lipids from aromatics is a clean, efficient, and competitive path to achieve "a sustainable development" towards biodiesel production. However, the lacking of potent oleaginous yeasts to transform lipids from various aromatics, and an unknown metabolic regulation mechanism presented in the natural oleaginous yeast cells are the fundamental challenge we have to face for a potential cell factory development. Under this scope, this review has proposed a novel concept and approach strategy in utilization of oleaginous yeasts as the cell factory to convert aromatic wastes to lipids as the substrate for biodiesel transformation. Therefore, screening robust oleaginous yeast strain(s) from wood-feeding termite gut system with a set of the desirable specific tolerance characteristics is essential. In addition, to reconstruct a desirable metabolic pathway/network to maximize the lipid transformation and accumulation rate from the aromatic wastes with the applications of various "omics" technologies or a synthetic biology approach, where the work agenda will also include to analyze the genome characteristics, to develop a new base mutation gene editing technology, as well as to clarify the influence of the insertion position of aromatic compounds and other biosynthetic pathways in the industrial chassis genome on the expressional level and genome stability. With these unique designs running with a set of the advanced biotech approaches, a novel metabolic pathway using robust oleaginous yeast developed as a cell factory concept can be potentially constructed, integrated and optimized, suggesting that the hypothesis we proposed in utilizing aromatic wastes as a feedstock towards biodiesel product is technically promising and potentially applicable in the near future.

A critical review on the treatment of dye-containing wastewater: Ecotoxicological and health concerns of textile dyes and possible remediation approaches for environmental safety

The synthetic dyes used in the textile industry pollute a large amount of water. Textile dyes do not bind tightly to the fabric and are discharged as effluent into the aquatic environment. As a result, the continuous discharge of wastewater from a large number of textile industries without prior treatment has significant negative consequences on the environment and human health. Textile dyes contaminate aquatic habitats and have the potential to be toxic to aquatic organisms, which may enter the food chain. This review will discuss the effects of textile dyes on water bodies, aquatic flora, and human health. Textile dyes degrade the esthetic quality of bodies of water by increasing biochemical and chemical oxygen demand, impairing photosynthesis, inhibiting plant growth, entering the food chain, providing recalcitrance and bioaccumulation, and potentially promoting toxicity, mutagenicity, and carcinogenicity. Therefore, dye-containing wastewater should be effectively treated using eco-friendly technologies to avoid negative effects on the environment, human health, and natural water resources. This review compares the most recent technologies which are commonly used to remove dye from textile wastewater, with a focus on the advantages and drawbacks of these various approaches. This review is expected to spark great interest among the research community who wish to combat the widespread risk of toxic organic pollutants generated by the textile industries.

Performance of Meyerozyma caribbica as a novel manganese peroxidase-producing yeast inhabiting wood-feeding termite gut symbionts for azo dye decolorization and detoxification

For hazardous toxic pollutants such as textile wastewater and azo dyes, microbial-based and peroxidase-assisted remediation represents a highly promising and environmentally friendly alternative. Under this scope, gut symbionts of the wood-feeding termites Coptotermes formosanus and Reticulitermes chinenesis were used for the screening of manganese peroxidase (MnP) producing yeasts intended for decolorization and detoxification of textile azo dyes, such as Acid Orange 7 (AO7). To this end, nine out of 38 yeast isolates exhibited high levels of extracellular MnP activity ranging from 23 to 27 U/mL. The isolate PPY-27, which had the highest MnP activity, was able to decolorize various azo dyes with an efficiency ranging from 87.2 to 98.8%. This isolate, which represents the molecularly identified species Meyerozyma caribbica, was successfully characterized in terms of morphological and physiological traits, as well as enzymatic activities. Almost complete decolorization was achieved by the MnP-producing M. caribbica strain SSA1654 after 6 h of incubation with 50 mg/L of the sulfonated azo dye AO7 at 28 °C with an agitation speed of 150 rpm. The maximum decolorization efficiency of AO7 reached 93.8% at 400 mg/L. The decolorization of AO7 was confirmed by Fourier transform infrared (FTIR) and UV-Vis spectral analysis. High performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) were used to identify AO7 decomposition intermediates. Based on UV-Vis spectra, FTIR, HPLC, and GC-MS analyses, a plausible AO7 biodegradation mechanism pathway was explored, showing azo bond (-N=N-) cleavage and toxic aromatic amines mineralization CO₂ and H₂O. Microtox® and phytotoxicity assays confirmed that the AO7 metabolites produced by the strain SSA1654 were almost non-toxic compared to the original sulfonated azo dye.

Wood-feeding termite gut symbionts as an obscure yet promising source of novel manganese peroxidase-producing oleaginous yeasts intended for azo dye decolorization and biodiesel production

BACKGROUND

The ability of oxidative enzyme-producing micro-organisms to efficiently valorize organic pollutants is critical in this context. Yeasts are promising enzyme producers with potential applications in waste management, while lipid accumulation offers significant bioenergy production opportunities. The aim of this study was to explore manganese peroxidase-producing oleaginous yeasts inhabiting the guts of wood-feeding termites for azo dye decolorization, tolerating lignocellulose degradation inhibitors, and biodiesel production.

RESULTS

Out of 38 yeast isolates screened from wood-feeding termite gut symbionts, nine isolates exhibited high levels of extracellular manganese peroxidase (MnP) activity ranged between 23 and 27 U/mL after 5 days of incubation in an optimal substrate. Of these MnP-producing yeasts, four strains had lipid accumulation greater than 20% (oleaginous nature), with Meyerozyma caribbica SSA1654 having the highest lipid content (47.25%, w/w). In terms of tolerance to lignocellulose degradation inhibitors, the four MnP-producing oleaginous yeast strains could grow in the presence of furfural, 5-hydroxymethyl furfural, acetic acid, vanillin, and formic acid in the tested range. M. caribbica SSA1654 showed the highest tolerance to furfural (1.0 g/L), 5-hydroxymethyl furfural (2.5 g/L) and vanillin (2.0 g/L). Furthermore, M. caribbica SSA1654 could grow in the presence of 2.5 g/L acetic acid but grew moderately. Furfural and formic acid had a significant inhibitory effect on lipid accumulation by M. caribbica SSA1654, compared to the other lignocellulose degradation inhibitors tested. On the other hand, a new MnP-producing oleaginous yeast consortium designated as NYC-1 was constructed. This consortium demonstrated effective decolorization of all individual azo dyes tested within 24 h, up to a dye concentration of 250 mg/L. The NYC-1 consortium's decolorization performance against Acid Orange 7 (AO7) was investigated under the influence of several parameters, such as temperature, pH, salt concentration, and co-substrates (e.g., carbon, nitrogen, or agricultural wastes). The main physicochemical properties of biodiesel produced by AO7-degraded NYC-1 consortium were estimated and the results were compared to those obtained from international standards.

CONCLUSION

The findings of this study open up a new avenue for using peroxidase-producing oleaginous yeasts inhabiting wood-feeding termite gut symbionts, which hold great promise for the remediation of recalcitrant azo dye wastewater and lignocellulosic biomass for biofuel production.

Nanobiotechnological advancements in agriculture and food industry: Applications, nanotoxicity, and future perspectives

The high demand for sufficient and safe food, and continuous damage of environment by conventional agriculture are major challenges facing the globe. The necessity of smart alternatives and more sustainable practices in food production is crucial to confront the steady increase in human population and careless depletion of global resources. Nanotechnology implementation in agriculture offers smart delivery systems of nutrients, pesticides, and genetic materials for enhanced soil fertility and protection, along with improved traits for better stress tolerance. Additionally, nano-based sensors are the ideal approach towards precision farming for monitoring all factors that impact on agricultural productivity. Furthermore, nanotechnology can play a significant role in post-harvest food processing and packaging to reduce food contamination and wastage. In this review, nanotechnology applications in the agriculture and food sector are reviewed. Implementations of nanotechnology in agriculture have included nano- remediation of wastewater for land irrigation, nanofertilizers, nanopesticides, and nanosensors, while the beneficial effects of nanomaterials (NMs) in promoting genetic traits, germination, and stress tolerance of plants are discussed. Furthermore, the article highlights the efficiency of nanoparticles (NPs) and nanozymes in food processing and packaging. To this end, the potential risks and impacts of NMs on soil, plants, and human tissues and organs are emphasized in order to unravel the complex bio-nano interactions. Finally, the strengths, weaknesses, opportunities, and threats of nanotechnology are evaluated and discussed to provide a broad and clear view of the nanotechnology potentials, as well as future directions for nano-based agri-food applications towards sustainability.

Plastic wastes biodegradation: Mechanisms, challenges and future prospects

The growing accumulation of plastic wastes is one of the main environmental challenges currently faced by modern societies. These wastes are considered a serious global problem because of their effects on all forms of life. There is thus an urgent need to demonstrate effective eco-environmental techniques to overcome the hazardous environmental impacts of traditional disposal paths. However, our current knowledge on the prevailing mechanisms and the efficacy of synthetic plastics' biodegradation still appears limited. Under this scope, our review aims to comprehensively highlight the role of microbes, with special emphasis on algae, on the entire plastic biodegradation process focusing on the depolarization of various synthetic plastic types. Moreover, our review emphasizes on the ability of insects' gut microbial consortium to degrade synthetic plastic wastes. In this view, we discuss the schematic pathway of the biodegradation process of six types of synthetic plastics. These findings may contribute to establishing bio-upcycling processes of plastic wastes towards biosynthesis of valuable metabolic products. Finally, we discuss the challenges and opportunities for microbial valorization of degraded plastic wastes.

Coupling azo dye degradation and biodiesel production by manganese-dependent peroxidase producing oleaginous yeasts isolated from wood-feeding termite gut symbionts

BACKGROUND

Textile industry represents one prevalent activity worldwide, generating large amounts of highly contaminated and rich in azo dyes wastewater, with severe effects on natural ecosystems and public health. However, an effective and environmentally friendly treatment method has not yet been implemented, while concurrently, the increasing demand of modern societies for adequate and sustainable energy supply still remains a global challenge. Under this scope, the purpose of the present study was to isolate promising species of yeasts inhabiting wood-feeding termite guts, for combined azo dyes and textile wastewater bioremediation, along with biodiesel production.

RESULTS

Thirty-eight yeast strains were isolated, molecularly identified and subsequently tested for desired enzymatic activity, lipid accumulation, and tolerance to lignin-derived metabolites. The most promising species were then used for construction of a novel yeast consortium, which was further evaluated for azo dyes degradation, under various culture conditions, dye levels, as well as upon the addition of heavy metals, different carbon and nitrogen sources, and lastly agro-waste as an inexpensive and environmentally friendly substrate alternative. The novel yeast consortium, NYC-1, which was constructed included the manganese-dependent peroxidase producing oleaginous strains Meyerozyma caribbica, Meyerozyma guilliermondii, Debaryomyces hansenii, and Vanrija humicola, and showed efficient azo dyes decolorization, which was further enhanced depending on the incubation conditions. Furthermore, enzymatic activity, fatty acid profile and biodiesel properties were thoroughly investigated. Lastly, a dye degradation pathway coupled to biodiesel production was proposed, including the formation of phenol-based products, instead of toxic aromatic amines.

CONCLUSION

In total, this study might be the first to explore the application of MnP and lipid-accumulating yeasts for coupling dye degradation and biodiesel production.

Valorizing lignin-like dyes and textile dyeing wastewater by a newly constructed lipid-producing and lignin modifying oleaginous yeast consortium valued for biodiesel and bioremediation

Construction of a multipurpose yeast consortium suitable for lipid production, textile dye/effluent removal and lignin valorization is critical for both biorefinery and bioremediation. Therefore, a novel oleaginous consortium, designated as OYC-Y.BC.SH has been developed using three yeast cultures viz. Yarrowia sp. SSA1642, Barnettozyma californica SSA1518 and Sterigmatomyces halophilus SSA1511. The OYC-Y.BC.SH was able to grow on different carbon sources and accumulate lipids, with its highest lipid productivity (1.56 g/L/day) and lipase activity (170.3 U/mL) exhibited in xylose. The total saturated fatty acid content was 36.09 %, while the mono-unsaturated and poly-unsaturated fatty acids were 45.44 and 18.30 %, respectively, making OYC-Y.BC.SH valuable for biodiesel production. The OYC-Y.BC.SH showed its highest decolorization efficiency of Red HE3B dye (above 82 %) in presence of sorghum husk as agricultural co-substrate, suggesting its feasibility for simultaneous lignin valorization. The significant higher performance of OYC-Y.BC.SH on decolorizing the real dyeing effluent sample at pH 8.0 suggests its potential and suitability for degrading most of the wastewater textile effluents. Clearly, toxicological studies underline the additional advantage of using OYC-Y.BC.SH for bioremediation of industrial dyeing effluents in terms of decolorization and detoxification. A possible mechanism of Red HE3B biodegradation and ATP synthesis was also proposed.

Construction of a new lipase- and xylanase-producing oleaginous yeast consortium capable of reactive azo dye degradation and detoxification

A new oleaginous yeast consortium Y-BC-SH which stands for molecularly identified species Yarrowia sp., Barnettozyma californica and Sterigmatomyces halophilus was successfully constructed in this study. This multipurpose oleaginous yeast consortium was developed based on its higher ability to accumulate large amounts of lipids in the form of triacylglycerol, grow on xylose, produce lipase and xylanase and it could rapidly decolorize and degrade commonly-used textile reactive azo dyes. The specific enzyme activities of lipase, xylanase, xylan esterase, β-xylosidase, CMCase, β-glucosidase and cellobiohydrolase produced by Y-BC-SH were significantly higher than that of individual strains. As chemical oxygen demand reduction had occurred in the dye mixture solutions, it was evidence of their color removal and mineralization by Y-BC-SH. The significant induction of oxidoreductive enzymes by Y-BC-SH was probably due to the coordinated metabolic interactions of the individual strains. Phytotoxicity assay confirmed that metabolites generated after dye degradation by Y-BC-SH are non-toxic.

Performance of a Newly Isolated Salt-Tolerant Yeast Strain Sterigmatomyces halophilus SSA-1575 for Azo Dye Decolorization and Detoxification

The effective degradation of hazardous contaminants remains an intractable challenge in wastewater processing, especially for the high concentration of salty azo dye wastewater. However, some unique yeast symbionts identified from the termite gut system present an impressive function to deconstruct some aromatic compounds, which imply that they may be valued to work on the dye degradation for various textile effluents. In this investigation, a newly isolated and unique yeast strain, Sterigmatomyces halophilus SSA-1575, was identified from the gut system of a wood-feeding termite (WFT), Reticulitermes chinensis. Under the optimized ambient conditions, the yeast strain SSA-1575 showed a complete decolorization efficiency on Reactive Black 5 (RB5) within 24 h, where this azo dye solution had a concentration of a 50 mg/L RB5. NADH-dichlorophenol indophenol (NADH-DCIP) reductase and lignin peroxidase (LiP) were determined as the key reductase and oxidase of S. halophilus SSA-1575. Enhanced decolorization was recorded when the medium was supplemented with carbon and energy sources, including glucose, ammonium sulfate, and yeast extract. To understand a possible degradation pathway well, UV-Vis spectroscopy, FTIR and Mass Spectrometry analyses were employed to analyze the possible decolorization pathway by SSA-1575. Determination of relatively high NADH-DCIP reductase suggested that the asymmetric cleavage of RB5 azo bond was mainly catalyzed by NADH-DCIP reductase, and finally resulting in the formation of colorless aromatic amines devoid of any chromophores. The ecotoxicology assessment of RB5 after a decolorization processing by SSA-1575, was finally conducted to evaluate the safety of its metabolic intermediates from RB5. The results of Microtox assay indicate a capability of S. halophilus SSA-1575, in the detoxification of the toxic RB5 pollutant. This study revealed the effectiveness of halotolerant yeasts in the eco-friendly remediation of hazardous pollutants and dye wastewater processing for the textile industry.

Lycium shawii Roem. & Schult.: A new bioactive antimicrobial and antioxidant agent to combat multi-drug/pan-drug resistant pathogens of wound burn infections

The Multidrug Drug Resistance (MDR) and Pan-Drug Resistance (PDR) remain an intractable challenge issue in public health, worldwide. Plant extracts-based biological macromolecules containing a diverse array of secondary metabolites could be potentially used as alternative approaches to control or limit MDR/PDR infections. Plants of the Solanaceae family exhibit a wide variety of secondary metabolites with antioxidant and antimicrobial properties, which render them a significant role in food and pharmaceutical applications. To our knowledge, this is the first report on phytochemical constituents, antioxidant, antimicrobial activities and in vivo toxicological safety of Lycium shawii leaf extracts. Results revealed that phenolics and flavonoids were found to be the most abundant compounds in all extracts. Antioxidant activity of extracts was measured using DPPH^• and ABTS^•+ assays and the methanol extract displayed superior scavenging activity (IC₅₀ = 0.06 and 0.007 mg/mL for DPPH^• and ABTS^•+, respectively). Results of the GC-MS analysis revealed the identity of 10 compounds. Moreover, in vivo toxicological assessment can confirm the safety of L. shawii for use. Overall, L. shawii leaves are a promising natural source for the development of novel antimicrobial and antioxidant agents that could potentially combat clinical MDR/PDR pathogens.

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The drug resistance remains an intractable challenge in public health.

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Phenolics and flavonoids were the most abundant compounds in all extracts.

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Methanol extract was the most antioxidant and antimicrobial agent.

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p-coumaric acid, apigenin, and fisetin are the major identified compounds.

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In vivo toxicological assessment can confirm the safety of L. shawii for use.