Microbial lipid biosynthesis from lignocellulosic biomass pyrolysis products

Exploring industrial lignocellulosic waste: Sources, types, and potential as high-value molecules

Lignocellulosic biomass has a promising role in a circular bioeconomy and may be used to produce valuable molecules for green chemistry. Lignocellulosic biomass, such as food waste, agricultural waste, wood, paper or cardboard, corresponded to 15.7% of all waste produced in Europe in 2020, and has a high potential as a secondary raw material for industrial processes. This review first presents industrial lignocellulosic waste sources, in terms of their composition, quantities and types of lignocellulosic residues. Secondly, the possible high added-value chemicals obtained from transformation of lignocellulosic waste are detailed, as well as their potential for applications in the food industry, biomedical, energy or chemistry sectors, including as sources of polyphenols, enzymes, bioplastic precursors or biofuels. In a third part, various available transformation treatments, such as physical treatments with ultrasound or heat, chemical treatments with acids or bases, and biological treatments with enzymes or microorganisms, are presented. The last part discusses the perspectives of the use of lignocellulosic waste and the fact that decreasing the cost of transformation is one of the major issues for improving the use of lignocellulosic biomass in a circular economy and green chemistry approach, since it is currently often more expensive than petroleum-based counterparts.

Strategic Developments in Polymer-Functionalized Liposomes for Targeted Colon Cancer Therapy: An Updated Review of Clinical Trial Data and Future Horizons

Liposomes, made up of phospholipid bilayers, are efficient nanocarriers for drug delivery because they can encapsulate both hydrophilic and lipophilic drugs. Conventional cancer treatments sometimes involve considerable toxicities and adverse drug reactions (ADRs), which limits their clinical value. Despite liposomes' promise in addressing these concerns, clinical trials have revealed significant limitations, including stability, targeted distribution, and scaling challenges. Recent clinical trials have focused on enhancing liposome formulations to increase therapeutic efficacy while minimizing negative effects. Notably, the approval of liposomal medications like Doxil demonstrates their potential in cancer treatment. However, the intricacy of liposome preparation and the requirement for comprehensive regulatory approval remain substantial impediments. Current clinical trial updates show continued efforts to improve liposome stability, targeting mechanisms, and payload capacity in order to address these issues. The future of liposomal drug delivery in cancer therapy depends on addressing these challenges in order to provide patients with more effective and safer treatment alternatives.

Enhanced bioethanol production by evolved Escherichia coli LGE2-H in a microbial electrolysis cell system

Lignocellulose pretreated using pyrolysis can yield clean energy (such as bioethanol) via microbial fermentation, which can significantly contribute to waste recycling, environmental protection, and energy security. However, the acids, aldehydes, and phenols present in bio-oil with inhibitory effects on microorganisms compromise the downstream utilization and conversion of lignocellulosic pyrolysates. In this study, we constructed a microbial electrolysis cell system for bio-oil detoxification and efficient ethanol production using evolved Escherichia coli to overcome the bioethanol production and utilization challenges highlighted in previous studies. In electrically treated bio-oil media, the E. coli-H strain exhibited significantly higher levoglucosan consumption and ethanol production capacities compared with the control. In undetoxified bio-oil media containing 1.0% (w/v) levoglucosan, E. coli-H produced 0.54 g ethanol/g levoglucosan, reaching 94% of the theoretical yield. Our findings will contribute to developing a practical method for bioethanol production from lignocellulosic substrates, and provide a scientific basis and technical demonstration for its industrialized application.

Bacterial transformation of lignin: key enzymes and high-value products

Lignin, a natural organic polymer that is recyclable and inexpensive, serves as one of the most abundant green resources in nature. With the increasing consumption of fossil fuels and the deterioration of the environment, the development and utilization of renewable resources have attracted considerable attention. Therefore, the effective and comprehensive utilization of lignin has become an important global research topic, with the goal of environmental protection and economic development. This review focused on the bacteria and enzymes that can bio-transform lignin, focusing on the main ways that lignin can be utilized to produce high-value chemical products. Bacillus has demonstrated the most prominent effect on lignin degradation, with 89% lignin degradation by Bacillus cereus. Furthermore, several bacterial enzymes were discussed that can act on lignin, with the main enzymes consisting of dye-decolorizing peroxidases and laccase. Finally, low-molecular-weight lignin compounds were converted into value-added products through specific reaction pathways. These bacteria and enzymes may become potential candidates for efficient lignin degradation in the future, providing a method for lignin high-value conversion. In addition, the bacterial metabolic pathways convert lignin-derived aromatics into intermediates through the "biological funnel", achieving the biosynthesis of value-added products. The utilization of this "biological funnel" of aromatic compounds may address the heterogeneous issue of the aromatic products obtained via lignin depolymerization. This may also simplify the separation of downstream target products and provide avenues for the commercial application of lignin conversion into high-value products.

Lipid Accumulation by Snf-β Engineered Mucor circinelloides Strains on Glucose and Xylose

Sucrose non-fermenting 1 (SNF1) protein kinase plays the regulatory roles in the utilization of selective carbon sources and lipid metabolism. Previously, the role of β subunit of SNF1 in lipid accumulation was evaluated by overexpression and knockout of Snf-β in oleaginous fungus M. circinelloides. In the present study, the growth and lipid accumulation of Snf-β overexpression and knockout strains were further analyzed and compared with glucose or xylose as a single or mixed carbon sources. The results showed that the lipid contents in Snf-β knockout strain improved by 23.2% (for glucose), 28.4% (for xylose), and 30.5% (for mixed glucose and xylose) compared with that of the control strain, respectively. The deletion of Snf-β subunit also altered the transcriptional level of acetyl-CoA carboxylase (ACC). The highest transcriptional levels of ACC1 in Snf-β knockout strain at 24 h were increased by 2.4-fold (for glucose), 2.8-fold (for xylose), and 3.1-fold (for mixed glucose and xylose) compared with that of the control strain, respectively. Our results indicated that Snf-β subunit enhanced lipid accumulation through the regulation of ACC1 in response to xylose or mixed sugars of glucose and xylose more significantly than that of response to glucose. This is the first study to explore the effect of Snf-β subunit of M. circinelloides in regulating lipid accumulation responding to different carbon nutrient signals of glucose and xylose. This study provides a foundation for the future application of the Snf-β engineered strains in lipid production from lignocellulose.

A comprehensive review on microbial lipid production from wastes: research updates and tendencies

Microbial lipids have recently attracted attention as an intriguing alternative for the biodiesel and oleochemical industries to achieve sustainable energy generation. However, large-scale lipid production remains limited due to the high processing costs. As multiple variables affect lipid synthesis, an up-to-date overview that will benefit researchers studying microbial lipids is necessary. In this review, the most studied keywords from bibliometric studies are first reviewed. Based on the results, the hot topics in the field were identified to be associated with microbiology studies that aim to enhance lipid synthesis and reduce production costs, focusing on the biological and metabolic engineering involved. The research updates and tendencies of microbial lipids were then analyzed in depth. In particular, feedstock and associated microbes, as well as feedstock and corresponding products, were analyzed in detail. Strategies for lipid biomass enhancement were also discussed, including feedstock adoption, value-added product synthesis, selection of oleaginous microbes, cultivation mode optimization, and metabolic engineering strategies. Finally, the environmental implications of microbial lipid production and possible research directions were presented.

Bioupgrading of the aqueous phase of pyrolysis oil from lignocellulosic biomass: a platform for renewable chemicals and fuels from the whole fraction of biomass

Pyrolysis, a thermal decomposition without oxygen, is a promising technology for transportable liquids from whole fractions of lignocellulosic biomass. However, due to the hydrophilic products of pyrolysis, the liquid oils have undesirable physicochemical characteristics, thus requiring an additional upgrading process. Biological upgrading methods could address the drawbacks of pyrolysis by utilizing various hydrophilic compounds as carbon sources under mild conditions with low carbon footprints. Versatile chemicals, such as lipids, ethanol, and organic acids, could be produced through microbial assimilation of anhydrous sugars, organic acids, aldehydes, and phenolics in the hydrophilic fractions. The presence of various toxic compounds and the complex composition of the aqueous phase are the main challenges. In this review, the potential of bioconversion routes for upgrading the aqueous phase of pyrolysis oil is investigated with critical challenges and perspectives.

Microbial Lipid Based Biorefinery Concepts: A Review of Status and Prospects

The use of lignocellulosic biomass as a raw material for the production of lipids has gained increasing attention, especially in recent years when the use of food in the production of biofuels has become a current technology. Thus, the competition for raw materials for both uses has brought the need to create technological alternatives to reduce this competition that could generate a reduction in the volume of food offered and a consequent commercial increase in the value of food. Furthermore, the use of microbial oils has been studied in many industrial branches, from the generation of renewable energy to the obtainment of several value-added products in the pharmaceutical and food industries. Thus, this review provides an overview of the feasibility and challenges observed in the production of microbial lipids through the use of lignocellulosic biomass in a biorefinery. Topics covered include biorefining technology, the microbial oil market, oily microorganisms, mechanisms involved in lipid-producing microbial metabolism, strain development, processes, lignocellulosic lipids, technical drawbacks, and lipid recovery.

Lipid accumulation and SNF1 transcriptional analysis of Mucor circinelloides on xylose under nitrogen limitation

Sucrose non-fermenting 1 (SNF1) plays a crucial role in utilizing non-glucose carbon sources and regulating lipid metabolism. However, the mechanism by which SNF1 regulates lipid accumulation in oleaginous filamentous fungi in response to nutrient signals remains unclear. In the present study, by analysing the growth and lipid accumulation of M. circinelloides on xylose under nitrogen limitation, combined with the transcriptional changes of each subunit of SNF1, the regulation of SNF1 between nutrient signal and lipid accumulation was explored. The results showed that with the increase of carbon/nitrogen (C/N) ratio, the xylose consumption and cell growth of M. circinelloides decreased, and the lipid accumulation increased gradually. The optimal C/N ratio was 160:1, and the maximum lipid yield was 4.1 g/L. Two subunits of SNF1, Snf-α1 and Snf-β, are related to the regulation of lipid metabolism in response to nutrient signals from different external nitrogen sources. This is the first report on the transcriptional analysis of SNF1 subunits on xylose metabolism under nitrogen limitation. This study provides a basis for further understanding of lipid synthesis mechanism on xylose in oleaginous fungi, and it also lays a foundation for the genetic engineering of high-lipid strain.

Discovery of Oleaginous Yeast from Mountain Forest Soil in Thailand

As an interesting alternative microbial platform for the sustainable synthesis of oleochemical building blocks and biofuels, oleaginous yeasts are increasing in both quantity and diversity. In this study, oleaginous yeast species from northern Thailand were discovered to add to the topology. A total of 127 yeast strains were isolated from 22 forest soil samples collected from mountainous areas. They were identified by an analysis of the D1/D2 domain of the large subunit rRNA (LSU rRNA) gene sequences to be 13 species. The most frequently isolated species were Lipomyces tetrasporus and Lipomyces starkeyi. Based on the cellular lipid content determination, 78 strains of ten yeast species, and two potential new yeast that which accumulated over 20% of dry biomass, were found to be oleaginous yeast strains. Among the oleaginous species detected, Papiliotrema terrestris and Papiliotrema flavescens have never been reported as oleaginous yeast before. In addition, none of the species in the genera Piskurozyma and Hannaella were found to be oleaginous yeast. L. tetrasporus SWU-NGP 2-5 accumulated the highest lipid content of 74.26% dry biomass, whereas Lipomyces mesembrius SWU-NGP 14-6 revealed the highest lipid quantity at 5.20 ± 0.03 g L-1. The fatty acid profiles of the selected oleaginous yeasts varied depending on the strain and suitability for biodiesel production.