Biotransformation of toxic lignin and aromatic compounds of lignocellulosic feedstock into eco-friendly biopolymers by Pseudomonas putida KT2440

Bacterial valorization of lignin for the sustainable production of value-added bioproducts

As the most abundant aromatic biopolymer in the biosphere, lignin represents a promising alternative feedstock for the industrial production of various value-added bioproducts with enhanced economical value. However, the large-scale implementation of lignin valorization remains challenging because of the heterogeneity and irregular structure of lignin. General fragmentation and depolymerization processes often yield various products, but these approaches necessitate tedious purification steps to isolate target products. Moreover, microbial biocatalytic processes, especially bacterial-based systems with high metabolic activity, can depolymerize and further utilize lignin in an eco-friendly way. Considering that wild bacterial strains have evolved several metabolic pathways and enzymatic systems for lignin degradation, substantial efforts have been made to exploit their potential for lignin valorization. This review summarizes recent advances in lignin valorization for the production of value-added bioproducts based on bacterial systems. Additionally, the remaining challenges and available strategies for lignin biodegradation processes and future trends of bacterial lignin valorization are discussed.

Biological conversion of lignin-derived ferulic acid from wheat bran into vanillin

Lignin is a promising feedstock for producing vanillin, one of the most extensively used flavor enhancers. However, the biotransformation performance of lignin derivatives into vanillin is still unsatisfactory. In this study, an efficient conversion strategy of lignin into vanillin was established by employing engineered Saccharomyces cerevisiae as a whole-cell biocatalyst. Optimization of cell culture media and whole-cell bioconversion improved the production efficiency of vanillin. The vanillin titer reached 15.3 mM with a molar yield of 71 % in fed-batch fermentation mode, while incorporating in-situ product separation, demonstrated a remarkable 2.6-fold increase. The whole-cell bioconversion, coupled with in-situ separation, successfully converted real lignin hydrolysate into a record vanillin titer of 21.1 mM, equivalent to 1.8 mg of vanillin per gram of wheat bran biomass. The whole-cell bioconversion process integrated in-situ product separation, represents a sustainable approach for vanillin production and offers a promising pathway for lignin valorization.

A comprehensive review on biological funnel mechanism in lignin valorization: Pathways and enzyme dynamics

Lignin, a significant byproduct of the paper and pulp industry, is attracting interest due to its potential utilization in biomaterial-based sectors and biofuel production. Investigating biological methods for converting lignin into valuable products is crucial for effective utilization and has recently gained growing attention. Several microorganisms effectively decomposed low molecular weight lignins, transforming them into intermediate compounds via upper and lower metabolic pathways. This review focuses on assessing bacterial metabolic pathways involved in the breakdown of lignin into aromatic compounds and their subsequent utilization by different bacteria through various metabolic pathways. Understanding these pathways is essential for developing efficient synthetic metabolic systems to valorize lignin and obtain valuable industrial aromatic chemicals. The concept of "biological funneling," which involves examining key enzymes, their interactions, and the complex metabolic pathways associated with lignin conversion, is crucial in lignin valorization. By manipulating lignin metabolic pathways and utilizing biological routes, many aromatic compounds can be synthesized within cellular factories. Although there is insufficient evidence regarding the complete metabolism of polyaromatic hydrocarbons by particular microorganisms, understanding lignin-degrading enzymes, regulatory mechanisms, and interactions among various enzyme systems is essential for optimizing lignin valorization. This review highlights recent advancements in lignin valorization, bio-funneling, multi-omics, and analytical characterization approaches for aromatic utilization. It provides up-to-date information and insights into the latest research findings and technological innovations. The review offers valuable insights into the future potential of biological routes for lignin valorization.

Bioconversion of L-Tyrosine into p-Coumaric Acid by Tyrosine Ammonia-Lyase Heterologue of Rhodobacter sphaeroides Produced in Pseudomonas putida KT2440

p-Coumaric acid (p-CA) is a valuable compound with applications in food additives, cosmetics, and pharmaceuticals. However, traditional production methods are often inefficient and unsustainable. This study focuses on enhancing p-CA production efficiency through the heterologous expression of tyrosine ammonia-lyase (TAL) from Rhodobacter sphaeroides in Pseudomonas putida KT2440. TAL catalyzes the conversion of L-tyrosine into p-CA and ammonia. We engineered P. putida KT2440 to express TAL in a fed-batch fermentation system. Our results demonstrate the following: (i) successful integration of the TAL gene into P. putida KT2440 and (ii) efficient bioconversion of L-tyrosine into p-CA (1381 mg/L) by implementing a pH shift from 7.0 to 8.5 during fed-batch fermentation. This approach highlights the viability of P. putida KT2440 as a host for TAL expression and the successful coupling of fermentation with the pH-shift-mediated bioconversion of L-tyrosine. Our findings underscore the potential of genetically modified P. putida for sustainable p-CA production and encourage further research to optimize bioconversion steps and fermentation conditions.

Establishment of low-cost production platforms of polyhydroxyalkanoate bioplastics from Halomonas cupida J9

Microbial production of polyhydroxyalkanoate (PHA) is greatly restricted by high production cost arising from high-temperature sterilization and expensive carbon sources. In this study, a low-cost PHA production platform was established from Halomonas cupida J9. First, a marker-less genome-editing system was developed in H. cupida J9. Subsequently, H. cupida J9 was engineered to efficiently utilize xylose for PHA biosynthesis by introducing a new xylose metabolism module and blocking xylonate production. The engineered strain J9UΔxylD-P8xylA has the highest PHA yield (2.81 g/L) obtained by Halomonas with xylose as the sole carbon source so far. This is the first report on the production of short- and medium-chain-length (SCL-co-MCL) PHA from xylose by Halomonas. Interestingly, J9UΔxylD-P8xylA was capable of efficiently utilizing glucose and xylose as co-carbon sources for PHA production. Furthermore, fed-batch fermentation of J9UΔxylD-P8xylA coupled to a glucose/xylose co-feeding strategy reached up to 12.57 g/L PHA in a 5-L bioreactor under open and unsterile condition. Utilization of corn straw hydrolysate as the carbon source by J9UΔxylD-P8xylA reached 7.0 g/L cell dry weight (CDW) and 2.45 g/L PHA in an open fermentation. In summary, unsterile production in combination with inexpensive feedstock highlights the potential of the engineered strain for the low-cost production of PHA from lignocellulose-rich agriculture waste.

Pharmaceutical Applications of Biomass Polymers: Review of Current Research and Perspectives

Polymers derived from natural biomass have emerged as a valuable resource in the field of biomedicine due to their versatility. Polysaccharides, peptides, proteins, and lignin have demonstrated promising results in various applications, including drug delivery design. However, several challenges need to be addressed to realize the full potential of these polymers. The current paper provides a comprehensive overview of the latest research and perspectives in this area, with a particular focus on developing effective methods and efficient drug delivery systems. This review aims to offer insights into the opportunities and challenges associated with the use of natural polymers in biomedicine and to provide a roadmap for future research in this field.

Genome-scale and pathway engineering for the sustainable aviation fuel precursor isoprenol production in Pseudomonas putida

Sustainable aviation fuel (SAF) will significantly impact global warming in the aviation sector, and important SAF targets are emerging. Isoprenol is a precursor for a promising SAF compound DMCO (1,4-dimethylcyclooctane) and has been produced in several engineered microorganisms. Recently, Pseudomonas putida has gained interest as a future host for isoprenol bioproduction as it can utilize carbon sources from inexpensive plant biomass. Here, we engineer metabolically versatile host P. putida for isoprenol production. We employ two computational modeling approaches (Bilevel optimization and Constrained Minimal Cut Sets) to predict gene knockout targets and optimize the "IPP-bypass" pathway in P. putida to maximize isoprenol production. Altogether, the highest isoprenol production titer from P. putida was achieved at 3.5 g/L under fed-batch conditions. This combination of computational modeling and strain engineering on P. putida for an advanced biofuels production has vital significance in enabling a bioproduction process that can use renewable carbon streams.

Bacteria for Bioplastics: Progress, Applications, and Challenges

Bioplastics are one of the answers that can point society toward a sustainable future. Under this premise, the synthesis of polymers with competitive properties using low-cost starting materials is a highly desired factor in the industry. Also, tackling environmental issues such as nonbiodegradable waste generation, high carbon footprint, and consumption of nonrenewable resources are some of the current concerns worldwide. The scientific community has been placing efforts into the biosynthesis of polymers using bacteria and other microbes. These microorganisms can be convenient reactors to consume food and agricultural wastes and convert them into biopolymers with inherently attractive properties such as biodegradability, biocompatibility, and appreciable mechanical and chemical properties. Such biopolymers can be applied to several fields such as packing, cosmetics, pharmaceutical, medical, biomedical, and agricultural. Thus, intending to elucidate the science of microbes to produce polymers, this review starts with a brief introduction to bioplastics by describing their importance and the methods for their production. The second section dives into the importance of bacteria regarding the biochemical routes for the synthesis of polymers along with their advantages and disadvantages. The third section covers some of the main parameters that influence biopolymers' production. Some of the main applications of biopolymers along with a comparison between the polymers obtained from microorganisms and the petrochemical-based ones are presented. Finally, some discussion about the future aspects and main challenges in this field is provided to elucidate the main issues that should be tackled for the wide application of microorganisms for the preparation of bioplastics.

Bio-based Pickering emulsifier from mangosteen residues-derived sodium caseinate grafted spherical cellulose nanocrystals: Stability, rheological properties and microstructure studies

This study focuses on the preparation of mangosteen rind-derived nanocellulose via green ascorbic acid hydrolysis. Subsequently, milk protein-grafted nanocellulose particles were developed as a renewable Pickering emulsifier for water-oil stabilization. The stabilizing efficiency of modified nanocellulose (NC-S) at different caseinate (milk protein) concentrations (1.5, 3.0, and 4.0 % w/v) was tested in a water-in-oil emulsion (W/O ratio of 40:60). At a concentration 3.0 % w/v of caseinate (3.0NC-S), the emulsion exhibited a stronger network of adsorption between water, Pickering emulsifier, and oil. This resulted in reduced oil droplet flocculation, increased stability over a longer period, and favorable emulsifying properties, as depicted in the creaming index profile, oil droplet distribution, and rheology analysis. Since 3.0NC-S demonstrated the best colloidal stability, further focus will be placed on its microstructural properties, comparing them with those of mangosteen rind (MG), cellulose, and nanocellulose (NC-L). The XRD profile indicated that both NC-L and NC-S possessed a cellulose nanocrystal structure characterized as type I beta with a high crystallinity index above 60 %. Morphology investigation shown that the NC-L present in the spherical shape of particles with nanosized ranging at diameters of 11.27 ± 0.50 nm and length 11.76 ± 0.46 nm, while modified NC-S showed increase sized at 14.26 ± 4.60 nm and length 14.96 ± 4.94 nm. The increment of particle sizes from NC-L to NC-S indicated 2.82 × 10-15 mg/m2 of surface protein coverage by caseinate functional groups.

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.

Mechanism of furfural toxicity and metabolic strategies to engineer tolerance in microbial strains

Lignocellulosic biomass represents a carbon neutral cheap and versatile source of carbon which can be converted to biofuels. A pretreatment step is frequently used to make the lignocellulosic carbon bioavailable for microbial metabolism. Dilute acid pretreatment at high temperature and pressure is commonly utilized to efficiently solubilize the pentose fraction by hydrolyzing the hemicellulose fibers and the process results in formation of furans-furfural and 5-hydroxymethyl furfural-and other inhibitors which are detrimental to metabolism. The presence of inhibitors in the medium reduce productivity of microbial biocatalysts and result in increased production costs. Furfural is the key furan inhibitor which acts synergistically along with other inhibitors present in the hydrolysate. In this review, the mode of furfural toxicity on microbial metabolism and metabolic strategies to increase tolerance is discussed. Shared cellular targets between furfural and acetic acid are compared followed by discussing further strategies to engineer tolerance. Finally, the possibility to use furfural as a model inhibitor of dilute acid pretreated lignocellulosic hydrolysate is discussed. The furfural tolerant strains will harbor an efficient lignocellulosic carbon to pyruvate conversion mechanism in presence of stressors in the medium. The pyruvate can be channeled to any metabolite of interest by appropriate modulation of downstream pathway of interest. The aim of this review is to emphasize the use of hydrolysate as a carbon source for bioproduction of biofuels and other compounds of industrial importance.

Production of polyhydroxyalkanoates as a feasible alternative for an integrated multiproduct lignocellulosic biorefinery

Polyhydroxyalkanoates (PHAs) are considered an alternative to fossil fuel-based plastics. However, in spite of their interesting properties and their multiple applications, PHAs have not taken off as an industrial development. The reason is mainly due to the associated high-production costs, which represent a significant constraint. In recent years, the interest in lignocellulosic biomass (LCB) derived from crop, forestry or municipal waste by-products has been growing, since LCB is plentiful, cheap, renewable and sustainable. On this matter, the valorization of LCB into PHAs represents a promising route within circular economy strategies. However, much effort still needs to be made to improve the bioconversion yields and to enhance PHA production efficiency. So, this review focuses on reviewing the different options for PHA synthesis from LCB, stressing the progress in biomass deconstruction, enzymatic hydrolysis and microbial conversion. In addition, some of the current biological strategies for improving the process of bioconversion are discussed.

Customized valorization of waste streams by Pseudomonas putida: State-of-the-art, challenges, and future trends

Preventing catastrophic climate events warrants prompt action to delay global warming, which threatens health and food security. In this context, waste management using engineered microbes has emerged as a long-term eco-friendly solution for addressing the global climate crisis and transitioning to clean energy. Notably, Pseudomonas putida can valorize industry-derived synthetic wastes including plastics, oils, food, and agricultural waste into products of interest, and it has been extensively explored for establishing a fully circular bioeconomy through the conversion of waste into bio-based products, including platform chemicals (e.g., cis,cis-muconic and adipic acid) and biopolymers (e.g., medium-chain length polyhydroxyalkanoate). However, the efficiency of waste pretreatment technologies, capability of microbial cell factories, and practicability of synthetic biology tools remain low, posing a challenge to the industrial application of P. putida. The present review discusses the state-of-the-art, challenges, and future prospects for divergent biosynthesis of versatile products from waste-derived feedstocks using P. putida.