Pseudomonas fluorescens MFE01 uses 1-undecene as aerial communication molecule

Bacterial communication is a fundamental process used to synchronize gene expression and collective behavior among the bacterial population. The most studied bacterial communication system is quorum sensing, a cell density system, in which the concentration of inductors increases to a threshold level allowing detection by specific receptors. As a result, bacteria can change their behavior in a coordinated way. While in Pseudomonas quorum sensing based on the synthesis of N-acyl homoserine lactone molecules is well studied, volatile organic compounds, although considered to be communication signals in the rhizosphere, are understudied. The Pseudomonas fluorescens MFE01 strain has a very active type six secretion system that can kill some competitive bacteria. Furthermore, MFE01 emits numerous volatile organic compounds, including 1-undecene, which contributes to the aerial inhibition of Legionella pneumophila growth. Finally, MFE01 appears to be deprived of N-acyl homoserine lactone synthase. The main objective of this study was to explore the role of 1-undecene in the communication of MFE01. We constructed a mutant affected in undA gene encoding the enzyme responsible for 1-undecene synthesis to provide further insight into the role of 1-undecene in MFE01. First, we studied the impacts of this mutation both on volatile organic compounds emission, using headspace solid-phase microextraction combined with gas chromatography-mass spectrometry and on L. pneumophila long-range inhibition. Then, we analyzed influence of 1-undecene on MFE01 coordinated phenotypes, including type six secretion system activity and biofilm formation. Next, to test the ability of MFE01 to synthesize N-acyl homoserine lactones in our conditions, we investigated in silico the presence of corresponding genes across the MFE01 genome and we exposed its biofilms to an N-acyl homoserine lactone-degrading enzyme. Finally, we examined the effects of 1-undecene emission on MFE01 biofilm maturation and aerial communication using an original experimental set-up. This study demonstrated that the ΔundA mutant is impaired in biofilm maturation. An exposure of the ΔundA mutant to the volatile compounds emitted by MFE01 during the biofilm development restored the biofilm maturation process. These findings indicate that P. fluorescens MFE01 uses 1-undecene emission for aerial communication, reporting for the first time this volatile organic compound as bacterial intraspecific communication signal.

A dual cellular-heterogeneous catalyst strategy for the production of olefins from glucose

Living systems provide a promising approach to chemical synthesis, having been optimized by evolution to convert renewable carbon sources, such as glucose, into an enormous range of small molecules. However, a large number of synthetic structures can still be difficult to obtain solely from cells, such as unsubstituted hydrocarbons. In this work, we demonstrate the use of a dual cellular-heterogeneous catalytic strategy to produce olefins from glucose using a selective hydrolase to generate an activated intermediate that is readily deoxygenated. Using a new family of iterative thiolase enzymes, we genetically engineered a microbial strain that produces 4.3 ± 0.4 g l^-1 of fatty acid from glucose with 86% captured as 3-hydroxyoctanoic and 3-hydroxydecanoic acids. This 3-hydroxy substituent serves as a leaving group that enables heterogeneous tandem decarboxylation-dehydration routes to olefinic products on Lewis acidic catalysts without the additional redox input required for enzymatic or chemical deoxygenation of simple fatty acids.

Enzymes, In Vivo Biocatalysis, and Metabolic Engineering for Enabling a Circular Economy and Sustainability

Since the industrial revolution, the rapid growth and development of global industries have depended largely upon the utilization of coal-derived chemicals, and more recently, the utilization of petroleum-based chemicals. These developments have followed a linear economy model (produce, consume, and dispose). As the world is facing a serious threat from the climate change crisis, a more sustainable solution for manufacturing, i.e., circular economy in which waste from the same or different industries can be used as feedstocks or resources for production offers an attractive industrial/business model. In nature, biological systems, i.e., microorganisms routinely use their enzymes and metabolic pathways to convert organic and inorganic wastes to synthesize biochemicals and energy required for their growth. Therefore, an understanding of how selected enzymes convert biobased feedstocks into special (bio)chemicals serves as an important basis from which to build on for applications in biocatalysis, metabolic engineering, and synthetic biology to enable biobased processes that are greener and cleaner for the environment. This review article highlights the current state of knowledge regarding the enzymatic reactions used in converting biobased wastes (lignocellulosic biomass, sugar, phenolic acid, triglyceride, fatty acid, and glycerol) and greenhouse gases (CO₂ and CH₄) into value-added products and discusses the current progress made in their metabolic engineering. The commercial aspects and life cycle assessment of products from enzymatic and metabolic engineering are also discussed. Continued development in the field of metabolic engineering would offer diversified solutions which are sustainable and renewable for manufacturing valuable chemicals.

Fatty Acids and their Derivatives as Renewable Platform Molecules for the Chemical Industry

Oils and fats of vegetable and animal origin remain an important renewable feedstock for the chemical industry. Their industrial use has increased during the last 10 years from 31 to 51 million tonnes annually. Remarkable achievements made in the field of oleochemistry in this timeframe are summarized herein, including the reduction of fatty esters to ethers, the selective oxidation and oxidative cleavage of C-C double bonds, the synthesis of alkyl-branched fatty compounds, the isomerizing hydroformylation and alkoxycarbonylation, and olefin metathesis. The use of oleochemicals for the synthesis of a great variety of polymeric materials has increased tremendously, too. In addition to lipases and phospholipases, other enzymes have found their way into biocatalytic oleochemistry. Important achievements have also generated new oil qualities in existing crop plants or by using microorganisms optimized by metabolic engineering.

P450Jα : A New, Robust and α-Selective Fatty Acid Hydroxylase Displaying Unexpected 1-Alkene Formation

Oxyfunctionalization of fatty acids (FAs) is a key step in the design of novel synthetic pathways for biobased/biodegradable polymers, surfactants and fuels. Here, we show the isolation and characterization of a robust FA α-hydroxylase (P450_Jα ) which catalyses the selective conversion of a broad range of FAs (C6:0-C16:0) and oleic acid (C18:1) with H₂ O₂ as oxidant. Under optimized reaction conditions P450_Jα yields α-hydroxy acids all with >95 % regioselectivity, high specific activity (up to 15.2 U mg^-1 ) and efficient coupling of oxidant to product (up to 85 %). Lauric acid (C12:0) turned out to be an excellent substrate with respect to productivity (TON=394 min^-1 ). On preparative scale, conversion of C12:0 reached 83 % (0.9 g L^-1 ) when supplementing H₂ O₂ in fed-batch mode. Under similar conditions P450_Jα allowed further the first biocatalytic α-hydroxylation of oleic acid (88 % conversion on 100 mL scale) at high selectivity and in good yields (1.1 g L^-1 ; 79 % isolated yield). Unexpectedly, P450_Jα displayed also 1-alkene formation from shorter chain FAs (≤C10:0) showing that oxidative decarboxylation is more widely distributed across this enzyme family than reported previously.

Heterogeneous Non-noble Catalyst for Highly Selective Production of Linear α-Olefins from Fatty Acids: A Discovery of NiFe/C

Catalytic deoxygenation of even-numbered fatty acids into odd-chain linear α-olefins (LAOs) has emerged as a complementary strategy to oligomerization of ethylene, which only affords even-chain LAOs. Although enzymes and homogeneous catalysts have shown promising potential for this application, industrial production of LAOs through these catalytic systems is still very difficult to accomplish to date. A recent breakthrough involves the use of an expensive noble-metal catalyst, Pd/C, through a phosphine ligands-assisted method for LAOs production from fatty acid conversion. This study presents a unique, cost-friendly, non-noble bimetallic NiFe/C catalyst for highly selective LAOs production from fatty acids through decarbonylative dehydration. In the presence of acetic anhydride and phosphine ligand, a remarkable improvement in the yield of 1-heptadecene from the conversion of stearic acid was found over the supported bimetallic catalyst (NiFe/C) as compared to corresponding monometallic counterparts (Ni/C and Fe/C). Through optimization of the reaction conditions, a 70.1 % heptadecene yield with selectivity to 1-heptadecene as high as 92.8 % could be achieved over the bimetallic catalyst at just 190 °C. This unique bimetallic NiFe/C catalyst is composed of NiFe alloy in the material bulk phase and a surface mixture of NiFe alloy and oxidized NiFe^δ+ species, which offer a synergized contribution towards decarbonylative dehydration of stearic acid for 1-heptadecene production.

Highly selective production of linear 1-heptadecene from stearic acid over a partially reduced MoOx catalyst

Here, a MoO_x-T based catalyst was developed by a simple reduction of MoO₃ precursors at different temperatures. Interestingly, a partially reduced MoO_x-600 catalyst obtained by reducing the MoO₃ precursor at 600 °C shows the co-existence of a mixture of different valence states (0, +4, ∼+6) of Mo, and as a result, provides a superior catalytic activity.

Synthesis and characterization of a supported Pd complex on carbon nanofibers for the selective decarbonylation of stearic acid to 1-heptadecene: the importance of subnanometric Pd dispersion

Evaluation of the dispersion of Pd active sites on the catalyst performance during fatty acids decarbonylation to α-olefins was explored in this work. Pd subnanometric particles, clusters and aggregates were found to modulate the catalyst activity.

Benefit of a hemilabile ligand in deoxygenation of fatty acids to 1-alkenes

One of the most important tasks for chemistry in our time is to contribute to sustainable chemical production. A green industrial process for linear α-olefins, the arguably most important class of petrochemical intermediates, from renewable resources would be a major contribution to this end. Plant oils are attractive renewable feedstocks for this purpose because their triglycerides can be hydrolyzed to fatty acids that contain valuable long-chain hydrocarbons (C16-C22). These hydrocarbons may, in turn, be converted to α-olefins by the deoxygenation of the fatty acids. For the most selective of these deoxygenation reactions, transition-metal catalyzed decarbonylative dehydration, the density functional theory (DFT) calculations have just started to offer valuable mechanistic insight, and the use of this insight in rational catalyst design has been facilitated by the arrival of the first well-defined precatalyst for this reaction, Pd(cinnamyl)Cl(DPEphos) (1). Here, we present DFT calculations showing how, in 1, the hemilability of DPEphos, a classical P-O-P diphosphine, contributes to a low overall barrier and high α-selectivity. DPEphos facilitates decarbonylation by first switching from bidentate to monodentate binding to create a coordination site for CO. The recoordination of the dangling phosphine displaces the Pd-bound CO, a co-product that must leave the reactor for the reaction to proceed, and the escaping CO is here modelled using a low pressure in the calculation of its thermochemical corrections. Finally, the role of the hemilabile ligand suggests that further improvements in the decarbonylative dehydration of fatty acids to α-olefins might be achieved by exploring new, potentially asymmetric, hemilabile ligands.

Alkene Synthesis by Photocatalytic Chemoenzymatically Compatible Dehydrodecarboxylation of Carboxylic Acids and Biomass

Direct conversion of renewable biomass and bioderived chemicals to valuable synthetic intermediates for organic synthesis and materials science applications by means of mild and chemoselective catalytic methods has largely remained elusive. Development of artificial catalytic systems that are compatible with enzymatic reactions provides a synergistic solution to this enduring challenge by leveraging previously unachievable reactivity and selectivity modes. We report herein a dual catalytic dehydrodecarboxylation reaction that is enabled by a crossover of the photoinduced acridine-catalyzed O-H hydrogen atom transfer (HAT) and cobaloxime-catalyzed C-H-HAT processes. The reaction produces a variety of alkenes from readily available carboxylic acids. The reaction can be embedded in a scalable triple-catalytic cooperative chemoenzymatic lipase-acridine-cobaloxime process that allows for direct conversion of plant oils and biomass to long-chain terminal alkenes, precursors to bioderived polymers.

Reaction mechanisms at the homogeneous–heterogeneous frontier: insights from first-principles studies on ligand-decorated metal nanoparticles

The frontiers between homogeneous and heterogeneous catalysis are progressively disappearing.

Irradiation-induced palladium-catalyzed decarboxylative desaturation enabled by a dual ligand system

Generation of alkenes through decarboxyolefination of alkane carboxylates has significant synthetic value in view of the easy availability of a variety of carboxylic acids and the synthetic versatility of alkenes. Herein we report that palladium catalysts under irradiation with blue LEDs (440 nm) catalyze decarboxylative desaturation of a variety of aliphatic carboxylates to generate aliphatic alkenes, styrenes, enol ethers, enamides, and peptide enamides under mild conditions. The selection of a dual phosphine ligand system is the key enabler for the successful development of this reaction. The Pd-catalyzed decarboxylative desaturation is utilized to achieve a three-step divergent synthesis of Chondriamide A and Chondriamide C in overall 68% yield from simple starting materials. Mechanistic studies suggest that, distinct from palladium catalysis under thermal condition, irradiation-induced palladium catalysis involves irradiation-induced single-electron transfer and dynamic ligand-dissociation/association process to allow two phosphine ligand to work synergistically.

Production of alkenes through decarboxyolefination of carboxylates is a synthetically useful process. Here, the authors report a palladium/dual ligand-enabled decarboxylative desaturation reaction under mild irradiation conditions and apply it to the synthesis of Chondriamide A and C.

Amines as effective ligands in iridium-catalyzed decarbonylative dehydration of biosourced substrates

Linear α-olefins (LAOs) and linear internal olefins (LIOs) are essential intermediates in the synthesis of surfactants, lubricants, and polymers.