Biotransformation of Linoleic Acid into Hydroxy Fatty Acids and Carboxylic Acids Using a Linoleate Double Bond Hydratase as Key Enzyme

Advances in research on microbial conjugated linoleic acid bioconversion

Conjugated linoleic acid (CLA) is a functional food ingredient with prebiotic properties that provides health benefits for various human pathologies and disorders. However, limited natural CLA sources in animals and plants have led microorganisms like Lactobacillus and Bifidobacterium to emerge as new CLA sources. Microbial conversion of linoleic acid to CLA is mediated by linoleic acid isomerase and multicomponent enzymatic systems, with CLA production efficiency dependent on microbial species and strains. Additionally, complex factors like LA concentration, growth status, culture substrates, precursor type, prebiotic additives, and co-cultured microbe identity strongly influence CLA production and isomer composition. This review summarizes advances in the past decade regarding microbial CLA production, including bacteria and fungi. We highlight CLA production and potential regulatory mechanisms and discuss using microorganisms to enhance CLA content and nutritional value of fermented products. We also identify primary microbial CLA production bottlenecks and provide strategies to address these challenges and enhance production through functional gene and enzyme mining and downstream processing. This review aims to provide a reference for microbial CLA production and broaden the understanding of the potential probiotic role of microbial CLA producers.

Diet-derived male sex pheromone compounds affect female choice in a noctuid moth

Sexual signals often function in species recognition and may also guide mate choice within a species. In noctuid moths, both males and females may exercise mate choice. Females of the tobacco budworm Chloridea virescens prefer to mate with larger males, but the signal(s) underlying female choice remain unknown. Male hairpencil volatiles are emitted during close range courtship displays. However, previously identified male hairpencil volatiles, namely acetate esters, aldehydes, alcohols, and fatty acids, are not associated with female choice. Recently, two new hairpencil compounds were identified that elicit strong electrophysiological responses in female antennae: methyl salicylate (MeSA) and δ-decalactone. In this study, we investigated the effect of larval diet and adult feeding on MeSA and δ-decalactone content in hairpencils and determined whether these compounds are involved in female choice. We found that larval diet affected MeSA content in hairpencils, but not δ-decalactone. Conversely, adult feeding affected the level of δ-decalactone, but not MeSA: sugar-water feeding increased δ-decalactone content compared to plain water. In two-choice assays, females mated more with males that had higher amounts of δ-decalactone, and less with males with higher amounts of MeSA.

Building Flexible Escherichia coli Modules for Bifunctionalizing n-Octanol: The Byproduct of Oleic Acid Biorefinery

Artificial biorefinery of oleic acid into 1,10-decanedioic acid represents a revolutionizing route to the sustainable production of chemically difficult-to-make bifunctional chemicals. However, the carbon atom economy is extremely low (56%) due to the formation of unifunctional n-octanol. Here, we report a panel of recombinant Escherichia coli modules for diverse bifunctionalization, where the desired genetic parts are well distributed into different modules that can be flexibly combined in a plug-and-play manner. The designed ω-functionalizing modules could achieve ω-hydroxylation, consecutive ω-oxidation, or ω-amination of n-octanoic acid. By integrating these advanced modules with the reported oleic acid-cleaving modules, high-value C8 and C10 products, including ω-hydroxy acid, ω-amino acid, and α,ω-dicarboxylic acid, were produced with 100% carbon atom economy. These ω-functionalizing modules enabled the complete use of all of the carbon atoms from oleic acid (released from plant oil) for the green synthesis of structurally diverse bifunctional chemicals.

Production of lactones for flavoring and pharmacological purposes from unsaturated lipids: an industrial perspective

The enantiomeric pure and natural (+)-Lactones (C ≤ 14) with aromas obtained from fruits and milk are considered flavoring compounds. The flavoring value is related to the lactones' ring size and chain length, which blend in varying concentrations to produce different stone-fruit flavors. The nature-identical and enantiomeric pure (+)-lactones are only produced through whole-cell biotransformation of yeast. The industrially important γ-decalactone and δ-decalactone are produced by a four-step aerobic-oxidation of ricinoleic acid (RA) following the lactonization mechanism. Recently, metabolic engineering strategies have opened up new possibilities for increasing productivity. Another strategy for increasing yield is to immobilize the RA and remove lactones from the broth regularly. Besides flavor impact, γ-, δ-, ε-, ω-lactones of the carbon chain (C8-C12), the macro-lactones and their derivatives are vital in pharmaceuticals and healthcare. These analogues are isolated from natural sources or commercially produced via biotransformation and chemical synthesis processes for medicinal use or as active pharmaceutical ingredients. The various approaches to biotransformation have been discussed in this review to generate more prospects from a commercial point of view. Finally, this work will be regarded as a magical brick capable of containing both traditional and genetic engineering technology while contributing to a wide range of commercial applications.

Production of 8,11-dihydroxy fatty acids from oleic and palmitoleic acids by Escherichia coli cells expressing variant 6,8-linoleate diol synthases from Penicillium oxalicum

Recombinant Escherichia coli cells expressing 8,11-linoleate diol synthase (LDS) from Penicillium chrysogenum convert oleic and palmitoleic acids to 8-hydroperoxy-9(Z)-octadecenoic acid (HPOME) and 8-hydroperoxy-9(Z)-hexadecenoic acid (HPHME) only, respectively. However, recombinant E. coli cells expressing Q889A variant 6,8-LDS from Penicillium oxalicum as an 8,11-LDS converted oleic and palmitoleic acids to 8,11-dihydroxy-9(Z)-octadecenoic acid (DiHOME) and 8,11-dihydroxy-9(Z)-hexadecenoic acid (DiHHME), respectively, which were identified using LC-MS/MS analysis. To select suitable variants for producing these compounds, position 889 of 6,8-LDS from P. oxalicum was substituted with other amino acids, and recombinant E. coli cells expressing Q889L and Q889A variants were chosen as the best biocatalysts for producing 8,11-DiHOME and 8,11-DiHHME, respectively. The optimal conditions for producing 8,11-DiHOME or 8,11-DiHHME using cells expressing Q889L or Q889A variant 6,8-LDS were pH 6.5 and 30 °C with 5% (v/v) dimethyl sulfoxide (DMSO), 60 g L^-1 cells, and 10 g L^-1 oleic acid or 7.5 g L^-1 palmitoleic acid, respectively. Under these conditions, 10.7 g L^-1 8,11-DiHOME and 8.1 g L^-1 8,11-DiHHME were produced for 1.5 h with molar yields of 96.4 and 96.2% and productivities of 7.1 and 5.4 g L^-1  h^-1 , respectively. The molar yields and concentrations of 8,11-DiHOME and 8,11-DiHHME were highest among those of other reported DiHOMEs and DiHHMEs. To the best of our knowledge, this is the first quantitative production of 8,11-DiHOME and 8,11-DiHHME. This article is protected by copyright. All rights reserved.

Biotechnological formation of dairy flavor inducing δ-lactones from vegetable oil

Agroscope Culture Collection was screened to identify bacterial strains effective in production of dairy flavor inducing lactones using grapeseed oil as a substrate. Lentilactobacillus parafarraginis FAM-1079, Lactococcus lactis subsp. lactis FAM-17918, and L. lactis subsp. lactis biovar diacetylactis FAM-22003 showed the most efficient formation of targeted δ-lactones. The application of sublethal heat stress significantly increased target lactone production. The most profound improvement was for L. lactis subsp. lactis biovar diacetylactis where δ-octadecalactone generation was improved by factor of 9. The pre-fermentation step as well as growth phase in which bacteria are harvested did not have a significant impact on lactones yield. The lactone production process from vegetable oil developed in this study offers a new way of developing a natural flavor ingredient for incorporation into plant-based products.

Oleate Hydratase from Lactobacillus rhamnosus ATCC 53103: A FADH2-Dependent Enzyme with Remarkable Industrial Potential

Recently, we described the preparation of the recombinant oleate hydratase from Lactobacillus rhamnosus ATCC 53103. We observed that the purified C-terminal His-tagged enzyme was completely inactive and the catalytic activity was partially restored only in presence of a large amount of flavin adenine dinucleotide (FAD). In the present work, we assess that this hydratase in the presence of the reduced form of flavin adenine dinucleotide (FADH2) is at least one hundred times as active as in the presence of the same concentration of FAD. By means of two different biochemical processes, we demonstrated unambiguously that oleate hydratase from Lactobacillus rhamnosus ATCC 53103 is a FADH2-dependent enzyme. As a first relevant application of this discovery, we devised a preparative procedure for the stereoselective synthesis of (R)-10-hydroxystearic acid. Accordingly, the hydration of oleic acid (up to 50 g/L) is performed on a multigram scale using the recombinant hydratase and FADH2 generated in situ as cofactor. The produced (R)-10-hydroxystearic acid (ee > 97%) precipitates from the reaction solvent (water/glycerol/ethanol) and is conveniently recovered by simple filtration (>90% yield).

Discovery and Engineering of a Novel Baeyer-Villiger Monooxygenase with High Normal Regioselectivity

Baeyer-Villiger monooxygenases (BVMOs) are remarkable biocatalysts for the Baeyer-Villiger oxidation of ketones to generate esters or lactones. The regioselectivity of BVMOs is essential for determining the ratio of the two regioisomeric products ("normal" and "abnormal") when catalyzing asymmetric ketone substrates. Starting from a known normal-preferring BVMO sequence from Pseudomonas putida KT2440 (PpBVMO), a novel BVMO from Gordonia sihwensis (GsBVMO) with higher normal regioselectivity (up to 97/3) was identified. Furthermore, protein engineering increased the specificity constant (k_cat /K_M ) 8.9-fold to 484 s^-1  mM^-1 for 10-ketostearic acid derived from oleic acid. Consequently, by using the variant GsBVMO_C308L as an efficient biocatalyst, 10-ketostearic acid was efficiently transformed into 9-(nonanoyloxy)nonanoic acid, with a space-time yield of 60.5 g L^-1  d^-1 . This study showed that the mutant with higher regioselectivity and catalytic efficiency could be applied to prepare medium-chain ω-hydroxy fatty acids through biotransformation of long-chain aliphatic keto acids derived from renewable plant oils.

In-Depth Annotation Strategy of Saturated Hydroxy Fatty Acids Based on Their Chromatographic Retention Behaviors and MS Fragmentation Patterns

Hydroxy fatty acids are a class of bioactive compounds in a variety of organisms. The identification of hydroxy fatty acids in biological samples has still been a challenge because of their low abundance, high structural similarity, and limited availability of authentic hydroxy fatty acid standards. Here, we present a strategy for the annotation of saturated monohydroxyl fatty acids (OH-FAs) based on the integration of chromatographic retention rules and MS² fragmentation patterns. Thirty-nine authentic OH-FA standards were used to investigate their retention behavior on a reversed-phase stationary phase (C18) of liquid chromatography, and we found that their retention simultaneously follows two kinds of "carbon number rules". Using the "carbon number rules", the retention index (RI) of all OH-FAs that contain carbon numbers from 8 to 18 (C_8-18) can be predicted. Additionally, by studying the MS² fragmentation of OH-FAs under collision-induced dissociation, we found that the intensity ratio (IR) of the characteristic fragment ions ([M + H]⁺-63 and [M + H]⁺-45) is closely related to the position of the hydroxyl group on the OH-FA structure, which is helpful to further identify and confirm the OH-FA isomers. As a result, 97 of 107 potential OH-FAs detected in honey, human serum, and rice seedling by chemical isotope labeling-assisted liquid chromatography-mass spectrometry were annotated upon the RI matching and IR confirming. Furthermore, in order to simplify the annotation process of OH-FAs, we constructed an OH-FA library to facilitate the annotation of OH-FAs. Overall, this study provides a new and promising tool for the in-depth annotation of OH-FA isomers.

Enhancing detection and characterization of lipids using charge manipulation in electrospray ionization-tandem mass spectrometry

Heightened awareness regarding the implication of disturbances in lipid metabolism with respect to prevalent human-related pathologies demands analytical techniques that provide unambiguous structural characterization and accurate quantitation of lipids in complex biological samples. The diversity in molecular structures of lipids along with their wide range of concentrations in biological matrices present formidable analytical challenges. Modern mass spectrometry (MS) offers an unprecedented level of analytical power in lipid analysis, as many advancements in the field of lipidomics have been facilitated through novel applications of and developments in electrospray ionization tandem mass spectrometry (ESI-MS/MS). ESI allows for the formation of intact lipid ions with little to no fragmentation and has become widely used in contemporary lipidomics experiments due to its sensitivity, reproducibility, and compatibility with condensed-phase modes of separation, such as liquid chromatography (LC). Owing to variations in lipid functional groups, ESI enables partial chemical separation of the lipidome, yet the preferred ion-type is not always formed, impacting lipid detection, characterization, and quantitation. Moreover, conventional ESI-MS/MS approaches often fail to expose diverse subtle structural features like the sites of unsaturation in fatty acyl constituents or acyl chain regiochemistry along the glycerol backbone, representing a significant challenge for ESI-MS/MS. To overcome these shortcomings, various charge manipulation strategies, including charge-switching, have been developed to transform ion-type and charge state, with aims of increasing sensitivity and selectivity of ESI-MS/MS approaches. Importantly, charge manipulation approaches afford enhanced ionization efficiency, improved mixture analysis performance, and access to informative fragmentation channels. Herein, we present a critical review of the current suite of solution-based and gas-phase strategies for the manipulation of lipid ion charge and type relevant to ESI-MS/MS.

Recombinant Oleate Hydratase from Lactobacillus rhamnosus ATCC 53103: Enzyme Expression and Design of a Reliable Experimental Procedure for the Stereoselective Hydration of Oleic Acid

Different microbial strains are able to transform oleic acid (OA) into 10-hydroxystearic acid (10-HSA) by means of the catalytic activity of the enzymes oleate hydratase (EC 4.2.1.53). Lactobacillus rhamnosus ATCC 53103 performs this biotransformation with very high stereoselectivity, affording enantiopure (R)-10-HSA. In this work, we cloned, in Escherichia coli, the oleate hydratase present in the above-mentioned probiotic strain. Our study demonstrated that the obtained recombinant hydratase retains the catalytic properties of the Lactobacillus strain but that its activity was greatly affected by the expression procedure. According to our findings, we devised a reliable procedure for the hydration of oleic acid using a recombinant E. coli whole-cell catalyst. We established that the optimal reaction conditions were pH 6.6 at 28 °C in phosphate buffer, using glycerol and ethanol as co-solvents. According to our experimental protocol, the biocatalyst does not show significant substrate inhibition as the hydration reaction can be performed at high oleic acid concentration (up to 50 g/L).

Fatty Acid Hydratases: Versatile Catalysts to Access Hydroxy Fatty Acids in Efficient Syntheses of Industrial Interest

The utilization of hydroxy fatty acids has gained more and more attention due to its applicability in many industrial building blocks that require it, for example, polymers or fragrances. Furthermore, hydroxy fatty acids are accessible from biorenewables, thus contributing to a more sustainable raw material basis for industrial chemicals. Therefore, a range of investigations were done on fatty acid hydratases (FAHs), since these enzymes catalyze the addition of water to an unsaturated fatty acid, thus providing an elegant route towards hydroxy-substituted fatty acids. Besides the discovery and characterization of fatty acid hydratases (FAHs), the design and optimization of syntheses with these enzymes, the implementation in elaborate cascades, and the improvement of these biocatalysts, by way of mutation in terms of the substrate scope, has been investigated. This mini-review focuses on the research done on process development using fatty acid hydratases as a catalyst. It is notable that biotransformations, running at impressive substrate loadings of up to 280 g L−1, have been realized. A further topic of this mini-review is the implementation of fatty acid hydratases in cascade reactions. In such cascades, fatty acid hydratases were, in particular, combined with alcohol dehydrogenases (ADH), Baeyer-Villiger monooxygenases (BVMO), transaminases (TA) and hydrolases, thus enabling access to a broad variety of molecules that are of industrial interest.

Design and engineering of whole-cell biocatalytic cascades for the valorization of fatty acids

This review presents the key factors to construct a productive whole-cell biocatalytic cascade exemplified for the biotransformation of renewable fatty acids.

Organocatalyzed ring opening polymerization of regio-isomeric lactones: reactivity and thermodynamics considerations

Study of the kinetics and thermodynamics of the organocatalyzed ring opening polymerization of a regio-isomeric mixture of β,δ-trimethyl-ε-caprolactones (TMCL).

A single-host fermentation process for the production of flavor lactones from non-hydroxylated fatty acids

Lactone flavors with fruity, milky, coconut, and other aromas are widely used in the food and fragrance industries. Lactones are produced by chemical synthesis or by biotransformation of plant-sourced hydroxy fatty acids. We established a novel method to produce flavor lactones from abundant non-hydroxylated fatty acids using yeast cell factories. Oleaginous yeast Yarrowia lipolytica was engineered to perform hydroxylation of fatty acids and chain-shortening via β-oxidation to preferentially twelve or ten carbons. The strains could produce γ-dodecalactone from oleic acid and δ-decalactone from linoleic acid. Through metabolic engineering, the titer was improved 4-fold, and the final strain produced 282 mg/L γ-dodecalactone in a fed-batch bioreactor. The study paves the way for the production of lactones by fermentation of abundant fatty feedstocks.

Generating Fatty Acid Profiles in the Gas Phase: Fatty Acid Identification and Relative Quantitation Using Ion/Ion Charge Inversion Chemistry

Representing the most fundamental lipid class, fatty acids (FA) play vital biological roles serving as energy sources, cellular signaling molecules, and key architectural components of complex lipids. Direct infusion electrospray ionization spectrometry, also known as shotgun lipidomics, has emerged as a rapid and powerful toolbox for lipid analysis. While shotgun lipidomics can be a sensitive approach to FA detection, the diverse molecular structure of FA presents challenges for unambiguous identification and the relative quantification of isomeric contributors. In particular, pinpointing double bond position(s) in unsaturated FA and determining the relative contribution of double bond isomers has limited the application of the shotgun approach. Recently, we reported the use of gas-phase ion/ion reactions to facilitate the identification of FA. Briefly, singly deprotonated FA anions undergo charge inversion when reacted in the gas phase with tris-phenanthroline magnesium dications by forming [FA - H + MgPhen]+ complex ions. These charge-inverted FA complex cations fragment upon ion-trap collision-induced dissociation (CID) to generate product ion spectra unique to individual FA isomers. Herein, we report the development of a mass spectral library comprised of [FA - H + MgPhen]+ product ion spectra. The developed FA library permits confident FA identification, including polyunsaturated FA isomers. Furthermore, we demonstrate the ability to determine relative contributions of isomeric FA using multiple linear regression analysis paired with gas-phase ion/ion reactions. We successfully applied the presented method to generate a FA profile for bovine liver phospholipidome based entirely on gas-phase chemistries.

Sustainable Biotransformation of Oleic Acid to 10-Hydroxystearic Acid by a Recombinant Oleate Hydratase from Lactococcus garvieae

Enzymatic hydration of oleic acid into 10-hydroxystearic acid (10-HSA) represents a theme of substantial scientific and practical interest. In this study, a fatty acid hydratase (OHase) from Lactococcus garvieae was cloned and expressed in Escherichia coli. The recombinantly expressed enzyme was identified as oleate hydratase (EC 4.2.1.53) confirming its highest hydration activity for oleic acid. The optimally yielded enzyme fraction was purified and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A solitary band on SDS-PAGE confirmed the molecular weight of 65 kDa. Gas chromatography-mass spectrometry (GC-MS) analysis scrutinized the silylated hydroxy fatty acid products acquired from the hydration of oleic acid by the oleate hydratase from L. garvieae. Optimal reaction conditions for the enzymatic production of 10-HSA from oleic acid using the purified oleate hydratase were pH 7.5, 30 °C, 105.49 U/mL enzyme solution and 30 g/L oleic acid. In the presence of activity stimulators, that is, magnesium (II) (Mg2+), the oleate hydratase activity was found to be greatly improved at 30 °C. In conclusion, the results revealed the potential efficacy of recombinant enzyme for the biotechnological conversion of oleic acid to 10-HSA acid with high efficiency. The results would be useful for the improved industrial-scale biosynthesis of 10-HSA via an economical and environmentally friendly bioprocess approach.

Biocatalytic Oxidation Reactions: A Chemist's Perspective

Oxidation chemistry using enzymes is approaching maturity and practical applicability in organic synthesis. Oxidoreductases (enzymes catalysing redox reactions) enable chemists to perform highly selective and efficient transformations ranging from simple alcohol oxidations to stereoselective halogenations of non-activated C-H bonds. For many of these reactions, no "classical" chemical counterpart is known. Hence oxidoreductases open up shorter synthesis routes based on a more direct access to the target products. The generally very mild reaction conditions may also reduce the environmental impact of biocatalytic reactions compared to classical counterparts. In this Review, we critically summarise the most important recent developments in the field of biocatalytic oxidation chemistry and identify the most pressing bottlenecks as well as promising solutions.

Improving catalytic activity of the Baeyer-Villiger monooxygenase-based Escherichia coli biocatalysts for the overproduction of (Z)-11-(heptanoyloxy)undec-9-enoic acid from ricinoleic acid

Baeyer–Villiger monooxygenases (BVMOs) can be used for the biosynthesis of lactones and esters from ketones. However, the BVMO-based biocatalysts are not so stable under process conditions. Thereby, this study focused on enhancing stability of the BVMO-based biocatalysts. The biotransformation of ricinoleic acid into (Z)-11-(heptanoyloxy)undec-9-enoic acid by the recombinant Escherichia coli expressing the BVMO from Pseudomonas putida and an alcohol dehydrogenase from Micrococcus luteus was used as a model system. After thorough investigation of the key factors to influence stability of the BVMO, Cys302 was identified as an engineering target. The substitution of Cys302 to Leu enabled the engineered enzyme (i.e., E6BVMO_C302L) to become more stable toward oxidative and thermal stresses. The catalytic activity of E6BVMO_C302L-based E. coli biocatalysts was also greater than the E6BVMO-based biocatalysts. Another factor to influence biocatalytic performance of the BVMO-based whole-cell biocatalysts was availability of carbon and energy source during biotransformations. Glucose feeding into the reaction medium led to a marked increase of final product concentrations. Overall, the bioprocess engineering to improve metabolic stability of host cells in addition to the BVMO engineering allowed us to produce (Z)-11-(heptanoyloxy)undec-9-enoic acid to a concentration of 132 mM (41 g/L) from 150 mM ricinoleic acid within 8 h.

Use of Lactobacillus rhamnosus (ATCC 53103) as Whole-Cell Biocatalyst for the Regio- and Stereoselective Hydration of Oleic, Linoleic, and Linolenic Acid

Natural hydroxy fatty acids are relevant starting materials for the production of a number of industrial fine chemicals, such as different high-value flavour ingredients. Only a few of the latter hydroxy acid derivatives are available on a large scale. Therefore, their preparation by microbial hydration of unsaturated fatty acids, affordable from vegetable oils, is a new biotechnological challenge. In this study, we describe the use of the probiotic bacterium Lactobacillus rhamnosus (ATCC 53103) as whole-cell biocatalyst for the hydration of the most common unsaturated octadecanoic acids, namely oleic acid, linoleic acid, and linolenic acid. We discovered that the addition of the latter fatty acids to an anaerobic colture of the latter strain, during the early stage of its exponential growth, allows the production of the corresponding mono-hydroxy derivatives. In these experimental conditions, the hydration reaction proceeds with high regio- and stereoselectivity. Only 10-hydroxy derivatives were formed and the resulting (R)-10-hydroxystearic acid, (S)-(12Z)-10-hydroxy-octadecenoic acid, and (S)-(12Z,15Z)-10-hydroxy-octadecadienoic acid were obtained in very high enantiomeric purity (ee > 95%). Although overall conversions usually do not exceed 50% yield, our biotransformation protocol is stereoselective, scalable, and holds preparative significance.

New insights on the baker's yeast-mediated hydration of oleic acid: the bacterial contaminants of yeast are responsible for the stereoselective formation of (R)-10-hydroxystearic acid

AIMS

The preparation of the high-value flavour γ-dodecalactone is based on the biotransformation of natural 10-HSA, which is in turn obtained by microbial hydration of oleic acid. We want to establish a reliable baker's yeast-mediated procedure for 10-HSA preparation.

METHODS AND RESULTS

The previously reported yeast-mediated hydration procedures are unreliable because bacteria-free baker's yeast is not able to hydrate oleic acid. The actual responsible for performing this reaction are the bacterial contaminants present in baker's yeast. Moreover, we demonstrated that the enantioselectivity in the production of (R)-10-HSA is affected mainly by the temperature used in the biotransformation.

CONCLUSIONS

We demonstrated that Saccharomyces cerevisiae is not able to hydrate oleic acid, whereas different bacterial strains present in baker's yeast transform oleic acid into (R)-10-HSA. We reported a general procedure for the preparation of (R)-10-HSA starting from oleic acid and using commercially available baker's yeast.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study holds both scientific and industrial interest. It unambiguously establishes that the eukaryote micro-organisms present in baker's yeast are not able to hydrate oleic acid. The isolation of oleic acid hydrating bacterial strains from commercial baker's yeast points to their prospective use for the industrial synthesis of 10-HSA.

(De)hydratases-recent developments and future perspectives

Hydratases have gained attention as alternative to chemical catalysts for their ability to add and eliminate water with high regio-selectivity, stereo-selectivity and enantio-selectivity. Recently, especially cofactor-independent hydratases came into research focus as they are of particular interest for industrial application. The investigation of the substrate scope as well as mutagenesis studies combined with high-resolution crystal structures and bioinformatic methods shed light on this promising enzyme class. This review presents latest findings in the field of fatty acid hydratases, linalool dehydratase isomerase and carotenoid hydratases focusing on mechanistic und structural aspects as well as the expansion of the substrate scope and new applications in organic synthesis.

Bacterial conjugated linoleic acid production and their applications

Conjugated linoleic acid (CLA) has been shown to exert various potential physiological properties including anti-carcinogenic, anti-obesity, anti-cardiovascular and anti-diabetic activities, and consequently has been considered as a promising food supplement. Bacterial biosynthesis of CLA is an attractive approach for commercial production due to its high isomer-selectivity and convenient purification process. Many bacterial species have been reported to convert free linoleic acid (LA) to CLA, hitherto only the precise CLA-producing mechanisms in Propionibacterium acnes and Lactobacillus plantarum have been illustrated completely, prompting the development of recombinant technology used in CLA production. The purpose of the article is to review the bacterial CLA producers as well as the recent progress on describing the mechanism of microbial CLA-production. Furthermore, the advances and potential in the heterologous expression of CLA genetic determinants will be presented.

Production of 7,8-Dihydroxy Unsaturated Fatty Acids from Plant Oils by Whole Recombinant Cells Expressing 7,8-Linoleate Diol Synthase from Glomerella cingulata

The reaction conditions for the production of 7S,8S-dihydroxy-9,12(Z,Z)-octadecadienoic acid from linoleic acid by recombinant Escherichia coli expressing 7,8-linoleate diol synthase from Glomerella cingulata were optimized using response surface methodology. The optimal reaction conditions were pH 7.0, 18.6 °C, 10.8% (v/v) dimethyl sulfoxide, 44.9 g/L cells, and 14.3 g/L linoleic acid, with agitation at 256 rpm. Under these conditions, recombinant cells produced 7,8-dihydroxy unsaturated fatty acids in the range of 7.0-9.8 g/L from 14.3 g/L linoleic acid, 14.3 g/L oleic acid, and plant oil hydrolysates such as waste oil and olive oil containing 14.3 g/L linoleic acid or oleic acid. To the best of the authors' knowledge, this is the first report on the biotechnological production of 7,8-dihydroxy unsaturated fatty acids.

3'-UTR engineering to improve soluble expression and fine-tuning of activity of cascade enzymes in Escherichia coli

3′-Untranslated region (3′UTR) engineering was investigated to improve solubility of heterologous proteins (e.g., Baeyer-Villiger monooxygenases (BVMOs)) in Escherichia coli. Insertion of gene fragments containing putative RNase E recognition sites into the 3′UTR of the BVMO genes led to the reduction of mRNA levels in E. coli. Importantly, the amounts of soluble BVMOs were remarkably enhanced resulting in a proportional increase of in vivo catalytic activities. Notably, this increase in biocatalytic activity correlated to the number of putative RNase E endonucleolytic cleavage sites in the 3′UTR. For instance, the biotransformation activity of the BVMO BmoF1 (from Pseudomonas fluorescens DSM50106) in E. coli was linear to the number of RNase E cleavage sites in the 3′UTR. In summary, 3′UTR engineering can be used to improve the soluble expression of heterologous enzymes, thereby fine-tuning the enzyme activity in microbial cells.

Engineering of Baeyer-Villiger monooxygenase-based Escherichia coli biocatalyst for large scale biotransformation of ricinoleic acid into (Z)-11-(heptanoyloxy)undec-9-enoic acid

Baeyer-Villiger monooxygenases (BVMOs) are able to catalyze regiospecific Baeyer-Villiger oxygenation of a variety of cyclic and linear ketones to generate the corresponding lactones and esters, respectively. However, the enzymes are usually difficult to express in a functional form in microbial cells and are rather unstable under process conditions hindering their large-scale applications. Thereby, we investigated engineering of the BVMO from Pseudomonas putida KT2440 and the gene expression system to improve its activity and stability for large-scale biotransformation of ricinoleic acid (1) into the ester (i.e., (Z)-11-(heptanoyloxy)undec-9-enoic acid) (3), which can be hydrolyzed into 11-hydroxyundec-9-enoic acid (5) (i.e., a precursor of polyamide-11) and n-heptanoic acid (4). The polyionic tag-based fusion engineering of the BVMO and the use of a synthetic promoter for constitutive enzyme expression allowed the recombinant Escherichia coli expressing the BVMO and the secondary alcohol dehydrogenase of Micrococcus luteus to produce the ester (3) to 85 mM (26.6 g/L) within 5 h. The 5 L scale biotransformation process was then successfully scaled up to a 70 L bioreactor; 3 was produced to over 70 mM (21.9 g/L) in the culture medium 6 h after biotransformation. This study demonstrated that the BVMO-based whole-cell reactions can be applied for large-scale biotransformations.

Metabolic engineering of Escherichia coli for the production of hydroxy fatty acids from glucose

Background

Hydroxy fatty acids (HFAs) are valuable chemicals for a broad variety of applications. However, commercial production of HFAs has not been established so far due to the lack of low cost routes for their synthesis. Although the microbial transformation pathway of HFAs was extensively studied decades ago, these attempts mainly focused on converting fatty acids or vegetable oils to their hydroxyl counterparts. The use of a wider range of feedstocks to produce HFAs would reduce the dependence on oil crops and be expected to cut down the manufacturing cost.

Results

In this study, the industrially important microorganism Escherichia coli was engineered to produce HFAs directly from glucose. Through the coexpression of the acetyl-CoA carboxylase (ACCase) and the leadless acyl-CoA thioesterase (‘TesA), and knockout of the endogenous acyl-CoA synthetase (FadD), an engineered E. coli strain was constructed to efficiently synthesize free fatty acids (FFAs). Under shake-flask conditions, 244.8 mg/L of FFAs were obtained by a 12 h induced culture. Then the fatty acid hydroxylase (CYP102A1) from Bacillus megaterium was introduced into this strain and high-level production of HFAs was achieved. The finally engineered strain BL21ΔfadD/pE-A1’tesA&pA-acc accumulated up to 58.7 mg/L of HFAs in the culture broth. About 24 % of the FFAs generated by the thioesterase were converted to HFAs. Fatty acid composition analysis showed that the HFAs mainly consisted of 9-hydroxydecanoic acid (9-OH-C10), 11-hydroxydodecanoic acid (11-OH-C12), 10-hydroxyhexadecanoic acid (10-OH-C16) and 12-hydroxyoctadecanoic acid (12-OH-C18). Fed-batch fermentation of this strain further increased the final titer of HFAs to 548 mg/L.

Conclusions

A robust HFA-producing strain was successfully constructed using glucose as the feedstock, which demonstrated a novel strategy for bioproduction of HFAs. The results of this work suggest that metabolically engineered E. coli has the potential to be a microbial cell factory for large-scale production of HFAs.

Electronic supplementary material

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Production of δ-decalactone from linoleic acid via 13-hydroxy-9(Z)-octadecenoic acid intermediate by one-pot reaction using linoleate 13-hydratase and whole Yarrowia lipolytica cells

OBJECTIVE

To produce δ-decalactone from linoleic acid by one-pot reaction using linoleate 13-hydratase with supplementation with whole Yarrowia lipolytica cells.

RESULTS

Whole Y. lipolytica cells at 25 g l(-1) produced1.9 g l(-1) δ-decalactone from 7.5 g 13-hydroxy-9(Z)-octadecenoic acid l(-1) at pH 7.5 and 30 °C for 21 h. Linoleate 13-hydratase from Lactobacillus acidophilus at 3.5 g l(-1) with supplementation with 25 g Y. lipolytica cells l(-1) in one pot at 3 h produced 1.9 g l(-1) δ-decalactone from 10 g linoleic acid l(-1) via 13-hydroxy-9(Z)-octadecenoic acid intermediate at pH 7.5 and 30°C after 18 h, with a molar conversion yield of 31 % and productivity of 106 mg l(-1) h(-1).

CONCLUSION

To the best of our knowledge, this is the first production of δ-decalactone using unsaturated fatty acid.

Adding value to plant oils and fatty acids: Biological transformation of fatty acids into ω-hydroxycarboxylic, α,ω-dicarboxylic, and ω-aminocarboxylic acids

Not only short chain ω-hydroxycarboxylic acids, α,ω-dicarboxylic acids, and ω-aminocarboxylic acids but also medium to long chain carboxylic acids are widely used as building blocks and intermediates in the chemical, pharmaceutical, and food industries. Thereby, recent achievements in biological production of medium to long chain carboxylic acids are addressed here. ω-Hydroxycarboxylic and α,ω-dicarboxylic acids were synthesized via terminal CH bond oxygenation of fatty acids and/or internal oxidative cleavage of the fatty acid carbon skeletons. ω-Aminocarboxylic acids were enzymatically produced from ω-hydroxycarboxylic acids via ω-oxocarboxylic acids. Productivities and product yields of some of the products are getting close to the industrial requirements for large scale production.

Microbial synthesis of plant oxylipins from γ-linolenic acid through designed biotransformation pathways

Secondary metabolites of plants are often difficult to synthesize in high yields because of the large complexity of the biosynthetic pathways and challenges encountered in the functional expression of the required biosynthetic enzymes in microbial cells. In this study, the biosynthesis of plant oxylipins--a family of oxygenated unsaturated carboxylic acids--was explored to enable a high-yield production through a designed microbial synthetic system harboring a set of microbial enzymes (i.e., fatty acid double-bond hydratases, alcohol dehydrogenases, Baeyer-Villiger monooxygenases, and esterases) to produce a variety of unsaturated carboxylic acids from γ-linolenic acid. The whole cell system of the recombinant Escherichia coli efficiently produced (6Z,9Z)-12-hydroxydodeca-6,9-dienoic acid (7), (Z)-9-hydroxynon-6-enoic acid (15), (Z)-dec-4-enedioic acid (17), and (6Z,9Z)-13-hydroxyoctadeca-6,9-dienoic acid (2). This study demonstrated that various secondary metabolites of plants can be produced by implementing artificial biosynthetic pathways into whole-cell biocatalysis.