Production of ω-hydroxyundec-9-enoic acid and n-heptanoic acid from ricinoleic acid by recombinant Escherichia coli-based biocatalyst

Metabolic engineering of Saccharomyces cerevisiae for de novo production of odd-numbered medium-chain fatty acids

Odd-numbered fatty acids (FAs) have been widely used in nutrition, agriculture, and chemical industries. Recently, some studies showed that they could be produced from bacteria or yeast, but the products are almost exclusively odd-numbered long-chain FAs. Here we report the design and construction of two biosynthetic pathways in Saccharomyces cerevisiae for de novo production of odd-numbered medium-chain fatty acids (OMFAs) via ricinoleic acid and 10-hydroxystearic acid, respectively. The production of OMFAs was enabled by introducing a hydroxy fatty acid cleavage pathway, including an alcohol dehydrogenase from Micrococcus luteus, a Baeyer-Villiger monooxygenase from Pseudomonas putida, and a lipase from Pseudomonas fluorescens. These OMFA biosynthetic pathways were optimized by eliminating the rate-limiting step, generating heptanoic acid, 11-hydroxyundec-9-enoic acid, nonanoic acid, and 9-hydroxynonanoic acid at 7.83 mg/L, 9.68 mg/L, 9.43 mg/L and 13.48 mg/L, respectively. This work demonstrates the biological production of OMFAs in a sustainable manner in S. cerevisiae.

Lactones from Unspecific Peroxygenase-Catalyzed In-Chain Hydroxylation of Saturated Fatty Acids

γ- and δ-lactones are valuable flavor and fragrance compounds. Their synthesis depends on the availability of suitable hydroxy fatty acid precursors. Three short unspecific peroxygenases were identified that selectively hydroxylate the C4 and C5 positions of C8-C12 fatty acids to yield after lactonization the corresponding γ- and δ-lactones. A preference for C4 over C5 hydroxylation gave γ-lactones as the major products. Overoxidation of the hydroxy fatty acids was addressed via the reduction of the resulting oxo acids using an alcohol dehydrogenase in a bienzymatic cascade reaction.

Coding Synthetic Chemistry Strategies for Furan Valorization into Bacterial Designer Cells

Following a synthetic chemistry blueprint for the valorization of lignocellulosic platform chemicals, this study showcases a so far unprecedented approach to implement non-natural enzyme modules in vivo. For the design of a novel functional whole cell tool, two purely abiotic transformations, a styrene monooxygenase-catalyzed Achmatowicz rearrangement and an alcohol dehydrogenase-mediated borrowing hydrogen redox isomerization, were incorporated into a recombinant bacterial host. Introducing this type of chemistry otherwise unknown in biosynthesis, the cellular factories were enabled to produce complex lactone building blocks in good yield from bio-based furan substrates. This whole cell system streamlined the synthetic cascade, eliminated isolation and purification steps, and provided a high degree of stereoselectivity that has so far been elusive in the chemical methodology.

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.

ω-hydroxyundec-9-enoic acid induction of breast cancer cells apoptosis through generation of mitochondrial ROS and phosphorylation of AMPK

This study was performed to evaluate the anticancer effect of ω-hydroxyundec-9-enoic acid (ω-HUA), a microbial bio-catalyst product in breast cancer cells, through AMP-activated protein kinase (AMPK) regulation. ω-HUA mediated apoptosis was induced in breast cancer cells by AMPK activation, loss of mitochondrial membrane potential, and reactive oxygen species (ROS) generation. ω-HUA treatment of breast cancer cells increased the AMPK phosphorylation levels, cleaved caspase-3, and poly (ADP-ribose) polymerase (PARP) proteins. In addition, anti-apoptotic members, such as Bcl-2, were downregulated, while Bax, a pro-apoptotic member, was upregulated. ω-HUA decreased the mitochondrial membrane potential while increasing the expression of cytochrome c (cyt c). Treating the cells with compound C, an AMPK inhibitor, reversed the phenomena, leading to an increase in cell viability and a decrease in apoptosis induction. Treating the cells with an ROS scavenger, N-acetyl cysteine (NAC), led to AMPK inactivation and apoptosis inhibition, allowing the recovery of cell health. In conclusion, ω-HUA sequentially caused the production of mitochondrial ROS and the consequent AMPK activation, thereby inducing apoptosis in breast cancer cells. Thus, ω-HUA may prove useful as an anticancer agent that targets AMPK in breast cancer cells.

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.

Assembly of an atrazine catabolic operon and its introduction to Gram-negative hosts for robust and stable degradation of triazine herbicides

In 1995, Pseudomonas sp. ADP, capable of metabolizing atrazine, was isolated from contaminated soil. Genes responsible for atrazine mineralization were found scattered in the 108.8 kb pADP-1 plasmid carried by this strain, some of them flanked by insertion sequences rendering them unstable. The goal of this work was to construct a transcriptional unit containing the atz operon in an easy to transfer manner, to be introduced and inherited stably by Gram-negative bacteria. atz genes were PCR amplified, joined into an operon and inserted onto the mobilizable plasmid pBAMD1–2. Primers were designed to add efficient transcription and translation signals. Plasmid bearing the atz operon was transferred to different Gram-negative strains by conjugation, which resulted in Tn5 transposase-mediated chromosomal insertion of the atz operon. To test the operon activity, atrazine degradation by transposants was assessed both colorimetrically and by high-performance liquid chromatography (HPLC). Transposants mineralized atrazine more efficiently than wild-type Pseudomonas sp. ADP and did not accumulate cyanuric acid. Atrazine degradation was not repressed by simple nitrogen sources. Genes conferring atrazine-mineralizing capacities were stable and had little or null effect on the fitness of different transposants. Introduction of catabolic operons in a stable fashion could be used to develop bacteria with better degrading capabilities useful in bioremediation.

Chemoenzymatic Synthesis of Fragrance Compounds from Stearic Acid

Fatty acids are versatile precursors for fuels, fine chemicals, polymers, perfumes, etc. The properties and applications of fatty acid derivatives depend on chain length and on functional groups and their positions. To tailor fatty acids for desired properties, an engineered P450 monooxygenase has been employed here for enhanced selective hydroxylation of fatty acids. After oxidation of the hydroxy groups to the corresponding ketones, Baeyer-Villiger oxidation could be applied to introduce an oxygen atom into the hydrocarbon chains to form esters, which were finally hydrolyzed to afford either hydroxylated fatty acids or dicarboxylic fatty acids. Using this strategy, we have demonstrated that the high-value-added flavors exaltolide and silvanone supra can be synthesized from stearic acid through a hydroxylation/carbonylation/esterification/hydrolysis/lactonization reaction sequence with isolated yields of about 36 % (for ω-1 hydroxylated stearic acid; 100, 60, 80, 75 % yields for the individual reactions, respectively) or 24 % (for ω-2 hydroxylated stearic acid). Ultimately, we obtained 7.91 mg of exaltolide and 13.71 mg of silvanone supra from 284.48 mg stearic acid.

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.

Artificial Biocatalytic Linear Cascades to Access Hydroxy Acids, Lactones, and α- and β-Amino Acids

α-, β-, and ω-Hydroxy acids, amino acids, and lactones represent common building blocks and intermediates for various target molecules. This review summarizes artificial cascades published during the last 10 years leading to these products. Renewables as well as compounds originating from fossil resources have been employed as starting material. The review provides an inspiration for new cascade designs and may be the basis to design variations of these cascades starting either from alternative substrates or extending them to even more sophisticated products.

Whole-cell biocatalysts by design

Whole-cell biocatalysts provide unique advantages and have been widely used for the efficient biosynthesis of value-added fine and bulk chemicals, as well as pharmaceutically active ingredients. What is more, advances in synthetic biology and metabolic engineering, together with the rapid development of molecular genetic tools, have brought about a renaissance of whole-cell biocatalysis. These rapid advancements mean that whole-cell biocatalysts can increasingly be rationally designed. Genes of heterologous enzymes or synthetic pathways are increasingly being introduced into microbial hosts, and depending on the complexity of the synthetic pathway or the target products, they can enable the production of value-added chemicals from cheap feedstock. Metabolic engineering and synthetic biology efforts aimed at optimizing the existing microbial cell factories concentrate on improving heterologous pathway flux, precursor supply, and cofactor balance, as well as other aspects of cellular metabolism, to enhance the efficiency of biocatalysts. In the present review, we take a critical look at recent developments in whole-cell biocatalysis, with an emphasis on strategies applied to designing and optimizing the organisms that are increasingly modified for efficient production of chemicals.

Bioprocess engineering to produce 9-(nonanoyloxy) nonanoic acid by a recombinant Corynebacterium glutamicum-based biocatalyst

Here, Corynebacterium glutamicum ATCC13032 expressing Baeyer-Villiger monooxygenase from Pseudomonas putida KT2440 was designed to produce 9-(nonanoyloxy) nonanoic acid from 10-ketostearic acid. Diverse parameters including cultivation and reaction temperatures, type of detergent, and pH were found to improve biotransformation efficiency. The optimal temperature of cultivation for the production of 9-(nonanoyloxy) nonanoic acid from 10-ketostearic acid using whole cells of recombinant C. glutamicum was 15 °C, but the reaction temperature was optimal at 30 °C. Enhanced conversion efficiency was obtained by supplying 0.05 g/L of Tween 80 at pH 7.5. Under these optimal conditions, recombinant C. glutamicum produced 0.28 mM of 9-(nonanoyloxy) nonanoic acid with a 75.6% (mol/mol) conversion yield in 2 h. This is the first report on the biotransformation of 10-ketostearic acid to 9-(nonanoyloxy) nonanoic acid with a recombinant whole-cell C. glutamicum-based biocatalyst and the results demonstrate the feasibility of using C. glutamicum as a whole-cell biocatalyst.

Hydrolase BioH knockout in E. coli enables efficient fatty acid methyl ester bioprocessing

Fatty acid methyl esters (FAMEs) originating from plant oils are most interesting renewable feedstocks for biofuels and bio-based materials. FAMEs can also be produced and/or functionalized by engineered microbes to give access to, e.g., polymer building blocks. Yet, they are often subject to hydrolysis yielding free fatty acids, which typically are degraded by microbes. We identified BioH as the key enzyme responsible for the hydrolysis of medium-chain length FAME derivatives in different E. coli K-12 strains. E. coli ΔbioH strains showed up to 22-fold reduced FAME hydrolysis rates in comparison with respective wild-type strains. Knockout strains showed, beside the expected biotin auxotrophy, unchanged growth behavior and biocatalytic activity. Thus, high specific rates (~80 U gCDW  −1) for terminal FAME oxyfunctionalization catalyzed by a recombinant alkane monooxygenase could be combined with reduced hydrolysis. Biotransformations in process-relevant two-liquid phase systems profited from reduced fatty acid accumulation and/or reduced substrate loss via free fatty acid metabolization. The BioH knockout strategy was beneficial in all tested strains, although its effect was found to differ according to specific strain properties, such as FAME hydrolysis and FFA degradation activities. BioH or functional analogs can be found in virtually all microorganisms, making bioH deletion a broadly applicable strategy for efficient microbial bioprocessing involving FAMEs.

Activation of the Glutamic Acid-Dependent Acid Resistance System in Escherichia coli BL21(DE3) Leads to Increase of the Fatty Acid Biotransformation Activity

The biosynthesis of carboxylic acids including fatty acids from biomass is central in envisaged biorefinery concepts. The productivities are often, however, low due to product toxicity that hamper whole-cell biocatalyst performance. Here, we have investigated factors that influence the tolerance of Escherichia coli to medium chain carboxylic acid (i.e., n-heptanoic acid)-induced stress. The metabolic and genomic responses of E. coli BL21(DE3) and MG1655 grown in the presence of n-heptanoic acid indicated that the GadA/B-based glutamic acid-dependent acid resistance (GDAR) system might be critical for cellular tolerance. The GDAR system, which is responsible for scavenging intracellular protons by catalyzing decarboxylation of glutamic acid, was inactive in E. coli BL21(DE3). Activation of the GDAR system in this strain by overexpressing the rcsB and dsrA genes, of which the gene products are involved in the activation of GadE and RpoS, respectively, resulted in acid tolerance not only to HCl but also to n-heptanoic acid. Furthermore, activation of the GDAR system allowed the recombinant E. coli BL21(DE3) expressing the alcohol dehydrogenase of Micrococcus luteus and the Baeyer-Villiger monooxygenase of Pseudomonas putida to reach 60% greater product concentration in the biotransformation of ricinoleic acid (i.e., 12-hydroxyoctadec-9-enoic acid (1)) into n-heptanoic acid (5) and 11-hydroxyundec-9-enoic acid (4). This study may contribute to engineering E. coli-based biocatalysts for the production of carboxylic acids from renewable biomass.

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.

Fatty acid hydration activity of a recombinant Escherichia coli-based biocatalyst is improved through targeting the oleate hydratase into the periplasm

Whole-cell biotransformation of fatty acids can be influenced by the activities of catalytic enzymes and by the efficiency of substrate transport into host cells. Here, we improved fatty acid hydration activity of the recombinant Escherichia coli expressing an oleate hydratase of Stenotrophomonas maltophilia by targeting the catalytic enzyme into the periplasm instead of the cytoplasm. Recombinant E. coli producing OhyA in the periplasm under guidance of the PelB signal sequence (E. coli OhyA_PP) exhibited significantly greater hydration activity with oleic acid and linoleic acid compared to a recombinant E. coli producing OhyA in the cytoplasm (E. coli OhyA_CS). For example, the oleate double bond hydration rate of E. coli OhyA_PP was >400 μmol/g dry cells/min (400 U/g dry cells), which is >10-fold higher than that of E. coli OhyA_CS. As the specific activities of the enzymes targeted into the cytoplasm and periplasm were comparable, we assumed that targeting OhyA into the periplasm could accelerate fatty acid transport to the catalytic enzymes by skipping the major mass transport barrier of the cytoplasmic membrane. Our results will contribute to the development of whole-cell biocatalysts for fatty acid biotransformation.

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.