Synthesis of cinnabarinic acid by metabolically engineeredPseudomonas chlororaphisGP72

A Review on the Role and Function of Cinnabarinic Acid, a "Forgotten" Metabolite of the Kynurenine Pathway

In the human body, the majority of tryptophan is metabolized through the kynurenine pathway. This consists of several metabolites collectively called the kynurenines and includes, among others, kynurenic acid, L-kynurenine, or quinolinic acid. The wealth of metabolites, as well as the associated molecular targets and biological pathways, bring about a situation wherein even a slight imbalance in the kynurenine levels, both in the periphery and central nervous system, have broad consequences regarding general health. Cinnabarinic acid (CA) is the least known trace kynurenine, and its physiological and pathological roles are not widely understood. Some studies, however, indicate that it might be neuroprotective. Information on its hepatoprotective properties have also emerged, although these are pioneering studies and need to be replicated. Therefore, in this review, I aim to present and critically discuss the current knowledge on CA and its role in physiological and pathological settings to guide future studies.

Efficient production of an antitumor precursor actinocin and other medicinal molecules from kynurenine pathway in Escherichia coli

Kynurenine pathway has a potential to convert L-tryptophan into multiple medicinal molecules. This study aims to explore the biosynthetic potential of kynurenine pathway for the efficient production of actinocin, an antitumor precursor selected as a proof-of-concept target molecule. Kynurenine pathway is first constructed in Escherichia coli by testing various combinations of biosynthetic genes from four different organisms. Metabolic engineering strategies are next performed to improve the production by inhibiting a competing pathway, and enhancing intracellular supply of a cofactor S-adenosyl-L-methionine, and ultimately to produce actinocin from glucose. Metabolome analysis further suggests additional gene overexpression targets, which finally leads to the actinocin titer of 719 mg/L. E. coli strain engineered to produce actinocin is further successfully utilized to produce 350 mg/L of kynurenic acid, a neuroprotectant, and 1401 mg/L of 3-hydroxyanthranilic acid, an antioxidant, also from glucose. These competitive production titers demonstrate the biosynthetic potential of kynurenine pathway as a source of multiple medicinal molecules. The approach undertaken in this study can be useful for the sustainable production of molecules derived from kynurenine pathway, which are otherwise chemically synthesized.

Production of Antibacterial Questiomycin A in Metabolically Engineered Pseudomonas chlororaphis HT66

Pseudomonas chlororaphis has been demonstrated as a valuable source of antimicrobial metabolites for plant disease biocontrol and biopesticide development. Although phenazine-1-carboxylic acid (PCA) secreted by P. chlororaphis has been commercialized as an antifungal biopesticide, it shows poor antibacterial activity. Questiomycin A, with versatile antibacterial activities, is mainly discovered in some well-known phenazine-producing strains but not in Pseudomonas. Its low titer hinders practical applications. In this work, a metabolite was first identified as Questiomycin A in P. chlororaphis-derived strain HT66ΔphzBΔNat. Subsequently, Questiomycin A has been elucidated to share the same biosynthesis process with PCA by gene deletion and in vitro assays. Through rational metabolic engineering, heterologous phenoxazinone synthase introduction, and medium optimization, the titer reached 589.78 mg/L in P. chlororaphis, the highest production reported to date. This work contributes to a better understanding of Questiomycin A biosynthesis and demonstrates a promising approach to developing a new antibacterial biopesticide in Pseudomonas.

Cinnabarinic acid from Trametes coccinea fruiting bodies exhibits antibacterial activity through inhibiting the biofilm formation

Wild mushrooms are rich sources of natural compounds with potent bioactive properties. Several important metabolites have been reported from mushrooms, which possess clinically important bioactive properties like antibacterial, anticancer, antidiabetic, and neuroprotective activity. In this study, we have evaluated the antimicrobial activity of Trametes coccinea fruiting body extracts against different bacterial isolates, viz., Bacillus subtilis, Bacillus cereus, and Escherichia coli. Fruiting bodies of three T. coccinea samples, of which two were collected from Santipur, Arunachal Pradesh and one collected from Jorhat, Assam, were used for extraction using methanol. The extracts showed significant antimicrobial activity against all the test bacteria. Minimum Inhibitory Concentration (MIC) of the extracts against Bacillus subtilis, Bacillus cereus, and Escherichia coli was recorded as 400 µg/ml, 400 µg/ml, and 300 µg/ml, respectively. Furthermore, the bioactive compounds of the extract were separated and detected using Thin Layer Chromatography (TLC). Presence of cinnabarinic acid (CBA)-a potent antimicrobial compound- was detected in TLC, which was further confirmed through High Performance Liquid Chromatography (HPLC) and Electrospray Ionization-Mass Spectrometry (ESI-MS). Cinnabarinic acid was able to inhibit the formation of biofilms in Bacillus subtilis and B. cereus, suggesting that the compound can be beneficial in the management of biofilm-based antimicrobial resistance.

Characterization and Engineering of Pseudomonas chlororaphis LX24 with High Production of 2-Hydroxyphenazine

The take-all disease of wheat is one of the most serious diseases in the field of food security in the world. There is no effective biological pesticide to prevent the take-all disease of wheat. 2-Hydroxyphenazine (2-OH-PHZ) was reported to possess a better inhibitory effect on the take-all disease of wheat than phenazine-1-carboxylic acid, which was registered as "Shenqinmycin" in China in 2011. The aim of this study was to construct a 2-OH-PHZ high-producing strain by strain screening, genome sequencing, genetic engineering, and fermentation optimization. First, the metabolites of the previously screened new phenazine-producing Pseudomonas sp. strain were identified, and the taxonomic status of the new Pseudomonas sp. strain was confirmed through 16S rRNA and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS). Then, the new Pseudomonas sp. strain was named Pseudomonas chlororaphis subsp. aurantiaca LX24, which is a new subspecies of P. chlororaphis that can synthesize 2-OH-PHZ. Next, the draft genome of strain LX24 was determined, and clusters of orthologous group (COG) analysis, KEGG analysis, and gene ontology (GO) analysis of strain LX24 were performed. Furthermore, the production of 2-OH-PHZ increased to 351.7 from 158.6 mg/L by deletion of the phenazine synthesis negative regulatory genes rpeA and rsmE in strain LX24. Finally, the 2-OH-PHZ production of strain LX24 reached 677.1 mg/L after fermentation optimization, which is the highest production through microbial fermentation reported to date. This work provides a reference for the efficient production of other pesticides and antibiotics.

Biosynthesis and Characterization of Medium-Chain-Length Polyhydroxyalkanoate with an Enriched 3-Hydroxydodecanoate Monomer from a Pseudomonas chlororaphis Cell Factory

Polyhydroxyalkanoates (PHAs) have been reported with agricultural and medical applications in virtue of their biodegradable and biocompatible properties. Here, we systematically engineered three modules for the enhanced biosynthesis of medium-chain-length polyhydroxyalkanoate (mcl-PHA) in Pseudomonas chlororaphis HT66. The phzE, fadA, and fadB genes were deleted to block the native phenazine pathway and weaken the fatty acid β-oxidation pathway. Additionally, a PHA depolymerase gene phaZ was knocked out to prevent the degradation of mcl-PHA. Three genes involved in the mcl-PHA biosynthesis pathway were co-overexpressed to increase carbon flux. The engineered strain HT4Δ::C1C2J exhibited an 18.2 g/L cell dry weight with 84.9 wt % of mcl-PHA in a shake-flask culture, and the 3-hydroxydodecanoate (3HDD) monomer was increased to 71.6 mol %. Thermophysical and mechanical properties of mcl-PHA were improved with an enriched ratio of 3HDD. This study demonstrated a rational metabolic engineering approach to enhance the production of mcl-PHA with the enriched dominant monomer and improved material properties.

Engineering of glycerol utilization in Pseudomonas chlororaphis GP72 for enhancing phenazine-1-carboxylic acid production

Glycerol is a by-product of biodiesel, and it has a great application prospect to be transformed to synthesize high value-added compounds. Pseudomonas chlororaphis GP72 isolated from the green pepper rhizosphere is a plant growth promoting rhizobacteria that can utilize amount of glycerol to synthesize phenazine-1-carboxylic acid (PCA). PCA has been commercially registered as "Shenqinmycin" in China due to its characteristics of preventing pepper blight and rice sheath blight. The aim of this study was to engineer glycerol utilization pathway in P. chlororaphis GP72. First, the two genes glpF and glpK from the glycerol metabolism pathway were overexpressed in GP72ANO separately. Then, the two genes were co-expressed in GP72ANO, improving PCA production from 729.4 mg/L to 993.4 mg/L at 36 h. Moreover, the shunt pathway was blocked to enhance glycerol utilization, resulting in 1493.3 mg/L PCA production. Additionally, we confirmed the inhibition of glpR on glycerol metabolism pathway in P. chlororaphis GP72. This study provides a good example for improving the utilization of glycerol to synthesize high value-added compounds in Pseudomonas.