Coalition of Biology and Chemistry for Ameliorating Antimicrobial Drug Discovery

Role of gut-microbiota in disease severity and clinical outcomes

A delicate balance of nutrients, antigens, metabolites and xenobiotics in body fluids, primarily managed by diet and host metabolism, governs human health. Human gut microbiota is a gatekeeper to nutrient bioavailability, pathogens exposure and xenobiotic metabolism. Human gut microbiota starts establishing during birth and evolves into a resilient structure by adolescence. It supplements the host's metabolic machinery and assists in many physiological processes to ensure health. Biotic and abiotic stressors could induce dysbiosis in gut microbiota composition leading to disease manifestations. Despite tremendous scientific advancements, a clear understanding of the involvement of gut microbiota dysbiosis during disease onset and clinical outcomes is still awaited. This would be important for developing an effective and sustainable therapeutic intervention. This review synthesizes the present scientific knowledge to present a comprehensive picture of the role of gut microbiota in the onset and severity of a disease.

Functional characterization of a naphthalene-O-methyltransferase from Nocardia sp. CS682

Methylation plays important roles in biosynthesis, metabolism, signal transduction, detoxification, protein sorting and repair, and nucleic acid processing. Generally the methyltransferases transfer methyl groups in various natural products using S-adenosyl methionine (SAM) as a cofactor. In this study, we examined and functionally characterized ThnM3 (enzyme), by testing various substrates with different chemical structures. Among the tested substrates, 1,8-dihydroxynaphthalene was the best substrate for methylation. Whole-cell biotransformation was performed using the enzyme in engineered Escherichia coli to produce 8-methoxynaphthalene-1-ol, and 1,8-dimethoxynaphthalene derivatives of 1,8-dihydroxynaphthalene. The products were confirmed using high-performance liquid chromatography, mass spectrometry, and nuclear magnetic resonance spectroscopic analyses. Therefore, this study is the first to amplify, express the thnM3 (gene), and functionally characterize theThnM3, which exhibits the regioselective modifications of 1,8-dihydroxynaphthalene.

UPLC-PDA coupled HR-TOF ESI/MS2 -based identification of derivatives produced by whole-cell biotransformation of epothilone A using Nocardia sp. CS692 and a cytochrome P450 overexpressing strain

Epothilone A, a microtubule-stabilizing agent used as therapeutics for the treatment of cancers, was biotransformed into three metabolites using Nocardia sp. CS692 and recombinant Nocardia overexpressing a cytochrome P450 from Streptomyces venezuelae (PikC). Among three metabolites produced in the biotransformation reaction mixtures, ESI/MS² analysis predicted two metabolites (M1 and M2) as novel hydroxylated derivatives (M1 is hydroxylated at the C-8 position and M2 is hydroxylated at C-10 position), each with an opened-epoxide ring in their structure. Interestingly, metabolite M3 lacks an epoxide ring and is known as deoxyepothilone A, which is also called epothilone C. Metabolite M1 was produced only in PikC overexpressing strain. The endogenous enzymes of Nocardia sp. catalyzed hydroxylation of epothilone A to produce metabolite M2 and removed epoxide ring to produce metabolite M3. All the metabolites were identified based on UV-vis analysis and rigorous ESI/MS² fragmentation based on epothilone A standard. The newly produced metabolites are anticipated to display novel cytotoxic effects and could be subjects of further pharmacological studies.

Heterologous production of cyanobacterial compounds

Cyanobacteria produce a plethora of compounds with unique chemical structures and diverse biological activities. Importantly, the increasing availability of cyanobacterial genome sequences and the rapid development of bioinformatics tools have unraveled the tremendous potential of cyanobacteria in producing new natural products. However, the discovery of these compounds based on cyanobacterial genomes has progressed slowly as the majority of their corresponding biosynthetic gene clusters (BGCs) are silent. In addition, cyanobacterial strains are often slow-growing, difficult for genetic engineering, or cannot be cultivated yet, limiting the use of host genetic engineering approaches for discovery. On the other hand, genetically tractable hosts such as Escherichia coli, Actinobacteria, and yeast have been developed for the heterologous expression of cyanobacterial BGCs. More recently, there have been increased interests in developing model cyanobacterial strains as heterologous production platforms. Herein, we present recent advances in the heterologous production of cyanobacterial compounds in both cyanobacterial and noncyanobacterial hosts. Emerging strategies for BGC assembly, host engineering, and optimization of BGC expression are included for fostering the broader applications of synthetic biology tools in the discovery of new cyanobacterial natural products.

Recent Advances in Strategies for Activation and Discovery/Characterization of Cryptic Biosynthetic Gene Clusters in Streptomyces

Streptomyces spp. are prolific sources of valuable natural products (NPs) that are of great interest in pharmaceutical industries such as antibiotics, anticancer chemotherapeutics, immunosuppressants, etc. Approximately two-thirds of all known antibiotics are produced by actinomycetes, most predominantly by Streptomyces. Nevertheless, in recent years, the chances of the discovery of novel and bioactive compounds from Streptomyces have significantly declined. The major hindrance for obtaining such bioactive compounds from Streptomyces is that most of the compounds are not produced in significant titers, or the biosynthetic gene clusters (BGCs) are cryptic. The rapid development of genome sequencing has provided access to a tremendous number of NP-BGCs embedded in the microbial genomes. In addition, the studies of metabolomics provide a portfolio of entire metabolites produced from the strain of interest. Therefore, through the integrated approaches of different-omics techniques, the connection between gene expression and metabolism can be established. Hence, in this review we summarized recent advancements in strategies for activating cryptic BGCs in Streptomyces by utilizing diverse state-of-the-art techniques.

Recent Advances in Exploration and Biotechnological Production of Bioactive Compounds in Three Cyanobacterial Genera: Nostoc, Lyngbya, and Microcystis

Cyanobacteria, are only Gram-negative bacteria with the capacity of oxygenic photosynthesis, so termed as “Cyanophyta” or “blue-green algae.” Their habitat is ubiquitous, which includes the diverse environments, such as soil, water, rock and other organisms (symbiosis, commensalism, or parasitism, etc.,). They are characterized as prominent producers of numerous types of important compounds with anti-microbial, anti-viral, anti-inflammatory and anti-tumor properties. Among the various cyanobacterial genera, members belonging to genera Nostoc, Lyngbya, and Microcystis possess greater attention. The major reason for that is the strains belonging to these genera produce the compounds with diverse activities/structures, including compounds in preclinical and/or clinical trials (cryptophycin and curacin), or the compounds retaining unique activities such as protease inhibitor (micropeptins and aeruginosins). Most of these compounds were tested for their efficacy and mechanism of action(MOA) through in vitro and/or in vivo studies. Recently, the advances in culture techniques of these cyanobacteria, and isolation, purification, and chromatographic analysis of their compounds have revealed insurmountable novel bioactive compounds from these cyanobacteria. This review provides comprehensive update on the origin, isolation and purification methods, chemical structures and biological activities of the major compounds from Nostoc, Lyngbya, and Microcystis. In addition, multi-omics approaches and biotechnological production of compounds from selected cyanobacterial genera have been discussed.

Engineering actinomycetes for biosynthesis of macrolactone polyketides

Actinobacteria are characterized as the most prominent producer of natural products (NPs) with pharmaceutical importance. The production of NPs from these actinobacteria is associated with particular biosynthetic gene clusters (BGCs) in these microorganisms. The majority of these BGCs include polyketide synthase (PKS) or non-ribosomal peptide synthase (NRPS) or a combination of both PKS and NRPS. Macrolides compounds contain a core macro-lactone ring (aglycone) decorated with diverse functional groups in their chemical structures. The aglycon is generated by megaenzyme polyketide synthases (PKSs) from diverse acyl-CoA as precursor substrates. Further, post-PKS enzymes are responsible for allocating the structural diversity and functional characteristics for their biological activities. Macrolides are biologically important for their uses in therapeutics as antibiotics, anti-tumor agents, immunosuppressants, anti-parasites and many more. Thus, precise genetic/metabolic engineering of actinobacteria along with the application of various chemical/biological approaches have made it plausible for production of macrolides in industrial scale or generation of their novel derivatives with more effective biological properties. In this review, we have discussed versatile approaches for generating a wide range of macrolide structures by engineering the PKS and post-PKS cascades at either enzyme or cellular level in actinobacteria species, either the native or heterologous producer strains.

Bioactive molecules from Nocardia: diversity, bioactivities and biosynthesis

Nocardia spp. are catalase positive, aerobic, and non-motile Gram-positive filamentous bacteria. Many Nocarida spp. have been reported as unusual causes of diverse clinical diseases in both humans and animals. Therefore, they have been studied for a long time, primarily focusing on strain characterization, taxonomic classification of new isolates, and host pathophysiology. Currently, there are emerging interests in isolating bioactive molecules from diverse actinobacteria including Nocardia spp. and studying their biosynthetic mechanisms. In addition, these species possess significant metabolic capacity, which has been utilized for generating diverse functionalized bioactive molecules by whole cell biotransformation. This review summarizes the structural diversity and biological activities of compounds biosynthesized or biotransformed by Nocardia spp. Furthermore, the recent advances on biosynthetic mechanisms and genetic engineering approaches for enhanced production or structural/functional modification are presented.

Production of a Novel Tetrahydroxynaphthalene (THN) Derivative from Nocardia sp. CS682 by Metabolic Engineering and Its Bioactivities

Nargenicin A1 is major secondary metabolite produced by Nocardia sp. CS682, with an effective antibacterial activity against various Gram-positive bacteria. Most Nocardia spp. have metabolic ability to produce compounds of diverse nature, so one-strain-many-compounds (OSMAC) approach can be applied for obtaining versatile compounds from these strains. In this study, we characterized a novel 1, 3, 6, 8-tetrahydroxynaphthalene (THN) derivative by metabolic engineering approach leading to the inactivation of nargenicin A1 biosynthesis. By using genome mining, metabolite profiling, and bioinformatics, the biosynthetic gene cluster and biosynthetic mechanism were elucidated. Further, the antibacterial, anticancer, melanin formation, and UV protective properties for isolated THN compound were performed. The compound did not exhibit significant antibacterial and cytotoxic activities, but it exhibited promising UV protection effects. Thus, metabolic engineering is an effective strategy for discovering novel bioactive molecules.

Improved production of 1-deoxynojirymicin in Escherichia coli through metabolic engineering

Azasugars, such as 1-deoxynojirymicin (1-DNJ), are associated with diverse pharmaceutical applications, such as antidiabetic, anti-obesity, anti-HIV, and antitumor properties. Different azasugars have been isolated from diverse microbial and plant sources though complicated purification steps, or generated by costly chemical synthesis processes. But the biosynthesis of such potent molecules using Escherichia coli as a heterologous host provides a broader opportunity to access these molecules, particularly by utilizing synthetic biological, metabolic engineering, and process optimization approaches. This work used an integrated approach of synthetic biology, enzyme engineering, and pathway optimization for rational metabolic engineering, leading to the improved production of 1-DNJ. The production of 1-DNJ in recombinant E. coli culture broth was confirmed by enzymatic assays and mass spectrometric analysis. Specifically, the pathway engineering for its key precursor, fructose-6-phosphate, along with optimized media condition, results in the highest production levels. When combined, 1-DNJ production was extended to ~ 273 mg/L, which is the highest titer of production of 1-DNJ reported using E. coli.

Genome-guided exploration of metabolic features of Streptomyces peucetius ATCC 27952: past, current, and prospect

Streptomyces peucetius ATCC 27952 produces two major anthracyclines, doxorubicin (DXR) and daunorubicin (DNR), which are potent chemotherapeutic agents for the treatment of several cancers. In order to gain detailed insight on genetics and biochemistry of the strain, the complete genome was determined and analyzed. The result showed that its complete sequence contains 7187 protein coding genes in a total of 8,023,114 bp, whereas 87% of the genome contributed to the protein coding region. The genomic sequence included 18 rRNA, 66 tRNAs, and 3 non-coding RNAs. In silico studies predicted ~ 68 biosynthetic gene clusters (BCGs) encoding diverse classes of secondary metabolites, including non-ribosomal polyketide synthase (NRPS), polyketide synthase (PKS I, II, and III), terpenes, and others. Detailed analysis of the genome sequence revealed versatile biocatalytic enzymes such as cytochrome P450 (CYP), electron transfer systems (ETS) genes, methyltransferase (MT), glycosyltransferase (GT). In addition, numerous functional genes (transporter gene, SOD, etc.) and regulatory genes (afsR-sp, metK-sp, etc.) involved in the regulation of secondary metabolites were found. This minireview summarizes the genome-based genome mining (GM) of diverse BCGs and genome exploration (GE) of versatile biocatalytic enzymes, and other enzymes involved in maintenance and regulation of metabolism of S. peucetius. The detailed analysis of genome sequence provides critically important knowledge useful in the bioengineering of the strain or harboring catalytically efficient enzymes for biotechnological applications.

Marine Rare Actinobacteria: Isolation, Characterization, and Strategies for Harnessing Bioactive Compounds

Actinobacteria are prolific producers of thousands of biologically active natural compounds with diverse activities. More than half of these bioactive compounds have been isolated from members belonging to actinobacteria. Recently, rare actinobacteria existing at different environmental settings such as high altitudes, volcanic areas, and marine environment have attracted attention. It has been speculated that physiological or biochemical pressures under such harsh environmental conditions can lead to the production of diversified natural compounds. Hence, marine environment has been focused for the discovery of novel natural products with biological potency. Many novel and promising bioactive compounds with versatile medicinal, industrial, or agricultural uses have been isolated and characterized. The natural compounds cannot be directly used as drug or other purposes, so they are structurally modified and diversified to ameliorate their biological or chemical properties. Versatile synthetic biological tools, metabolic engineering techniques, and chemical synthesis platform can be used to assist such structural modification. This review summarizes the latest studies on marine rare actinobacteria and their natural products with focus on recent approaches for structural and functional diversification of such microbial chemicals for attaining better applications.