Biosynthesis of aminocyclitol-aminoglycoside antibiotics and related compounds

Phylogenomic analyses and comparative genomics of Pseudomonas syringae associated with almond (Prunus dulcis) in California

We sequenced and comprehensively analysed the genomic architecture of 98 fluorescent pseudomonads isolated from different symptomatic and asymptomatic tissues of almond and a few other Prunus spp. Phylogenomic analyses, genome mining, field pathogenicity tests, and in vitro ice nucleation and antibiotic sensitivity tests were integrated to improve knowledge of the biology and management of bacterial blast and bacterial canker of almond. We identified Pseudomonas syringae pv. syringae, P. cerasi, and P. viridiflava as almond canker pathogens. P. syringae pv. syringae caused both canker and foliar (blast) symptoms. In contrast, P. cerasi and P. viridiflava only caused cankers, and P. viridiflava appeared to be a weak pathogen of almond. Isolates belonging to P. syringae pv. syringae were the most frequently isolated among the pathogenic species/pathovars, composing 75% of all pathogenic isolates. P. cerasi and P. viridiflava isolates composed 8.3 and 16.7% of the pathogenic isolates, respectively. Laboratory leaf infiltration bioassays produced results distinct from experiments in the field with both P. cerasi and P. syringae pv. syringae, causing significant necrosis and browning of detached leaves, whereas P. viridiflava conferred moderate effects. Genome mining revealed the absence of key epiphytic fitness-related genes in P. cerasi and P. viridiflava genomic sequences, which could explain the contrasting field and laboratory bioassay results. P. syringae pv. syringae and P. cerasi isolates harboured the ice nucleation protein, which correlated with the ice nucleation phenotype. Results of sensitivity tests to copper and kasugamycin showed a strong linkage to putative resistance genes. Isolates harbouring the ctpV gene showed resistance to copper up to 600 μg/ml. In contrast, isolates without the ctpV gene could not grow on nutrient agar amended with 200 μg/ml copper, suggesting ctpV can be used to phenotype copper resistance. All isolates were sensitive to kasugamycin at the label-recommended rate of 100μg/ml.

Modifications of Acyl Carrier Protein-Bound Glycosylated Polyketides in Pactamycin Biosynthesis

The potent antitumor antibiotic pactamycin is an aminocyclopentitol-containing natural product produced by the soil bacterium Streptomyces pactum. Recent studies showed that the aminocyclopentitol unit is derived from N-acetyl-D-glucosamine, which is attached to an acyl carrier protein (ACP)-bound polyketide by a glycosyltransferase enzyme, PtmJ. Here, we report a series of post-glycosylation modifications of the sugar moiety of the glycosylated polyketide while it is still attached to the carrier protein. In vitro reconstitution of PtmS (an AMP-ligase), PtmI (an ACP), PtmJ, PtmN (an oxidoreductase), PtmA (an aminotransferase), and PtmB (a putative carbamoyltransferase) showed that the N-acetyl-D-glucosamine moiety of the glycosylated polyketide is first oxidized by PtmN and then transaminated by PtmA to give ACP-bound 3-amino-3-deoxy-N-acetyl-D-glucosaminyl polyketide. The amino group is then coupled with carbamoyl phosphate by PtmB to give a urea functionality. We also show that PtmG is a deacetylase that hydrolyses the C-2 N-acetyl group to give a free amine.

Recent Advances in Chemical Synthesis of Amino Sugars

Amino sugars are a kind of carbohydrates with one or more hydroxyl groups replaced by an amino group. They play crucial roles in a broad range of biological activities. Over the past few decades, there have been continuing efforts on the stereoselective glycosylation of amino sugars. However, the introduction of glycoside bearing basic nitrogen is challenging using conventional Lewis acid-promoted pathways owing to competitive coordination of the amine to the Lewis acid promoter. Additionally, diastereomeric mixtures of O-glycoside are often produced if aminoglycoside lack a C2 substituent. This review focuses on the updated overview of the way to stereoselective synthesis of 1,2-cis-aminoglycoside. The scope, mechanism, and the applications in the synthesis of complex glycoconjugates for the representative methodologies were also included.

Heterologous production of the D-cycloserine intermediate O-acetyl-L-serine in a human type II pulmonary cell model

Tuberculosis (TB) is the second leading cause of death by a single infectious disease behind COVID-19. Despite a century of effort, the current TB vaccine does not effectively prevent pulmonary TB, promote herd immunity, or prevent transmission. Therefore, alternative approaches are needed. We seek to develop a cell therapy that produces an effective antibiotic in response to TB infection. D-cycloserine (D-CS) is a second-line antibiotic for TB that inhibits bacterial cell wall synthesis. We have determined D-CS to be the optimal candidate for anti-TB cell therapy due to its effectiveness against TB, relatively short biosynthetic pathway, and its low-resistance incidence. The first committed step towards D-CS synthesis is catalyzed by the L-serine-O-acetyltransferase (DcsE) which converts L-serine and acetyl-CoA to O-acetyl-L-serine (L-OAS). To test if the D-CS pathway could be an effective prophylaxis for TB, we endeavored to express functional DcsE in A549 cells as a human pulmonary model. We observed DcsE-FLAG-GFP expression using fluorescence microscopy. DcsE purified from A549 cells catalyzed the synthesis of L-OAS as observed by HPLC-MS. Therefore, human cells synthesize functional DcsE capable of converting L-serine and acetyl-CoA to L-OAS demonstrating the first step towards D-CS production in human cells.

N-Formimidoylation/-iminoacetylation modification in aminoglycosides requires FAD-dependent and ligand-protein NOS bridge dual chemistry

Oxidized cysteine residues are highly reactive and can form functional covalent conjugates, of which the allosteric redox switch formed by the lysine-cysteine NOS bridge is an example. Here, we report a noncanonical FAD-dependent enzyme Orf1 that adds a glycine-derived N-formimidoyl group to glycinothricin to form the antibiotic BD-12. X-ray crystallography was used to investigate this complex enzymatic process, which showed Orf1 has two substrate-binding sites that sit 13.5 Å apart unlike canonical FAD-dependent oxidoreductases. One site could accommodate glycine and the other glycinothricin or glycylthricin. Moreover, an intermediate-enzyme adduct with a NOS-covalent linkage was observed in the later site, where it acts as a two-scissile-bond linkage facilitating nucleophilic addition and cofactor-free decarboxylation. The chain length of nucleophilic acceptors vies with bond cleavage sites at either N-O or O-S accounting for N-formimidoylation or N-iminoacetylation. The resultant product is no longer sensitive to aminoglycoside-modifying enzymes, a strategy that antibiotic-producing species employ to counter drug resistance in competing species.

Genome-wide identification of Kanamycin B binding RNA in Escherichia coli

BACKGROUND

The aminoglycosides are established antibiotics that inhibit bacterial protein synthesis by binding to ribosomal RNA. Additional non-antibiotic aminoglycoside cellular functions have also been identified through aminoglycoside interactions with cellular RNAs. The full extent, however, of genome-wide aminoglycoside RNA interactions in Escherichia coli has not been determined. Here, we report genome-wide identification and verification of the aminoglycoside Kanamycin B binding to Escherichia coli RNAs. Immobilized Kanamycin B beads in pull-down assays were used for transcriptome-profiling analysis (RNA-seq).

RESULTS

Over two hundred Kanamycin B binding RNAs were identified. Functional classification analysis of the RNA sequence related genes revealed a wide range of cellular functions. Small RNA fragments (ncRNA, tRNA and rRNA) or small mRNA was used to verify the binding with Kanamycin B in vitro. Kanamycin B and ibsC mRNA was analysed by chemical probing.

CONCLUSIONS

The results will provide biochemical evidence and understanding of potential extra-antibiotic cellular functions of aminoglycosides in Escherichia coli.

Kasugamycin Is a Novel Chitinase 1 Inhibitor with Strong Antifibrotic Effects on Pulmonary Fibrosis

Pulmonary fibrosis is a devastating lung disease with few therapeutic options. CHIT1 (chitinase 1), an 18 glycosyl hydrolase family member, contributes to the pathogenesis of pulmonary fibrosis through the regulation of TGF-β (transforming growth factor-β) signaling and effector function. Therefore, CHIT1 is a potential therapeutic target for pulmonary fibrosis. This study aimed to identify and characterize a druggable CHIT1 inhibitor with strong antifibrotic activity and minimal toxicity for therapeutic application to pulmonary fibrosis. Extensive screening of small molecule libraries identified the aminoglycoside antibiotic kasugamycin (KSM) as a potent CHIT1 inhibitor. Elevated concentrations of CHIT1 were detected in the lungs of patients with pulmonary fibrosis. In in vivo bleomycin- and TGF-β-stimulated murine models of pulmonary fibrosis, KSM showed impressive antifibrotic effects in both preventive and therapeutic conditions. In vitro studies also demonstrated that KSM inhibits fibrotic macrophage activation, fibroblast proliferation, and myofibroblast transformation. Null mutation of TGFBRAP1 (TGF-β-associated protein 1), a recently identified CHIT1 interacting signaling molecule, phenocopied antifibrotic effects of KSM in in vivo lungs and in vitro fibroblasts responses. KSM inhibits the physical association between CHIT1 and TGFBRAP1, suggesting that the antifibrotic effect of KSM is mediated through regulation of TGFBRAP1, at least in part. These studies demonstrate that KSM is a novel CHIT1 inhibitor with a strong antifibrotic effect that can be further developed as an effective and safe therapeutic drug for pulmonary fibrosis.

Biosynthesis of cyclitols

Review covering up to 2021Cyclitols derived from carbohydrates are naturally stable hydrophilic substances under ordinary physiological conditions, increasing the water solubility of whole molecules in cells. The stability of cyclitols is derived from their carbocyclic structures bearing no acetal groups, in contrast to sugar molecules. Therefore, carbocycle-forming reactions are critical for the biosynthesis of cyclitols. Herein, we review naturally occurring cyclitols that have been identified to date and categorize them according to the type of carbocycle-forming enzymatic reaction. Furthermore, the cyclitol-forming enzymatic reaction mechanisms and modification pathways of the initially generated cyclitols are reviewed.

The chemistry and biology of natural ribomimetics and related compounds

Natural ribomimetics represent an important group of specialized metabolites with significant biological activities. Many of the activities, e.g., inhibition of seryl-tRNA synthetases, glycosidases, or ribosomes, are manifestations of their structural resemblance to ribose or related sugars, which play roles in the structural, physiological, and/or reproductive functions of living organisms. Recent studies on the biosynthesis and biological activities of some natural ribomimetics have expanded our understanding on how they are made in nature and why they have great potential as pharmaceutically relevant products. This review article highlights the discovery, biological activities, biosynthesis, and development of this intriguing class of natural products.

Spinning sugars in antigen biosynthesis: characterization of the Coxiella burnetii and Streptomyces griseus TDP-sugar epimerases

The sugars streptose and dihydrohydroxystreptose (DHHS) are unique to the bacteria Streptomyces griseus and Coxiella burnetii, respectively. Streptose forms the central moiety of the antibiotic streptomycin, while DHHS is found in the O-antigen of the zoonotic pathogen C. burnetii. Biosynthesis of these sugars has been proposed to follow a similar path to that of TDP-rhamnose, catalyzed by the enzymes RmlA, RmlB, RmlC, and RmlD, but the exact mechanism is unclear. Streptose and DHHS biosynthesis unusually requires a ring contraction step that could be performed by orthologs of RmlC or RmlD. Genome sequencing of S. griseus and C. burnetii has identified StrM and CBU1838 proteins as RmlC orthologs in these respective species. Here, we demonstrate that both enzymes can perform the RmlC 3'',5'' double epimerization activity necessary to support TDP-rhamnose biosynthesis in vivo. This is consistent with the ring contraction step being performed on a double epimerized substrate. We further demonstrate that proton exchange is faster at the 3''-position than the 5''-position, in contrast to a previously studied ortholog. We additionally solved the crystal structures of CBU1838 and StrM in complex with TDP and show that they form an active site highly similar to those of the previously characterized enzymes RmlC, EvaD, and ChmJ. These results support the hypothesis that streptose and DHHS are biosynthesized using the TDP pathway and that an RmlD paralog most likely performs ring contraction following double epimerization. This work will support the elucidation of the full pathways for biosynthesis of these unique sugars.

KasQ an Epimerase Primes the Biosynthesis of Aminoglycoside Antibiotic Kasugamycin and KasF/H Acetyltransferases Inactivate Its Activity

Kasugamycin (KSM), an aminoglycoside antibiotic, is composed of three chemical moieties: D-chiro-inositol, kasugamine and glycine imine. Despite being discovered more than 50 years ago, the biosynthetic pathway of KSM remains an unresolved puzzle. Here we report a structural and functional analysis for an epimerase, KasQ, that primes KSM biosynthesis rather than the previously proposed KasF/H, which instead acts as an acetyltransferase, inactivating KSM. Our biochemical and biophysical analysis determined that KasQ converts UDP-GlcNAc to UDP-ManNAc as the initial step in the biosynthetic pathway. The isotope-feeding study further confirmed that ¹³C, ¹⁵N-glucosamine/UDP-GlcNH₂ rather than glucose/UDP-Glc serves as the direct precursor for the formation of KSM. Both KasF and KasH were proposed, respectively, converting UDP-GlcNH₂ and KSM to UDP-GlcNAc and 2-N’-acetyl KSM. Experimentally, KasF is unable to do so; both KasF and KasH are instead KSM-modifying enzymes, while the latter is more specific and reactive than the former in terms of the extent of resistance. The information gained here lays the foundation for mapping out the complete KSM biosynthetic pathway.

From solo to duet, intersections of natural product assembly with self-resistance

Covering: up to 2021Self-resistance mechanisms adopted by natural product producers have long been recognized and studied as a standalone system separated from the assembly machinery. However, as more examples of self-resistance have been characterized in detail, it has been revealed that self-resistance could associate with the assembly machinery to fulfill the task of biosynthesis. This review summarizes different self-resistance mechanisms showing a common feature: intersection with natural product assembly. Furthermore, their possible evolutionary origin and synthetic biology applications are discussed.

N-7′ methylation in apramycin: its biosynthesis and biological role

This work characterized N-7′ methylation in apramycin's assembly line, which fills in the final step at the pseudotrisaccharide stage of the apramycin biosynthetic pathway and indicates the significant biological role of the N-7′ methyl group.

Structure of the mitoribosomal small subunit with streptomycin reveals Fe-S clusters and physiological molecules

The mitoribosome regulates cellular energy production, and its dysfunction is associated with aging. Inhibition of the mitoribosome can be caused by off-target binding of antimicrobial drugs and was shown to be coupled with a bilateral decreased visual acuity. Previously, we reported mitochondria-specific protein aspects of the mitoribosome, and in this article we present a 2.4-Å resolution structure of the small subunit in a complex with the anti-tuberculosis drug streptomycin that reveals roles of non-protein components. We found iron-sulfur clusters that are coordinated by different mitoribosomal proteins, nicotinamide adenine dinucleotide (NAD) associated with rRNA insertion, and posttranslational modifications. This is the first evidence of inter-protein coordination of iron-sulfur, and the finding of iron-sulfur clusters and NAD as fundamental building blocks of the mitoribosome directly links to mitochondrial disease and aging. We also report details of streptomycin interactions, suggesting that the mitoribosome-bound streptomycin is likely to be in hydrated gem-diol form and can be subjected to other modifications by the cellular milieu. The presented approach of adding antibiotics to cultured cells can be used to define their native structures in a bound form under more physiological conditions, and since streptomycin is a widely used drug for treatment, the newly resolved features can serve as determinants for targeting.

Genome Mining of Pseudomonas Species: Diversity and Evolution of Metabolic and Biosynthetic Potential

Microbial genome sequencing has uncovered a myriad of natural products (NPs) that have yet to be explored. Bacteria in the genus Pseudomonas serve as pathogens, plant growth promoters, and therapeutically, industrially, and environmentally important microorganisms. Though most species of Pseudomonas have a large number of NP biosynthetic gene clusters (BGCs) in their genomes, it is difficult to link many of these BGCs with products under current laboratory conditions. In order to gain new insights into the diversity, distribution, and evolution of these BGCs in Pseudomonas for the discovery of unexplored NPs, we applied several bioinformatic programming approaches to characterize BGCs from Pseudomonas reference genome sequences available in public databases along with phylogenetic and genomic comparison. Our research revealed that most BGCs in the genomes of Pseudomonas species have a high diversity for NPs at the species and subspecies levels and built the correlation of species with BGC taxonomic ranges. These data will pave the way for the algorithmic detection of species- and subspecies-specific pathways for NP development.

Aminoglycoside riboswitch control of the expression of integron associated aminoglycoside resistance adenyltransferases

The proliferation of antibiotic resistance has its origins in horizontal gene transfer. The class 1 integrons mediate gene transfer by assimilating antibiotic-resistance genes through site-specific recombination. For the class 1 integrons the first assimilated gene normally encodes an aminoglycoside antibiotic resistance protein which is either an aminoglycoside acetyltransferase (AAC), nucleotidyltransferase - (ANT), or adenyl transferase (AAD). An aminoglycoside-sensing riboswitch RNA in the leader RNA of AAC/AAD that controls the expression of aminoglycoside resistance genes has been previously described. Here we explore the relationship between the recombinant products of integron recombination and a series of candidate riboswitch RNAs in the 5' UTR of aad (aminoglycoside adenyltransferases) genes. The RNA sequences from the 5' UTR of the aad genes from pathogenic strains that are the products of site-specific DNA recombination by class 1 integrons were investigated. Reporter assays, MicroScale Thermophoresis (MST) and covariance analysis revealed that a functional aminoglycoside-sensing riboswitch was selected at the DNA level through integron-mediated site-specific recombination. This study explains the close association between integron recombination and the aminoglycoside-sensing riboswitch RNA.

Engineering of Streptoalloteichus tenebrarius 2444 for Sustainable Production of Tobramycin

Tobramycin is a broad-spectrum aminoglycoside antibiotic agent. The compound is obtained from the base-catalyzed hydrolysis of carbamoyltobramycin (CTB), which is naturally produced by the actinomycete Streptoalloteichus tenebrarius. However, the strain uses the same precursors to synthesize several structurally related aminoglycosides. Consequently, the production yields of tobramycin are low, and the compound’s purification is very challenging, costly, and time-consuming. In this study, the production of the main undesired product, apramycin, in the industrial isolate Streptoalloteichus tenebrarius 2444 was decreased by applying the fermentation media M10 and M11, which contained high concentrations of starch and dextrin. Furthermore, the strain was genetically engineered by the inactivation of the aprK gene (∆aprK), resulting in the abolishment of apramycin biosynthesis. In the next step of strain development, an additional copy of the tobramycin biosynthetic gene cluster (BGC) was introduced into the ∆aprK mutant. Fermentation by the engineered strain (∆aprK_1-17L) in M11 medium resulted in a 3- to 4-fold higher production than fermentation by the precursor strain (∆aprK). The phenotypic stability of the mutant without selection pressure was validated. The use of the engineered S. tenebrarius 2444 facilitates a step-saving, efficient, and, thus, more sustainable production of the valuable compound tobramycin on an industrial scale.

Comparative Transcriptome Analysis of Streptomyces nodosus Mutant With a High-Yield Amphotericin B

Antibiotics play an important role in human health. Most antibiotics are derived from microbial secondary metabolites. Amphotericin is a polyene macrolide antibiotic synthesized by Streptomyces nodosus. S. nodosus ZJB2016050 with high-yield amphotericin B (AmB) was obtained by traditional mutagenesis using S. nodosus ATCC14899 as the original strain. The differences in the characterization of the two strains were found in color, mycelium morphology, and AmB yield. Subsequent comparative transcriptome explained the yield differences between the two strains. Pathways including the carbohydrate metabolic pathway and the secondary product synthesis pathway were targeted. The upregulation of glucokinase, phosphoglycerate mutase, and pyruvate dehydrogenase accelerates the consumption of glucose and has great effects on the accumulation of precursors. One of the competitive secondary metabolites of the polyketone synthetase (PKS) II type sapromomycin analog synthesis gene cluster was downregulated, which competes for malonyl-CoA. Five PKS modules (except for the first module amphA) of the amphotericin synthetic gene cluster in the high-yielding strain were downregulated, which resulted in the total amphotericin A (AmA) and AmB of S. nodosus ZJB2016050 being less than that of the wild-type S. nodosus ATCC14899. Combined with gene differential expression in the pentose phosphate pathway and the reaction mechanism of the ER5 domain, the reason that S. nodosus ZJB2016050 preferred to synthesize AmB was probably related to intracellular reduction.

Genomic and Metabolomic Analysis of Antarctic Bacteria Revealed Culture and Elicitation Conditions for the Production of Antimicrobial Compounds

Concern about finding new antibiotics against drug-resistant pathogens is increasing every year. Antarctic bacteria have been proposed as an unexplored source of bioactive metabolites; however, most biosynthetic gene clusters (BGCs) producing secondary metabolites remain silent under common culture conditions. Our work aimed to characterize elicitation conditions for the production of antibacterial secondary metabolites from 34 Antarctic bacterial strains based on MS/MS metabolomics and genome mining approaches. Bacterial strains were cultivated under different nutrient and elicitation conditions, including the addition of lipopolysaccharide (LPS), sodium nitroprusside (SNP), and coculture. Metabolomes were obtained by HPLC-QTOF-MS/MS and analyzed through molecular networking. Antibacterial activity was determined, and seven strains were selected for genome sequencing and analysis. Biosynthesis pathways were activated by all the elicitation treatments, which varies among strains and dependents of culture media. Increased antibacterial activity was observed for a few strains and addition of LPS was related with inhibition of Gram-negative pathogens. Antibiotic BGCs were found for all selected strains and the expressions of putative actinomycin, carotenoids, and bacillibactin were characterized by comparison of genomic and metabolomic data. This work established the use of promising new elicitors for bioprospection of Antarctic bacteria and highlights the importance of new "-omics" comparative approaches for drug discovery.

A Validamycin Shunt Pathway for Valienamine Synthesis in Engineered Streptomyces hygroscopicus 5008

Valienamine is the key functional component of many natural glycosidase inhibitors, including the crop protectant validamycin A and the clinical antidiabetic agent acarbose. Due to its important biomedical activity, it is also the prominent lead compound for the exploration of therapeutic agents, such as the stronger α-glucosidase inhibitor voglibose. Currently, the main route for obtaining valienamine is a multistep biosynthetic process involving the synthesis and degradation of validamycin A. Here, we established an alternative, vastly simplified shunt pathway for the direct synthesis of valienamine based on an envisioned non-natural transamination in the validamycin A producer Streptomyces hygroscopicus 5008. We first identified candidate aminotransferases for the non-natural ketone substrate valienone and conducted molecular evolution in vitro. The WecE enzyme from Escherichia coli was verified to complete the envisioned step with >99.9% enantiomeric excess and was further engineered to produce a 32.6-fold more active mutant, VarB, through protein evolution. Subsequently, two copies of VarB were introduced into the host, and the new shunt pathway produced 0.52 mg/L valienamine after a 96-h fermentation. Our study thus illustrates a dramatically simplified alternative shunt pathway for valienamine production and introduces a promising foundational platform for increasing the production of valienamine and its valuable N-modified derivatives for use in pharmaceutical applications.

A role for antibiotic biosynthesis monooxygenase domain proteins in fidelity control during aromatic polyketide biosynthesis

The formicamycin biosynthetic gene cluster encodes two groups of type 2 polyketide antibiotics: the formicamycins and their biosynthetic precursors the fasamycins, both of which have activity against methicillin-resistant Staphylococcus aureus. Here, we report the formicapyridines which are encoded by the same gene cluster and are structurally and biosynthetically related to the fasamycins and formicamycins but comprise a rare pyridine moiety. These compounds are trace-level metabolites formed by derailment of the major biosynthetic pathway. Inspired by evolutionary logic we show that rational mutation of a single gene in the biosynthetic gene cluster encoding an antibiotic biosynthesis monooxygenase (ABM) superfamily protein leads to a significant increase both in total formicapyridine production and their enrichment relative to the fasamycins/formicamycins. Our observations broaden the polyketide biosynthetic landscape and identify a non-catalytic role for ABM superfamily proteins in type II polyketide synthase assemblages for maintaining biosynthetic pathway fidelity.

Survey of Biosynthetic Gene Clusters from Sequenced Myxobacteria Reveals Unexplored Biosynthetic Potential

Coinciding with the increase in sequenced bacteria, mining of bacterial genomes for biosynthetic gene clusters (BGCs) has become a critical component of natural product discovery. The order Myxococcales, a reputable source of biologically active secondary metabolites, spans three suborders which all include natural product producing representatives. Utilizing the BiG-SCAPE-CORASON platform to generate a sequence similarity network that contains 994 BGCs from 36 sequenced myxobacteria deposited in the antiSMASH database, a total of 843 BGCs with lower than 75% similarity scores to characterized clusters within the MIBiG database are presented. This survey provides the biosynthetic diversity of these BGCs and an assessment of the predicted chemical space yet to be discovered. Considering the mere snapshot of myxobacteria included in this analysis, these untapped BGCs exemplify the potential for natural product discovery from myxobacteria.

Silencing cryptic specialized metabolism in Streptomyces by the nucleoid-associated protein Lsr2

Lsr2 is a nucleoid-associated protein conserved throughout the actinobacteria, including the antibiotic-producing Streptomyces. Streptomyces species encode paralogous Lsr2 proteins (Lsr2 and Lsr2-like, or LsrL), and we show here that of the two, Lsr2 has greater functional significance. We found that Lsr2 binds AT-rich sequences throughout the chromosome, and broadly represses gene expression. Strikingly, specialized metabolic clusters were over-represented amongst its targets, and the cryptic nature of many of these clusters appears to stem from Lsr2-mediated repression. Manipulating Lsr2 activity in model species and uncharacterized isolates resulted in the production of new metabolites not seen in wild type strains. Our results suggest that the transcriptional silencing of biosynthetic clusters by Lsr2 may protect Streptomyces from the inappropriate expression of specialized metabolites, and provide global control over Streptomyces’ arsenal of signaling and antagonistic compounds.

Synthesis and Biological Evaluation of the Novel Growth Inhibitor Streptol Glucoside, Isolated from an Obligate Plant Symbiont

The plant Psychotria kirkii hosts an obligatory bacterial symbiont, Candidatus Burkholderia kirkii, in nodules on their leaves. Recently, a glucosylated derivative of (+)-streptol, (+)-streptol glucoside, was isolated from the nodulated leaves and was found to possess a plant growth inhibitory activity. To establish a structure-activity relationship study, a convergent strategy was developed to obtain several pseudosugars from a single synthetic precursor. Furthermore, the glucosylation of streptol was investigated in detail and conditions affording specifically the α or β glucosidic anomer were identified. Although (+)-streptol was the most active compound, its concentration in P. kirkii plant leaves extract was approximately ten-fold lower than that of (+)-streptol glucoside. These results provide compelling evidence that the glucosylation of (+)-streptol protects the plant host against the growth inhibitory effect of the compound, which might constitute a molecular cornerstone for this successful plant-bacteria symbiosis.

Genome-guided and mass spectrometry investigation of natural products produced by a potential new actinobacterial strain isolated from a mangrove ecosystem in Futian, Shenzhen, China

Actinobacteria, a group of gram-positive bacteria, can produce plenty of valuable bioactive secondary metabolites, especially antibiotics. Hence, in order to search for new actinobacteria, actinobacterial isolates were obtained from rhizosphere soil collected from the Futian mangrove ecosystem in Shenzhen, China. According to 16S rRNA sequences, 14 actinobacterial strains of the genus Streptomyces, Rhodococcus, Microbacterium, Micromonospora, Actinoplanes and Mycobacterium were isolated and identified. Among these, strain Mycobacterium sp.13 was described as a potential new species belonging to the genus Mycobacterium within the class of actinobacteria according to the genomic analysis. The genome-based 16S rRNA sequences had 98.48% sequence similarity with Mycobacterium moriokaense DSM 44221^T. Meanwhile, the genome sequences of Mycobacterium sp.13 showed an average nucleotide identity (ANI) with the Mycobacterium mageritense DSM 44476, Mycobacterium smegmatis MKD8 and Mycobacterium goodii strain X7B of only 74.79%, 76.12% and 76.42%, respectively. Furthermore, genome-mining results showed that Mycobacterium sp.13 contained 105 gene clusters encoding to the secondary metabolite biosynthesis, where many kinds of terpene, bacteriocin, T1pks, Nrps, saccharide, fatty acid, butyrolactone, ectoine and resorcinol were included. Finally, through LC-MS and HR-MS, analyzing the small molecules from ethyl acetate extract of this strain, asukamycin C and apramycin were for the first time found present to be in Mycobacterium moriokaense strain. Our study provides evidence in support of the potential new Mycobacterium sp.13 isolated from the mangrove environment as a possible novel source of natural products.

Isolation of Nabscessin C from Nocardia abscessus IFM 10029T and a Study on Biosynthetic Pathway for Nabscessins

A new aminocyclitol derivative, designated nabscessin C (1), was isolated from Nocardia abscessus IFM 10029^T. Nabcessin C is an isomer of nabscessins A (2) and B (3) with different positioning of the acyl group. Absolute configuration of nabscessin A was determined by conversion into the 2-deoxy-scyllo-inosamine pentaacetyl derivative (4) by hydrolysis and acetylation of 2. The biosynthetic pathway of nabscessins is proposed based on gene expression analysis.

Isolation by Miniaturized Culture Chip of an Antarctic bacterium Aequorivita sp. with antimicrobial and anthelmintic activity

•

Novel microbial isolation approach allowed the identification of a Gram-negative Antarctic bacterium belonging to the genus Aequorivita.

•

Aequorivita sp. showed antimicrobial and anthelmintic activity without toxic effect towards eukaryotic cells.

•

The whole genome of Aequorivita sp. was sequenced and compared with other strains to identify biosynthetic gene clusters.

•

This novel approach represents a promising strategy to isolate rare or novel strains useful for biotechnological applications.

Microbes are prolific sources of bioactive molecules; however, the cultivability issue has severely hampered access to microbial diversity. Novel secondary metabolites from as-yet-unknown or atypical microorganisms from extreme environments have realistic potential to lead to new drugs with benefits for human health. Here, we used a novel approach that mimics the natural environment by using a Miniaturized Culture Chip allowing the isolation of several bacterial strains from Antarctic shallow water sediments under near natural conditions. A Gram-negative Antarctic bacterium belonging to the genus Aequorivita was subjected to further analyses. The Aequorivita sp. genome was sequenced and a bioinformatic approach was applied to identify biosynthetic gene clusters. The extract of the Aequorivita sp. showed antimicrobial and anthelmintic activity towards Multidrug resistant bacteria and the nematode Caenorhabditis elegans. This is the first multi-approach study exploring the genomics and biotechnological potential of the genus Aequorivita that is a promising candidate for pharmaceutical applications.

Biosynthesis and Metabolic Engineering of Pseudo-oligosaccharides

Pseudo-oligosaccharides are microbial-derived secondary metabolites whose chemical structures contain pseudosugars (glycomimetics). Due to their high resemblance to the molecules of life (carbohydrates), most pseudo-oligosaccharides show significant biological activities. Some of them have been used as drugs to treat human and plant diseases. Because of their significant economic value, efforts have been put into understanding their biosynthesis, optimizing their fermentation conditions, and engineering their metabolic pathways to obtain better production yields. A number of unusual enzymes participating in diverse biosynthetic pathways to pseudo-oligosaccharides have been reported. Various methods and conditions to improve the production yields of the target compounds and eliminate byproducts have also been developed. This review article describes recent studies on the biosynthesis, fermentation optimization, and metabolic engineering of high-value pseudo-oligosaccharides.

Interaction of antidiabetic α-glucosidase inhibitors and gut bacteria α-glucosidase

Carbohydrate hydrolyzing α-glucosidases are commonly found in microorganisms present in the human intestine microbiome. We have previously reported crystal structures of an α-glucosidase from the human gut bacterium Blaubia (Ruminococcus) obeum (Ro-αG1) and its substrate preference/specificity switch. This novel member of the GH31 family is a structural homolog of human intestinal maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI) with a highly conserved active site that is predicted to be common in Ro-αG1 homologs among other species that colonize the human gut. In this report, we present structures of Ro-αG1 in complex with the antidiabetic α-glucosidase inhibitors voglibose, miglitol, and acarbose and supporting binding data. The in vitro binding of these antidiabetic drugs to Ro-αG1 suggests the potential for unintended in vivo crossreaction of the α-glucosidase inhibitors to bacterial α-glucosidases that are present in gut microorganism communities. Moreover, analysis of these drug-bound enzyme structures could benefit further antidiabetic drug development.

On an algorithmic definition for the components of the minimal cell

Living cells are highly complex systems comprising a multitude of elements that are engaged in the many convoluted processes observed during the cell cycle. However, not all elements and processes are essential for cell survival and reproduction under steady-state environmental conditions. To distinguish between essential from expendable cell components and thus define the ‘minimal cell’ and the corresponding ‘minimal genome’, we postulate that the synthesis of all cell elements can be represented as a finite set of binary operators, and within this framework we show that cell elements that depend on their previous existence to be synthesized are those that are essential for cell survival. An algorithm to distinguish essential cell elements is presented and demonstrated within an interactome. Data and functions implementing the algorithm are given as supporting information. We expect that this algorithmic approach will lead to the determination of the complete interactome of the minimal cell, which could then be experimentally validated. The assumptions behind this hypothesis as well as its consequences for experimental and theoretical biology are discussed.

d-Sedoheptulose-7-phosphate is a common precursor for the heptoses of septacidin and hygromycin B

Seven-carbon-chain-containing sugars exist in several groups of important bacterial natural products. Septacidin represents a group of l-heptopyranoses containing nucleoside antibiotics with antitumor, antifungal, and pain-relief activities. Hygromycin B, an aminoglycoside anthelmintic agent used in swine and poultry farming, represents a group of d-heptopyranoses-containing antibiotics. To date, very little is known about the biosynthesis of these compounds. Here we sequenced the genome of the septacidin producer and identified the septacidin gene cluster by heterologous expression. After determining the boundaries of the septacidin gene cluster, we studied septacidin biosynthesis by in vivo and in vitro experiments and discovered that SepB, SepL, and SepC can convert d-sedoheptulose-7-phosphate (S-7-P) to ADP-l-glycero-β-d-manno-heptose, exemplifying the involvement of ADP-sugar in microbial natural product biosynthesis. Interestingly, septacidin, a secondary metabolite from a gram-positive bacterium, shares the same ADP-heptose biosynthesis pathway with the gram-negative bacterium LPS. In addition, two acyltransferase-encoding genes sepD and sepH, were proposed to be involved in septacidin side-chain formation according to the intermediates accumulated in their mutants. In hygromycin B biosynthesis, an isomerase HygP can recognize S-7-P and convert it to ADP-d-glycero-β-d-altro-heptose together with GmhA and HldE, two enzymes from the Escherichia coli LPS heptose biosynthetic pathway, suggesting that the d-heptopyranose moiety of hygromycin B is also derived from S-7-P. Unlike the other S-7-P isomerases, HygP catalyzes consecutive isomerizations and controls the stereochemistry of both C2 and C3 positions.

The sedoheptulose 7-phosphate cyclases and their emerging roles in biology and ecology

Covering up to: 1999-2016This highlight covers a family of enzymes of growing importance, the sedoheptulose 7-phosphate cyclases, initially of interest due to their involvement in the biosynthesis of pharmaceutically relevant secondary metabolites. More recently, these enzymes have been found throughout Prokarya and Eukarya, suggesting their broad potential biological roles in nature.

Parallel pathways in the biosynthesis of aminoglycoside antibiotics

Despite their inherent toxicity and the global spread of bacterial resistance, aminoglycosides (AGs), an old class of microbial drugs, remain a valuable component of the antibiotic arsenal. Recent studies have continued to reveal the fascinating biochemistry of AG biosynthesis and the rich potential in their pathway engineering. In particular, parallel pathways have been shown to be common and widespread in AG biosynthesis, highlighting nature’s ingenuity in accessing diverse natural products from a limited set of genes. In this review, we discuss the parallel biosynthetic pathways of three representative AG antibiotics—kanamycin, gentamicin, and apramycin—as well as future directions towards the discovery and development of novel AGs.

Biosynthesis of nitrogen-containing natural products, C7N aminocyclitols and bis-indoles, from actinomycetes

Actinomycetes are a major source of bioactive natural products with important pharmaceutical properties. Understanding the natural enzymatic assembly of complex small molecules is important for rational metabolic pathway design to produce “artificial” natural products in bacterial cells. This review will highlight current research on the biosynthetic mechanisms of two classes of nitrogen-containing natural products, C7N aminocyclitols and bis-indoles. Validamycin A is a member of C7N aminocyclitol natural products from Streptomyces hygroscopicus. Here, two important biosynthetic steps, pseudoglycosyltranferase-catalyzed C–N bond formation, and C7-sugar phosphate cyclase-catalyzed divergent carbasugar formation, will be reviewed. In addition, the bis-indolic natural products indolocarbazole, staurosporine from Streptomyces sp. TP-A0274, and rearranged bis-indole violacein from Chromobacterium violaceum are reviewed including the oxidative course of the assembly pathway for the bis-indolic scaffold. The identified biosynthesis mechanisms will be useful to generating new biocatalytic tools and bioactive compounds.

Evolution and Distribution of C7-Cyclitol Synthases in Prokaryotes and Eukaryotes

2-Epi-5-epi-valiolone synthase (EEVS), a C₇-sugar phosphate cyclase (SPC) homologous to 3-dehydroquinate synthase (DHQS), was discovered during studies of the biosynthesis of the C₇N-aminocyclitol family of natural products. EEVS was originally thought to be present only in certain actinomycetes, but analyses of genome sequences showed that it is broadly distributed in both prokaryotes and eukaryotes, including vertebrates. Another SPC, desmethyl-4-deoxygadusol synthase (DDGS), was later discovered as being involved in the biosynthesis of mycosporine-like amino acid sunscreen compounds. Current database annotations are quite unreliable, with many EEVSs reported as DHQS, and most DDGSs reported as EEVS, DHQS, or simply hypothetical proteins. Here, we identify sequence features useful for distinguishing these enzymes, report a crystal structure of a representative DDGS showing the high similarity of the EEVS and DDGS enzymes, identify notable active site differences, and demonstrate the importance of two of these active site residues for catalysis by point mutations. Further, we functionally characterized two representatives of a distinct clade equidistant from known EEVS and known DDGS groups and show them to be authentic EEVSs. Moreover, we document and discuss the distribution of genes that encode EEVS and DDGS in various prokaryotes and eukaryotes, including pathogenic bacteria, plant symbionts, nitrogen-fixing bacteria, myxobacteria, cyanobacteria, fungi, stramenopiles, and animals, suggesting their broad potential biological roles in nature.

Istamycin aminoglycosides profiling and their characterization in Streptomyces tenjimariensis ATCC 31603 culture using high-performance liquid chromatography with tandem mass spectrometry

A high-performance liquid chromatography with electrospray ionization ion trap tandem mass spectrometry method was developed and validated for the robust profiling and characterization of biosynthetic congeners in the 2-deoxy-aminocyclitol istamycin pathway, from the fermentation broth of Streptomyces tenjimariensis ATCC 31603. Gradient elution on an Acquity CSH C₁₈ column was performed with a gradient of 5 mM aqueous pentafluoropropionic acid and 50% acetonitrile. Sixteen natural istamycin congeners were profiled and quantified in descending order; istamycin A, istamycin B, istamycin A₀ , istamycin B₀ , istamycin B₁ , istamycin A₁ , istamycin C, istamycin A₂ , istamycin C₁ , istamycin C₀ , istamycin X₀ , istamycin A₃ , istamycin Y₀ , istamycin B₃ , and istamycin FU-10 plus istamycin AP. In addition, a total of five sets of 1- or 3-epimeric pairs were chromatographically separated using a macrocyclic glycopeptide-bonded chiral column. The lower limit of quantification of istamycin-A present in S. tenjimariensis fermentation was estimated to be 2.2 ng/mL. The simultaneous identification of a wide range of 2-deoxy-aminocyclitol-type istamycin profiles from bacterial fermentation was determined for the first time by employing high-performance liquid chromatography with tandem mass spectrometry analysis and the separation of istamycin epimers.

Interrogating the Tailoring Steps of Pactamycin Biosynthesis and Accessing New Pactamycin Analogues

Pactamycin is a bacteria-derived aminocyclitol antibiotic with a wide-range of biological activity. Its chemical structure and potent biological activities have made it an interesting lead compound for drug discovery and development. Despite its unusual chemical structure, many aspects of its formation in nature remain elusive. Using a combination of genetic inactivation and metabolic analysis, we investigated the tailoring processes of pactamycin biosynthesis in Streptomyces pactum. The results provide insights into the sequence of events during the tailoring steps of pactamycin biosynthesis and explain the unusual production of various pactamycin analogues by S. pactum mutants. We also identified two new pactamycin analogues that have better selectivity indexes than pactamycin against malarial parasites.

Synthesis of an Orthogonally Protected Polyhydroxylated Cyclopentene from l-Sorbose

The use of l-sorbose in the synthesis of functionalized cyclopentene derivatives was accomplished. These cyclopentene derivatives are related to those found in naturally occurring jatrophane frameworks and in other bioactive compounds. The formation of allyl α-l-sorbopyranoside was a key synthetic step. Regioselective introduction of protecting groups was followed by the hydrolysis of the allyl glycoside to furnish a fully protected acyclic l-sorbose derivative. This acyclic intermediate was subsequently used to give an orthogonally protected polyhydroxylated cyclopentene, which has potential for further synthesis of bioactive compounds. The protected cyclopentene itself showed a clear cytotoxic activity when tested against a panel of human cancer cell lines (HT29, LS174T, SW620, A549, and HeLa cells).

Physiology, Biochemistry, and Applications of F420- and Fo-Dependent Redox Reactions

5-Deazaflavin cofactors enhance the metabolic flexibility of microorganisms by catalyzing a wide range of challenging enzymatic redox reactions. While structurally similar to riboflavin, 5-deazaflavins have distinctive and biologically useful electrochemical and photochemical properties as a result of the substitution of N-5 of the isoalloxazine ring for a carbon. 8-Hydroxy-5-deazaflavin (Fo) appears to be used for a single function: as a light-harvesting chromophore for DNA photolyases across the three domains of life. In contrast, its oligoglutamyl derivative F420 is a taxonomically restricted but functionally versatile cofactor that facilitates many low-potential two-electron redox reactions. It serves as an essential catabolic cofactor in methanogenic, sulfate-reducing, and likely methanotrophic archaea. It also transforms a wide range of exogenous substrates and endogenous metabolites in aerobic actinobacteria, for example mycobacteria and streptomycetes. In this review, we discuss the physiological roles of F420 in microorganisms and the biochemistry of the various oxidoreductases that mediate these roles. Particular focus is placed on the central roles of F420 in methanogenic archaea in processes such as substrate oxidation, C1 pathways, respiration, and oxygen detoxification. We also describe how two F420-dependent oxidoreductase superfamilies mediate many environmentally and medically important reactions in bacteria, including biosynthesis of tetracycline and pyrrolobenzodiazepine antibiotics by streptomycetes, activation of the prodrugs pretomanid and delamanid by Mycobacterium tuberculosis, and degradation of environmental contaminants such as picrate, aflatoxin, and malachite green. The biosynthesis pathways of Fo and F420 are also detailed. We conclude by considering opportunities to exploit deazaflavin-dependent processes in tuberculosis treatment, methane mitigation, bioremediation, and industrial biocatalysis.

Detection and Quantification of Ribosome Inhibition by Aminoglycoside Antibiotics in Living Bacteria Using an Orthogonal Ribosome-Controlled Fluorescent Reporter

The ribosome is the quintessential antibacterial drug target, with many structurally and mechanistically distinct classes of antibacterial agents acting by inhibiting ribosome function. Detecting and quantifying ribosome inhibition by small molecules and investigating their binding modes and mechanisms of action are critical to antibacterial drug discovery and development efforts. To develop a ribosome inhibition assay that is operationally simple, yet provides direct information on the drug target and the mechanism of action, we have developed engineered E. coli strains harboring an orthogonal ribosome-controlled green fluorescent protein (GFP) reporter that produce fluorescent signal when the orthogonal ribosome is inhibited. As a proof of concept, we demonstrate that these strains, when coexpressing homogeneous populations of aminoglycoside resistant ribosomes, act as sensitive and quantitative detectors of ribosome inhibition by a set of 12 structurally diverse aminoglycoside antibiotics. We suggest that this strategy can be extended to quantifying ribosome inhibition by other drug classes.

A comprehensive review of glycosylated bacterial natural products

A systematic analysis of all naturally-occurring glycosylated bacterial secondary metabolites reported in the scientific literature up through early 2013 is presented. This comprehensive analysis of 15 940 bacterial natural products revealed 3426 glycosides containing 344 distinct appended carbohydrates and highlights a range of unique opportunities for future biosynthetic study and glycodiversification efforts.

Identification and engineering of regulation-related genes toward improved kasugamycin production

Kasugamycin, produced by Streptomyces kasugaensis and Streptomyces microaureus, is an important amino-glycoside family antibiotic and widely used for veterinary and agricultural applications. In the left flanking region of the previously reported kasugamycin gene cluster, four additional genes (two-component system kasW and kasX, MerR-family kasV, and isoprenylcysteine carboxyl methyltransferase kasS) were identified both in the low-yielding S. kasugaensis BCRC12349 and high-yielding S. microaureus XM301. Deletion of regulatory gene kasT abolished kasugamycin production, and its overexpression in BCRC12349 resulted in an increased titer by 186 %. Deletion of kasW, kasX, kasV, and kasS improved kasugamycin production by 12, 19, 194, and 22 %, respectively. qRT-PCR analysis demonstrated that the transcription of kas genes was significantly increased in all the four mutants. Similar gene inactivation was performed in the high-yielding strain S. microaureus XM301. As expected, the deletion of kasW/X resulted in a 58 % increase of the yield from 6 to 9.5 g/L. However, the deletion of kasV and over-expression of kasT had no obvious effect, and the disruption of kasS surprisingly decreased kasugamycin production. In addition, trans-complementation of the kasS mutant with a TTA codon-mutated kasS increased the kasugamycin yield by 20 %. A much higher transcription of kas genes was detected in the high-yielding XM301 than in the low-yielding BCRC12349, which may partially account for the discrepancy of gene inactivation effects between them. Our work not only generated engineered strains with improved kasugamycin yield, but also pointed out that different strategies on manipulating regulatory-related genes should be considered for low-yielding or high-yielding strains.

Aminoglycoside Antibiotics: New Insights into the Biosynthetic Machinery of Old Drugs

2-Deoxystreptamine (2DOS) is the unique chemically stable aminocyclitol scaffold of clinically important aminoglycoside antibiotics such as neomycin, kanamycin, and gentamicin, which are produced by Actinomycetes. The 2DOS core can be decorated with various deoxyaminosugars to make structurally diverse pseudo-oligosaccharides. After the discovery of biosynthetic gene clusters for 2DOS-containing aminoglycoside antibiotics, the function of each biosynthetic enzyme has been extensively elucidated. The common biosynthetic intermediates 2DOS, paromamine and ribostamycin are constructed by conserved enzymes encoded in the gene clusters. The biosynthetic intermediates are then converted to characteristic architectures by unique enzymes encoded in each biosynthetic gene cluster. In this Personal Account, we summarize both common biosynthetic pathways and the pathways used for structural diversification.

Structural Basis for the Stereochemical Control of Amine Installation in Nucleotide Sugar Aminotransferases

Sugar aminotransferases (SATs) are an important class of tailoring enzymes that catalyze the 5'-pyridoxal phosphate (PLP)-dependent stereo- and regiospecific installation of an amino group from an amino acid donor (typically L-Glu or L-Gln) to a corresponding ketosugar nucleotide acceptor. Herein we report the strategic structural study of two homologous C4 SATs (Micromonospora echinospora CalS13 and Escherichia coli WecE) that utilize identical substrates but differ in their stereochemistry of aminotransfer. This study reveals for the first time a new mode of SAT sugar nucleotide binding and, in conjunction with previously reported SAT structural studies, provides the basis from which to propose a universal model for SAT stereo- and regiochemical control of amine installation. Specifically, the universal model put forth highlights catalytic divergence to derive solely from distinctions within nucleotide sugar orientation upon binding within a relatively fixed SAT active site where the available ligand bound structures of the three out of four representative C3 and C4 SAT examples provide a basis for the overall model. Importantly, this study presents a new predictive model to support SAT functional annotation, biochemical study and rational engineering.

Inositol-phosphodihydroceramides in the periodontal pathogen Tannerella forsythia: Structural analysis and incorporation of exogenous myo-inositol

BACKGROUND

Unique phosphodihydroceramides containing phosphoethanolamine and glycerol have been previously described in Porphyromonas gingivalis. Importantly, they were shown to possess pro-inflammatory properties. Other common human bacteria were screened for the presence of these lipids, and they were found, amongst others, in the oral pathogen Tannerella forsythia. To date, no detailed study into the lipids of this organism has been performed.

METHODS

Lipids were extracted, separated and purified by HPTLC, and analyzed using GC-MS, ESI-MS and NMR. Of special interest was how T. forsythia acquires the metabolic precursors for the lipids studied here. This was assayed by radioactive and stable isotope incorporation using carbon-14 and deuterium labeled myo-inositol, added to the growth medium.

RESULTS

T. forsythia synthesizes two phosphodihydroceramides (Tf GL1, Tf GL2) which are constituted by phospho-myo-inositol linked to either a 17-, 18-, or 19-carbon sphinganine, N-linked to either a branched 17:0(3-OH) or a linear 16:0(3-OH) fatty acid which, in Tf GL2, is, in turn, ester-substituted with a branched 15:0 fatty acid. T. forsythia lacks the enzymatic machinery required for myo-inositol synthesis but was found to internalize inositol from the medium for the synthesis of both Tf GL1 and Tf GL2.

CONCLUSION

The study describes two novel glycolipids in T. forsythia which could be essential in this organism. Their synthesis could be reliant on an external source of myo-inositol.

GENERAL SIGNIFICANCE

The effects of these unique lipids on the immune system and their role in bacterial virulence could be relevant in the search for new drug targets.