Role of galE on biofilm formation by Thermus spp

Multi-omics analysis reveals genes and metabolites involved in Bifidobacterium pseudocatenulatum biofilm formation

Bacterial biofilm is an emerging form of life that involves cell populations living embedded in a self-produced matrix of extracellular polymeric substances (EPS). Currently, little is known about the molecular mechanisms of Bifidobacterium biofilm formation. We used the Bifidobacterium biofilm fermentation system to preparation of biofilms on wheat fibers, and multi-omics analysis of both B. pseudocatenulatum biofilms and planktonic cells were performed to identify genes and metabolites involved in biofilm formation. The average diameter of wheat fibers was around 50 μm, while the diameter of particle in wheat fibers culture of B. pseudocatenulatum was over 260 μm at 22 h with 78.96% biofilm formation rate (BR), and the field emission scanning electron microscopy (FESEM) results showed that biofilm cells on the surface of wheat fibers secreted EPS. Transcriptomic analysis indicated that genes associated with stress response (groS, mntH, nth, pdtaR, pstA, pstC, radA, rbpA, whiB, ybjG), quorum sensing (dppC, livM, luxS, sapF), polysaccharide metabolic process (rfbX, galE, zwf, opcA, glgC, glgP, gtfA) may be involved in biofilm formation. In addition, 17 weighted gene co-expression network analysis (WGCNA) modules were identified and two of them positively correlated to BR. Metabolomic analysis indicated that amino acids and amides; organic acids, alcohols and esters; and sugar (trehalose-6-phosphate, uridine diphosphategalactose, uridine diphosphate-N-acetylglucosamine) were main metabolites during biofilm formation. These results indicate that stress response, quorum sensing (QS), and EPS production are essential during B. pseudocatenulatum biofilm formation.

Functional metagenomic libraries generated from anthropogenically impacted environments reveal importance of metabolic genes in biocide and antibiotic resistance

Anthropogenic activities result in the release of antimicrobial resistant bacteria and a cocktail of antimicrobial compounds into the environment that may directly select or indirectly co-select for antimicrobial resistance (AMR). Many studies use metagenome sequencing or qPCR-based approaches to study the environmental resistome but these methods are limited by a priori knowledge. In this study, a functional metagenomic approach was used to explore biocide resistance mechanisms in two contaminated environments and a pristine site, and to identify whether potentially novel genes conferring biocide resistance also conferred resistance or reduced susceptibility to antibiotics. Resistance was predominately mediated through novel mechanisms exclusive of the well-known qac efflux genes. UDP-galactose 4-epimerase (galE) -like genes were identified in both contaminated environments and were shown to confer cross-resistance to biocides and clinically important antibiotics for the first time (to our knowledge), compared to knockout mutants. GalE -like genes were also co-located with transposons, suggesting mobilisation potential. These results show that housekeeping genes may play a significant yet underappreciated role in AMR in environmental microbiomes.

Biofilm characteristics and transcriptomic profiling of Acinetobacter johnsonii defines signatures for planktonic and biofilm cells

Most bacteria in the natural environment have a biofilm mode of life, which is intrinsically tolerant to antibiotics. While until now, the knowledge of biofilm formation by Acinetobacter johnsonii is not well understood. In this study, the characteristics and the effect of a sub-inhibitory concentration of antibiotic on A. johnsonii biofilm and planktonic cells were determined. We discovered a positive relationship between biofilm formation and tetracycline resistance, and biofilms rapidly evolve resistance to tetracycline they are treated with. Persister cells commonly exist in both planktonic and biofilm cells, with a higher frequency in the latter. Further transcriptomic analysis speculates that the overexpression of multidrug resistance genes and stress genes were mainly answered to sub lethal concentration of tetracycline in planktonic cells, and the lower metabolic levels after biofilm formation result in high resistance level of biofilm cells to tetracycline. Altogether, these data suggest that A. johnsonii can adjust its phenotype when grown as biofilm and change its metabolism under antibiotic stress, and provide implications for subsequent biofilm control.

Bacillus licheniformis MCC 2514 genome sequencing and functional annotation for providing genetic evidence for probiotic gut adhesion properties and its applicability as a bio-preservative agent

Bacillus licheniformis is a well-known probiotic that can be found in a variety of foods. The strain Bacillus licheniformis MCC 2514 was previously characterized by our group for its bio-physiological capabilities establishing it as a promising probiotic, but information on the genetic evidence for its attributes was lacking. In the current study, whole genome analysis identified the underlying molecular determinants responsible for its probiotic potential. The circular genome of MCC 2514 was 4,230,480 bp with 46.2% GC content, 24 rRNA, and 83 tRNA genes. The pangenome analysis between B. licheniformis MCC 2514 and 12 other B. licheniformis strains revealed a pangenome of 6008 genes and core genome of 3775 genes. Genome mining revealed NRPS and bacteriocins producing gene clusters indicating its biocontrol properties. Several genes encoding carbohydrate degrading enzymes, which aid in proper food degradation in the intestine, were also observed. Stress tolerance, vitamin, and essential amino acids biosynthesis related genes were found, which are important characteristics of a probiotic strain. Additionally, vital genes responsible for gut adhesion and biofilm formation were observed in its genome. The bacterium has been shown to improve the shelf life of idli batter by preventing whey separation, CO_2, and odour production while maintaining the pH of 3.96-4.29, especially at cold temperatures. It has significantly reduced coliform contamination at both room and low temperatures, demonstrating its bio-preservative ability, which is also corroborated by the presence of the NRPS and bacteriocin gene clusters in its genome. The present study helped to understand both, the ability of B. licheniformis MCC 2514 to adapt the intestinal gut environment and its probiotic functionality for food preservation.

Extracellular riboflavin induces anaerobic biofilm formation in Shewanella oneidensis

BACKGROUND

Some microorganisms can respire with extracellular electron acceptors using an extended electron transport chain to the cell surface. This process can be applied in bioelectrochemical systems in which the organisms produce an electrical current by respiring with an anode as electron acceptor. These organisms apply flavin molecules as cofactors to facilitate one-electron transfer catalyzed by the terminal reductases and in some cases as endogenous electron shuttles.

RESULTS

In the model organism Shewanella oneidensis, riboflavin production and excretion trigger a specific biofilm formation response that is initiated at a specific threshold concentration, similar to canonical quorum-sensing molecules. Riboflavin-mediated messaging is based on the overexpression of the gene encoding the putrescine decarboxylase speC which leads to posttranscriptional overproduction of proteins involved in biofilm formation. Using a model of growth-dependent riboflavin production under batch and biofilm growth conditions, the number of cells necessary to produce the threshold concentration per time was deduced. Furthermore, our results indicate that specific retention of riboflavin in the biofilm matrix leads to localized concentrations, which by far exceed the necessary threshold value.

CONCLUSION

This study describes a new quorum-sensing mechanism in S. oneidensis. Biofilm formation of S. oneidensis is induced by low concentrations of riboflavin resulting in an upregulation of the ornithine-decarboxylase speC. The results can be applied for the development of strains catalyzing increased current densities in bioelectrochemical systems.

Molecular evolution and functional divergence of UDP-hexose 4-epimerases

UDP-glucose 4-epimerase (GalE) catalyzes the interconversion of UDP-glucose (UDP-Glc) and UDP-galactose (UDP-Gal) and/or the interconversion of UDP-N-acetylglucosamine (UDP-GlcNAc) and UDP-N-acetylgalactosamine (UDP-GalNAc) in sugar metabolism. GalEs belong to the short-chain dehydrogenase/reductase superfamily, use a conserved 'transient keto intermediate' mechanism and have variable substrate specificity. GalEs have been classified into three groups based on substrate specificity: group 1 prefers UDP-Glc/Gal, group 3 prefers UDP-GlcNAc/GalNAc, and group 2 has comparable activities for both types of the substrates. The phylogenetic relationship and structural basis for the specificities of GalEs revealed possible molecular evolution of UDP-hexose 4-epimerases in various organisms. Based on the recent advances in studies on GalEs and related enzymes, an updated view of their evolutional diversification is presented.

Determinants of the Nucleotide Specificity in the Carbohydrate Epimerase Family 1

In recent years, carbohydrate epimerases have attracted increasing attention as promising biocatalysts for the production of specialty sugars and derivatives. The vast majority of these enzymes are active on nucleotide-activated sugars, rather than on their free counterparts. Although such epimerases are known to have a clear preference for a particular nucleotide (UDP, GDP, CDP, or ADP), very little is known about the determinants of the respective specificities. In this work, sequence motifs are identified that correlate with the different nucleotide specificities in one of the main epimerase superfamilies, carbohydrate epimerase 1 (CEP1). To confirm their relevance, GDP- and CDP-specific residues are introduced into the UDP-glucose 4-epimerase from Thermus thermophilus, resulting in a 3-fold and 13-fold reduction in K_M for GDP-Glc and CDP-Glc, respectively. Moreover, several variants are severely crippled in UDP-Glc activity, which further underlines the crucial role of the identified positions. Hence, the analysis should prove to be valuable for the further exploration and application of epimerases involved in carbohydrate synthesis.

iTRAQ-Based Proteomics Reveals Potential Anti-Virulence Targets for ESBL-Producing Klebsiella pneumoniae

Purpose

Treatment of infections with Klebsiella pneumoniae strains producing extended-spectrum beta-lactamases (ESBLs) is challenging due to the coexistence of multiple resistance mechanisms and the hypervirulent variant. Therefore, new targets or more effective treatment options aimed at ESBL-producing Klebsiella pneumoniae are urgently needed.

Materials and Methods

Here, we collected ESBL-producing and non-ESBL Klebsiella pneumoniae isolates and studied their differences from a proteomic point of view.

Results

We revealed treA, wza, gnd, rmlA, rmlC, rmlD, galE, aceE, and sucD as important virulence-related proteins in ESBL-producing Klebsiella pneumoniae, distinct from those in non-ESBL strains.

Conclusion

Our findings provide plausible anti-virulence targets and suggest new therapeutic avenues against ESBL-producing Klebsiella pneumoniae.

Molecular regulation of adhesion and biofilm formation in high and low biofilm producers of Bacillus licheniformis using RNA-Seq

RNA sequencing was used to reveal transcriptional changes during the motile-to-sessile switch in high and low biofilm-forming dairy strains of B. licheniformis isolated from Chinese milk powders. A significant part of the whole gene content was affected during this transition in both strains. In terms of the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, seven metabolic pathways were significantly downregulated in the planktonic state compared to the biofilm state in both strains. Lipid and sugar metabolism seemed to play an important role in matrix production. Several genes involved in adhesion, matrix production and the matrix coating were either absent or less expressed in the biofilm state of the low biofilm producer compared to the high biofilm producer. Genes related to sporulation and the production of extracellular polymeric substances were concomitantly expressed in the biofilm state of both strains. These comprehensive insights will be helpful for future research into mechanisms and targets.

Quorum sensing in thermophiles: prevalence of autoinducer-2 system

BACKGROUND

Quorum sensing is a mechanism of cell to cell communication that requires the production and detection of signaling molecules called autoinducers. Although mesophilic bacteria is known to utilize this for synchronization of physiological processes such as bioluminescence, virulence, biofilm formation, motility and cell competency through signaling molecules (acyl homoserine lactones, AI-1; oligopeptides, peptide based system and furanosyl borate diester, AI-2), the phenomenon of quorum sensing in thermophiles is largely unknown.

RESULTS

In this study, proteomes of 106 thermophilic eubacteria and 21 thermophilic archaea have been investigated for the above three major quorum sensing systems to find the existence of quorum sensing in these thermophiles as there are evidences for the formation of biofilms in hot environments. Our investigation demonstrated that AI-1 system is absent in thermophiles. Further, complete peptide based two component systems for quorum sensing was also not found in any thermophile however the traces for the presence of response regulators for peptide based system were found in some of them. BLASTp search using LuxS (AI-2 synthase) protein sequence of Escherichia coli str. K-12 substr. MG1655 and autoinducer-2 receptors (LuxP of Vibrio harveyi, LsrB of E. coli str. K-12 substr. MG1655 and RbsB of Aggregatibacter actinomycetemcomitans) as queries revealed that 17 thermophilic bacteria from phyla Deinococcus- Thermus and Firmicutes possess complete AI-2 system (LuxS and LsrB and/or RbsB). Out of 106 thermophilic eubacteria 18 from phyla Deinococcus- Thermus, Proteobacteria and Firmicutes have only LuxS that might function as AI-2 synthesizing protein whereas, 16 are having only LsrB and/or RbsB which may function as AI-2 receptor in biofilms.

CONCLUSIONS

We anticipate that thermophilic bacteria may use elements of LsrB and RbsB operon for AI-2 signal transduction and they may use quorum sensing for purposes like biofilm formation. Nevertheless, thermophiles in which no known quorum sensing system was found may use some unknown mechanisms as the mode of communication. Further information regarding quorum sensing will be explored to develop strategies to disrupt the biofilms of thermophiles.

UDP-hexose 4-epimerases: a view on structure, mechanism and substrate specificity

UDP-sugar 4-epimerase (GalE) belongs to the short-chain dehydrogenase/reductase (SDR) superfamily of proteins and is one of enzymes in the Leloir pathway. They have been shown to be important virulence factors in a number of Gram-negative pathogens and to be involved in the biosynthesis of different polysaccharide structures. The metabolic disease type III galactosemia is caused by detrimental mutations in the human GalE. GalE and related enzymes display unusual enzymologic, chemical, and stereochemical properties; including irreversible binding of the cofactor NAD and uridine nucleotide-induced activation of this cofactor. These epimerases have been found active on UDP-hexoses, the N-acetylated and uronic acid forms thereof as well as UDP-pentoses. As they are involved in different pathways and functions, a deeper understanding of the enzymes, and their substrate promiscuity and/or selectivity, could lead to drug and vaccine design as well as antibiotic and probiotic development. This review summarizes the research performed on UDP-sugar 4-epimerases' structure, mechanism and substrate promiscuity.

Transcriptional regulation of the iac locus from Acinetobacter baumannii by the phytohormone indole-3-acetic acid

The iac locus is involved in indole-3-acetic acid (IAA) catabolism in Acinetobacter baumannii. Nine structural genes of iac are transcribed in the same direction, whereas iacR, which encodes a MarR-type transcriptional regulator, is transcribed in the opposite direction. The IacA protein, which is encoded by the second structural gene of the iac locus, is expressed in an IAA-dependent manner. Here, we characterized gene expression from this locus in wild type A. baumannii and in an iacR mutant; this revealed that the iacH promoter is negatively regulated by IacR. The transcriptional site of iacH was determined by using 5' rapid amplification of cDNA ends; one IacR-binding site was identified between positions -35 and +28 of the iacH promoter. Sequence analysis and an electrophoretic mobility shift assay indicated that recombinant IacR binds specifically to a sequence with dyad symmetry in the iacR-iacH overlapping promoters in the absence of IAA. In addition, a two-plasmid expression system in Escherichia coli showed that IAA probably serves as a ligand that binds to IacR and releases it from the iacH promoter, thereby allowing RNA polymerase to transcribe iac. Thus, iac is expressed in order to promote IAA degradation, whereas free IacR is required for iac repression. We conclude that IacR serves as a key regulator of IAA degradation in A. baumannii in the rhizosphere. These results provide new insights into the possible role of A. baumannii in the environment.

Pseudomonas aeruginosa isolates from dental unit waterlines can be divided in two distinct groups, including one displaying phenotypes similar to isolates from cystic fibrosis patients

Pseudomonas aeruginosa displays broad genetic diversity, giving it an astonishing capacity to adapt to a variety of environments and to infect a wide range of hosts. While many P. aeruginosa isolates of various origins have been analyzed, isolates from cystic fibrosis (CF) patients have received the most attention. Less is known about the genetic and phenotypic diversity of P. aeruginosa isolates that colonize other environments where flourishing biofilms can be found. In the present study, 29 P. aeruginosa isolates from dental unit waterlines and CF patients were collected and their genetic and phenotypes profiles were compared to determine whether environmental and clinical isolates are related. The isolates were first classified using the random amplified polymorphic DNA method. This made it possible to distribute the isolates into one clinical cluster and two environmental clusters. The isolates in the environmental cluster that were genetically closer to the clinical cluster also displayed phenotypes similar to the clinical isolates. The isolates from the second environmental cluster displayed opposite phenotypes, particularly an increased capacity to form biofilms. The isolates in this cluster were also the only ones harboring genes that encoded specific epimerases involved in the synthesis of lipopolysaccharides, which could explain their increased ability to form biofilms. In conclusion, the isolates from the dental unit waterlines could be distributed into two clusters, with some of the environmental isolates resembled the clinical isolates.

LOV-domain photoreceptor, encoded in a genomic island, attenuates the virulence of Pseudomonas syringae in light-exposed Arabidopsis leaves

In Arabidopsis thaliana, light signals modulate the defences against bacteria. Here we show that light perceived by the LOV domain-regulated two-component system (Pst-Lov) of Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) modulates virulence against A. thaliana. Bioinformatic analysis and the existence of an episomal circular intermediate indicate that the locus encoding Pst-Lov is present in an active genomic island acquired by horizontal transfer. Strains mutated at Pst-Lov showed enhanced growth on minimal medium and in leaves of A. thaliana exposed to light, but not in leaves incubated in darkness or buried in the soil. Pst-Lov repressed the expression of principal and alternative sigma factor genes and their downstream targets linked to bacterial growth, virulence and quorum sensing, in a strictly light-dependent manner. We propose that the function of Pst-Lov is to distinguish between soil (dark) and leaf (light) environments, attenuating the damage caused to host tissues while releasing growth out of the host. Therefore, in addition to its direct actions via photosynthesis and plant sensory receptors, light may affect plants indirectly via the sensory receptors of bacterial pathogens.

Toward repurposing ciclopirox as an antibiotic against drug-resistant Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae

Antibiotic-resistant infections caused by gram-negative bacteria are a major healthcare concern. Repurposing drugs circumvents the time and money limitations associated with developing new antimicrobial agents needed to combat these antibiotic-resistant infections. Here we identified the off-patent antifungal agent, ciclopirox, as a candidate to repurpose for antibiotic use. To test the efficacy of ciclopirox against antibiotic-resistant pathogens, we used a curated collection of Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae clinical isolates that are representative of known antibiotic resistance phenotypes. We found that ciclopirox, at 5–15 µg/ml concentrations, inhibited bacterial growth regardless of the antibiotic resistance status. At these same concentrations, ciclopirox reduced growth of Pseudomonas aeruginosa clinical isolates, but some of these pathogens required higher ciclopirox concentrations to completely block growth. To determine how ciclopirox inhibits bacterial growth, we performed an overexpression screen in E. coli. This screen revealed that galE, which encodes UDP-glucose 4-epimerase, rescued bacterial growth at otherwise restrictive ciclopirox concentrations. We found that ciclopirox does not inhibit epimerization of UDP-galactose by purified E. coli GalE; however, ΔgalU, ΔgalE, ΔrfaI, or ΔrfaB mutant strains all have lower ciclopirox minimum inhibitory concentrations than the parent strain. The galU, galE, rfaI, and rfaB genes all encode enzymes that use UDP-galactose or UDP-glucose for galactose metabolism and lipopolysaccharide (LPS) biosynthesis. Indeed, we found that ciclopirox altered LPS composition of an E. coli clinical isolate. Taken together, our data demonstrate that ciclopirox affects galactose metabolism and LPS biosynthesis, two pathways important for bacterial growth and virulence. The lack of any reported fungal resistance to ciclopirox in over twenty years of use in the clinic, its excellent safety profiles, novel target(s), and efficacy, make ciclopirox a promising potential antimicrobial agent to use against multidrug-resistant problematic gram-negative pathogens.

Phosphoproteomic analysis reveals the effects of PilF phosphorylation on type IV pilus and biofilm formation in Thermus thermophilus HB27

Thermus thermophilus HB27 is an extremely thermophilic eubacteria with a high frequency of natural competence. This organism is therefore often used as a thermophilic model to investigate the molecular basis of type IV pili-mediated functions, such as the uptake of free DNA, adhesion, twitching motility, and biofilm formation, in hot environments. In this study, the phosphoproteome of T. thermophilus HB27 was analyzed via a shotgun approach and high-accuracy mass spectrometry. Ninety-three unique phosphopeptides, including 67 in vivo phosphorylated sites on 53 phosphoproteins, were identified. The distribution of Ser/Thr/Tyr phosphorylation sites was 57%/36%/7%. The phosphoproteins were mostly involved in central metabolic pathways and protein/cell envelope biosynthesis. According to this analysis, the ATPase motor PilF, a type IV pili-related component, was first found to be phosphorylated on Thr-368 and Ser-372. Through the point mutation of PilF, mimic phosphorylated mutants T368D and S372E resulted in nonpiliated and nontwitching phenotypes, whereas nonphosphorylated mutants T368V and S372A displayed piliation and twitching motility. In addition, mimic phosphorylated mutants showed elevated biofilm-forming abilities with a higher initial attachment rate, caused by increasing exopolysaccharide production. In summary, the phosphorylation of PilF might regulate the pili and biofilm formation associated with exopolysaccharide production.

Metagenomic analysis of ammonia-oxidizing archaea affiliated with the soil group

Ammonia-oxidizing archaea (AOA) have recently been recognized as a significant component of many microbial communities and represent one of the most abundant prokaryotic groups in the biosphere. However, only few AOA have been successfully cultivated so far and information on the physiology and genomic content remains scarce. We have performed a metagenomic analysis to extend the knowledge of the AOA affiliated with group I.1b that is widespread in terrestrial habitats and of which no genome sequences has been described yet. A fosmid library was generated from samples of a radioactive thermal cave (46°C) in the Austrian Central Alps in which AOA had been found as a major part of the microbial community. Out of 16 fosmids that possessed either an amoA or 16S rRNA gene affiliating with AOA, 5 were fully sequenced, 4 of which grouped with the soil/I.1b (Nitrososphaera-) lineage, and 1 with marine/I.1a (Nitrosopumilus-) lineage. Phylogenetic analyses of amoBC and an associated conserved gene were congruent with earlier analyses based on amoA and 16S rRNA genes and supported the separation of the soil and marine group. Several putative genes that did not have homologs in currently available marine Thaumarchaeota genomes indicated that AOA of the soil group contain specific genes that are distinct from their marine relatives. Potential cis-regulatory elements around conserved promoter motifs found upstream of the amo genes in sequenced (meta-) genomes differed in marine and soil group AOA. On one fosmid, a group of genes including amoA and amoB were flanked by identical transposable insertion sequences, indicating that amoAB could potentially be co-mobilized in the form of a composite transposon. This might be one of the mechanisms that caused the greater variation in gene order compared to genomes in the marine counterparts. Our findings highlight the genetic diversity within the two major and widespread lineages of Thaumarchaeota.

The third plasmid pVV8 from Thermus thermophilus HB8: isolation, characterization, and sequence determination

The extremely thermophilic bacterium Thermus thermophilus is a model organism for structural biology and systems biology, and the so-called "Structural and Functional Whole-Cell Project for T. thermophilus HB8" is in progress. The released genomic sequence of the strain HB8 is composed of chromosome, pTT27 megaplasmid, and pTT8 plasmid. In this paper, however, a third plasmid was demonstrated and its sequence was determined. Although this plasmid pVV8 had been reported before, limited information and an unfortunate dropout in the substrain, whose genomic sequence was determined, would have prevented the plasmid from coming to public attention. The intrinsic circular plasmid, which was estimated to be six to ten copies in a cell, is 81151 bp and its G + C content is 68%. Among the identified 91 ORFs, a single gene has been experimentally analyzed before and is known as xylose isomerase. The phnCDEGHIJKLMX operon related to phosphonate metabolism, alkaline phosphatase, putative transcriptional regulators, several sets of toxin-antitoxin system, and transposase-like ORFs are also encoded on the pVV8 plasmid. Although association with cell aggregation was the one phenotypic characteristic of the plasmid that had been reported, it was never confirmed. Comparison of T. thermophilus HB8 strains suggests that the pVV8 is nonessential for growth.

The first C-glycosidic analogue of a novel galactosyltransferase inhibitor

Structural analogues and mimics of the natural sugar-nucleotide UDP-galactose (UDP-Gal) are sought after as chemical tools for glycobiology and drug discovery. We have recently developed a novel class of galactosyltransferase (GalT) inhibitors derived from UDP-Gal, bearing an additional substituent at the 5-position of the uracil base. Herein we report the first C-glycosidic derivative of this new class of GalT inhibitors. We describe a practical convergent synthesis of the new UDP-C-Gal derivative, including a systematic study into the use of radical chemistry for the preparation of galactosyl ethylphosphonate, a key synthetic intermediate. The new inhibitor showed activity against a bacterial UDP-Gal 4'-epimerase at micromolar concentrations. This is the first example of a base-modified UDP-sugar as an inhibitor of a UDP-sugar-dependent enzyme which is not a glycosyltransferase, and these results may therefore have implications for the design of inhibitors of these enzymes in the future.